APPLICATION OF ATOMIC ENGINES IN AVIATION

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP81-01043R002100060011-6
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 98
• Document Creation Date: December 27, 2016
• Document Release Date: July 1, 2013
• Sequence Number: 11
• Publication Date: January 1, 1957
• Content Type: REPORT

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TERRS111.11011
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APPLICATION OF ATOMIC EncinEs in mmmon
(PRIMENENIYE ATOMNYKH DVIGATELEY v AVIATSI I
By G. N. Nesterenko, A. I. Sobolev, Yu. N. Sushkov
Military Press of the Ministry of Defense of the USSR
Moscow, 1957
STAT
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WRIGHT-PATTERSON AIR FORCE BASE, OHIO
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(
POPULAR SCIENCE
LIBRARY
GA.Nestei;enko, A.I.Sobolev, Yu.N.Sushkov
APPLICATfON'
OF ATOMIC ENGINES
IN AVIATION
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To The Reader:
The Military Press requests that you send
your comments on this book to the follow-
ing address: Management, Military Press,
18 Tverskaya Boulevard, Moscow 104
Nesterenko, Gennadiy Nikolayevich; Sobolev, Anatoliy Ivanovich;
Sushkov, Yuriy Nikolayevich
"Application of Atomic Engines in Aviation"
Editor Ya.M.Kader
Consultants to the Publisher:
Maj.Gen.Prof.Dr.Eng. G.I.Pokrovskiy of the Engineering and
Technological Services
Col.Dr.Eng. M.L.Novikov, Engineer
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Production Editor: LA.Strelinikova; Proofreader: L.K.Tsvetkova
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of the Management of the Military Press of the USSR Defense Ministry
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Price 2 rubles 60 kopeks
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INTRODUCTION
.0.116.0
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One of the most outstanding scientific achievements of our day has been the
discovery of atomic energy and of practical methods of obtaining and applying it.
We have already entered the Atomic Age. Atom, atomic energy, atom bomb, atomic
power plant, atomic icebreaker: these are terns and words that may be heard every-
where today.
Atomic energy is having a major influence on the development of science and
engineering.
As soon as it became clear that the chain reaction of fission of the uranium
nucleus could produce an explosion of enormously destructive force, the imperialists
hastened to apply this discovery to military purposes. During World War II the
United States of America was able to gather "atomic secrets" from the entire capt-
talist world, mobilize scientists and engineers and, by the outlay of enormous
funds, make the atom bomb.
The ruling circles of the United States marked the beginning of the Atomic Age
by the barbaric destruction of the Japanese cities of Hiroshima and Nagasaki, al-
though there was no military necessity for this whatever. The United States frankly
made use of the termination of the World War II to proclaim the unprecedented power
of the atonic weapon, to threaten the peoples of the world with a "new force", on
which the United States seriously believed to have a monopoly. Everyone knows what
happened to the "monopoly" of the atomic bomb and later of the hydrogen bomb. The
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Soviet Union did not permit itself to be frightened by bombs of whatever kind, but,
exercising constant concern for its security, it created its own atomic and thermo-
nuclear weapons.
The Twentieth Congress of the Communist Party of the Soviet Union noted once
again that the Soviet people, engaged in peaceful labors, is forced to reckon with
the military preparations in the capitalist countries.
In the development of the Soviet Armed Forces we proceed from the conviction
that the means and forms of war in the future will differ considerably from all wars
of the past. If a war should come in the future, it will be characterized by mass
use of military aircraft, a variety of rocket weapons, and various means of mass
destruction such as atomic, thermonuclear, chemical, and bacteriological weapons.
However, the various types of the most modern arms, including the means of mass
destruction, do not diminish the decisive significance of the ground, air, and naval
forces. Without strong ground forces, and without strategic, long-range, and
ground-attack aircraft and a powerful navy, it is impossible to wage modern war
successfully.
Thanks to the constant concern of the Commmnist Party and the Soviet government
with the defensive capability of our country, the Soviet Armed Forces have been
basically reorganized and have advanced far in quality from the level they had at-
tained at the end of the Great Patriotic War. The increasing capabilities of the
Soviet economy and the major accomplishments of heavy industry in particular have
made it possible to re-equip our army, air force, and navy with first-class military
technology.
The share of the Military Air Forces in the total make-up of our Armed Forces
has considerably increased. The Soviet Armed Forces are in possession of first-
class aviation, and powerful rocket and jet armament of various classes, including
long-range rockets.
In view. of the continuing progress of science and engineering and the develop-
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ment of new means of destruction and new military technology, it is our duty con-
stantly to perfect our knowledge, to study and master the most desirable methods and
forms of the conduct of military operations under conditions in which modern means
of armed combat - including the very latest - are employed.
Today's strategic bombers with chemical-fuel engines are capable of nonstop
flights of many thousands of kilometers. They are capable of successfully solving
military problems at a considerable distance from their bases, in the deep rear of
the enemy. However, the range of modern bombers is limited by the amount of fuel
that can be stored aboard. In this connection, aircraft with atomic engines, whose
range will considerably exceed that of today's aircraft, are of particular interest.
In recent years, work on producing atomically powered aircraft has been done
on a large scale in the capitalist countries. The significance ascribed to this
work by the government of the United States now and in the past is obvious from an
official report to the Congress of the United States on this matter: "In ease of
war ... atomic aircraft engines will play a role equal to that of the atom bomb it-
self. The limitations of range imposed by any chemical fuel greatly complicate the
aerial delivery of atonic bombs over long distances. Therefore, if the United
States possessed atomic aircraft engines in. addition to the atom bomb, this would be
a decisive factor".
Thus, after the creation of atom and hydrogen bombs, the American imperialists
consider the next stage in their program the development of intercontinental bombers
and rockets with atomic engines, to ,be used to deliver bombs of enormous destructive
power to any point on the earth's surface.
-- In-order-to perform theoretical investigations in the field of atomic engines
for aircraft, special plans and research organizations have been developed in the
United States and England, and a number of major scientific research. laboratories,
scientists, ancl companies have been drawn into this activity.
At the present time more than ten aircraft engine manufacturers are engaged in
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the United States on the production of atOmic aircraft engines and reactors: These
include such important companies as General Electric, Pratt & Whitney, General
Motors, and others. The Lockheed, Convair, Boeing and other aircraft-building firms
are engaged in producing a glider for an aircraft, with an atomic power plant.
The overall control of all the work in this field is in the hands of the United
States Atomic Energy Commission and the Command of the Air Force.
The Soviet Union has been compelled, in view of the military preparations of
the capitalist countries, to develop armed forces capable of repulsing an attack by
an aggressor at any time. Our scientists, designers, and engineers have been giving
and are giving much effort to the reinforcement of the military strength of our
homeland and to the uninterrupted perfection and progress of Soviet military science
and engineering.
The Soviet people is moving successfully along the road of building communism
in our country. An important step along that road is the fulfillment of the Sixth
Five-Year Plan. Much attention is being given, during the Sixth Five-Year Plan, to
the peaceful use of atomic energy. In the period from 1956 to 1960, new atomic
power plants of large capacity will be built, atomic power plants for transportation
purposes will be further developed, and an icebreaker with an atomic engine will be
built.
Speaking before the Twentieth Congress of the Communist Party of the Soviet
Union, Academician I.V.Kurchatov stated: "The use of atomic energy for transporta-
tion purposes has to be further expanded.
"During the present Five-Year Plan, work on atomic power plants not only for an
icebreaker, but for other vessels, for air and land transport has to be develoioed
on a large scale
At the present time, science and engineering are on the verge of creating air-
craft with atomic engines. The possibilities of such aircraft are being studied,
the economic benefits, advantages and disadvantages of atomic aviation of the future
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are being investigated, and a broad program of experiments and experimental work is
being conducted. An increasing volume of literature, scientific and popular scien-
tific-books and articles, deal directly or indirectly with the problems of develop-
ing atomic power plants for aircraft and rockets. Extensive theoretical research
is being done on the problem of the use of atomic energy for interplanetary flights.
The purpose of the present pamphlet is to systematize the scattered data in the
literature on the utilization of atomic power plants in aviation and rocket engin-
eering and to review these data in popular form, accessible to wide groups of read-
ers.
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CHAPTER I
PERSPECTIVES FOR THE USE OF ATOMIC ENERGY IN AVIATION
The discovery of atomic energy and, later, the development of practical means
of producing and utilizing this energy is one of the most important scientific a-
chievements of today. In order to conceive of the full significance of this remark-
able discovery it is enough to remember that throughout all history the question of
the sources of energy used for actuating machines has been one of the most important
factors tending to either retard or accelerate the development of technology.
Thus, the appearance of the steam engine converting the energy of fuel into
mechanical motion resulted in an industrial revolution leading to a development of
science and technology without precedent to that day. The invention of internal
combustion engines at the end of the Nineteenth Century made possible the creation
and development of the automobile industry and aircraft. At the beginning of the
Twentieth Century electrical energy began to play an enormous role.
Whenever a new source of energy has come into use, the productive forces of
society have made giant strides forward.
At present, we are witnesses to the beginning of a new epoch in the history of
human society, that of utilization of the energy locked in the atomic nucleus.
The prime source of all types of energy, and the source of life on earth has
hitherto been solar energy. It is known that this energy is the result of nuclear
transformations occurring in the enormous mass of the sun. Scientists, believe that
on the sun there occurs the fusion of hydrogen nuclei to helium nuclei, accompanied
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by the release of colossal amounts of atomic nuclear energy. Modern science has
begun to obtain and utilize atomic energy under terrestrial conditions, which has
opened new possibilities for the development of productive power.
We are on the threshold of a new scientific, engineering and industrial revolu-
tion, far exceeding in significance the industrial revolutions that followed the
discovery of steam and electricity.
The introduction of atomic energy into industry and transport will proceed by
stages governed by the difficulty of the engineering and technical solutions of the
problems encountered. The first stage, relatively simple and easy to reach, was the
development of atomic power plants. The second stage was the formulation and solu-
tion of the problem of development of sea-going vessels with atomic power plants.
The third stage is the use of atomic energy in aircraft engines. This problem has
proved to be one of the most difficult for technical realization and therefore has
not yet found a practical solution. Further serious efforts are required for its
solution.
However, history has shown that when a new and more powerful source of energy
is found, its practical application wherever it is most needed is something that
will-of necessity occur in the not-too-dietant future. The present-day rapid de-
velopment of nuclear physics and power engineering, the development of the atomic
industry, the experience acquired in theoretical and experimental research on sta-
tionary atomic power plants have made it possible for Soviet and foreign scientists,
engaged in the development of atomic aircraft power plants, to proceed even today
from scientific and purely theoretical. research to the engineering calculations and
experiments required.
The development of aviation is prinarily governed by the development of the
aircraft engine industry. The speeds, altitudes, and ranges of aircraft attained
are largely dependent upon the perfection of aircraft engines: their power, opera-
tional ceiling, economy, reliability in operation, weight, and dimensions. Figure 1
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presents an interesting graph, reflecting the opinions of a number of foreign scien-
tists with regard to the development of aircraft engines. This graph shows that the
potential possibilities of development of internal combustion and, later, of turbo-
jet engines (TJE) have already been exhausted to a considerable degree, while the
development of turboprop engines (TPE) is now rapidly under way, as is that of
liquid-fuel jet engines and ram-jet engines (LJE and RJE). According to this graph,
100
1940 1950 198" 1970
Fig.1 - Graph of the Development of Aircraft Engines in
Conventional Percentages
a) Percentage of potential development attained; b) Internal combustion engines;
c) Turbojet engines; d) Turboprop. and turbojet engines with after-burners;
e) Liquid-fuel and ram-jet engines; f) Atonic engines
1955 may be regarded as the year of the beginning of development of atomic aircraft
engines, and they should make their appearance in the very next few years. However,
it is true that thus far it is difficult to assert whether the curve of development
of atomic aircraft engines will continue as smoothly and sharply upward as indicated
by the graph. It is still possible that there will be plateaus and uneven segments,
depending on the success or failure of experiments under way, new discoveries, and
other attendant factors.
Wherever the problem .of the creation of a new type of engine arises, a new
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question is posed: in what respect is it better and superior to those we already
have at our disposal? Why do we need atomic aircraft engines?
This question may be answered if we examine certain general perspectives of the
development of aircraft engineering: primarily the prospective increase in range of
aircraft, and questions having to do with the supply of chemical fuels for aircraft.
Range of Aircraft Using Chemical and Nuclear Fuels
The constant effort to increase the range of aircraft and helicopters employing
chemical fuel is encountering ever greater difficulties, sometimes insurmountable.
a)
150
too
50
10
15
20
c)
Fig.2 - Ratio of Weight of Aircraft to Range and Flying Speed
a) Weight in tons; b) Aircraft with atomic engines (over 2000 km/hr);
c) Flying range in 1000 km
It is particularly difficult to provide adequate range for modern transonic and
supersonic aircraft. The increase in speeds is attained primarily by increasing the
engine power, and greater power results in greater fuel consumption. It suffices
to say that a modern fighter aircraft weighing 6 - 8 tons and flying at supersonic
speed, consumes 150 - 200 kg of kerosene per minute. Consequently, in an hour of
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flight such a fighter aircraft requires 9 - 12 tons of fuel. It is impossible to
store this much fuel in a fighter aircraft, and therefore the range and duration of
flight of fighter aircraft operating on chemical fuels is difficult to increase.
Designers have long known the relationship between speed and range, on the one
hand, and weight of an aircraft on the other. The study of an approximate graph of
this relationship (Fig.2) shows that, in the attempt to increase the range at a giv-
en flying speed, the designer is compelled to increase the flying weight of the air-
craft and the percentage of the fuel weight within the total weight. The heating
value of modern chemical fuels such as kerosene and gasoline is 10 - 11,000 kcal/kg.
This comparatively low heating value limits the range of aircraft, particularly of
rockets, in which it is often necessary to have a large supply of oxidizer in addi-
tion to a large reserve of fuel. The overall heating value of rocket fuels (fuel
plus oxidizer) is 2000 - 3000 kcal/kg. As a result, long-range aircraft have CORR
increasingly to resemble flying tank ears. This is true of rockets to an even
greater degree. We need only note that the total fuel capacity of a modern long-
distance bomber is 50 - 100 tons and more. Tens of tons of fuel are required to
fuel the latest transport and passenger aircraft equipped with powerful jet engines.
An approximate calculation of the range of supersonic aircraft now in the pro-
ject stage shows that aircraft weighing up to 100 tons and flying at 2000 - 3000
km/hr will have a maximum range of 3000 - 5000 km. The heaviest aircraft (200 -
- 250 tons) flying at these speeds will have ranges of 10,000 - 12,000 km, i.e.,
their radius of action will be 5000 - 6000 km. The weight of aircraft with atomic
power plants, as shown in Fig.2, is relatively independent of the range and flying
speed. According to opinions now held, the weight of the first aircraft with atomic
engines will be 100 - 150 tons, and these aircraft will be able to fly any required
distance over the surface of the earth.
Is it possible to increase the range of aircraft operated on chemical fuel?
Yes, this is entirely possible. In recent years, numerous experiments have been
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conducted in this field with the object of refueling aircraft in flight.
The idea is not new. As early as 1929, K.E.Tsiolkovskiy suggested that cosmic
speeds can be attained by using so-called cosmic rocket trains instead of single
rockets. A rocket train consists of a number
exhausted, transfers its residual fuel to the
and returned to earth. As a result, the last
of rockets
subsequent
near" of a
each of which, as it becomes
rocket, is then separated,
rocket train, i.e., the
final rocket, is enabled to attain cosmic speeds.
-Refueling in air, as practiced today, is the application in aviation of the
idea of this type of rocket train. The essence of this measure consists in classi-
fying aircraft into groups - primary aircraft and tanker aircraft, which makes it
possible to increase the range of the primary aircraft by transferring fuel to it
from the tanker in the air at a given distance from the earth. Figure 3 illustrates
a simplified variant of air refueling. Let us imagine three aircraft, each of which
-
1000stn
2500 KM
_ .?-?-?:?-?????
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Fig.3 - Refueling of Aircraft in the Air with the Object of
Increasing Its Range
a) Refueling rendezvous; b) Refueling pass
has a maximum range, at full tanks, of 3000 km. The first two completely fueled
aircraft take Dff: a primary aircrift and a tanker. Hailing flown approximately
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one-third of its total range, i.e., about 1000 km, the tanker establishes connection
with the other aircraft by a special hose or flying boom and transfers one third of
its kerosene to the latter. The tanker then returns to its home base on the remain-
ing third of the fuel, while the primary aircraft, now again fully fueled, is capa-
ble of flying another 1500 km forward, accomplishing a military mission and return-
ing to a rendezvous with the other tanker at a distance 1000 km from its home base.
Here, tanker No.2, retaining two thirds of its own fuel, transfers one third to the
primary aircraft, and the two return to the airfield together. Thus the use of two
tankers makes it possible to increase the radius of action of the third aircraft
by 60 - 65% under ideal conditions.
In order for aircraft in flight to rendezvous dependably, both in terms of
location and time, and in order for the fuel to be transferred in flight, special
training and high skill on the part of the air crews is necessary. Therefore, the
refueling of aircraft in flight may be classified in the category of necessary half-
measures which, in the first place, are exceedingly complicated and expensive and,
in the second place, do not provide any significant increase in range. In addition,
the refueling of aircraft in the air at supersonic speeds is a practical impossibil-
ity. Before being refueled, an aircraft must slow down to subsonic speed and then,
in order to return to supersonic speed, it will require almost as much fuel as can
be gained by refueling. Increases and decreases in the speed and altitude of super-
sonic aircraft very sharply reduce their range, since each successive acceleration
and climb results in increased fuel consumption.
Considerable increase in range ray be attained by aircraft, without refueling,
only if nuclear-fuel-engines are used, since nuclear fuel contains approximately
two million times as much energy per unit weight as does an equal unit weight of
modern aircraft fuels.
The design, i.e., the calculated range of aircraft with atomic power plants is
not determined by the fuel supply but by the engine life, i.e., by the number of
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hours the engine can operate before wearing out or before failure of its weakest
structural parts and also by certain other factors, such as fatigue of the crew,
etc. According to certain data from other countries, the range of a single flight
of an atomic aircraft is of the order of 90,000 - 100,000 km or more. Moreover, ad-
justments in the speed and altitude of the aircraft will not greatly effect its
range, since the consumption of nuclear fuel under any conditions of flight is rath-
er small.
Calculations show that an aircraft having a flying weight of 120 tons, cruising
at 2000 km/hr at constant 20% efficiency, will consume approximately 25 grams of
uranium253 per hour. Therefore, a flight round the world (0,000 km in 20 hours)
by such an aircraft would require the consumption of no more than 500 - 600 gm of
nuclear fuel.
In order to make the same flight with chemical fuel, more than 1000 tons of
kerosene, or 20 railway tank carloads would be required. The aircraft would have
to make approximately 15 landings for refueling purposes. Due to the consumption
of kerosene in flight, the amount of fuel needed per hour will decrease as the air-
craft gradually becomes lighter. However, this apparent advantage is completely
canceled by the increased fuel consumption for the next following take-off, for
gaining altitude and speed after each landing en route.
The attainment of supersonic speeds by heavy aircraft requires exceedingly high
thrust and-power of the power plants. A power of the 'order of 150,000 - 200,000 hp
and more is required. Designing aircraft engines of such power for use with chemi-
cal fuel encounters numerous difficulties. In principle, greater power may be at-
tained more readily in atomic power plants than in conventional aircraft engines.
The prospects for the creation of high-power atomic aircraft engines and par-
ticularly the prospects for ensuring any desired range are naturally quite intri-
guing. However, they are misleading as far as military aircraft is concerned, where
such problems as increased speed, altitude, and range will never cease to be impor-
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tant. The po'ssibilities are even more appealing as far as use of such aircraft for
peaceful purposes is concerned: passenger and transport aircraft. We will discuss
these prospectives in greater detail in examining a number of projects for atomic
aircraft; for the time being, we will draw the conclusion that to attain a further
sharp increase in range of modern high-speed aircraft, engines operating on nuclear
fuel will be required.
Preserving the World Petroleum Reserve's
The second important problem compelling the use of atomic energy in aircraft
engines is the problem of the excessive depletion of the world petroleum resources
and the difficulty of providing an adequate supply of chemical fuels for aviation.
The modern jet engine is one of the most important consumers of the higher
fractions of oil refining: kerosene and the best grades of gasoline. The intensi-
fied consumption of the world petroleum resources for combustion in transport and
power-producing power plants is regarded by science as a matter of necessity and not
at all of wisdom. Petroleum is a most valuable organic raw material for various
tranches of industry: mechanical, paint, and many others, including the food in-
dustry. Long ago, the 'great Russian scientist, D.I.Mendeleyev, spoke of petroleum
as being "black gold" and, speaking of the barbaric inroads made on the resources of
petroleum, said with deep emotion: "Let us rather burn our stock certificates".
The cost of producing, refining, and transporting petroleum, and the cost of
aviation fuels derived from it, is comparatively high. In addition, the world re-
sources of petroleum are not inexhaustable. Statistics show that at the present
level of consumption of petroleum, the world reserves nay be exhausted within 185
years. If we take into consideration the uninterrupted growth in the total. capacity
of power plants operated on chemical fuels, calculations show that the depletion of
oil reserves will be felt within 25 - 50 years.
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of calculation cannot, of course, claim to be completely correct and
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accurate, since depth prospecting for oil is revealing new oil deposits, but the
figures demonstrate nonetheless that the world reserves of petroleum are very defin-
itely limited. If conversion of aviation from chemical to nuclear fuels is success-
fulr? the petroleum reserves will not be depleted as intensively: more petroleum
will be freed for satisfying other pressing needs of the national economy.
The above facts raise the question of world resources of nuclear fuels, the
cost of nuclear fuel, its capacity as a source of energy, and so forth.
Let us deal with these questions and attempt to analyze them. It need only be
borne in mind that the process of discovery and assaying of the world resources of
nublear fuel and of its possibilities in terms of power generation is far from being
complete. The dynamics of this process will become clear from a study of the rela-
tively short but very exciting history of the discovery of the various sources of
atomic nuclear fuel.
Two or Methods of Obtaining Nuclear Energy
Despite the fact that the past several years have been marked by a rapid devel-
opment of atonic power production, science does not have
on the nature of the forces acting in the nucleus of the
The single fact that the nature of nuclear force is
sufficiently complete data
atom.
not clearly understood or
fully studied is no obstacle for the practical utilization of nuclear energy. The
British physicist, 0.Heaviside, once said, "Am I going to refrain, from eating dinner
just because I do not completely understand the process of digestion?" However, in ?
order to understand the methods of obtaining atomic energy it is necessary to review
briefly the properties of the atomic nucleus and atomic energy.
The atomic nucleus consists, as we know, of protons and neutrons which together
are called nucleons. Nucleons are retained in the nucleus by special nuclear forces
,of attraction that keep them in fixed positions relative to one another. ,These
forces are complex in nature. At present, all that 'has been firmly established is
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that nuclear forces are neither gravitational or electromagnetic. It is also known
that nuclear forces are "short-range" forces and exist only in the nucleus itself.
It is rather easy for us to conceive of the manner in which the molecules of liquid
constituting a drop of liquid are mutually attracted. The forces within the nucleus
are externally similar to the forces of molecular attraction in liquids. At the
surface of the nucleus they create an effect similar to the surface tension in a
liquid. This leads to the development in the nucleus of a kind of "surface tension"
which gives the nucleus its spherical form. The nucleus is like a drop of positiv-
ely charged liquid. But the forces of molecular attraction are tens of millions of
times smaller than the forces of nuclear energy. Therefore, a comparison of the
atomic nucleus with a drop of liquid is only a very crude approximation.
Now let us examine the energetics of nuclei and nuclear forces. Not possessing
adequate information as to the nature of nuclear forces, modern science is never-
theless able to determine the nuclear binding energy, depending on the existence of
these forces.
The nuclear binding energy - the energy which must be expended to perform the
work of dissociating the nucleus into its component nucleons - has to overcome the
action of nuclear forces.
In the reverse process, in the-formation (fusion) of a nucleus from nucleons,
a similar energy is released., Thus, the binding energy may be defined as the energy
which is released in the formation of the nucleus from nucleons.
. The unit most widely ,employed in nuclear physics is the electron-volt (ev). We
will have to refer to this unit of energy repeatedly so that it is useful to famil-
iarize ourselves with it. One electron-volt is equal to the energy acquired by a
particle whose electric charge is equal to the charge on an electron as it passes
through an electric field having a potential difference of one volt. In practice,
larger units are employed more frequently. Thee-units are derivatives of the
electron-volt: 1000 electron volts (the kiloelectron-volt or Key) and 1,000,000
? : -
16
electron-volts (the mega-electron-volt or Mev).
The binding energy possessed by a ,single nucleon is not identical for nuclei
differing in atomic weight (Fig.4). The greatest binding energy possessed by a,
single nucleon is found in nuclei whose atomic weights range from 40 to 80. This is
'the-atomic weight of the nuclei of iron, nickel, krypton, and certain other ele-
7
6
5
a) 4
3
2
1
t."P---."------"---
CZ
_
h)
f) _
-
-
,
41)
,
_.
P. 7._.
1 20 40 SO AD 100 no /40 160 MW 200 220 2,
1)
Fig.4 Ratio of Energy per Particle in the. Nucleus to the Atomic Weight
- a) Binding energy per nucleon, in Mev; b) Fission "fragments"; c) Energy
released in the fission of the uranium nucleus per nucleon; d) Helium;
e) Lithium; f) Energy of nuclear fusion of helium from. hydrogen per nude-
on; g) Hydrogen; h) Uranium; i).Atomic weight
monts. The binding energy per nucleon of heavy hydrogen is approximately
1,000,000 electron-volts (one Mev). As the atomic weight increases, the binding
energy per nucleon rises rapidly in the light elements to a maximum '(about 8.75 Mev)
in-the elements having an atomic weight of about 6Q,(iron and nickel), and then
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gradually declines to a value of the order of 7.5 Mev in the elements at the end of
Mendeleyevls periodic table.
As shown by the graph (Fig.L) the binding energy per particle increases as it
moves along the curve to the center from both sides, i.e., from the lighter and from
the heaviest elements. The result is that there will be two basic types of nuclear
transmutation (reactions), proceeding with the liberation of energy: the reaction
of fusion of the nuclei of light elements taking the form of what is known as
thermonuclear reactions, and the reaction of fission of heavy nuclei into nuclei of
medium weight - the reaction of fission.
The energy released per unit weight of the initial product in thermonuclear
reactions of the light elements is several times larger than that in the fission of
nuclei of heavy elements. At present, it is fission reactions that man has learned
to control. Control of thermonuclear reactions such as to permit their practical
application has not yet been attained and is a matter for the future. Therefore,
we will mainly discuss here fission reactions which dissociate various materials,
their resources, and their power potentialities.
The major fissionable material (nuclear fuel) at present is uranium. Let us
describe the basic properties'of uranium that make it possible to use it as a 'quell'
for _transport power plants.
Uranium is a bright metal, softer than steel, with a specific gravity of 18.95,
and can be worked by any mechanical method. A specific feature of uranium is its
high susceptibility to oxidation. At a temperature as low as 100?C, uranium is
capable of combustion and rapidly burns in an oxygen atmosphere. In an ordinary
chemical reaction, the heat value of uranium is very low and does not exceed
1075 cal/kg. The fusing point of uranium in an inert medium is 1130?C. This com-
paratively low fusing point and the-structural.transformations occurring in uranium
.at various temperatures have caused considerable difficulty in designing high-
temperature reactors for power plants for use in' transport.
18
r
The fission reaction of the nucleus of uranium235, shown in rough outline
in Fig.5, takes place as follows: A free neutron penetrating the nucleus brings it
into a state of excitation. This destroys the equilibrium of the nucleus, causing
Fig.5 - Fission Reaction of Uranium235 Nucleus
a) Free neutron; b) Intermediate excited stage; c) Nucleus of
Uranium235; d) Fission "fragments"; e) Secondary neutrons;
f) Gamma rays; g) Beta rays
it_usually to divide (split) into two unequal "fragments". This results in an ex-
pulsion of two or three new neutrons, known as secondaries.
A portion of the energy locked in the uranium235 nucleus (nuclear energy) is
converted into kinetic energy of the flying "fragments" and into radiant energy of
various types. The Table given below provides an approximate picture of the energy
balance of a nuclear fission reaction.
Thus the bulk of the energy, comprising approximately 166 Mev per fission, is
,tbat of the ?fragments". The "fragments" fly off in various directions at tremen-
dous speeds, collide with surrounding nuclei and, increasing the speed of their
chaotic thermal motion, heat the medium in which the process of nuclear fission is
taking place. Conversion of the kinetic energy of the "fragments" (at nuclear fis-
sion of 1 uranium235) into units of heat energy produces approximately 17.4 bil-
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lion i kcal and the total energy release from the fission of One kilogram uranium235
is 19.7 kcal. Complete combustion of one kilogram of chemical aviation fuel (kero-
sene) yields only 10,300 kcal.
The tremendous difference in the quantities of thermal energy derived from
nuclear and chemical reactions, respectively, is due to the fact that, in the ordin-
Table 1
Distribution of Energy of Fission of Uranium235 Nucleus
1. Kinetic energy of "fragments"
2. Kinetic energy of secondary
neutrons
3. Total energy of direct gamma
radiation
4. Total energy of radioactive
radiation of "fragments"
83%
3%
5%
9%
166 Mev
6 Mev
10 Mev
18 Mev
100%
200 Mev
ary combustion reaction, changes occur only in the electron shells of the atoms; no
structural changes occur within the atomic nucleus. In nuclear reactions, a change
(rearrangement) occurs in the nuclei themselves. Since the mass of a nucleus ex-
ceeds by thousands of times the mass.of the electron shell of the atom of any ele-
ment, the energy released in nuclear reactions is therefore greater. As early
as 1905, the German physicist Einstein formulated a law that defined the quantita-
tive mass-energy interrelation in nature. This law is expressed by the familiar
equation
E --= rnc2,
in which E. is the total energy of a body, In ergs;
.m is the mass of the body, in grams;
.c is the velocity of light, in am/sec.
20
In accordance with this law, every change in the energy of a body involves a
corresponding change in its mass, and vice versa.
In ordinary chemical combustion reactions, it is a practical impossibility to
observe changes in the mass of the reacting substances. This is explained by the
fact that the amount of energy being released is relatively small, and therefore the
change in mass is negligible. For example, complete combustion of 100 tons of kero-
sene in an oxidation reaction involves the participation of approximately 1500 tons
of air, and the total change in the mass of the combustion products due to the
liberation of energy is only 0.03 grams. Naturally, to detect such a quantity in
the total mass of reacting products (1600 tons) is impossible. However, the law of
the mass-energy interrelation is demonstrated most strikingly in nuclear reactions,
which are characterized by considerable changes in the energy of the nuclei and by
a noticeable change in mass.
The law of the mass-energy interrelation is the basis of one of the methods of
determining the ?heating value' of nuclear fuel, and yields accurate quantitative
results.
From the equation, E = ma2, it follows that, for m = 1 kg, the theoretical va-
lue of the energy E (in thermal units) will be 21,600 billion kcal.
In the splitting (fission) reaction of nuclear fuel, the mass of the end prod-
ucts of fission is smaller than the mass of the initial substance by a definite
magnitude, which may be called the mass defect (loss). Experimental and mathemati-
cal data have established that, for uranium235, the mass defect per kilogram of
substance is
0,000911 0,001 Kg.
Thus, when all the nuclei in 1 kg of uranium235 have undergone fission, the
mass of the end products of the nuclear reaction is almost one whole gram less than
the mass of the initial substance before fission.
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The amounts of energy released may thus be determined on the basis of the quan-
tity of mass liberated (according to the mass defect). Since the total energy ?
of 1 kg of the substance, as indicated above, is 21,600 billion kcal, the energy re-
leased in this case will be
Q ----- 21600 0,000914 19,7 billion kcal
This number is the heating value of uranium2351 i.e., the amount of energy released
when all. the nuclei in one kilogram of uranium have undergone fission.
It should be mentioned that the complete combustion of 1 kg kerosene liberates
1
a total of 10,300 kcal, or approximately only
as much.
2,000,000
A comparison of the heating value of nuclear fuel with that of modern chemical
aviation fuels leads to the conclusion that the consumption of nuclear fuel will be
a fraction of that of chemical fuel, for the same effective power of power plants.
This fact offers the possibility of a considerable increase in the range of aircraft
and rockets when using nuclear fuel.
Comparison of the World Resources of Chemical and Nuclear Fuels
On the basis of data published in the 'press, the prospected resources of chem-
ical fuels and nuclear fissionable materials are approximately as follows:
Coal 2000 billion tone
Oil 25 billion tons
Uranium 0.01 billion tons
As we see, there is considerably less uranium in the earth than coal and
petroleum. Nevertheless, despite this apparently unfavorable relationship in terms
of weight, the margin of energy in uranium is approximately ten times greater than
the margin of energy in. coal and oil combined.
In order to get an idea on the distribution of uranium in nature, let us ex:-
22
amine-the content by weight (in percent) of certain metals in the earth's crust.
Copper 0.010% (100 gm/ton of earth)
Uranium 0.007$ (70 gm/ton of earth)
Zinc 0.004%
Lead 0.002%
Gold 0.0000001%
It will be seen from these data that uranium is an element more widely dis-
tributed in nature than zinc, lead, and gold combined.
Natural native uranium is obtained from ores and is a mixture of three iso-
topes: uranium238 (99.282%), uranium 235 (0.712%), uranium234 (0.006%).
Only uranium235 is available as a fissionable material satisfying the require-
ments of power production. Uranium235 is capable of self-sustaining (chain) nuclear
reaction, i.e., of effectuating an uninterrupted release of energy. But the very
small content of the 235-isotope renders natural uranium unacceptable for use in
power plants for purposes of transportation. It is necessary either to separate the
uranium235 in its pure form or to enrich natural uranium with this isotope.
-The process of separating the isotopes of uranium is to this day one of the
most-expensive and complex?processes in the atomic industry. The problem o? wide-
spread use of nuclear fuel for power production would be hopelessly insoluble, be-
cause of the small amount of natural uranium235 and the difficulties of obtaining '
it in pure form, if there had not been discovered methods of obtaining artificial
nUClear fuels from the natural resources of uranium238 andsthorium232.
-:Artificial nuclear fuels now available include the following: plutonium239
(obtained in special breeder reactors from uranium238), uranium233 (obtained in re-
actors from natural thorium232) and certain others.
In view of the fact that methods have been obtained for the application of
artificial nuclear fuels, permitting the use of uranium238 and thorium2324 ealcula-
_
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tions 'of the energy resources in nuclear fuels have been made on the basis of natur-
al uranium and thorium (see Table 2).
This Table shows that the total margin of energy in nuclear fuels is approximr-
Table 2
World Resources of Energy in Various Types of Fuel
Type of Fuel
World Supply
Energy Content
Coal
Oil
Natural gas
Uranium + thorium
3,482 billion tons
197 billion m3
15,850 billion m3
0.026 billion tons
21.10 x 106 billion kw-hrs
2.22 x 106 billion kw-hrs
0.17 x 106 billion kw-hrs
519.00 x 106 billion kw-hrs
ately 22 times as great as the total energy resources in all organic fuels com-
bined.
In addition, there is reason to expect a considerable increase in the sources
of nuclear fuels as a result of the discovery of new methods of fission and fusion
of the nuclei of other chemical elements. At present, science has already discov-
ered the possibility of experimental work toward controlled thermonuclear reactions
with the light elements. A controlled thermonuclear reaction makes it possible to
obtain energy due to the formation of helium from heavy hydrogen (deuterium) which
is widely disseminated in nature. Every ton of ordinary water in nature contains
as much as 200gm of heavy water, whose molecules contain atoms of heavy hydrogen.
The conditions needed for fusion of hydrogen into helium have thus far been created
only in the hydrogen bomb. Scientists are working to produce the conditions for a
decelerated controllable course of thermonuclear reaction without explosion, so as
to learn to control this reaction and use it for purposes of power generation. The
solution of this most difficult and challenging' task will increase the resources of
t the disposal of man by hundreds of thousands of times.
24
The cost of nuclear fuel is still high but is decreasing gradually from year to
year. Today, it is only in rare cases that nuclear fuel is cheaper and more desir-
able to use than chemical fuel, but as nuclear power generation and the atomic in-
dustry develop further, the cost of nuclear fuel will become considerably lower than
that-of chemical fuels.
- The wide utilization of atomic energy in industry, transport, and all branches
- ? _
of the national economy is one of the most difficult, but at the same time most
lofty and noteworthy undertaking of contemporary science and, technology.
First Conception of Atomic Aircraft Engines
The first thoughts as to the possibility of wide-scale use of atomic energy
begin to appear even before the discovery
of nuclear fission chain reaction. For
example, as early as January 1935, the
journal uTekhnika Molodezhift (Technics for
Youth) carried an article by 0.Petrovskiy,
which examined the problem of using atomic
energy in the national economy, this being
the energy obtained by fusion of helium
nuclei from hydrogen nuclei.
The practical introduction of atomic
A
NNA:
- Schematic Layout of a Hypo-
thetical Nuclear Rain-Jet Engine
a) Reflector; b) Nuclear fuel
6
energy into the national economy was begun by the Soviet Union where the world's
first atonic electric power plant was erected which has been working successfully
since the summer of 1954. Then the question was posed, and has since been success-
fully solved, of developing atomic power plants for sea-going surface and submarine
a
vessels. In the Soviet Union, a powerful atomic ice-breaker is under construction,
and 1n the United States the first submarines with atomic engines have been tested.
The problem of using atomic energy in aircraft engines has proved to be one of
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the most difficult to realize from the point of view of engineering. This problem
is complex primarily because of. the fact that an aircraft presents exceedingly rigid
specifications with respect to engine weight, engine power, and absolute reliability
in operation. Let us evaluate the probable future trend in the application of atom-
ic energy to aircraft engines.
At first glance, it would seem that the simplest atomic aircraft engine would
be one making use of the direct reaction of nfragmentsu resulting from the fission
of heavy nuclei. .Such an engine would simply be a lump of atomic fuel, encased in
a container which reflects neutrons (Fig.6). The fission products of the nuclear
fuel in this ease would move only in the one open direction, thus creating thrust
due to reactive forces.' This simple design of an atomic rocket entine comprises
fundamental contradictions, which necessarily render it unrealizable. Only a very
thin surface layer is capable of radiating decomposition products into space. The
fission reaction has to take place throughout the entire mass of fuel, and heat will
be liberated throughout this entire volume. This creates instantaneous heating,
melts the nuclear fuel, and converts it into vapor. In other words, this hypotheti-
cal engine would necessarily explode instantaneously. It is impossible to conduct
a chain reaction only in the thin surface layer.
Is it conceivable to convert atomic energy directly into electric power and
then make use of electric motors rotated by propellers?
Direct conversion of atomic energy into electricity is possible with the aid of
an atomic electric 'generator or atomic battery. This battery or cell (Fig.?) is
arranged as follows:
A spherical metal shell constituting an electrode of the atomic cell contains
a second spherical electrode, coated with a thin layer of radioactive substance
which emits beta particles. The air is exhausted from-such a device. The internal
?electrode emitting beta particles of negative electric charge, is given a positive
charge. The outer shell, on which the beta particles collect, is given a negative
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charge.
Such an atomic battery would be able to yield high-voltage currents, but the
current strength would be very small. This is due to the fact that the charge is
transmitted to the outer shell only by the beta particles emitted by a thin surface
layer of radioactive substance.
An atomic electric cell might also be built on the basis of utilizing artificial
radioactive isotopes in combination with certain semiconductors. However, such
"batteries" would also be so weak in power
b) as to make their use for feeding of elec-
tric motors impossible.
Thus, direct conversion of atomic
energy into electric energy cannot be em-
ployed today in power plants.
The reaction of the fission of heavy
nuclei is accompanied, as we know, by the
liberation of large amounts of heat. The
Fig.7 - Diagram of "Atomic Electric
question arises as to whether atomic ener-
Generatorn (Battery)
gy cannot be utilized in a heat engine of
a) Nuclear fuel; b) Evacuated space;
some kind?
c) Shell; d) Insulator
Let us take, for example, an internal
combustion engine and instead of the fuel mixture let us charge a gaseous nuclear
fuel of some kind into a cylinder. The engine must be so designed that, during the
compression process, the density of the gaseous nuclear fuel is greatly increased'
and a nuclear chain reaction sets in. During the nuclear reaction, the emitted heat
would be many times greater than that obtainable by the combustion of gasoline, so
that-' such an engine would be much more powerful. However, an engine of this type is
unrealizable since, in order for nuclear fuel to undergo a chain reaction-in the
gaseous form, even when compressed, an engine-of colossal dimensions would be re-
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quired.
Perhaps then solid nuclear fuel might be used in a two-cycle engine? TO do
this, a lump of nuclear fuel would be placed in the cylinder head, and another on
the piston. When the piston reaches top dead center, the two lumps would approach
so closely that a nuclear reaction would be initiated. The heat liberated would heat
the air in the cylinder, thus starting the power stroke of the piston. In actuality,
however, such an engine would explode the moment it is started. In fact, the atom
bomb is designed in exactly this manner. Two pieces of the charge of uranium235 are
brought together, with the result that a charge of uranium235 having greater-than-
critical mass is produced, and a chain nuclear fission reaction results, causing an
explosion.
Many similar fantastic schemes could be listed. Nevertheless we were justified
in centering attention on heat engines, in view of the fact that more than 80% of
the energy in the fission reaction is liberated in the form of heat.
Let vs recall what an ordinary power plant for transport purposes comprises.
Such a plant includes, as we know, an engines a transmission, and a propulsive de-
vice. Within the engine, liberation of heat energy from .the fuel and its conversion
into mechanical energy takes place. These two processes may occur in a single sys-
tem, as in an internal combustion engine, or in eeparate unite as in a steam engine.
The propulsive unit is the device that does the work of thrust created by the me-
chanical energy received from the engine. The wheels are the propulsive unit of an
automobile; the propeller serves that function in an aircraft. The transmission
transmits the energy from the engine to the propulsive device.
These three basic parts must by necessity be present also in an atomic power
plant (Fig.8).. Here the emission of heat occurs in a nuclear reactor as a result of
the "combustion" of nuclear fuel as the nuclei undergo fission. In order to dissi-
pate the heat from the reactor, it is honeycombed with channels through which a'
heat-transfer agent is propelled by pump. The heat-transfer agent may be either
fused metals of low melting point, gases (helium, nitrogen, carbon dioxide) or else
ordinary or heavy water under high pressure. The heat-transfer agent, heated in the
-reactor as it passes through the heat exchanger, yields part of its heat energy to
the-substance actuating the engine and is returned to the reactor by a pump. Thus,
a)
Fig.8 - Possible Schematic layout of Aircraft Atomic Power Plant
a) Reactor; b) Heat exchanger; c) Pump for heat-transfer agent-;
d) Pump for working fluid; e) Turbine; f) Reduction gear;
g) Propeller; h) Condenser; i) Coolant
circulating in a closed circuit formed by the reactors the heat exchanger, the pump
-anethe reactor, the transfer agent heats-the substance actuating the engine, by way
of atomic energy.
The engine used nay, either be a steam engine or a gas turbine. The actuating
substance may be either water, mercury vapors-hydrogen; or helium, for example.
Circulation,.of_the actuating substance is by a pump, driven by the main Or by an, ,
_
auxiliary .turbine. For operation of the turbine; the exhausted steam must be disr.
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charged into a condenser. In the condenser the steam is condensed into liquid and
is recycled to the heat exchanger by the pump. The coolant medium on ship installa-
tions may be water of the surrounding medium, while in aircraft it may be the rela-
tive airflow. A condenser is necessary also if the working substance is a gas. Thus,
we get the following circulating pattern for the working substance: heat exchanger -
- turbine - condenser - pump - heat exchanger.
The turbine is connected to the driver by a transmission. In aircraft power
plants mechanical transmissions are generally used. Shipboard power plants use
electric transmissions, in which a number of electric motors connected to propellers
are fed from a single powerful generator.
Aviation is the area in which atomic power plants may have broadest applica-
tion. In addition to the above designs in which the turbine shaft is connected to
a propeller over a reduction gear, the various types of aircraft engines in use to-
day may be adapted for operation on atomic energy.
The reactor is a component of all atomic power plants. Many designs include
heat exchangers. An examination of these vital components of atomic power plants is
the subject of the next Chapter.
4
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I
CHAPTER ii
NUCLEAR REACTORS FOR AIRCRAFT POWER PLANTS
A nuclear reactor is a device within, which a controllable chain reaction in-
volving the fission of nuclei of fuel, accompanied by the conversion of atomic into
thermal energy, takes place. The rapid progress in nuclear engineering and reactor
design in recent years has led to the result that today nuclear reactors are being
built successfully not only for stationary power plants, but for power plants of
ships of various types. The first success in the design of nuclear reactors for
aircraft power plants, no doubt, is imminent. According to reports in the fOreign
press, nuclear reactors for atomic aircraft engines, to reach flying speeds of the
order of 900 km/hr for heavy aircraft, are already being ground-tested and flight-
tested on experimental aircraft.
Main Features of Aircraft Nuclear. Reactors and Their Specifications ,
To makeit possible for an atomic aircraft to ay at-high Speed, an aircraft -
nuclear reactor must develop extremely high power. The power of a nuclear reactor,
like .that of any source of thermal energy, is measured. by the amount of heat lib-
erated in unit time. For example, if 1 kcal of heat-is liberated per.seccind of-
op61.ation of a reactor, the power of the reactor will be 1 kcal/sec, or
3600 kcal/hr. In today's literature, the heating value of nuclear reactors is most
frequently given in kilowatts (1 kw is equal to 860 kcal/hr).
Let us cite an example indicating the power requirement of an aircraft react-or.
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Let us assume that an atoffiic aircraft weighs 150 tons and has a very advanced aero-
dynamic form: Calculations show that, to enable this aircraft to fly at the speed
of sound at an altitude of 11 km, the nuclear reactor must have a power of about
300,000 kw. This is ten times as high as the power of the nuclear reactor in the
first Soviet powerplant, and approximately twice as large as the reactor of the
Soviet atomic ice-breaker. In order for the atomic aircraft to fly at an altitude
of 11 km, at 1.5 times the speed of sound, the power of its reactor would have to be
approximately 900,000 kw.
The high power of an aircraft nuclear reactor has to be obtained within the
smallest possible dimensions. If its dimensions are large, it will be difficult to
house the reactor within the aircraft, especially if the aircraft is to remain fully
streamlined. In addition, the larger the dimensions of the reactor, the greater
will be the weight of the casings and shields needed to protect the crew and pas-
sengers of an atomic aircraft from the effects of the harmful radiations from the
reactor. The exceedingly great weight of the radiation-shielding system is today
one of the main obstacles to the design of an atomic aircraft useful for military
and civil purposes.
The nuclear reactor for an aircraft power plant must weigh as little as pos-
sible. This requirement is particularly important for an atomic aircraft and is
again based on the exceedingly great weight of the IldeadR load - the radiation-
shielding system.
An aircraft nuclear reactor must be a high-temperature reactor. The higher
the temperature in the reactor, the smaller can be its size and weight and the
smaller will be the size and weight required to yield a given power. An increase
in the teiperature results in an in-crease in efficiency of atomic engines of any..
type. This is very important, since the greater the efficiency, the less must be
the power of the reactor in order to. yield the required engine power. If it is
borne in mind that the entire system of radiation shielding is dependent upon the
32
?
dimensions and size of the reactor, the major importance of achieving high temper-
atures will become obvious. Approximate calculations show that, in order to obtain
the same flight characteristics for atomic aircraft as for chemical-fuel aircraft
now in Series production, the reactor surfaces must be heated to not less than
1000oC.
A nuclear reactor for aircraft must be highly reliable in operation. The re-
quirement of reliability in an aircraft reactor for the desired term of service life
is considerably stricter than for reactors in fixed positions. Unlike stationary
reactors, the aircraft reactor must function normally no matter what its position in
space. The functioning of the reactor must not be affected by inertia loads de-
veloping on changes in speed or direction of the aircraft.
General Design of a Nuclear Reactor and its Main Processes
The major processes in a nuclear reactor comprise a controllable fission chain
reaction and dissipation of the heat generated by this reaction. The portion of
the nuclear reactor in which the fission reaction occurs is called the active sec-
tion or core. As a rule, the core contains the following materials: nuclear fuel,
the moderator, the heat-transfer agent, material of the control or regulator de-
vices, structural materials, i.e., materials needed to reinforce and fix the vari-
ous design elements in their mutually correct position, to seal the heat-transfer
ducts, to protect the nuclear fuel from oxidation, etc. The core is usually sur-
rounded by a layer of substance that reflects neutrons.
Figure 9 shows one of the possible principal layouts of a nuclear reactor.
Nuclear fuel, in the form of cylindrical rods contained in protective metal casings,
is placed in grooves within the solid moderator. The generated heat is dissipated
by a liquid heat-transfer agent, whose flow is shown by arrows in the diagram. Con-
trol of the nuclear fission reaction is by means of a control rod made of a material
that is a good neutron absorber. The core of the reactor is shown by the broken
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line in the drawing. The reaction of fission of heavy nuclei and all the attendent
phenomena, such as liberation of heat, escape of secondary neutrons, etc., have been
Fig.9 - Principal Schematic Layout of a Nuclear Reactor
a) Outer shell of reactor; b) Control or regulating rod; c) Retainer plate;
d) Side reflector; e) Moderator; f) Protective shells; g) Hold-down rod;
h) Rod of nuclear fuel
described in the preceding Chapter. Here we will deal with other processes in
which neutrons participate.
Let us first examine the processes leading to variations-in the kinetic energy
of neutrons, i.e., the energy with which they,move. The collision of neutrons with
atomic nuclei of various materials, including nuclei of fuel, is not always ac-
companied by neutron capture. Often, the neutrons bounce off the nuclei, trans-
ferring to them a certain portion of their kinetic energy. As a result, the speed
34.
?
?
?
?
?
of the neutrons decreases and, in addition, a change in the direction of motion
takes place. This process has come to be called neutron scattering. The process of
A)
4
b)
e)
Fig.10 - Schematic Sketch of Neutron Scattering
a) Neutron before scattering; b) Neutron after scattering;
c) Nucleus before scattering; d) Scattering angle; e) Nucleus after sc.
scattering is shown in schematic form in Fig.10. Here, V1 is the speed of the neu-
tron before collision with the nucleus, and V2 is its speed after collision. At
identical scattering angles, the magnitude of the kinetic energy released by the
neutron depends upon the mass of the nucleus. The magnitude of the energy trans-
mitted reaches a maximum when the mass of the neutron and the nucleus is identical.
A caae of this type may occur, for example, when a neutron collides with a hydrogen
nucleus. Scattering, characterized by a considerable reduction in the energy of
the neutron at each collision with the nucleus, is known as deceleration or moder-
ation. The moderation of neutrons is a nuclear process artificially induced when-
ever _a rapid reduction in neutron energy is required.
The secondary neutrons escaping on nuclear fission, possess a very high kin-
etic energy at their moment of "birth". The energy of the absolute majority of
secondary neutrons lies withida range of 1 - 2 Mev corresponding to a speed of
14,000 - 20,000 km/sec. Neutrons of this velocity are called fast neutrons. In
the course of the-scittering process, partioular1y-in the process of deceleration,
35
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STAT
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the kinetic energy of neutrons may decline to a level corresponding to the energy of
thermal motion of the particles in the surrounding medium. Such neutrons are called
slaw or thermal. Their energy depends upon the temperature of the surrounding me-
dium. For example, at a temperature of + 20?C, this energy is approximately
. 0.025 ev. The mean velocity of neutrons in this case is approximately 2 km/sec. At
a temperature of + 700?C, the neutron energy is approximately 0.085 ev, and their
velocity is 4 km/sec. All neutrons with a kinetic energy lower than that of the
fast neutrons and higher than that of the thermal neutrons, are called intermediate
neutrons.
The kinetic energy of the neutrons governs the relative number of neutrons in
each generation participating in any given nuclear process, or as the saying goes,
the probability that one or another process will occur.
Fission of the nuclei of urani235 urani33, and plutonium239
um um may be ef-
fected by thermal, intermediate, and fast neutrons. However, the probability of
fission increases with decreasing energy of the neutrons because of the fact that,
in this case, the probability that a neutron will be captured by the nucleus in-
creases. These are the properties that make uranium35, uranium233, and
plutonium239 highly efficient nuclear fuels.
Capture of the nuclei of uranium238 and thorium232 by thermal and intermediate
neutrons does not result in fission. The fission of these nuclei is induced only
by certain.fast neutrons. For this reason, uranium238 and thorium232 cannot serve
as nuclear fuels. The chain reaction in any nuclear reactor occurs primarily due
to the fission of the nuclei of highly efficient fuels.
Now let us review briefly the processes, useless for the fission reaction it-
self but resulting in neutron loss. These processes include:
Capture of neutrons by fuel nuclei without subsequent fission;
Capture of neutrons,by nuclei of all other materials used in the reactor;
Capture of neutrons by nuclei of fission products accumulated during regular
36
?
1
r.
operation of the reactor.
4?10^
All these processes can be categorized by the Single concept: neutron absorp-
tion. Like scattering, the absorption of neutrons is inevitable, in view of the
a)
b)
Ems
Fig.11 - Typical Graph of the Neutron Absorption Probability as a
Function of the Energy of Their Motion
a) Absorption probability; b) Neutron energy
fact that all known materials absorb neutrons to some degree. At certain levels of
neutron energies, which vary with the type of material, the absorption probability
increases sharply. This phenomenon is known as resonance absorption. The phenom-:
anon of resonance absorption is observed'in a number of materials used in the man-
ufacture of reactors, but it is most pronounced in the case of uranium238.
_
Figure 11 gives a characteristic graph of the relationship between the proba-
bility of neutron absorption and their energy, for the case of uranium238. The
; e
graph indicates that, at 4 neutron energy equal to E" , neutrons are absorbed
res
I 1
..toomeam??????????m....
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particularly "avidlet. The value of Eres is approximately 7 ev, corresponding to a
neutron velocity of approximately 40 km/sec.
When a nuclear reactor is in operation, still another phenomenon resulting in
?a neutron loss is observed. A certain portion of the neutrons may escape from the
bounds of the reactor, without undergoing fission. This phenomenon is called loss
of neutrons by escape or neutron leakage. Neutron leakage is inevitable in any
practical nuclear reactor.
The process of absorption and escape means that not nearly all neutrons gen-
erated during the fission process, actually participate in subsequent fissions.
Therefore, the nuclear fission reaction can become a self-sustaining (chain) re-
action only under certain circumstances.
The Critical State of a Nuclear Reactor
In order to make practical use of the atomic energy liberated during the fis-
sion of fuel nuclei, the prime requisite is that the fission reaction be self-
sustaining. In other words, once having begun, it must continue spontaneously. The
possibility of realizing such a reaction is based on the fact that, on splitting of
each nucleus, two or three new (secondary) neutrons are produced; these are capable
of inducing the fission of further nuclei. However, an attempt to realize this
possibility is greatly hampered by the inevitable neutron loss: absorption and
leakage. The minimum condition for realization of a self-sustaining fission re-
action is that each generation of neutrons produced on nuclear fission gives rise
to a new generation consisting of the same number as the preceding one. In other
'words, an identical number of neutrons participates in each successive act of fis-
sion, after the losses have been discounted. The condition of a reactor in which
this requirement is met is ,termed the critical state.
The critical state is characterized by a neutron flux constant in time, by a
constant number of fissions per second, and consequently by a constant quantity of
38
?
heat liberated per second, i.e., by a thermal capacity constant in time. The criti-
cal state is therefore also called the steady state, and the operating conditions of
the reactor in this state are known as stationary or steady conditions. The amount
of thermal power depends upon the number of fissions taking place in the reactor
each second. It has been calculated that a power of one kilowatt represents
31,000 billion fissions per second.
What practical steps will have to be taken in order to attain the critical
state?
Let us first consider the reaching of a critical state in a solid lamp of
highly effective nuclear fuel. We find that if the piece of fuel is exceedingly
small, the nuclear reaction, after initiation, rapidly ceases. The main reason for
this is the excessively large loss of neutrons by escape, due to the fact that, in
a small lump, the collision probability with nuclei is very small. Neutron leakage
occurs on the surface layer, while capture, resulting in fission, occurs throughout
the entire volume of the lump. Consequently, neutron leakage may be reduced by re-
ducing the ratio of surface to volume. For a given geometric form of the lump,
this is attained by increasing its absolute dimensions, i.e., by the addition of
nuclear fuel. As soon as dimensions of a certain size are reached, the leakage is
reduced to the point that the same number of neutrons will participate in subsequent
fission processes as in the preceding processes. This means that, in practice, the
critical state in nuclear fuel is reached by bringing its quantity up to a certain
definite size. The size and mass of a lump of nuclear fuel representing the criti-
cal state, are called the critical size and critical mass. Minimum critical mass
.
of nuclear tail will be obtained with lumps of spherical form, since a sphere rep-
resents the minimum ratio of surface to volume. For uranium235, the critical mass
of a spherical lump is approximately the mass weighing 1 kg.
In a practical nuclear reactor, the fuel is distributed more or less uniformly
throughout the volume of the core. Loss of neutrons by escape, in this case,: depends
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not only on the quantity of nuclear fuel but also on the dimensions and geometric
shape of the core. In addition to fuel, the core contains other materials neces-
sarily participating in the scattering and absorption of neutrons. The ability of
these materials to scatter and capture neutrons varies with variations in tempera-
ture.
The properties of these materials, the relative quantity of each in the core,
and the relative position of each determines the mean velocity of the neutrons at
which the overwhelming majority of nuclear fissions of the fuel takes place. This
velocity is the basis on which reactors are classified into thermal, intermediate,
and fast-neutron reactors.
As we see, the condition of a practical nuclear reactor depends upon a number
of circumstances, but in practice the critical condition is reached by charging a
specific amount of nuclear fuel into the core, in view of the fact that all the
other conditions are usually present to begin with. For example, the type of re-
actor is selected in the light of its purpose and the properties of the nuclear fuel
available. The dimensions of the core are based on the conditions required to at-
tain the desired power and, consequently, the necessary heat transfer per unit time.
The'operating temperature is based on the properties of the mAerials used, etc.
Thus, in an atomic power plant, it is necessary to 'have an adequate quantity
of nuclear.fuel only to permit utilization of a portion thereof to liberate the
enclosed energy. In other words, an atomic power plant is capable of functioning
other conditions being equal, only so long as the quantity of unused nuclearTuel
remains above the critical level. Further consumption of fuel is simply impossible.
When it is stated that an aircraft with an atomic engine will burn 500 - 600 gm of
nuclear fuel in the,course of a flight around the world, this does not mean that
sucfi a flight can be performed with only: 500 - 600 gm of fuel aboard the aircraft.
These 506- 600 gm can be consumed only if they represent merely a small portion of
(iL,..4'71-t)' of the total fuel aboard the aircraft and in the reactor.
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f
As we shall soon see, the quantity of nuclear fuel required to maintain a criti-
cal state, does not remain constant during operation of the reactor, and increases
as the temperature increases and also as fission products accumulate. In the very
best reactors now in operation and under construction, the critical weight of highly
efficient nuclear fuel at the end of the period of operation is not less than 80% of
the weight after the initial charge. This means that not more than 20% of the in-
itial charge can be consumed in the course of operation. This is one of the peculi-
arities of an atomic power plant as compared with those using chemical fuels. In
the latter, as we know, the entire available fuel can be completely consumed.
Enormous amounts of labor and materials are required to obtain highly efficient
nuclear fuels. It is natural therefore that tremendous efforts have been made by
scientists and engineers of all countries working in the field of nuclear energy
and reactor design, with the object of finding means of reducing the critical
weight (mass) of nuclear fuel.
Reduction in the critical weight is facilitated by all measures that tend to
diminish the neutron loss. One of these measures is the use, in the manufacture of
reactors, of materials that absorb as few neutrons as possible. The minimum criti-
cal weight is obtained when the moderator and heat-transfer agent is heavy water,
while zirconium is used as the structural material. However, the use of these ma-
_
terias is not always possible. Specifically, to attain high operating tempera-
tures, it is sometimes necessary to use fused metals as the heat-transfer agent,
and-heat-resistant nickel alloys as the structural materials. Since .these materials
have high neutron-absorbing properties, the quantity of such materials used within
the core must be reduced in order to lower the critical weight of the. fuel.
The critical weight of nuclear fuel may be reduced by making provision to have
the neutrons leaving the core reflected back into that core. If the core of a re-.
actor is surrounded by a scattering substance, it will act as a reflector, i.e.,
a portion of the neutrons leaking from the core will be returned to there. Thi
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will result in a reduction in the loss of neutrons by leakage, and the critical
state will be reached with a lower quantity of nuclear fuel than is the case when no
reflector is used.
In selecting the material for the reflector, the following are the governing
conditions: In the first place, the amount of neutrons returned is greater, the
closer to the boundary of the core the point is located at which the scattering col-
lisions of neutrons with nuclei from the reflector take place, and in the second
place, the fewer the collisions resulting in neutron absorption. Consequently, in
order to arrange for effective reflection, it is necessary to select a material for
which the probability of neutron scattering would be as great as possible and the
probability of absorption as small as possible. Heavy water is the best material
for this purpose. Graphite, beryllium, ordinary water, zirconium, and certain other
substances follow in order of diminishing the reflectivity.
Let us see what effect the thickness of a reflecting layer has on the process
of reflection. Let us assume that we gradually increase the thickness of the re-
flector. The results are shown in the graph in Fig.12. The number of neutrons re-
turned by the reflector into the core are laid off, on the vertical axis, while the
thickness of the reflecting layer is plotted on the horizontal axis. The graph
shows that, as the thickness of the reflector increases, the quantity of neutrons,
returned to the core also increases. The sharpest increase is produced by the
layers closest to the core. The following layers, although they do return neutrons,
do this to a lesser degree than the preceding ones. Finally, starting at some par-
ticular thickness, represented by the segment OA, the number of neutrons returned
ceases' to increase for all practical purposes. Any further increase in the thick-
ness of the reflector is purposeless, since the bulk of the neutrons will be re-
flected or absorbed before the outer boundary of the reflector is reached. The
thickness of the layer to which the reflection effect continues to increase sub-
stantially, is approximately as follows: 1.5 - 2.0 m for heavy water, 0.8 - 1.0m
-
42
for graphite, and 0.45 - 0.5 m for beryllium.
When a reflector is used, there is an increase in the number of fissions of the
nuclear fuel per second, immediately adjacent to the boundary of the core of the
reactor.
obtain the desired quantity with a core of smaller dimensions than in a reactor not
using a reflector. This is most important as far as aircraft reactOrs are con-
cerned, in which the requirement of a reduction in dimensions of the core is of
prime importance. It is true that the overall dimensions of the reactor are greater.
whea a reflector is used than when it is not, but it must not be forgotten that .the
reflector, in any, case, is an integral-part of the shielding from the neutron ?
stream. The thicker the reflector, the less will be the required thickness of the
special shielding. In order for the reflector to form an effective portion of the
A
b)
Fig.12 - Effect of Thickness of Reflecting Layer on the
Process of Reflection
a) Number of neutrons returned to the core by the reflector;
b) Thickness of the reflecting layer
More efficient utilization of the peripheral zone makes it possible to.
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aircraft shielding system, it is preferable ,to use a material. that,slows neutrons ?_
effectively:- The decelerated neutrons moving past the reflector 'will.. be;,completely
absorbed in a_relatively thin layer of special protective shielding.. - -
In the nuclear reactors of modern stationary and sea-going power plants, water
and graphite are the materials most often used for the reflector, since they are
cheapest and adequately efficient. In high-temperature aircraft reactors, the use
_
of water is impossible because of its law boiling point. Therefore, graphite is
the only cheap material remaining. A reactor with reflector will have the smallest
dimensions if metallic beryllium is used as refleCtor. Beryllium has a relatively
high melting point (1315?C):, is light, and inert to neutron irradiation. A disad-
vantage of beryllium is its high price.
Unstable Operating Conditions of Nuclear Reactors
A steady state, in which the neutron flux and the capacity of the reactor re-
main constant inctime, is ,observed when the.-_reactoria.in.the,criticalistate by the
fact that the neutron multiplication-'constant Kis equal to unity. The multiplica-
tion constant-KAs'theTatio of,the:nuMberof neutronsJundergoing-fission in a
given generation to the number7,0,neutrons.,that have-,fiSsioned in the preceding gen-
eration. If the multiplier deviates from unity for any reason, the neutron flux,
7.?.?:'
the number of fissions per second, and the power of the reactor will also vary with
n
time, increasing or decreasing accordingly. The operating conditions of a reactor
ei 1111
in which its power changes with time are called nonstationary or unstable.
- - _E
L:-
The multiplication constant is equal to unity when the amount of nuclear fuel
-?
within the reactor core is exactly equal to the critical quantity for the given
;17?.,J;
operating conditions. A change in the multiplication constant occurs when this
: s'C fl"--f.1) al
equality is violated.
t.F.21 V .7 4;51.i3.4
If the weight of the nuclear' fuel within the core is less than critical, the
flz c' -z3.1J -7r.!"-/
multiplication constant is less than unity. This condition is called subcritical;
44
and- the parier ,or. the .reactor ili drop steadily. so,,long:,as this is the, case:. Acr.
tua.lity,...the -reactor 'is converted to. subcritical conditions when-fit, is, necessary, to; .
red-uce the 'generated L.power,:or- to: 'shut. down the- reactor., .
.1 .
; !
-If the -reactor contains more -than the critical amount- of-.nuclear
multiplication constant will be greater than ux4ty.-.1-: This ?is: .the,supercr.it4.7.:
cal state of the reactor '-and.; is. characterized Thy a ,constant -increase ? in Tower
vie' i "of the-fact ,that-...the fissionz-reaction now becomes, a.,:virtual: -avalanche,. ?1.n.,ac7
tual operation, a reactor placed- in the _supercritical state for :the purpose ,of,_
"racing it", i.e., to increase its power. A special case of racing or "riding up"
is the starting of a nuclear reactor.
fissiatireattions,:withoutJAiscussing hawi:theyi.,are
initiatedet"iie take:tgaddLthiS'oMission. be toundAhati.in any nuclear
readtiorithei.oLit'ABayS-a certain-number ofAfrefrorrastthey are,called;-,stray
neutrons. A percentage of these are generated as the result of the spontaneous-fis7
sian of-tuarnuelei*'i another' pOrtion isial=kedout,.of themuclei.-.7byloarticles of
cosMiefriaiatibri:-'Althaughntfiel number of stray .neutrons is small, 'it is quite Sjuf'.
fibientr=titi=itart-a-Chainftission-reaction.-().-In order fox an inoperatiyeiyeactor-
"comelalive",-liteis--enaughr(tof-bi.ifig theqoultiplication%constant toaa;-quantity-,.-,,
slightly larger than unity.
importantz., characteristic of ;-Junstable? operating ponditians,...is the time
rate, i Chinger:;in power: It isif.most import.5uioAcnow incre
prer--izi the).superci-itical:, state of .thc-reactor.c-.-APE3Pacc.e?PiY913ri,irET,34:-..PF.?F.-P.:9,..i.0
of --thereadtion1/41 er eat e s difficulties, in tottralli' it.p:,:_-14psternystemssf2Sfa,lit,a7"
matid chiitieil,'Ilicillaatter, hair hquickT7actingy they,..;:may..pbe require_ ?certain., ,:-,Amouri.;
F `. 4 %. TC.); - lc) ut),. :2-?4;
*"The phenomenon of spontaneous fission of the uranium nucleus was discovered by
'21,) Da:s
the Soviet scientists, G.N.Flerov and K.A.Petrzhak. They showed that in one gram
-.2, ,t7OSEEZ 1--4n1-.1 A ".-tC
of natural uranium there occur on the average 23 spontaneous fission's per hour.
,5;170J ,i.0
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time to function. It may happen that; during this time, the liberation of heat in
the reactor will greatly exceed the removal of heat, so that the reactor will melt.
An excessively slaw increase in power is also not always desirable, particularly in
an aircraft reactor. An aircraft reactor must have good -pickup, i.e., it must be
able to change rapidly from one steady state to another.
The rate of increase in power is greater, the greater the so-called excess re-
activity or the reactivity ofthe reactor. By excess reactivity kex we mean the
degree to which the multiplication constant is greater than unity
Kex =K-1.
For example, if the multiplication constant is 1.05, the excess reactivity is 0.05.
The amount of excess reactivity indicates the relative increase in the number of
neutrons fissioning from one
crease is 5%.
The rate of increase in
generation to the next. In the given case, this in-
power also depends on the type of nuclear reactor. In
a fast-neutron reactor, it is greater than in a thermal-neutron reactor. To anti-
cipate the discussion for a moment, it should be mentioned here that different types
of reactors will not always exhibit a significant difference in rate of accelera-
tion.
Let us define the rate at which the power of a reactor increases. Let us as-
sume that we are dealing with a thermal-neitron reactor in the critical state and
developing some given power. Let us assume that we have effected a sudden increase
in the multiplication constant toK = 1.1, i.e., that we have introduced a-reacti-
vity kex = 0.1. Calculations show that, at this reactivity, the power of the re-
actor will increase in two thousandths of a second by a factor of 2.7; in one hun-
dredth of a second it will increase by 1500 times, and in two hundredths of .a second
by approximately 20,000 times. A breakdown is therefore almost inevitable. In a
fast-neutron reactor, at kex = 0.1, the power increases approximately 150,000 times
4.6
gers?cm?r=^.?
?
in one millionth of a second. This rate of evolution of a chain fission reaction is ,
close to that occurring in an atomic explosion.
The rapid increase in the power of a reactor of any type is explained by the
fact that the velocity of motion, even of thermal neutrons, is sufficiently large
for this to occur, while the distance traversed by the neutrons before collision
with nuclei is small. As a result, very small intervals of time elapse from the
instant of generation of a neutron to the instant when the neutron is captured by a
nucleus of the fuel. Under these conditions, the process of fission rapidly en-
compasses an enormous number of nuclei.
The rate of acceleration may be reduced by lowering the reactivity, but even
if this rate is reduced to 0.01; it still is not possible to control a nuclear re-
actor. As soon as the reactivity drops below 0.01, the picture changes sharply.
The point is that, during the exceedingly brief period of time required for the act
of fission, only 99% of the total number of secondary neutrons escape. These are
known as prompt neutrons. The remaining neutrons (approximately 1%) appear in
groups, with a delay of up to 80 sec. These are the so-called delayed neutrons,
which are emitted in "fragments" of the fissioned nuclei, as they undergo radioac-
tive decay. If the degree of radioactivity is equal to or smaller than the per-
centage of delayed neutrons, then an increase in the number of fissions in each gen-
eration will result only due to the delayed neutrons. In this case, the rate of
increase in power is determined chiefly by the time during which the delayed neu-
trons appear. The time required for the neutrons to travel from the instant of
their generation to the instant of their encounter with the nuclei of the fuel id
not-a significant factor, since this time is exceedingly short relative to the time
lag of the neutrons. As a consequence, the rate at which the reactor is accelerated
will be considerably less, although for reactors of various types it is approxi-
mately identical at identical reactivity.
More exactly, the percentage of delayed neutrons is given by the figure 0.00755.
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TlierefOilskin ''Order ,to2e.irinte'e daTe orieration,duririi the, etarttip or " power -iricreas of the reactor, the reactivity introduced musti.be leee,than--0.00755 and domprise -ap4
proxiiiiatel,y: 0: 005,-.4.-- t.OW06; (this reactivity;-. a thermal-neutron 4-eadtor miLl re-
quire" apProximatelit 6 -sec to indreas e its: .poWer br'a factor Of 2.7, and will 'require
30 sed.to-increase :it by .500:tiled. ciTheAndrease: in ithe power Ofa fast-neutron
, 114 v?-?2
?
-;:
Fig.13 - Time Rate of Change in the Power of a Reactor, when
nRacedu or Shut Down
rtn ? Lirt:4 t.
a) Reactor power; b) ?Racingr = 0.0025);
4 r .?, ?
?
C) Shutdown Ckem = - 0.0025); d) Time
?=1.i.1: .
ti???
? .!--1111'?
'
readfortakei Pla44t apPrOxiiatelyAhe timerate:,-ItRaiable-regulationCe,A,ohain),
reaaTOn'is-coMPletelk;i6eured:fat thiefrat ,
AlOneWith th6 inc??e -lit' the) tinfe7reqUired tbj.raise the power,' the presencer
of delayed neutrons results in a decline of the' rite of i-edticti2on of ,Power
readtor'l?s -the -subcritical -stated' in iifactibev, theiYowet:,,oaraibt b?reduce&-more
?P:???,-,1
?
?
rapidly...than, is It permit t e by the delayed neutrons.- Figure strat es-- the
chariges in power- as:: a--fUnction: of time.; When a reactor'. is, addelerated. Or: shut -down- at
a given-) steady state'. ? The exceser', reactivity;N. in.- absolute 0.:0025. The
broken--Une shoWe.: ar number- of new:. stoady-1-states thatl-can be attained as - 8 'ult: Of -
increaling-- Ori1nil-thinitial aeiigried pbwer:1 7
"7.
What- are- the= 'cause& bf ? the-vitriationeAi the re.siativity of a. readtor13 '
? the firztn. plabe; the r eactiv-ity m? be Changed-at the-discretion Of. -the per-.
son controlling the readtor: This. :.includes the abtione=-:, of :automatic' deVicee:LWhiChp
set- by /i3?9?1i; -will substitute- for )'hi s adtion.- " One' o'f these actions' is thetehiftiiig
of-the control rod made of a material that is highly neutron-absorbent:-Whezi' the
rad Li pilehedi into' the cor,e;-?the--iientron loss bk ' Abe orPtiOn?? If, prior
to the - introduction': bf the rod,- the reactor had b'eezi 'ii the critical'. e Cate; will-
be'Come snli-eritical afterrOdubtiOn--::- Under the 'neif/Oonditibile, the amOlintP? of -mit= "
clear fuel.- in the bore' will be insufficient to- istain- a'forit.icil2:etate:f.' 'When-- the?
rod - id.thdraWn- from, the dore, -on the- other hiiia-; the gneuti-on doeii.se; deorea'se: and'
increiteee';''
-Se cOndlY;- *whin a. nuc-lar 'reabtor is -in-;:oper-ation.V ePOntaneoutj changes
MakrOccUr. '-Oxi?bftheaus?'o1'. thiie therInb Onti.istiontm Of the' it-lel:bar ;
fliJ-? with- the result that' atibunt: in, "the ore dropes the.--readtivity
In Order:'teST-preVent- sPonfaileauehiltdOWn, ofAhe reat tor!,r-it5ie necessary;- ?
either- to provide: Tor: a '.bonetant refueling:, oil in sbte wito redutetineutrow,lbes.:
during- operation or the- readtor: 't=-2 7 ^ - -
reaebn for- the'.= reduction An- reabtivity7is- -theaccumulationf of.: reaction:.
fiseiOnl:prodacto-' thatilate 'strong: neutron- abeorbers s'aor:las.: the saying- oe;-reactor
.., ,
_ , .. ?. :.
iioisoning.A Poisoning results .in 'an:--iridreaeet.in5-the7lbes ?-bfl-neutronsi:-bydab,sorption
and 'ConeisCitientlf in anAnCreas 6. .1n:the vreqiiired briticaP. Weight:Icliic. teirnier-of4-tany-,,--
specific reactor, the degree of drop- dti.e?.tb- fadisoning-iie ''great.er-ii the
greater the power level at, which the ,reactor has been operating. The poisoning- ef-
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497! ' STRi7C1,-'i
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feet is most noticeable in reactors using thermal neutrons, insofar as thermal neu-
trons are avidly absorbed by the nuclei of certain fission products.
Spontaneous changes in the reactivity of a reactor also occur when the core
temperature is changed. An increase in temperature usually results in a decrease in
reactivity. When overheating occurs, the density of all materials declines, i.e.,
there is an increase in the distance between the atomic nuclei. This leads to a
reduction in the collision probability between neutrons and nuclei, to a decrease in
the number of fissions, and an increase in neutron leakage. When the temperature is
decreased, the nature of the phenomena is the opposite, and the reactivity of the
reactor increases.
The fact that such a relationship exists between reactivity and temperature has
a positive effect on the functioning of a reactor and makes it easier to control.
Let us assume that, for some reason, the reactor has spontaneously entered a super-
critical state. This causes the number of fissions per unit time to increase, thus
also increasing the liberation of heat. Consequently, the temperature of the core
increases. However, when the temperature increases, the reactivity begins to drop
with the result that the further development of a chain reaction is somewhat slowed.
In some cases, when the accidental fluctuation in the reactivity of a reactor is
small, the reactor may spontaneously, without the intervention of a control system,
return to 'its previous power level. The thermal effect is most marked in reactors
using thermal neutrons, particularly if uranium3E1 is a constituent of the fuel.
As temperature increases, there is an increase in the kinetic energy of the
thermal neutrons. As a result, the probability of fission of nuclei of highly ef-
ficient fuels becomes less, while the probability of absorption by the nuclei of
uranium3E3 increases. In order to provide for maintenance of a steady state during
temperature fluctuations, some means of compensating the change in reactivity, oc-
curring under these conditions must be provided.
50
Declassified in Part - Sanitized Copy Approved for Release
Controlling the Nuclear Reactor
changing it in a desired direction. To control a reactor, provision must be made
for varying the reactivity of the reactor. This problem may be solved by the fol-
1d4ing methods:
Control of a nuclear reactor consists of sustaining the desired power or
By varying the amount of nuclear fuel in the core or by changing the mutual
arrangement of the components;
By changing the quantity of moderator;
By changing the effective area or thickness of the reflectors;
By changing the position of external neutron sources relative to the core;
By changing the position of the regulating (controlling) means, made of
materials that are good neutron absorbers.
At present, the last of the methods listed has came into wide use as being the
simplest in terms of design and as being adequately effective, particularly for re-
actors using thermal neutrons. The controlling means most often take the form of
cylindrical rods. The material used for these rods may be cadmium, boron, boron
carbide, or boron steel. Cadmium is the most avid neutron absorber but has a
rather low melting point (about 321?C), and is therefore less frequently used: An
advantage of boron, aside from its high absorptivity and high melting point, is the
virtually complete absence of induced radioactivity due to absorption of neutrons. '
As- mentioned before, the change in reactivity' obtained by means of the control rods,
due to change in the loss of neutrons of each generation by absorption. Intro-
duction of the rods into the core reduces the reactivity of the reactor, while with-
drawal of the rods increases it.
- The reactor core is so designed that the weight of the initial charge of
nu-
clear fuel will exceed the minimum critical Weight. A portion of the excess fuel
represents a reserve against consumption; i.e., it may be expended in iiroiducing
thermal energy. The other portion, the so-called'reserie against 'poisoning and,
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temperature effect, is not consumed in operating the reactor: -This-riartiOn-ofithe
fuel is used to sustain the critical condition in the reactor during acdumulation of
-
fission products and increase in. ,temperature.
The excess or reserve reactivity due to the, fact that :the amount of nuclear,
fuel present is greater than the minimum critical amount, is compensated by the con-
trol rods and. may be eliminated if necessary. The degree_ of reactiVity,freed when
the rod is completely withdrawn from the core, is known. as the compensating.papacity
of the control rod. The compensating' capacity depends upon the material of the rod,
its diameter, and its position in the core. Rods. passing through the center of the
_ .
core have the, greatest compensating capacity.... The total compensating capacity of
the control rods of a reactor must ,exceed the initial reserve reactivity.
Let us next. discuss the principal operating conditions of a control system. In
order., to proceed from one, steady state, to another *which the.. power is greater,
the rod must be withdrawn from the corp. , When this is done the: power of. the re7
_
actor begins: to increase. As, soon as a desired power level has been reached, the
rod .must be, retiumecl,to a position corre_sponding to , zero. reactivity. .If the change-
,. ,
over to the new operating conditions-is completed within a very short period ,of
time and. is not. .accompanied by significant changes:in. the , temperature of _ the core
the. rods will, be, returned_ almost to their _initial position..
Tn1,9rderto reduc,e.the. power.level,_ the. rode; must be inserted deep,int?Llthe.. _
core, and,. .after, the desired,,,,level: has: been, reached,- be:4 ,returne_d to. _their..?1*.tietl,
position. The :degree of displacement. ,o.f the ,rods determines the deg ee of reacti-.
vity, i.e.,,_ thettime .rate of change, in. power. , ,Compensation ,for, the reduction, in,
reactivity due to consumption of the fuel and poisoning .of.,..the,,reactoro_ is accom-
plished-by gradual withdrawal- of.. .the control _rods_ from, the core.:
ntenanc.e, of. the assi_Eped oper4ing, conditions oki the. 7.,E)42F is_automatic
A deviation _or the. Tower_....of the .reactor, f:rom, the.,requiredlev.el _causes. a change. ,
"- fltucAn.the.?reacto_r,...which-Ae?Amediately..recorded by?.ionization r
52
4
4
k=9
Al
4,4
Declassified in Part - Sanitized Copy Approved for Release5
countere'inounted arbilnd- the core. The signals -froli these 'counters", magnified!,:by:..l.r,,,
means of eleCtranic sYsterds, are tfanstiltted:to.-the .-elebtricLdrives ,which-effeetthe
necessary charige in the pobition Of thei-ContrOl- In:liedern nuClear.--reactors.,-.1:.
tr'?
the7adS1gned ?pOwer"is' maintained -with 'ail a:COUracy tb? Within TOne'tent.h. off a percent::
?,, ?
In addition to the rods contralling-the reactor in' norinal aperatibny.remergency:
protective rods must -be provided. ?? Their',purriosemie to stop the nuclear'ffission re-
action under conditions in which, even 'the briefeet deliy iris-shutdown'.mightcause
breakdown of the reactor. Such- conditions' include: 1,-P
Very', rapid inbrease in pbwer' during ?startup.;? '
'
Rise in temperatUre of 'the core above-the-permissible level;, ? .7
Drop in pressure of the heat-transfer agenty indicating,a-leak ,in:Aihe- system:
or failure of the pump; and several .other cases.
The emergency 'rods Usti-ally are introduced 7autcimaticall,. y4-;?1n,t,the, majority
reactors for .etationary 'installations, the-:eniergency'rods are. vertical. nedes.-'
sary; they are nchimpedn int& the' core. 'Th'e speed of freetfall?Of t:the:'emergencyi.-rods
?sufficient -to 'stop 'the '-ohadia. reaction' :aircraft reactorS,
gency rods' mdst necesearily-beE.-provided with az independent drive. },,lhis _he'ces-7:...,
,
sary to assure rapid insertion no matter what the conditions of :flight:: The?--L
simplest, lightest; drict7MOet: rli?e driVes are Spring-;aCtuated -or use :compressed
-gai-Or a liowder-tharge.'
Times of Nuclear Reactors
1
'''Abbve we have alf.eady indiCsited'?some driedific features-.of-nrarious?typeeJolFreF
actore."--, kliscuss, 'other ?_peculiarities -.EandrwiLl attempto
dmraw certain'CondlUsions-46 ta the 'applicability of=variousTeactore. for 4rcr.4.,ft
poWer' priulte:
Thermal-Neutron Reactors. The dervelopment of*iluclear)risactors7-for;,,,usewit,hs-ip
`-ifiiiiiiaViieffe.i.ofigTrwieiri,g'geiedilteinitiriVL:tynthe, !attempt -to UseimaturaIi5andclow-
- r 7/01 . - -01043R0n9 nnnAn
53.
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/07/01 : CIA-RDP81-01043R002100060011-6
enriched uranium as the nuclear fuel. The point is that it is impossible to cause
a chain reaction in a lump of natural uranium, even if the size of the piece were
increased to infinity. This is because of the low probability of fission of
. 235
uranium by high-energy neutrons and the exceedingly high losses of neutrons due
to resonance absorption by the nuclei of uranium238.
The fission reaction in natural uranium can become a chain reaction only if
thermal neutrons are used. The probability of capture of thermal neutrons by the
neutrons of highly efficient fuels, and resultant fission, is much higher. At the
same time, there is a reduction in loss of neutrons by absorption since a rapid
drop in energy results in a considerable increase in the number of neutrons which
?jump? regions of resonant energies.
In order to decelerate the neutrons, a neutron moderator is placed in the re-
actor core. The moderator is made of a material comprising chemical elements with
the lightest possible atomic nuclei. These are the elements at the very beginning
of Mendeleyev's periodic system. The lighter the nucleus of the moderator, the
more energy is lost by the colliding neutrons and, consequently, the greater is the
probability of skipping the energy levels at which resonance absorption into
uranium238 takes place.
However, a pronounced reduction in the energy of the neutrons during a single
collision is of no value if the collisions are very rare. In this case, the loss
of neutrons by leakage will be very great.
Moreover, the nucleus of the moderator must not be a powerful neutron absorber.
Thus, the moderator must consist of light nuclei, having the greatest scattering
probability for neutrons and the least absorption probability. Only a few good
moderators are known: heavy water, ,graphite, beryllium, beryllium oxide (Be0). In
high-temperature nuclear aircraft reactors, it is apparently possible to use 'only
graphite, beryllium and its oxide.
The use of natural and even low-enriched uranium in nuclear reactorsToratomic
54.
aircraft does not seem possible thus far, since this would require reactors of ex-
cessive dimensions and weight. The simplest calculations show that, at present, the
designing of an atomic aircraft flying at a speed somewhat higher than the speed of
sound is possible only if the fuel used is uranium enriched at least by 50%. The
design of aircraft with atomic engines for still higher supersonic speeds will re-
quire a greater degree of enrichment.
_Nuclear reactors for thermal neutrons have one great advantage over all other
types of reactors - minimum critical weight for the nuclear fuel. When the fuel is
diluted by the moderator, there is a decrease in loss of neutrons by leakage, be,
cause of the fact that, the lower the energy of the neutrons, the greater will be
the probability of their capture by the fuel nuclei. On the other hand, there is
an increase in the loss of neutrons by absorption by the nuclei of the moderator.
Up to a given degree of dilution, which is called optimum, the saving in neutrons
^
due to a reduction in leakage is greater than the loss by absorption, so that the
critical weight of the nuclear fuel decreases. At the optimum ratio of the amount
of fuel to that of moderator, the critical weight of a given fuel will reach a min-
imum. On further dilution, this weight increases because since reduction in leakage
is insufficient to compensate for the reduction of neutrons due to absorption.
Figure 14 gives a graph showing the change in the critical weight of nuclear
fuel and the critical dimensions of the core of a reactor, on gradual dilution of
the fuel by a moderator. The solid line is the change in the critical weight of
the fuel Cr" while the broken line represents the change in the critical size of
?
the core ORcr ). We see that the critieal weight of nuclear fuel (!min) is con-
siderably less than the critical weight Of the undiluted fuel (P0). True, the size
of core in this case is greater than the deficiency in moderator.
The use of thermal-neutron reactors in aviation is advantageous in cases in
which the greatest possible area of heating surface of the core is required. In
practi-Ce, this occurs in the design of ram-jet and turbojet atomic aircraft engines.,
STAT
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Declassified in Part - Sanitized Cop Approved for Release ? 50-Yr 2013/07/01 : CIA-RDP81-01043R002100060011-6
with direct heating of the air stream in the reactor. The emission of heat into the
air stream is characterized by a comparatively low coefficient of heat transfer, of
?
0
b)
Fig.14 - Variations in the Critical Weight of Nuclear Fuel and
Critical Dimensions of the Core of a Nuclear Reactor as a Function
of the Ratio of Fuel and Moderator Amounts
a) Critical weight of nuclear fuel and critical dimensions of core;
b) Percentage content of moderator in mixture with fuel
not more than 600 - 800
kcal
m2/hr ? deg
usually inadequate, without dilution of fuel. The use of a moderator results in an
increase in heating surface.
The mutual arrangement of the fuel and the moderator in a thermal-neutron re-
actor may vary. If the nuclear fuel is uniformly distributed throughout the moder-
ator, dissolved, or intermixed, the reactor is known as a homogeneous reactor. A
. Therefore, the area of heating surface is
4 56
?
homogeneous active mass may be solid, liquid, or gaseous. A liquid mass, in turn, .
may be a solution of fuel in a moderator, or a suspension, i.e., a uniform distri-
bution of solid fuel particles in a liquid moderator. A general advantage of homo-
geneous reactors is the simplicity of design of their cores.
Actually, this is the simple and reliable design applied in the boiling homo-
geneous reactor designed by the Academy of Sciences of the USSR. The design of this
reactor is shown in Fig.15. The-active mass, consisting of .a solution of uranium
salts in heavy water, is encased in a metal tank of spherical shape. The heat
liberated as a result of the fission reaction causes the liquid to heat up and boil.
High-pressure steam is tapped for use in steam-powered devices. The condensate from
the steam-powered device is returned to the reactor by pump. A fundamental short-
coming of homogeneous reactors is the comparatively high probability of absorption
of neutrons by nuclei of uranium238. Therefore, the realization of a self-
sustaining fission reaction, using natural uranium as the fuel, is possible only if
a better moderator than heavy water is used.
If nuclear fuel in the form of separate and rather large rods or blocks is
placed in an undiluted moderator, the device is called a heterogeneous reactor.
Heterogeneous means nonidentical. The distance between the blocks is so selected
that'the-energy of the neutrons exceeds the resonance levels in the spaces between
the blocks. One of the possible designs of heterogeneous reactors has already been
described and was shown in Fig.9. The design of the core of such a reactor is more
complicated than that of a homogeneous reactor, but the limitations of the latter,
with respect to possible moderator materials, do not exist here. In modern reactors
of stationary power plants, graphite and ordinary water are in wide use as 'moder-
ators. These materials are considerably cheaper than heavy water.
The nuclear reactor of the first Soviet power plant is a heterogeneous reactor
using thermal neutrons. Its core is a cylinder 1.5 m in diameter and 1.7 m in
height. Graphite is used as the moderator and reflector. The heat-transfer agent
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57
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is ordinary water. The nuclear fuel is metallic uranium enriched by its iso-
tope 235. The degree of enrichment is 5%. The initial fuel charge is about 550 kg.
Fig.15 - Schematic Diagram of Boiling ,Homogeneous
Nuclear Reactor
a) Reflector; b) To steam engine; c) Pressure vessel;
d) Control rod; e) Pump; f) From steam engine; g) Solu-
tion of uranium235 salt in heavy water
Of this, about27 kg is uranium235. ?The combustion reserve is approximately 3.5 kg.
Approximately the same amount is provided as a reserve against poisoning and tem-
perature effect. Consequently, the excess of nuclear fuel over the minimum criti-
cal weight is about 7 kg. The initial reactivity reserve is 0.13. In order to
compensate for excess reactivity .and for inaccurate control Of the reactor, 18 corn-
58
7
pensating rods of boron carbide are provided in the core. Another four rods are
provided for precise automatic control, plus two emergency protective rods for
stopping the reactor under emergency conditions. The overall compensating capacity
of the regulating rods is about 0.16. The compensating capacity of the emergency
rods is 0.02. The thermal capacity of the reactor is estimated as 30,000 kw.
The advantage of heterogeneous reactors in that they reduce resonance absorp-
tion within uranium238 is not significant for aircraft reactors. The selection of
some system of placing the fuel and the moderator in the aircraft reactor is based
primarily on the requirement of obtaining a simple reactor, reliable in operation.
Taken into consideration here are the type of aircraft engine to be driven by the
reactor, the high thermal load of an aircraft reactor, the possibilities of uneven
heating and fluctuations in temperature, the need to assure reliable dissipation of
heat no matter what the position of the reactor in space, and a number of other
factors.
Several authors in other countries have proposed using so-called porous homo-
geneous reactors in rocket-type atomic aircraft engines. The core of such a re-
actor is an assembly of conical tubes extruded from a homogeneous mixture of highly
efficient nuclear fuel and powdered graphite. The tube walls are honeycombed with
an. enormous number of fine channels, through which a fluid or gaseous heat-transfer
agent flows. This agent functions at the same time as the working substance of the
rocket. The design for such a reactor, housed in a rocket, is shown in.Fig.16. The
porous reactor has the following important advantages: a large surface area for
heating, combined with comparatively small dimensions of the core and a possibility
of reaching working temperatures above the melting point of the nuclear fuel. How-
ever, a porous reactor in the form in which it is proposed has the following int-
portant disadvantages which constitute an obstacle to its practical application,
specifically as a high-temperature reactor: A highly complex technology is required
for thi manufacture of the 'solid homogeneous mixtures, and the probability of de-
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struction of the solid mixture due to irregularity in the heating of the various
segments and fluctuations in temperature is great. In addition, clogging of the
b)
a)
Fig.16 - Design of an Atomic Rocket Aircraft Engine with a
Porous Homogeneous Uranium-Graphite Reactor
a) Control rod; b) Delivery of heat-transfer agent from pump;
c) Porous active mass; d) Shell; e) Jet nozzle
capillary channels by particles of the active mass and by "fragments" of the fis-
sioned nuclei may occur daring operation-of the reactor. Clogging of the channels
over even a short distance results in local overheating and, in the long run, in
breakdown of the entire reactor.
60
Sanitized Coov Arprov
?
a
?
The use; in thermal-neutron aircraft reactors, ofa homogeneous active mass
consisting of an alloy of metallic uranium and metallic beryllium offers good pos-
sibilities. The active Mass is housed in thin-walled cans of heat-resistant ma-
terial, which may be cylindrical or tubular (with double walls), or else spherical,
etc._ A portion of the active mass with its can is called the heat-producing ele-
ment or fuel element. The cans protect the mass from oxidation and shield the heat-
transfer agent from contamination by the radioactive fission .products, and also im-
part -mechanical strength and rigidity to the heat-producing elements at high tem-
peratures. The fuel assembly, with the individual elements attached to each other
and to the shell of the reactor, forms the structural essentials of the core.
Figure 17 shows one of the possible design variants of a core using uranium-
beryllium alloy. The design of the heat-producing elements and the method of com-
bining them into a single whole is readily understood from the drawing. A reactor
of this type may be used to heat a flow of air passing through its axis or a gaseous
intermediate heat-transfer agent. If the material of the containers holding the
heat-producing elements permits this, the working temperature can be raised above
the melting point of the active mass.
Still another variant of a possible design for the core of a uranium-beryllium
reactor, intended for direct heating of the airflow through the engine, is presented
in Fig.18. Here the uraniumberiimm alloy is housed in a hermetically sealed
cavity, penetrated by a large number of thin-wailed metal tubes. The active mass
occupies the space between the tithes. The air to be heated moves along the tubes
to the reactor. To obtain a hermetic seal of the front and Tear surfaces of-the
reactor-, the ends of the tubes are connected by welding. Usually the core of this
type of reactor consists of a; number of sections. The edges of one of the sections
are .shown as -a broken line in the:le;ft half of the drawing. Such a sectional de-
sign greatly simplifies the engineering required in making and assembling the core.
In orderto lower the neutron leakage, a solid outside reflector is provided': -
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Fig.17 - Design of a Uranium-Beryllium Homogeneous Reactor, Intended for the
Heating of a Gaseous Intermediate Heat-Transfer Agent
1) Heat-producing elements; 2) Section through AOB; 3) Reactor shell; 4) Re-
flectorwall; 5) Control rods
Fig.18 - Design of a Uranium-Beryllium Homogeneous Reactor for Direct
Heating of Airflow
1) Tubes for airflow; 2) Section through A0B; 3) Reactor shell; 4) Outside re-
flector; 5) Active mass (uranium-beryllium alloy); 6) Rear face of reflector;
7) Control plates
To reduce the cross-sectional dimensions of the reactor, it is desirable to use
metallic beryllium as the reflector material. Unfortunately, in this case it is
im-
possible to use continuous-end reflectors. A certain amount of reduction in neutron
leakage through the end surfaces is obtained by applying a layer of pure beryllium
betwein the tubes at the front and rear surfaces of the reactor. In order not to
crowd the access to and the exit from the reactor, the control devices are placed
betiteen the sections of the core and are displaced along the radius of the cylinder.
Let us review some data on a reactor designed on this basis. These data are
obtained from approximate calculation based on familiar formulas derived from the
theory of jet engines and the theory of nuclear reactors. The purpose of a reactor
is to provide direct heating of air in an atomic turbojet aircraft engine, devel-
oping mexissna static thrust at sea level of 32,000 kg. The maximum thermal capacity
of the reactor is 300,000 kw, corresponding to
The maxima temperature of the heating surface
heated to a temperature of 9500C. The reactor
core is 1.9 m in diameter and in length, while
made of beryllium, is 15 cm. The thickness of
a liberation of 258,000,000 kcal/hr.
of the core is 1100?C. The air is
core is cylindrical in form. The
the thickness of the side reflector,
the layer of pure beryllium of the
trent and rear surfaces of the reactor is 10 am. The number of airflow tubes is
17,000. The inside diameter of each tube is 10 mm. The tubes are made of heat-
resistant nickel alloy. The initial uranium23 charge is 70 kg. The combustion re,
serve, ensuring continuous operation at full capacity for 500 hrs, is 6.5 kg. The
weight of the metallic beryllium, alloyed with uranium, is about 2000 kg. The com-
bined weight of reactor and reflector is 9500 kg.
All three above designs assume the use of a homogeneous active mass. The use
of heterogeneous nuclear reactors in aviation offers more limited possibilities,
partitularly for the direct heating of air. The Core of a heterogeneous reactor, in
this case, is complex in design and not very reliable in operation.
. A shortcoming of nuclear reactors employing thermal neutrons is the necessity
? ?-?-?-n-1-
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of using only materials that are weak absorbers of thermal neutrons. Otherwise, the
critical weight of the nuclear fuel increases considerably, and the most important
advantage of thermal-neutron reactors may be canceled completely. In addition, re-
actors using thermal neutrons require cores of the largest critical size, relative
to other types of reactors.
Fast-Neutron Reactors. These reactors use no moderators at all. This explains
the major advantage of fast-neutron reactors, namely the fact that they have the
smallest critical size of all types of reactors. However, this is not all.
We already know that the probability of useless capture of neutrons by the
nuclei.of various elements, during an increase in energy of the neutrons, decreases
more rapidly than the probability of capture by nuclei of fuel available for fis-
sion. Therefore, the relative effect of poisoning in fast-neutron reactors is less
than in thermal-neutron reactors. The lowered probability of absorption of neu-
trons of high energy permits a freer selection of materials for the working process
in the reactor. Liquid metals may often be used as the intermediate heat-transfer
agent, and the structural materials may consist of the best modern heat-resistant
metals and alloys, regardless of their chemical composition.
In practice, the use of fast-neutron reactors in aviation is advantageous in
cases in which there iaa possibility of attaining high temperatures of the heating
surface of,the-core, while liquid metal heat-transfer itgehts are used to dissipate
the. heat. Dissipation of heat in a stream of liquid metal is characterized by very
high coefficients of heat loss,.attainiag.30,000 -, 40,000.
le/hr ? deg
tions show that even at a temperature of the heating surface of 1000?C, the critical
dimensions of the core of a fast-neutron reactor are in good agreement with the di-
mensionS required for heat dissipation if liquid metal is used as the heat-transfer
agent.
Consequently, the use of fast-neutron reactors with liquid metal heat-transfer
agents makes it possible to Obtain greater power per unit volume of core thau with
?1
64'
4
any other type of reactor or, what amounts to the same, with the smallest dimen-
sions of core for each given power level. This is extremely important from the
a)
b)
ill) gee 111 p
g
kidgilikaw
?% %.1:V? *
iii1=210
pliMMMMM=MMV
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11 311=1=
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=1:11"1.111
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Fig.19 - Diagram of a Fast-Neutron Nuclear Reactor Using
Molten Metal Cooling
a) Heat-producing elements; b) To heat exchanger; c) From
Pump; d) Retainer plates; e) Control rod; f) Cover of shell;
g) Reactor shell
viewpoint of convenience of shielding the reactor and reducing the weight of he
shields.
'Figure 19 shows one of the possible designs of the core of i fast-neutron nu-
clear reactor using liquid-metal heat transfer. In the given case, there is no re-
flector. The core of the reactor is cylindrical in form and consists of two drums,
each of which in turn consists of two retainer plates and an assembly of heat-
'produding elements. There is a gap of predetermined size between the two drums.
65
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The resolution of the core into individual sections slightly increases the critical
weight of the nuclear fuel but ensures, a more reliable functioning of the reactor at
high thermal loads. The shorter the length of the heat-producing elements at a
given diameter, the less will they sag under their awn weight, the less will be the
deformation at nonuniform heating, and the less will be the vibration.
The shell of the heat-producing element is a tube with thin double wall% The
nuclear fuel is housed in the hermetically-sealed space between the walls. The
fuel elements are inserted in accurately machined apertures in the retainer plates,
during assembly of the drums. Rigid mounting of these elements to the plates is
provided only on one side, the outer plate side. The heat-producing elements rest
freely in the holes in the inner plates. This permits unrestricted expansion on
heating.
The liquid-metal heat-transfer agent is forced into the gap between the drums
by means of a pump, at a definite pressure. Here the current of heat-transfer agent
divides in two. Moving through the tubes in an axial direction, the heat-transfer
agent enters the front and rear chambers of the reactor. Both chambers are con-
nected to the inner portion of the drums of each by means of channels in the lower
portion of the outer plates. Through these channels, the heat-transfer agent en-
ters the space between the plates from where it moves upward. .Thus it washes the
external surfaces of the heat-producing elements in a transverse direction.
In riming over the inside and outside surfaces of the fuel elements, the heat-
transfer agent is heated to a high temperature and enters the heat exchangers from
the two upper chambers of the reactor. There it yields the heat obtained in the
reactor to the air stream. From- the heat exchangers, the cooled heat-transfer
?
agent is recycled by pump to the reactor. The pressure in the reactor should be
such as to prevent the heat-transfer agent fram boiling within the core.
By means of equations familiar from the theory of heat exchange and the theory
of nuclear reactors, it is not difficult to make approximate calculations for a
66*
?
1!
?
reactor designed on this basis. 'Below we derive certain data for such a calcula-
tion: The thermal capacity of the reactor is 300,000 kw. The fuel is uranium en-
riched by a 50% addition of the 235 isotope. The heat-transfer agent is fused
lithium (melting point 180?C, boiling point at normal atmospheric pressure 1320?C).
The maximum temperature of the heating surface is 1000?C. The lithium is heated
from 750?C to 950?C. The diameter of the core is 0.8 m, and its length is the same.
There are 8000 heat-producing elements. The outside diameter of each fuel element
is 8 mm, and its inside diameter is 4 mm. The thickness of the shell is 0.5 mm.
The thickness of the fuel layer is 1 mm. The material of the shell is heat-
resistant nickel alloy. The weight of the structural materials in the core is about
900 kg. The initial charge of enriched uranium is 1100 kg. One half this quanti-
ty, i.e., about 550 kg, represents uranium235. The combustion reserve is 6.5 kg.
The total initial reserve of uranium235, with allowance for reserves for poisoning
and temperature effects, is about 9 kg. The initial reactivity excess is 0.012.
The duration of continuous operation of the reactor at full capacity, determined by
the reserve of fuel for combustion is 500 hrs. The dry weight of the nuclear re-
actor, without the reflector but including the control system, is 4000 kg. The
weight of lithium in the reactor is 1500 kg. The average pressure of the heat-
transfer agent in the reactor is about 20 atm.
The above example shows that the critical weight in the fast-neutron reactor
is considerably greater than that of a thermal-neutron reactor. This is the major
'shortcoming of fast-neutron reactors and can be explained, by the excessive neutron
leakage. The necessity for high-enriched fuels and a large initial .load places a
certain limitation on the wide use of fast-neutron reactors in stationary power
plants.
Alevertheless, the-use of such reactors is very profitable since it creates the
possibility of producing not only energy but highly effective nuclear fuel in a
antit ter than the amount actually burned;
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If the core of a fast-neutron reactor is surrounded by a relatively thick layer
of uranium238 or thorium, the loss of neutrons by leakage is no longer negligible.
The absorption of these neutrons by a nuclei of urani238 or of thorium32
um results
in the formation, respectively, of plutonium239 or uraniu233. In this case, as
soon as the amount of newly formed highly efficient nuclear fuel is equal to the
amount of "combusted" fuel, the reactor becomes a regenerative reactor, and as soon
as this amount is exceeded, it-becomes a breeder reactor. In aviation, such re-
actors cannot be used because of their exceedingly great weight.
Reactors Usim Intermediate Neutrons. In such reactors, the quantity of the
specially provided moderator is inadequate to moderate the neutrons dawn to thermal
velocities. In their properties, such reactors are somewhere midway between thermal
and fast-neutron reactors. By using a certain level of fuel dilution by a moder-
ator, it is possible to make use of the advantages of both extreme types of reactors
while eliminating their shortcomings to some degree. The dilution of nuclear fuel
by a moderator results in an increase in the dimensions and weight of the nuclear
reactor and slightly complicates the problem of protection from radiation; however,
at the same time it reduces the needed initial charge of expensive nuclear fuel.
In addition, an increase in the dimensions of the core when dilution of fuel
is used means primarily an increase in the area of heating surface. As a result,
the same amount of heat may be transferred at a lower temperature. In the above-
discussed reactor, using fast neutrons, a certain degree of dilution makes it pos-
sible to heat lithium to 950?C, at wall temperatures of the fuel elements differing
from 1000?C (for example, 975?C). A reduction in the maximum temperature of the ?
wall increases the reliability of operation of the heat-producing elements. Thus,
if we dilute the fuel with a moderator, we may obtain an optimum combination of the
engineering and economic possibilities for the development of an aircraft reactor.
According to the foreign press, the majority of aircraft reactors now in the design
stage are, as a matter of fact, in the class of intermediate-neutron reactors.
68
Calculations show that such a reactor is the most profitable for aviation if
helium is used as the intermediate heat-transfer agent. The heat-transfer coeffi-
cient from the heating surface to the helium stream in high-temperature aircraft re-
actors is approximately 5000 kcal
,
m2/hr ? deg
The design of the core of a reactor using intermediate neutrons depends upon
the heat-transfer agent used and does not differ greatly from the above-described
designs.
_
Major Difficulties in Developinx Aircraft Nuclear Reactors
The development of nuclear reactors for use in high-speed atomic aircraft is
hindered by the necessity to overcome a number of serious difficulties.
To begin with, to create high-power reactors despite small dimensions and
weight, a large amount of very expensive material is required. The most costly ma-
terial is the nuclear fuel. Above it was noted that the initial charge of high-
efficiency fuel in a fast-neutron reactor amounts to several hundred kilograms. To-
day this figure is quite high, since the resources of high-efficiency fuels are
still very limited. However, the production of nuclear fuel is being developed
rail-idly, processes of separating the isotope 235 from natural uranium are being per-
fected, and stockpiles of artificial, highly perfected fuels (uranium233 and plu-
tonium) are being accumulated. Therefore it may be stated with confidence that in
the-not-too-distant future, the production of high-efficiency fuels will be ade-
quate to permit the operation of a large number of aircraft reactors.
. The progress in aircraft reactor design is also facilitated by large-scale de-
velopment of regeneration or recovery (purification, rehabilitation) of nuclear
fuel. We know that, of the total fuel charged into the reactor, only a small por-
tion is expended. Thus, in the fast-neutron reactor examined above, of 550 kg of
urinium235, only 6.5 kg is "burned n during 500 hours of operation at top speed. The
remaining fuel becomes unsuited for further use, due to contamination with fission
? sT)STAT
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products. Regeneration, i.e., purification of the nuclear fuel from the contami-
nating impurities, makes most of it useful for re-use in reactors.
Serious difficulties are encountered in solving the problem of removing heat
from the reactor. Moreover, the process of heat dissipation determines all major
characteristics of an atomic power plant aircraft and the flying characteristics of
an atomic airplane.
One of the difficulties consists in attaining high temperatures of the heating
surface of the reactor core. The most widely used nuclear fuel, uranium, has proved
a very capricious material. When metallic uranium is heated to over 660?C, the
atoms in its crystal lattice undergo rearrangement, accompanied by a change in vol-
ume, density, and mechanical properties. In the temperature interval of 660 to
800?C, uranium is brittle, while above 800?C it is very soft and weak. Frequent
heating and cooling causes progressive changes in the shape and dimensions of ura-
nium blocks. A similar phenomenon results from the effects of irradiation and in
particular of the intensive bombardment of the uranium nuclei by fission "frag-
ments" and neutrons. The above properties of uranium cause serious difficulties in
developing reliably operating fuel elements for high-temperature reactors.
To reduce the stresses in the materials constituting the shell of the heat-
producing elements, set up as the fuel volume increases, the layer of 'fuel used
must be as thin as possible. The effect of radiations on uranium may be weakened
by alloying it, i.e., by fusing it with other metals, for example aluminum or beryl-
lium. A uranium-beryllium alloy' containing relatively little uranium is remarkably
stable to radiation. The change in volume undergone by this alloy is negligible,
even under very intensive bombardment by fission "fragments" and by neutrons.
The maximul temperature which can be attained in a reactor depends upon the
choice of the material for the shells of the heat-produang elements. When heat-
resistant steels are used, reaching a. temperature above 700?C is practically im-
possible, since the main component of steel (iron) forms 'an alloy with metallic
70
uranium that fuses at a temperature of 725?C. The use of heat-resistant alloys
based on nickel makes it possible to attain temperatures at the surface of the fuel
elements of the order of 1000 - 1100?C. A shortcoming of nickel alloys is their
high absorptivity for neutrons.
Good results can be obtaineTby the use of molybdenum (melting point, 2627?C).
The probability of neutron absorption by molybdenum is second only to that of zir-
conium among the refractive metals. A shortcoming of molybdenum (violent oxidation
on-heating) is overcome by coating it with a spray-deposited silicon film. If an
inert gas such as helium is used as the intermediate heat-transfer agent, no coating
of the molybdenum shells is required. In this case, the temperature of the heating
surface of the core may be raised to the order of 1500?C.
Even higher temperatures may be obtained if the fuel used is uranium
oxide (UO2) or uranium carbide (UC2) and if the shells of the heat-producing ele-
ments consist of ceramic-materials on the basis of aluminum, silicon, zirconium,
etc.
The material of the shells of the heat-producing elements of an aircraft re-
-.actor has to work under exceedingly severe conditions. Temporary stresses are set
up by the flaw of heat-transfer agent and high-temperature stresses, due to uneven
-heating, are created in. such materials. .At high' temperatures, oxidation and cor-
rosion processes are activated and the destruction of structural materials by the
flow of heat-transfer agent is accelerated. As a result of intensive irradiation
by-neutrons, the mechanical properties of the material are impaired, rendering the
material more brittle. True, in an aircraft reactor, the effect due to irradia- ?
tio-n is considerably weakened during heat-up of the material of the shells to high
_temperatures.
These causes have the effect that the period during which an atomic aircraft
povier plant can operate continuously becomes limited not so-much by the possible re-
serVe of nuclear fuel to compensate for the burned fuel, but by the length of re-
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?
liable operation of the 'shells of the heat-producing elements of the reactor. We
may hope that the best modern heat-resistant materials will result in a service life
for aircraft reactors, not shorter than that presently attained by gas-turbine en-
gines for aircraft.
Considerable difficulties are encountered in the selection of a heat-transfer
agent. Oases, liquid metals, fused salts, high-pressure water, and other materials
may be used for this Purpose. The highest power per unit volume of core is obtained
when liquid metal heat-transfer agents are used. In order for a nuclear reactor to
function steadily and reliably, the stream of heat-transfer agent must consist of a
single phase, without significant fluctuations in density, and the excess pressure
in the reactor must be as low as possible. Therefore, the metals used as heat-
transfer agents must have high boiling points. Conversely, in order to eliminate
the possibility of consolidation in various portions of the circulatory system, the
metals used must have a low fusing point. The heat-transfer agents must be chem-
ically stable and have the lowest possible probability of neutron absorption.
Lead, bismuth, mercury, sodium, potassium, and lithium are among the metals
that have these properties to a greater or lesser degree. Of the metals listed
above, it would appear that lead and bismuth are the best. They have the highest
boiling point .(1740?C for lead and 2/010?C for 'bismuth),, have high chemical sta-
bility, and the lowest probability of neutron absorption. Alloys of lead and bis-
muth have in addition, an adequately law fusing point (somewhat less than 150?C).
However, the use of lead, bismuth, and alloy, of bismuth and lead, as well as of
mercury as intermediate heat-transfer agents for atomic aircraft power plants has
not yet proved possible. The low specific heat capacity and the high specific .
gravity of these metals has the final result of an extremely high total weight of
the required quantities.
Approximate calculations show that, for flight of an aircraft weighing 150 tons.
hAight nf 111cm at the speed' of sound (4= 1), when the temperature of the
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heating surface of the reactor is 1000?C, the weight of the liquid lead within the
power plant has to be about 70 tons, i.e., almost one half the total flying weight.
If we take into consideration that the weight of the shielding system is also about
70 tons, the impossibility of developing an atomic aircraft with this type of re-
actor becomes obvious. The use of lead and bismuth in atomic aircraft will become
possible when science discovers more efficient methods of shielding from nuclear
-radiation, making possible a reduction in the weight of the shields to one fifth of
the present level, with a simultaneous increase in the temperature of the reactor
by-at least 50%.
The use of mercury, moreover, leads to the necessity of providing high posi-
tive pressures in order to attain high temperatures, which leads to an even heavier
power plant and a reduction in its reliability of operation. In addition, mercury
is a highly avid neutron absorber. Calculations show that mercury can be used to-
day only as the working medium in steam turbines designed to drive propellers for
atomic turboprop engines or for air compressors of atomic ram-jet engines. How-
ever, it is only possible to produce a power plant of suitable weight if the va-
porization of mercury takes place directly in the reactor. The problem of pro-
ducing such a reactor, suitable for installation even on a subsonic aircraft, is
exceedingly complex.
The use of sodium, potassium, lithium, and their alloys as intermediate heat-
transfer agents makes, it possible to reduce the weight of the metal in the system
as compared to lead by a factor of more than 10, thus creating factual possibil-
ities for the development of aircraft power plants operating on nuclear fuel. How-
ever, these metals are chemically highly active., .They oxidize rapidly in air, and
react violently with water. A general shortcoming of all liquid metal heat- ,
transfer agents is the radioactivity that develops on irradiation with neutrons.
The weight of an atomic power plant may be lowered, and the difficulties due
. .
to the high chemica1,reactivity.and radioactivity of the heat-transfer agents thay
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be reduced by using gaseous intermediate heat-transfer agents or by direct heating
of the airflow in the reactor. Helium is the gaseous heat-transfer agent that
offers the greatest *possibilities. Helium is an inert gas of very low specific
gravity, high specific thermal capacity, and almost nonexistent absorptivity for
neutrons. The main difficulty in the practical use of helium is that of adequate
sealing which will reliably prevent this substance from leaking from the system.
Direct heating of the airstream in a nuclear reactor makes it possible to
eliminAte this difficulty, but other and no less complex problems arise instead..
We will discuss these below.
Obviously, the use of any heat-transfer agent involves certain specific dif-
ficulties. Which of the possible heat-transfer agents might be the preferable
type? Today it is very difficult to answer this question. A correct answer might
be possible only after a careful study of practical data in the development and
operation of atomic aircraft power plants of various types with various heat-
transfer agents and types of nuclear reactors.
Considerable difficulties are encountered in developing systems for the con-
trol of aircraft reactors. The problems of controlling stationary reactors have
now been successfully resolved. The remaining problem is that of perfecting the
existing systems, i.e., reducing their weight and dimensions and increasing their
reliability and precision of operation.
The most serious difficulties are those in controlling fast-neutron aircraft
reactors. Generally speaking, a fast-neutron reactor is more dangerous to use than
a thermal-neutron reactor. If, for any reason, the reaetivity reaches a value of
0.00755, the fission reaction will proceed at such a speed that the existing sys-
tems of emergency protection will no longer be able to prevent breakdown of the re-
actor.
However, a number of factors make an aircraft reactor, using fast neutrons,
completely safe if the most elementary rules of operation are obeyed. The point
.
A.
?
c
is that the initial reserve of reactivity' in a fast-neutron aircraft reactor is very
small. This is due to the relatively law possible operating period of an aircraft
reactor and, consequently, the small reserve of fuel to replace the burned fuel. The
reactivity reserve to compensate for poisoning and temperature effects is also small
in a fast-neutron reactor. For example, to keep a 300,000 kw fast-neutron reactor
Operating for 500 hrs, the initial reactivity reserve need only be 0.012. In order
for fission in this reactor to occur with prompt neutrons, more than half of thp
entire reactivity reserve must be engaged in the reaction, i.e., all control rods
must be pulled out half-way.
- The main difficulty in developing control systems for the operation of fast-
neutron reactors lies in the problem of designing the control devices. To control
such a reactor by means of fine absorption rods is not possible, as all known ma-
terials are weak absorbers of fast neutrons. One of the methods of control may be
Nariation in the position of a certain portion of the nuclear fuel relative to the
core. In this case, the control devices take the form of rods of nuclear fuel en-
closed in protective metal cans and having an independent cooling system. A signi-
ficant shortcoming here is the need to dissipate large amounts of heat from the con-
trol devices, leading to a considerable complication of design.
The law compensating capacity required by the control devices of a fast-
neutron aircraft reactor permits a considerable simplification in their design. One
of the possible designs for a control device is shown in Fig.20. The control de-
vice is in the form of a rod whose material is a good retarding agent, for example,
graphite or beryllium. The rod is housed in a can consisting of a material that is
a good absorber of slowed neutrons. When the rod is withdrawn, the fast neutrons
pass through the thin walls of the can and participate in the fission reaction. If
the rod is introduced into the core, a portion of the neutrons passing. through it
will be decelerated and will then be absorbed by the material of the can. The can,
may form a part of the channel wall rather than of the rod itself. The smallest
74.
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diameter per unit compensating capacity is provided by a beryllium rod. The ma-
terial used for the rod may either be boron or boron carbide. In this case, the
hh,
mio.14.11?
a)
?? off, Ir.
VigrgrApx??;?re:
?-?-??? .`? :0:Vs -* -4 dr!
'4147t4 *Iv, 4% Alt*
Vr.b.4.4P1 ATA.0.41*.?.?. *AAA
MAI II,1114a4, /WIN
\
\ ? `N.
\
\
Fig.20 - Design of Control Rod for a Fast-Neutron Reactor
a) Core; b) Rod consisting of moderator; c) Can of material
with good absorptivity for delayed neutrons
control rods of fast-neutron reactors differ from the rods of thermal-neutron re-
actors only in having a somewhat greater diameter. Cans are not necessary, since
the boron, being a good moderator, is also a good absorber of delayed neutrons.
Above, we have examined only the major difficulties encountered in the devel-
opment of aircraft nuclear reactors. Scientists, engineers, and designers working
in the field of aircraft reactor construction, are often faced with the necessity
of solving a number of other problems and of overcoming of other difficulties in
the field of design, engineering, and operation. However, no matter haw great-
these difficulties may appear at any moment, they are not insuperable.
Heat Exchangers
The heating of the working medium of an atomic engine directly in the reactor
is often unprofitable and sometimes impossible.
?
?
actor, it is possible to heat an intermediate heat-transfer agent
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which yields its heat in a heat exchanger to the working medium of the engine. The
'presence of an intermediate heat-transfer agent of circulating pumps, and of heat
exchangers results in an increase in the weight of the power plant. Therefore, an
,analysis of the system for the intermediate heat-transfer agent is of considerably
greater importance for an aircraft atomic power plant than for any other type.
The intermediate heat-transfer agent system must primarily provide for dissi-
pation of all the heat liberated in the reactor. Then this heat has to be trans-
ferred to the heat exchanger and there again transferred to the working medium of
the engine. Let us examine, in sequence, how these problems are solved. In order
to prevent fluctuations in the temperature of the reactor, exactly as much heat as
is liberated must be dissipated. If more heat is liberated than is removed, the
reactor temperature will rise. The automatic control will go into operation to re-
duce the liberation of heat in the reactor, and the desired reactor temperature
will be restored. If, on the other hand, more heat is removed than liberated, this
same temperature control will increase the liberation of heat to equalize it with
the heat dissipation.
Thus, the reactor will produce exactly as much heat as the heat-transfer agent
is-able to remove from it.
The ability of the heat-transfer agent to accumulate heat is measured by its.
thermal capacity, i.e., by the amount of heat required' to raise the temperature of
-1 kg of heat-transfer agent by one degree. The amount of heat removed from the re-
actor per second is determined by the formula
ci= cm(ff.h ? tin ),
where Q is the amount of heat absorbed per second;
c is the thermal capacity of the heat-transfer agent;
in is the mass of the heat-transfer agent passing through the reactor per
second;
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t1. isthe final temperature of the heat-transfer agent;
tin
? is the initial temperature of the heat-transfer agent.
The final temperature to which the heat-transfer agent is heated is limited by
the mechanical strength or the corrosion properties of the reactor material. The
initial temperature of the heat-transfer agent, i.e., the temperature at which it
enters the reactor and the heat exchanger, is approximately equal to the temperature
to which the working medium of the engine is heated. The greater the thermal ca-
pacity of the heat-transfer agent, the less of it will be needed to transfer the
amount of heat which must pass through the reactor per second. When a heat-transfer
agent of high thermal capacity is used, the total amount of heat-transfer agent in
the system and its rate of flaw can be reduced or, in other words, pumps of lower
delivery can be used.
In order to transfer as much heat into the heat-transfer agent within the re-
actor as it is capable of absorbing, the reactor must have an adequate heating sur-
face. The ability of the heating surface to transmit heat to the heat-transfer
agent is measured by the coefficient of heat transfer. The coefficient of heat
transfer indicates the quantity of heat that will be transmitted to the heat-
-
transfer agent by 1 m2 of heating surface in the course of an hour, when the tem-
perature difference between the heating surface and the heat-transfer agent is one
degree. The coefficient of heat'transfer from a.metal heating surface to air,
under the service conditions in an aircraft reactor, amounts to several hundred
kcal/m2 ' deg ? hr, while to helium it is several thousand kcal/m2 ? deg ? hr, arid
to liquid metal it is several tens of thousands of kcal/m2 ? deg ' hr.
In order to provide for the transfer of heat to the heat-tradsfer agent, the
area of heating surface of an aircraft reactor must be several hundred square
meters. To have so large an area in a reactor of small dimensions, several thou-
sand channels must be provided, through which the heated heat-transfer agent may
branch out.
78
4
The transfer of heat from the heat-transfer agent to the working medium of the
engine takes place in the heat exchanger. The heat-exchanging surface, at a heat-
transfer agent and a working medium of specific
parameters, is determined on the basis of the co-
efficient of heat transfer from the heat-transfer
agent into the wall of the heat exchanger, of the
coefficient of thermal conductivity of the heat-
exchanger material, and of the coefficient of ,
heat transfer from the walls of the heat exchanger
to the working medium.
Both the heat-transfer agent in the reactor
and the working medium in the heat exchanger are
in motion and must overcome the force of friction
with the heating substance. Figure 21 shows the
velocity distribution of the flaw of the body
being heated, as it moves through a duct of round cross section.
A portion of the kinetic energy of the body being heated is expended in over-.
comink friction, which results in losses due to friction. The more intensive the
heating of the moving substance, the greater will be the friction losses.'
The heating of the substance driving an atomic engine, as we indicated above,
is either effected directly in the reactor or in a heat exchanger. The .design of
the heat exchanger depends both on the heat-transfer agent used-and on the working
medium of the atomic power plant. But the general problem to be solved in all heat
exchangers is that of providing a large heat-exchange surface in a heat. exchanger
of small dimensions and weight. The main types of heat exchangers of possible use
in aircraft atomic power plants' are the tubular (honeycomb) and the slotted types
(Fig.22).
Fig.21 - Diagram of Velocity
Distribution in Flow through
a Tube of Round Cross Section
A tubular heat exchanger resembles the ordinary honeycomb radiator. It con-
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sists of a large number of fine tubes in a single housing, with the tubes spaced at
certain intervals. Through the tubes flows the working medium to be heated. The
z)
a
Fig.22 - Diagrams of Heat Exchangers: a) Tubular, b) Slotted
1) Air; 2) Helium
heat-transfer agent washes the outside of the tubes. The slot-type heat exchanger
is .a kind of "layer cake" whose successive layers are represented by the working
medium of the engine and the heat-transfer agent. The layers are separated by?thin
sheets of metal, mechanically connected to -provide rigidity of Construction.
In both kinds of heat exchangers, the working medium of the engine and the
heat-transfer agent may either be made to hove in opposite directions or perpen-
dicular to each other, or parallel in the same direction. It is obvious that the
most effec4ve form is that of opposing motion of the working medium and the heat-
transfer agent, or what is known as countercurrent operation. In this design, the
most uniform and highest heating of the working medium is Obtained. In designing
heat exchangers, an attempt is made to achieve the required heating of the working
medium with the lowest possible friction losses.
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A difficult problem is that of keeping the heat exchanger free of deformation
due to temperature. On heating, as we know all metals expand, except for certain
special alloys. The heating temperature of various portions of a heat-exchanger is
not identical, so that the degree of heat deformation will vary. If no special
measures are taken, the heat exchanger may break down. This danger is particularly
great when the heat exchanger is heated and cooled along with the heat-transfer
agent at the instant of starting and stopping the engine, when the inequality of
heating is particularly great.
An important problem is that of developing reliably operating pumps for trans-
ferring the liquid-metal heat-transfer agents. The difficulties in providing re-
liable seals between the rotating shaft of the pump and its fixed housing, at ex-
ceedingly high temperatures, has led to the idea of substituting electromagnetic
pumps for the usual mechanical pumps. The operating principle of electromagnetic
pumps for liquid metals is based on utilization of the force of interaction of an
electric current and a magnetic field. The tube with the liquid metal is placed
within a magnetic field. Electrodes are inserted into the tube, and a current is
sent through the metal. The liquid metal is thus subjected to an expulsive force
and starts flawing through the tube.
The use of a liquid-metal heat-transfer agent requires an auxiliary system for
heating the heat-transfer agentoince, at the usual temperatures of the ambient air
particularly in winter, even the most fusible metal alloys available for use as
heat-transfer agents will be in the solid state. This inconvenience is eliminated
if gases are used as the heat-transfer agents. Hydrogen and helium, or a noncbtor-
bustible mixture of hydrogen and helium, are particularly suited to this purpose.
Less desirable are nitrogen, carbon dioxide, etc. In order to increase the co-
efficient of heat transfer and the volumetric thermal capacity of a gas, it has to .
be compressed to some tens of atmospheres.
An interesting special feature of the practical application of gaseous heat-
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transfer agents is the possibility of providing for their "self-circulation". The
gaseous heat-transfer agent compressor may be used to start the rotation of a gas
turbine, by using the energy of the heat-transfer agent itself. In this case, the
gaseous heat-transfer agent moves first from the reactor to the turbine, then to the
heat exchanger, and from there to the compressor which compresses the gas and re-
turns it to the reactor. The result is the usual closed cycle of operation of a
gas turbine, one specific feature of which is the fact that it does not perform use-
ful mechanical work. This explains the negligible reduction in the temperature of
the gaseous heat-transfer agent within the turbine. This reduction in temperature
is particularly small with hydrogen and helium.
The use of metals in vapor form as heat-transfer agents makes it possible to
utilize not only the thermal capacity but also the latent heat of evaporation to
transfer heat.
The desirability of this will be shown in the following example. Each kilo-
gram of gaseous sodium condensed at a temperature of 880?C, liberates about
1000 kcal in a heat exchanger. The temperature of the heat exchanger wall, during
this process is equal to the temperature of condensation. In order to transfer the
same amount of heat to the heat exchanger by means of 1 kg liquid sodium at the
same wall temperature, the sodium would have to enter the heat exchanger at an in-
itial temperature of 4200?C. If we take as the initial temperature of liquid so-
dium the more realistic value of 1200?C, it would require 13 - 15 kg of liquid so-
dium to equal the efficacy of 1 kg of sodium vapor.
If we refrain from transferring heat by means of the thermal capacity of
gaseous metals and make use only of the latent heat of evaporation, then the tem-
perature in the entire heat-transfer agent system will be virtually identical.
This temperature may be set at maximum permissible level for the structural ma-
terials of the heat-transfer system. When this is the case, the mechanical strength
of the material will be utilized to a much greater degree, and materials not in
?
such short supply can be used for the purpose. Thus, the use of vaporized metal
heat-transfer agents is advantageous both in terms of weight and in terms of econom-
ics.
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tr.
CHAPTER III
POSSIBLE DIAGRAMS OF AIRCRAFT ATONIC POWER PLANTS (AAPP)
The structural design of an atomic power plant discussed in Chapter I (Fig.8)
may be used both in aviation and in other fields of transport. To do so, it is
necessary to replace the propeller by an electric generator and to use electric
motors for rotating the propeller of a steamship, the driving wheels of an electric
locomotive, etc.
It seems logical that atomic power plants of designs especially adapted for
aviation will be developed to serve the modern types of aircraft engines. In ac-
cordance with the types of aircraft engines now in use, the possible types of AAPP
may be divided into three major groups: 1) rocket engines; 2) three types of ram-
jet engines: a) true athodyds, b) turbocompressor engines, c) motor-driven com-
pressors; and 3)turboprop engines.
Each of these groups contains -a large number of engine designs differing in
r ?
'complexity in accordance with the needs of various types of aircraft. Obviously,
certain designs will be realized in the comparatively near future. Others will re-
quire a longer period of development from the scientific, technological, and par-
ticularly from the metallurgical viewpoint before they can become a reality.
Certain designs will probably remain on paper only.
. In this Chapter, we will review the most typical designs of aircraft atomic
'power plants and will discuss the possibilities of their application.
?
?
Atomic Rocket_kriallg
Rocket is the name given to reaction engines that do not require atmospheric
air for their functioning. The simplest type is the powder rocket engine. This
type comprises a powder-filled cylindrical chamber, terminating in a specially pro-
filed jet nozzle (Fig.23). As the powder undergoes combustion, a large quantity of
Fig.23 - Schematic Sketch of Powder Rocket
a) Warhead; b) Powder charge; c) Jet nozzle
gases is generated, which press outward in all directions. The pressure of the
gases on the side walls is balanced (Fig.24). The force of the pressure of the
gases on the front_ wall is incompletely compensated, since the area subject to gas
-1111111-
Fig.24 - Schematic Sketch of the Pressure Distribution
of Combustion Gases
pressure on the nozzle side is smaller and since the pressure of the gases in a jet
nozzle decreases,with increasing velocity. This excess gas pressure is the reactive
force. A reactive force is produced only if there is a difference in surface areas,
i.e., if one side of the rocket is provided with an aperture through which the pow-
der gases can escape. The development of reactive force is impossible without an
ejection of gases. The greater.the gas pressure, 'the greater will be the velocity
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4.
CHAPTER III
POSSIBLE DIAGRAMS OF AIRCRAFT ATONIC POWER PLANTS (AAPP)
The structural design of an atomic power plant discussed in Chapter I (Fig.8)
may be used both in aviation and in other fields of transport. To do so, it is
necessary to replace the propeller by an electric generator and to use electric
motors for rotating the propeller of a steamship, the driving wheels of an electric
locomotive, etc.
It seems logical that atomic power plants of designs especially adapted for
aviation will be developed to serve the modern types of aircraft engines. In ac-
cordance with the types of aircraft engines now in use, the possible types of AAPP
may be divided into three major groups: 1) rocket engines; 2) three types of ram-
jet engines: a) true athodyds, b) turbocompressor engines, c) motor-driven com-
pressors; and 3)turboprop engines'.
Each of these groups contains a large number of engine designs differing in
complexity in accordance with the needs of various types of aircraft. Obviously,
certain designs will be realized in the comparatively near future. Others will re-
quire a longer period of development from the scientific technological, and par-
ticularly from the metallurgical viewpoint before they can become a reality.
Certain designs will probably-remain on paper only.
In this Chapter, we will review the most typical designs of aircraft atomic
power plants and will discuss the possibilities of their application.
84
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?
Atomic Rocket Engines
?
Rocket is the name given to reaction engines that do not require atmospheric
air for their functioning. The simplest type is the powder rocket engine. This
type comprises a powder-filled cylindrical chamber, terminating in a specially_pro-
fiied jet nozzle (Fig.23). As the powder undergoes combustion, a large quantity of
? ? ?
???%???????4
??????????? -
????????? ?
? %%.'
4.4 ? ?W ? ?
VV?? w r
Fig.23 - Schematic Sketch of Powder Rocket
a) Warhead; b) Powder charge; crJet nozzle
gases is generated, which press outward in all directions. 'The pressure of the
gases on the side walls" isbalanced (Fig.24). The force of the pressure of the
gases on the front., wall is incompletely compensated, since" the area subject to gas
HIM
Fig.24 - Schematic Sketch of the Pressure Distribution-
of Combustion Gases '
pressure on the nozzle side is smaller' and Since the pressure of the' gases in a jet
- .?
nozzle decreases,with increasing velocity. This excess gas pressure is the reactive'
,
force. A reactive force is produced only if there is a difference in surface areas,
- - .,:? Z?
one side of the rocket is provided with ah aperture through which the pow-
i.e., if
? ? .e ? '
der gases can escape. The development of reactiie force is impossible without an
ejection of gases.. The greater the gas pressUre,Ithe greater will be the' ielOcity,
STAT
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of flow stid the reactive force.
A powder rocket engine, in which the powder undergoes combustion within a few
SedOndai is uieful for aviation only as an auxiliary engine as a take-off assist for
heaViiy Lidded aircraft.
In liquid'-fuel rooket engines, the period of operation is considerably longer.
This type of engine has a. cylindrical combustion chamber equipped with a jet nozzle
(Fig.25). Fuel and oxidizer are sprayed into the combustion chamber. The fuel
burhi; while the oxidizer sustains the combustion. This results in the generation
Of high=teMpe6ature gases which are ejected through the jet nozzle, resulting in a
Fig. 25 - Schematic Diagram of a Liquid-Fuel Rocket Engine
a) Fuel; b) Combustion chamber; c) Jet nozzle; d) Oxidizer
reactive force. The higher the temperature of the gases, the slower will be their
discharge through the jet nozzle at the same pressure in the combustion chamber,
i.e., at the same reactive force.
Obviously, the production'of a reactive force in this type engine requires:
1)'the production of a large quantity of gases compressed to high pressure; 2) the
heating of these gases to the highest possible temperature; 3) the ejection of these
_gases through a jet nOzzle at the highest possible Velocity. -
These same problems must necessarily be solved in an atomic rocket engine.
The simplest design of such an engine is presented in Fig.26. A pump is used to
.deliver the working medium (i.e., the material for producing the gases) from the
tanka to the reactor, under high pressure. Passing through the ducts of the reactor,
86
i the working medium is converted to gas, heated to high temperature, and then ejected
through the jet nozzle.
The period of operation of an atomic rocket engine is limited by the supply of
.111 working substance that can be housed aboard an aircraft. Because of the very high
c)
Fig.26 - Schematic Diagram of an Atomic Rocket Engine
a) Tank with working medium; b) Pump; c) Reactor; d) Jet nozzle;
e) Control rods
consumption of this medium, an atomic rocket engine is unprofitable for flights at
the altitudes at which modern aircraft and the aircraft of the future customarily
fly. We will discuss the fields of application of this type of engine in Chapter V.
Ram-Jet Atomic Engines
In rami et atomic engines, the working medium is atmospherio air heated by the
combustion of a liquid fuel, usually kerosene. The consumption of kerosene is no
more than 2 - 3% of the air passing through the engine, a ramjet engine is able to
function for a considerably longer period of time aboard an aircraft than a 1iq4d...77r
fuel rocket engine. Ram-jet engines include: pulse jets, true athodyds,.turbojets,
?
and engines with motor-driven compressors.
The intermittent ram-jet engine (Fig.27) is a cylindrical tube, whose front end
is closed off by a valve-type grill and whose rear section ends in a jet, noz7le
This engine functions in the following manner: The fuel (gasoline) is injected- '
. -
through nozzles and is immediately ignited by a sparkping. The, gaao440.404ation
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products and the hot air seek to escape through the jet nozzle. The pressure of the
gases on the valve-type grill closes the valves and thus produces thrust. As the
gaseS are ejected from the jet 'nozzle at high velocity, they continue to flow by in-
ertia even after the pressure in the combustion chamber has returned to atmospheric
a)
d)
c)
e)
Fig.27 - Design of Intermittent Ram-Jet Engine
a) Fuel; b) Sparkplug; c) Jet nozzle; d) Valve grill;
e) Combustion chamber
pressure. This creates a vacuum in the combustion chamber and a new charge of at-
mospheric air is sucked through the valves. Then gasoline is again injected, and
the cycle is repeated. A total of 80 - 100 cycles occur in this engine within one
b)
C)
Fig.28 - Schematic Sketch of a Ram-jet Engine
a).Diffuser; b) Fuel; c) Sparkplug; d) Jet nozzle;
e) Combustion Chamber
second, each accompanied by pressure surges or pulsations. Therefore this type of
engine has become known as a pulse jet.
weresaras.......totrgemeern
.68
' The ram-jet engine is simpler in''-construction (Fig.28) and reqUires no vale
grill. However, in order for a ram-jet engine to function, the aircraft on Which it
,
is installed must .fly at high speed. The relative air *Wu-r-Oked-' into the nose- Of the
-
ram jet, called the diffuser, is decelerated. Its velocity decreases, while the
pressure increases. Fuel, ignited by a sparkplug, is injected into the air com-
pressed by the velocity head. The combustion produCts mixed with air are ejected
_
through the jet nozzle at high velocity. -The reactiveTorce'results from the pres-
,
?
sure drop between the nose (at the.diffuser). andthe,rear (at the jet nozzle).
In 1929, B.S.Stechkin, member of the Academy, was the first in the world to
develop and publish the fundamentals of the theory of ram-jet. engines. In addition
to a number of other important laws, he determined the relationship between the re-
active force of a ram-jet engine and the velocity difference between the exhaust of
gases from the jet nozzle of the engine and the flying speed:
P = Oa
where P is the reactive thrust;
Cf-052
g
Oa is the airflow through the engine;
cf is the rate of-flow;
oftis-the flying speed; -
g is the acceleration of gravity.
The equation permits determination of the reactive-fore,'withOut'knOWledge
the gas pressure distribution within the engine, merely on the-basis of-the flying .
speed, the exhaust velociti'of the gas, and the flow Of air through the. engine.
The greater the exhaust velocity, the greater Will'be:the!reaStilie-thrust:-
_A -major shortcoming of the ram-jet engine is the fact that it can create a:'re=
active force only at high flying speeds. The turbojet engine,(Fig.29) lacks this
shortcoming. The operating principle of this 'engine is as follows: As the engine is
_ -
run: on-:the -ground. -ail, is -suked the :7?Coneiiir ine6dmii4iieai &ieii at.-
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mospherep pressure. The compressed air is then directed into the combustion chamber.
The fuel is injected into this ohamber. The combustion products rotate a turbine
whose shaft is .connected with. the compressor; the combustion products are then
Fig.29 - Diagram of a Turbojet Engine
a) Diffuser; b) Compressor; c) Turbine; d) Jet nozzle;
e) Kerosene injectors; f) Combustion chamber
ejected through the jet nozzle. Tp this engine also, the reactive force is the re-
sultant of the forces of the air pressure and the combustion products over the en-
tire inside surface of the engine, an4 also may be calculated by Stechkints equation.
At the dawn of the development of ram-jet engines, when they were still of low
power, not a turbine but an internal combustion aircraft engine was used for driving
the compressor. This type of ram-jet engine was called an engine with motor-
compressor drive. This type did not come int9 wide use, in view Of the fact that's.
gas turbine can cleyelop .greater power than an internal combustion engine of
the same weight.
Except for the pulse jet, all types of ram-jet engines may be run by atomic
energi. Let us examine in sequence a number of probable designs of atomic ram-jet
.1,104.1q3;
Atomic Ram-Jet Engine (ARJE)
The atom# ram-,:jet engine (Fig,30 is the simplest type of atomic power plant.
?
4
What it amounts to is -a "flying reactor" with a diffuser in the nose and a jet
nozzle at the rear.
Within the
than 3 ? 4, the
Therefore, this
speeds, a shock
the increase in
the engine of a
speed range exceeding the speed of sound by a factor of not more
ramjet develops increased thrust in proportion to the flying speed.
type is used for high-speed aircraft. In flight at supersonic
wave develops ahead of the engine, which results in retardation of
engine thrust as the flying speed increases. Installation ahead of
cone such as that shown in Fig.30 facilitates reduction in the in-
tensity of the shock wave and thus leads to a reduction in the loss of thrust; The
cone can be used for housing electric motors to operate the control rods of the re-
actor.
One of the major parameters used for rating of jet engines is the specific
thrust. If the thrust of an engine is divided by the number of kilograms of air
passing through the engine per second, the magnitude of the specific thrust is ob-
tained. The greater the thrust created by each kilogram of air, the more ideal is
the engine.
The specific thrust of a ramjet is determined by the altitude and speed of
flight, the design of the diffuser and jet nozzle, and the temperature to which the
air' is heated in the engine. The higher the temperature of the air; the greater
the specific thrust. In modern ram-jet engines, the air is heated to approximately
15000C. It is impossible today to heat the air in an ARJE to this temperature:,
The structural materials of modern reactors can only withstand temperatures ofAhe'.
order of 1000 - 1100PC, and the temperature of the heated air will be even:lower,'.
than this. Moreover, the friction losses, as air Moves through the channelerhoey
combing the reactor, will be considerably greater than-the-losses in' the combustion
chamber of, the ordinary ram-jet engine. The restlt'is that the .specific thrust ;f:
and ARJE is inferior to that of a conventional type of ramjet engine.'
However, the thrust of an engine is determined not- 6111i by its sPecific,thrust
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but also by the air throughput, i.e., by the quantity of air passing through the
engine per second. If the dimensions of an ARJE are larger than those of a conven-
tional ramjet, then a larger amount of air will flow through it, and its thrust
b)
droolm.num ..m.????m.
Fig.30 - Schematic Diagram of an Atomic Ram-Jet Engine
a) Nose cone; b) Control rod; c) Reactor; d) Jet nozzle
will be greater. There is no need to worry about the fact that the increase in size
of the ARJE will increase the consumption of nuclear fuel. A fuel supply sufficient
for the entire possible service life of an ARJE is charged into the reactor at a
single time so that there is no need to refuel during the life of the engine.
The maximum, flying speed may be increased either by raising the thrust of the
engines or by reducing the drag of the aircraft. If the drag is reduced and the
thrust remains the same, the maximum speed will increase.
In terns of increasing the maximum speed of the aircraft, the perfection of an
aircraft engine is rated by its frontal thrust. The frontal' thrust of an engine is
the thrust of that engine per square meter of frontal cross-sectional area. The
cross-sectional area determines the drag experienced by the engine. The greater the'
frontal thrust, the smaller the cross-sectional area of the engine has to be to
reach a given total thrust, or the greater will be the maximum flying speed attain-
able. Therefore, it is desirable to have the greatest possible frontal thrust.
At a given rate of airflow, the cross-sectional area of the engine is deter-
mined-either by the dimendions of the'diffuser'or'by the dimensions'ofthe reactor
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or of the jet nozzle. The diameter of the jet nozzle usually is less than that cal-
culated in the original design, so as to prevent the jet nozzle from exceeding the
overall dimensions of the engine. This "cutdown" of the jet nozzle causes some re-
duction in thrust, but at the same time the drag of the engine is decreased to an
even, greater degree. Therefore, it may considered that the cross-sectional di-
mensions of an ARJE are determined either by the diffuser or by the reactor. Calcu
lationS show that only at very high flying' speeds, approximately, three times as high
as the speed of sound, will the lateral dimensions be determined by the diffuser.
At speeds less than 2.5 times the speed of sound, the diameter of the reactor,will
exceed the diameter of the diffuser. This means that, in order to increase the
frontal thrust, an effort must be made to reduce the cross-sectional area of the
reactor.
If the air throughput of the engine is taken as given, then at a flying con-
stant speed the cross-sectional area of all channels of the reactor will be smaller,
the greater the rate of airflow through these ducts.
Heating of the air as it flows through the ducts is accompanied by an increase
inits velocity, since the density of air decreases with increasinOemperature
while the cross-sectional area of the duct remains constant. The air velocity at
the reactor outlet is several times greater than at its inlet. At a.given air
velocity at the inlet, .itsspeed at the outlet of 'the reactor the speed
of sound. A further increase in the air velocity at the?reactor,inlet and, conse-
quently, free passage of air through the engine is impossible. What happens is,
"cutoff" of the reactor.
An engine will have its greatest frontal thrust 'when the velocity of the air.at-
the reactor outlet is equal to the speed of sound. If, in this case, the tempera-
ture of the heating surface is increased, the temperature of the air will also rise.
This causes the velocity of the air at the reactor outlet to increase somewhat, .but?
as tsual it will equal the speed of sound when.atemperature of specific magnitude-
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is attained. The velocity of the air at the reactor input decreases and the passage
of air through the engine is reduced.
What will be accomplished with such an engine? The specific thrust will in-
crease with increasing air temperature increases, and the rate of flow will decline.
The thrust of the engine, equal to the product of the specific thrust and the air -
flow, will either not change at all or change very little. Calculation results
showing the relationship between frontal thrust and speed of sound for two ARJE, in
which the temperatures of the heating surface of the reactor are 1100?C and 1600?C,
respectively, are presented in Fig.31 in the form of curves. A comparison of these
curves shows that it is not always necessary to strive for an extraordinary increase
in the air temperature by increasing the temperature of the heating surface of the
reactor.
Haw can the thrust of an ARJE be varied in flight? The thrust of a convention-
al ramjet is changed by changing the amount of fuel injected into the air. Control
of the thrust of an ARJE is even simpler and may be accomplished by means of the
regulating (control) rods of the reactor. To reduce the thrust of an ARJE, the rod
is pushed into the reactor, thus reducing the amount of heat liberated by the reac-
tor to the desired level. This causes the air temperature at the reactor output to
drop and, consequently, reduces the thrust. To increase the thrust, the thermal,
capacity of the reactor must be increased by withdrawing the control rods. To pre-
vent an excessive rise in temperature of an ARJE reactor, a temperature control has
to be provided.
In addition to the above-discussed ARJE design, in which the air is heated di-
rectly in the reactor, another design may be conceived, namely one involving heating
of the air by means of an intermediate heat-transfer agent. Figure 32 presents a
schematic diagram of an ARJE in this category. The air compressed by the velocity
head is heated in a heat exchanger. The transfer of heat from the reactor to the
air is performed by an intermediate heat-transfer agent, which is circulated by a
P
ifr 9
8000
60006
4000
Z000
sf r-I600?C
10a9 2000
111????
30(1g VHq/hr
Fig.31 - Ratio of Frontal Thrust of an Atomic Ram-Jet Engine to Flying Speed
alb ?
b)
?????.?
e) ? f )
Fig.32 - Schematic Sketch of an Atomic Ram-Jet Engine with
Intermediate Heat-Transfer Agent
a) Control rod; b) Reactor; c) Pump; d) Jet nozzle; e) Nose cone;
f) Heat exchanger
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special pump. This ARJE design permits the use?of a much smaller reactor. The co-
efficient of heat
transfer agent is
the heat-transfer
dimensions of the
transfer from the heating surface of the reactor to the heat-
many times larger than to air. Therefore, the heating surface of
agent need be only a fraction of that in the former case, and the
reactor may be reduced accordingly.
?
However, atomic ram-jet engines using intermediate heat-transfer agents are
more complex, both in design and in operation. For example, they will have poor
pickup. Pickup is the capacity of an engine rapidly to gain thrust at the desire of
the pilot, from any operating condition up to maximum thrust. The greater the
pickup of the engine, the more maneuverable the aircraft will be. The thrust of an
ARJE with direct heating of air in the reactor begins to increase at the instant of
pulling out the control rod, whereas the thrust of an ARJE with an intermediate
heat-transfer agent begins to increase only after the heat-transfer agent is heated
slightly.
A basic drawback of the ram-jet engine is its inability to produce thrust when
on the ground and at low /lying speeds. This shortcoming makes it impossible to use
an ARJE as the sole form of propulsion? It must necessarily be used in combination
with other types of engines to permit the aircraft to take off and to accelerate to
the speed at which the ARJE produces adequate thrust.
Atomic Turbojet Engines (ATJE)
The turbojet engine is the predominant type used' in modern jet aircraft. This
is due to the fact that the engine is simpler in design than the turboprop engine,
which can compete with it insofar as fuel consumption is concerned. In addition,
an aircraft with a turbojet engine can reach significantly greater speeds than one
with a turboprop engine, in view. of the fact that, at supersonic flying speeds, the
efficiency of thrust production by a propeller diminishes.
The ATJE is the simplest of atomic aircraft engines which can be used entirely
96
it
4.*
6
alone. Installation of an ATJE on an aircraft permits it tcitike off independently,
to fly with good maneuverability over the entire possible range of speeds and alti-
tudes, and also to make a normal landing. Let us discuss the possible design vari-.
ants of an ATJE. The simplest is a design that differs from that of the ordinary
turbojet engine only in that the combustion chamber is replaced by a reactor. This
design is illustrated in Fig.33. Air from the compressor enters the reactor, which
is placed between the compressor and the turbine. A portion of the energy of the
heated air is consumed in the turbine for rotating the compressor. Another portion
is converted into the kinetic energy of the exhaust from the engine, within the jet.
nozzle.
Proper selection of the compression ratio of the compressor is a major factor
b) f)
Fig.33 - Schematic Sketch of an Atomic Turbojet Engine
a) Nose cone; b) Compressor; c) Control rods; d) Reactor;
e) Turbine; f) Jet nozzle
-
in. designing a turbojet engine with high specific parameters.. In projecting an air-:
? - ;
craft engine, the designer knows, the speed at which the aircraft and its' engine will
- - ? .,:.
fly. He selects a compression ratio permitting development of the greatest: posiible
-thrhst at this calculated flying speed, with the lowest possible fuel conSumption
and the smallest possible engine weight. It is usually impoSsible to satisfy all
?
three of these requirements at onde. If the compression ratio is so selected that
,
,
the specific thrust of the engine is at its Maximum, the fuel consumption will be
,t , .
high'. If minimumpossible fuel consumption is desired, the specific '
ifidtfirust WIli
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decrease. The designer determines which factor is more important for the aircraft
and determines the compression ratio on that basis. Thus, an engine designed for a
long-range bomber must have minimum fuel consumption. As a result, the saving in
fuel weight during a flight of many hours duration permits an increase in range. On
the other hand, interceptor aircraft require maximum frontal thrust. The excess con-
sumption of fuel that is inevitable in this case is not of importance, since the
flying time of such an interceptor may be measured in minutes.
Haw then shall we approach the selection of the compression ratio for an ATJE?
The fact that ATJE are used for high-speed aircraft indicates that the compression
ratio must be such as to yield maximum frontal thrust. It is desirable, of course,
that the engine weigh as little as possible. However, it must not be forgotten that
the main portion of the weight of an atomic aircraft engine is the weight of the
radiation shielding. Therefore, a reduction in engine weight at the expense of a
reduction in frontal thrust will hardly be desirable.
Thus we have come to the conclusion that the compression ratio of the compres-
sor of an atomic engine for aircraft must be such as to give maximum frontal thrust.
As in conventional turbojet engines, it is to be expected that, with an increase in
the calculated flying speed, the compression within the compressor will be reduced.
This is explained by the increase in compression due to the velocity head. For ex-
ample, for sea-level operation of an engine the optimum compression ratio of a com-
pressor is six. At flying speeds equal to that of sound, the compression of the
air due to the velocity head is a little less than two, and in order to attain a
total compression ratio of six, the compression in the compressor need be only
slightly above three. .This is a crude example and does not reflect all the complex-
ities of the phenomena that must be taken into consideration in calculating the op-
timum degree of compression within a turbojet compressor designed to yield high fly-
ing speeds, but it is clear from this that, at increasing flying speed, compression
ratio of a turbojet compressor should be reduced.
98
When the daily press carried the first reports on possible designs of atomic
aircraft engines, it was believed that the compression ratio of an ATJE engine would
have to be considerably greater than that of a conventional turbojet engine. This
was explained by the increase in heat emission from a reactor with increasing pres-
sure of the airflow through this reactor and the attendent possibility of reducing'
the size of the reactor accordingly. The possibility of designing atomic, ram-jet
engines Was' completely denied. It was held that the degree of compression of the
air due to the velocity head, even at high flying speeds, would be insufficient to
drive the air through the ducts of the reactor. Liter, when the required calcula-
1E oPt)Pf, I
7
6
5
4
3
2
1
1110.1 1500 2000 .2500 . Ihymplr
Fig.34 - Optimum Calculated Compression Ratio of an Atomic Turbojet Engine,
to Obtain Maximum Frontal Thrust, as ,a Function of the Flying Speed,
tions had been made, it appeared that the optimum compression ratio of an ATJE_com-
pressor; calculated to yield a maxim= frontal thrust, differs much less from the
optimum compression ratio of.a conventional turbojet than had previously been.
mimed. The nature of the relationship of the optimum compression, ratio of, the com-
pressor of an ATJE and the flying speed is illustrated in Fig.34.-,This curve per-
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mitS selecting the compression ratio of the ATJE compressor for any desired flying
speed. It is obvious that, at high flying speeds of M = 2.5 - 3 or more, the opti-
mum compression ratio is unity, i.e., that at these speeds an atomic ram-jet engine
.develops greater.frontal thrust than does an atomic turbojet engine. This again
confirms the desirability of using ARJE for high flying speeds.
As indicated above, 'an increase in the compression ratio of the comPressor for
an ATJE results in a better dissipation of heat from the reactor and permits a re-
duction in its weight. However, at high flying speeds, the total degree of compres-
sion of the air due to the velocity head and due to the compressor rises excessively.
The temperature of the air past the compressor increases to such a 'degree that all
that is possible within the reactor is a very small rise in the heating of the air
With this object, the ATJE compressor may be designed as a multistage type, with
cooling after each stage. Figure 35 illustrates a two-stage ATJE compressor. The
heat exchanger between the compressor stages functions basically as a ram-jet engine
when both air intake and ejection are properly laid out, and will create additional
thrust.
The simplest design for an ATJE, illustrated in Fig.33, permits obtaining the
highest specific parameters. In this case, the air duct becomes a uniflow duct
where the airflow through the engine is at all times parallel to the engine axis
ji q)
0
Fig.35 - Atomic Turbojet Engine with Two-Stage Compressor and
Intermediate Cooling of Air
a) Nose cone; b) First-stage compressor; c) Cooling-air scoop; d) Second-stage
compressor; e) Control rods; f) Two-stage turbine; g) Jet nozzle; h) Reactor;
i) Outlet for cooling air; j) Heat exchanger
to that permissible in terms'of the thermal strength of the reactor. The thrust of
an engine decreases with a reduction' in the amount of heat delivered to the a1r. A
be avoided if the air is 'cooled during the compression process:
Fig.36 - Diagram of an Atomic Turbojet Engine with Reactor Outside the Engine
g) Nose cone; b) Control rod; c) Compressor;. d) Reactor; d) Turbine;
f) jet nozzle
in a straight line, so that the hydraulic resistance is at a minimum. The air is
heated directly in the reactor without an intermediate heat-transfer agent. This
'simplifies the design and eliminates excessive heat loss. However, this design,
which is-simple in principle is exceedingly difficult to realize. 'The shaft con-
'meting the turbine with the compressor has to pass through the reactor. Cooling
.the shaft under these conditions becomes a difficult-and actuallyy one might, say,
the 'key problem. The point is that the shaft not only becomes,heated-asa,result of
'heat-transfer from the hot reactor Parts, but cOnsiderableaiberation.of-heatSD?T.,AJ
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within the shaft itself, due to the scattering and absorption of neutrons and gamma
rays by the shaft material. So much heat is liberated in the shaft that cooling of
the shaft changes from a simple engineering matter to a complex problem, whose solu-
tion will govern the very possibility of developing an ATJE on the basis of this
"simplest" design.
In order to avoid the effect of reactor radiations on the shaft, the reactor
could be installed outside the engine
special ducts. Figure 36 illustrates
an .engine can no longer be considered
and deliver the air to the engine through
an engine of this type. The air duct of such
a ram jet. The air passing through the engine
and the reactor undergoes several changes in direction. This results in additional
e)
h).
Fig.37 Schematic Sketch of an Atomic Turbojet Engine with Intermediate
Heat-Transfer Agent
a) Nose cone; b) Compressor; c) Pump; d) Control rod; e Reactor;
r) 'Heat exchanger; g) Turbine; h) Jet nozzle
hydraulic losses, which reduce the specific thrust of the engine. In addition,
there are inevitable heat losses through the walls of the ducts as the air moves
from the reactor to, the turbine, which also impairs the specific parameters of the
engine. However, the reactor in this case has been moved far outside the engine,
and provision for shielding from radiation therefore becomes significantly simpler.
?? 102
A.
Ii
1
4
4
To realize an ATJE on the basis of this general scheme apparently is easier-than on
the basis of the design presented in Fig.33. An increase in hyaraulic losses can be
prevented by using a slightly more complicated design. Figure 37 shows a design for
an ATJE using an intermediate heat-transfer agent. The.function of the intermediate
heat-transfer agent is that of transmitting heat from the reactor to the air. The
advantages of this ATJE are the
termediate heat-transfer agent:
-losses than those in the engine
same as those of an atomic ram-jet engine with in-
a comparatively small reactor, and lower hydraulic
designed in accordance with Fig.36. The shortcom
ings lie in the field of greater complexity of design and operation. ?
Many modern turbojet engines are equipped with boosters. Boosting is an in-
crease in the thrust of an engine above its maximum for a short period by means of
some "overloading,' of the engine. The majority of turbojet engines with boosters
are provided with what is known as afterburner chambers placed between the turbine
and the jet nozzle. Considerably more air is delivered to the combustion chamber
of a turbojet engine than is required for burning the? injected fuel; consequently,
the combustion products still contain...a considerable amount of oxygen. Additional
fuel is injected into the after burner in Which this residual oxygen is used for
combustion. The temperature of the gases rises, the exhaust velocity increases,
and the thrust is augmented. However, the fuel consumption, almost doubled in this
procedure.. The temperature of the engine parts starts to rise sharply.: Therefore,
boosting is possible only for a brief period of time, not more than a few minutes.
Usually, the boosters are turned on when there is need for rapid acceleration or
? In this connection, the thought arises as. to whether it might be possible to
reheat the air after it has passed through the turbine of an ATJE? The simplest
solution is supplementary heating with an intermediate heat-transfer agent. '
for gaining altitude.
Figure 38 shows a schematic sketch of an ATJE with suppiementarr'heating'ofthe,air
downstream, of the turbine. The. heat-transfer agent movei:trom the1reaCtOr-first td
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the auxiliary heat source and then, having surrendered part of its heat, proceeds to
the other section of the heat exchanger Where the heat going to the turbine is
heated. The temperature of the air upstream of the turbine will be somewhat lower
than is the case without supplementary heating; in addition, the dimensions of the
turbine have to
same level. It
advantageous to
agent: one for
tary heating of
be increased somewhat so as to keep the power of the turbine at the
is possible that, as far as weight is concerned, it may prove more
use two independent circulation circuits for the heat-transfer
heating the air upstream of the turbine and the other for supplemen -
the air downstream of the turbine.
An objection to the use of an ATJE in which the air is heated directly in the
Fig.38 - Schematic Sketch of an Atomic Turbojet Engine, with the Air
Heated Downstream of the Turbine
a) Nose cone; b) Compressor; c) Control rod; d) Pump; e) Reactor;
f) Turbine; g) Cone; h) Jet nozzle; i) Auxiliary heat exchanger;
j) Heat exchanger
reactor may be raised on the grounds that the air, having passed through. the reac-
tor, will become radioactive and will constitute a hazard for the ground crew. Let
us define the 'extent of-this possible danger. The bulk of the radioactive radiation-
104
?
?
?
?
in the air will be argon, which constitutes 0.94%. of air. Radioactive radiations may
be produced by one of the isotopes of oxygen, by water vapor in the air, and also by
dust, The air passing through the engine is constantly intermixed with the. ambient
atmospheric air, so that the concentration of radioactive argon drops rapidly. In
practice, at the point where the temperature in the stream of hot air emitted from
the engine drops to the point where a person entering this air stream does not suffer
a burn, the radioactivity of the air has also dropped to. below the danger point for
the human organism. Somewhat more dangerous is the radioactive dust that may have
passed through the reactor. This dust, settling on the airfield, may create a sig-
niticant radiation level of rather long duration. The best methods of counteracting
this phenomenon are those used to prevent dust from forming on an airfield: laying
of concrete runways, proper dust removal from these strips, wetting with water be-
fore aircraft take-offs, etc.
In closing this Section, let us review data for calculation of the ATJE shown
in Fig.33. The weight of the engine, including the reactor and reflector surround-
ing the reactor, will be 15 tons. The length of the engine will be 6.5 m and its
diameter 2.3 m. At sea-level operation, the engine will develop a thrust of 32 tons.
An aircraft with a flying weight of 130 tons, equipped with two such engines, will
be able to develop a maximum flying-speed of 2100 km/hr at an altitude of.110000 m.
The aircraft will be able to fly at this speed and altitude more than-1,000,000km.
,(26 times around the earth) without the need for refueling., A total of 15 kg of- ,
uranium235 will be consumed in the course of such a flight..
Atomic Turbojet Engine with Motor-Driven Compressor (ATJEND)
,
It had been indicated above that supplementary heating of the air past the tur-
bine causes an increase in engine thrust. It is obvious that the same result will
be obtained if an auxiliary engine, not utilizing the energy of the ,air heated in ,
the heat exchanger or the reactor, is used for driving the compressor. A,steam or
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gas turbine may be used for this purpose. Figure 39 shows a schematic sketch of an
ATJEMC with a mercUry-vapor turbine. The mercury turbine operates on a closed cycle.
A pump forces the mercury under high pressure through the reactor. The mercury is
heated there and converted into vapor. The mercury vapor enters the turbine, ro-
tated it and, after passing through a condenser, condenses. The liquid mercury is
recycled by the pump into the reactor.
The mercury turbine rotates the compressor, which takes in air, compresses it,
id) ?42)
a)
f)
Fig.39 - Schematic Sketch of an Atomic Turbojet Engine, Using a Steam
-Turbine for Driving the Compressor
a) Nose cone; b) Compressor; c) Mercury turbine; d) Control rod;
e) Reactor; f) Mercury pump;.g) Condenser; h) Jet nozzle
and drives it to the condenser. In the condenser, the air absorbs the heat of the
mercury, becomes heated, and is ejected through the jet nozzle at high velocity.
The increase in the velocity of the air passing through the engine is accompanied
-by the production of reactive thrust, which, as in all ram-jet engines, represents
the difference between the pressure of the air at the frontal area of the engine and
the air pressure directed to the rear.
A reactor operating on this principle must use fast neutrons, since mercury is
an avid absorber of thermal neutrons. However, it will be rather difficult to de-
106
? ?
?
sign a fast-neutron reactor. The point is that the mercury, passing-through the re-
actor, is converted from liquid to vapor. Its density will differ: at various points
along its path through the reactor, the absorption of neutrons will be different,
and the conditions of heat transfer will vary. All these difficulties indicate that
it will be more desirable to heat the mercury in a heat exchanger by means of an in-
termediate heat-transfer agent.
Another possibility also exists. A gas turbine, e.g., a helium turbine, in-
stead of the mercury turbine can be used. Figure 40 presents the design of an
d)
mr.
e)
q)
Ii)
- .
Fig.40 - Diagram of Atomic Turbojet Engine with Gas Turbine
Driving Compressor
a) Nose cone; b) Air compressor; c) Gad turbine; d) Control rod;
e) Reactor; f) Gas compressor; g)-Heat exchanger; h) Jet nozzle
ATJEMC of this type. To supply the same power to an air compressor, the power-of,a"
helium turbine must be several times higher than the power of a mercury turbine-:
This is due' to the fact that a colossal power, sGveral.tens'of timesgreater than-
that required for a mercury pump,-is needed to drive a helium compresoor.
ample, if the power of the helium turbine is 150,000 hi), more than. 100,000,hp-Are
consumed in rotating the helium compressor, and less than.50,000 hp-retain,for,Ahei,
air compressor. To. provideAhe, same power .for an- air -compressor.; a (mercury turbine
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would need 53,000.- 54,000 hp, i.e., slightly more than a third of the amount re-
quired by a helium turbine. However, the power required by the reactor in both cases
is approximately the same; since the-efficiency of the helium turbine under the con-
ditions existing in an ATJEMC is considerably higher than with a mercury-vapor
turbine.
Both the pressure of the helium and the pressure of mercury vapor at the input
to the turbine must be several tens of atmospheres. 'A similar or even somewhat
higher pressure is needed in the reactor. This clearly indicates the need for pro-
viding a strong and reliable reactor. The thickness of the walls of the steel pres-
sure vessel of the reactor must be several centimeters, and dependable cooling of
the pressure vessel must be provided.
In the ATJEMC whose designs are illustrated in Figs.39 and 40, the air is
heated by the working medium of the turbine, which is mercury vapor condensing into
liquid mercury, or helium. The working medium is delivered from the turbine to a
condenser. Only when this happens, as we know from the Second Law of Thermodynamics,
will the turbine be able to do work. The condensation of mercury vapor and the
cooling of helium in the condenser take place as a result of heat exchange with the
air. The air is heated under these Conditions. In order to obtain high thrust, the
air must be'heated to the highest possible temperature. In the best case, the air
temperature will be 50 - 1000 lower than the temperature of the working medium ar-
riving in the condenser. In addition, the, temperature in the turbine decreases by
? ,
several tens of degrees. Thus, we see that the temperature to which the air is
?
heated in an ATJEMC is 150 - 2000.1ess than the temperature to which the working
medium is heated in the reactor. In order to increase the temperature to which the
air is heated, it is necessary to insert in its path downstream of the condenser,
J'
4)
h)
Fig.41 - Schematic Sketch of an Atomic Engine with Motor-Driven
Compressor and Supplementary. Heating;
a) Nose cone; b) Compressor; c) Helium-compressor; 4),Contro1 rod;
e) Reactor; f) Jet nozzle; g) Auxiliary heat exchanger; h) Heat
exchanger; i) Helium turbine,
an additional heat exchanger through which the heat-transfer agent is forced direct-
ly from the reactor, bypassing the turbine. Several designs for ATJEMC are possible,
using thietYpe of supplenientary heating:'-Two:of,theeel,areehOwn'in Figs .41 and 42.
Fig.42 - Schematic Sketch of an Atomic Ram-Jet Engine with Motor Driven
Compressor and Independent Circuit 'for Supplementary Heating
..?-?r.c.q ??? '
a) Nose cone; 13) Air compressor; c) Helium compressor; d) Pump for
OleatTtrangercagent; e)rJet.,nozzleM)...AuxiliaFyheat_e?cchanger,,z.,mi.
.g) Heat exchanger; h) Reactor; i) Control rod; j) Helium tul:.bine
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Figure 41 gives a sketch of an ATJEMC with one circuit for both working medium and
heat-transfer agent. From the reactor, the helium proceeds to the auxiliary heat
exchanger, then to the .turbine and to the condenser, finally being recycled to the
reactor by the compressor.
Figure 42 gives a sketch of an ATJEMC with two separate circuits, and with a
reactor divided into two parts. The circuit-for the working medium is the same as
in the ATJEMC illustrated in Fig.40. The heat-transfer agent of the auxiliary cir-
cuit may be either gaseous or a liquid metal. The circulation of the gaseous heat-
exchanger may be effected by a compressor, which is rotated by the main gas turbine
or by a specially provided turbine. In the latter case, the turbocompressor of the
auxiliary circuit may be installed independently of the engine. This results in a
simpler design of installation of the entire power plant on the aircraft.
The use of helium as the working medium and as a heat-transfer agent for rais-
ing the operating temperature of the reactor opens broad vistas. If special
chromium-nickel alloys are used as structural material for the reactor, the heating
surface of the reactor may be increased to 1000 - 11000C. At higher temperatures,
the mechanical strength of these alloys is inadequate. The temperature of the heat-
ing surface of the reactor may be raised by another 200 - 3000C if molybdenum alloys
are used. However, molybdenum combines readily with oxygen. Therefore, molybdenum
heated to a high temperature must not be-allowed to come into contact with air. If.
the molybdenum is Surrounded by helium and inert,gas,,it mill retain its mechanical
strength for a' long period at very high temperatures. If the temperature of the
heating surface of the reactor is increased, the possibility exists to increase the
temperature level of the entire power plant and, as a final result, to raise-the
temperature to which the air is heated, leading to an increase in engine thrust
without the need of increasing its dimensions and weight.
If the temperature level of the entire power plant cannot be raised, then an
increase in the temperature of the heating surface of the reactor will provide con-
110
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;S'r-"r"- ? ?
?
siderable benefits in terms of size and weight of the reactor required; In design-
ing a reactor for an aircraft power plant, its dimensions are determined on. the
basis of the required heating surface. This area will be smaller, the -greater-the_
temperature differential between the gas being heated and the heating surface. If
the temperature of the gas being heated is taken as constant and if.the'temperature
of the heating surface is increased, a reduction in the required heating surface
area becomes possible and consequently. a reduction in the dimensions of-the reactor
and its weight. This is exceedingly important for aircraft, since a reduction in
flying weight at a power plant of identical capacity, results in improvement of- the
flight characteristics.
Let us discuss the power fluctuations in-the turbine rotating the air-com--
pressor, with variations in flying speed. It was stated above that, in-..order-fora
gas turbine to operate.in a closed cycle, a condenser must be, installed between gas
turbine and gas compressor. We know that the power of the gas-compressor-depends on
the gat temperature. The lower the gas temperature at the compressor input,.-the
smaller will be the required power of the gas compressor and the greater the excess
power of the turbine which drives the air compressor. - If the,gas.temperature_At the
input to the gas turbine is equal to the-temperature of the gas at the turbine exit,
the required power of the gas compressor will equal the power of the,: gas turbipek-
and no excess power will be available at the air compressor drive. Thus,' the con--
denser is an important link. ii a gas-turbine system. If the temperature to' which?,
the gas is heated in the .reactor is regarded as constant, then the-excess power-of-
the gas turbine will be determined by -the condenser, namely by the amount: of heat
dissipated from the gas in the condenser. This-heat removed from theogas-is used.!:'
for heating the air passing through_the ATJEMC. The amount ofIlleat absorbed-by the
air; if we regard its thermal. capacity as constant, depends!,on,the,temperature,dif7.,
ference of the air, and the gas and on .the amount of--air passing4hrough:the-:-
. , ?
condenser.
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From the theory of ram-jet engines we know that, as the flying speed increases,
the air throughput of the engine' per second also rises. At the same time, an in-
crease also occurs in the temperature of the air at the engine input and, consequent-
ly, in the condenser. The temperature difference of gas and air in the condenser
P .declines., Thus, two opposing factors act upon the amount of heat withdrawn from the
L
(
gas. The increase in air consumption with increasing flying speed results in a
greater dissipation of heat from the gas, while the decrease in temperature differ-
ential-between air and gas tends to lower the dissipation. At low speeds the first
factor predominates. Therefore, at the beginning, as the flying speed increases,
the excess power of the gas turbine increases. Later, particularly at supersonic
flying speeds, the second factor is predominant, and the excess power of the gas
turbine decreases; there is also a drop in the compression ratio of the compressor.
At the flying speed at which the temperature of the air at the condenser input be-
comes equal to the temperature of the gas at the turbine outlet, the turbine yields
no excess power. The air compressor ceases to compress air, and the ATJEMC becomes
an atomic ram-jet engine. The flying speed at which this "conversions' occurs is
exceedingly high, several times that of sound. The resultant ARJE will develop
thrust only if supplementary heating of the air is provided, i.e., only when engine
designs such as those illustrated in Figs.41 and 42 are used. An aircraft with en-
gines of the type shown in Figs.39 and 40, never attains the speed of ',conversion's
from ATJEMC to ARJE, due to the fact that at speeds below this level the ATJEMC
ceases to develop thrust as a result of various types of losses.
Let us derive data for calculating aircraft power plants built around two
ATJEMC serving a single_reactor. Each -atomic engine develops 20 tons of thrust at
sea level. The engine has a helium turbine of 48,500 hp capacity, rotating an air
compressor. The circulation of helium in the closed cycle is provided by a helium
turbocompressor. The capacity of the turbine of the helium turbocompressor is
94,800 hp at a rated rotational speed of 16,000 rpm. The six-stage axial helium
aeonemnida,[1...monalelPe4091.15111M.4262,64?ir
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compressor has a compression ratio of 2.1. The helium pressure at-the compressor
input is 25 atm and at-the reactor input about 52-atm. The air compressor has. twos
supersonic stages. At 5850 rpm, the compression ratio is 2-.3. The air is heated by
helium in a slot-type heat-exchanger, having 2520 m2 heating surface. A total of
370 kg air passes through the heat-exchanger of each engine per second at sea-level
operation.
The reactor is of the uranium-beryllium type, using intermediate neutrons; Ite
thermal capacity, under design operating conditions, is 490,000 kw. At this rate,
the reactor consumes 21 gm uranium2.35 per hour.
Atomic Turboprop Engines
?
Turboprop engines-are used today primarily for heavy long-range.aircraft,flying
at speeds close to the speed of sound. At subsonic speeds, turboprop engines are
more economical than turbojets. Per kilogram of thrust, the former require consider-
b)
ornfin,?
411WEINI
1111111111111 I 114 at .41111
c)
f)
v
Fig.43 - Schematic Sketch of a Turboprop Engine
a) Propellersr.b) Compressor;, c) Kerosene injectors;-d) -Turbine;
e) Jet nozzle;.f) Combustion chamber; t) Reduction gear'
. . ? ?
ably less kerosene per hour. Moreover, turboprop engines provide the best flight
- : --;
characteristics for aircraft: ? the length and time-of the take-off run ie reduced,
and the rate of climb is increased. The design of turboprop engines (Fig;41'sYAT
113 -
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/07/01 : CIA-RDP81-01043R002100060011-6
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5" ?
-
similar to that of a turbojet engine. The turbine in a turboprop engine is usually
of.the multistage type. Such a turbine is considerably more powerful than that of a
turbojet having the same thrust. The excess thrust of the turboprop turbine over
that used to rotate the compressor is consumed in rotating the propellers. Usually
two coaxial propellers are rotated in opposite directions over a reduction gear.
The bulk of the thrust is produced by the propellers. Only 10% - 15% is created by
the reaction of the stream of gases ejected from the jet nozzle.
The use of atomic turboprop engines offers the simplest solution of the problem
of vertical take-off and landing of aircraft. ATJE and ATJEMC engines eject power-
ful jets of highly heated air. This would require the provision of special exhaust
ducts to prevent destruction of the runway surface. The aircraft remains dependent
upon properly equipped landing strips. If the power plant of the aircraft consists
of atomic turboprop engines, the streams of hot air will be only a fraction as in-
tense and will mix with the cold slipstream of the propeller. This will permit
landing on any level field with a hard surface.
However, the main advantage of atomic turboprop engines over atomic turbojet
engines and ATJEMC is the fact that the former develop a take-off thrust 20% - 30%
greater; with a reactor of identical power.
Atomic turboprop engines, ?be classified into two groups in terns of design.
The first group comprises engines using air turbines and the second group includes
engines using steam or 'gas turbines.
The design of engines in the first group is similar to that of the atomic
turbojet engines illustrated in Figs.331 36, and 37. The difference lie S in the
fact that in all atomic turboprop engine designs the turbine is not only connected
to a compressor but also (over a reduction gear) to propellers. Figure 44 shows the
design of a turboprop engine in this category. The air is sucked in by the corn-
pressor, compressed, and supplied to the reactor. In the_reactor, the air,is heated
and delivered to the turbine, where it is rotated and then, ejected through the jet
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?
21,
?'???,
nozzle. The turbine rotates the compressor and the attached coaxial propellers.
It is also possible to develop atomic turboprop engines with-two.independent
turbines, one rotating the compressor and the other the propellers. Figure 45 illus-
trates an atomic turboprop engine with two coaxial turbines. The front two-stage
turbine is connected to the compressor .by a hollow shaft, while the rear turbine is
Ii
d)
?
I)
e)
opow"'"!*.ilft,
q)
Fig.44 - Schematic Sketch of an Atomic Turboprop Engine with SeParately
Housed Reactor
a) Propellers; b) Air compressor; c) Control rod; d) Reactor;
e) Jet nozzle; f) Air turbine; g) Reduction gear
connected to the reduction gear via a long shaft passing within the turbocompresior-
shaft. ,This method of making the turbocompressor a separate asseMbly shouldLlogi-:
cally facilitate the control of the engine since the operating conditions-ofthe
turbocompressor and the propellers will be less interdependent-underthese-circum?:
stances. In the design of an atomic turboprop engine, illustrated inFig.44,-thel",.-2
rotational speed of the propellers and the compressor-are:interrelated,
change in the rotational speed of the propellers will cause -a change in that-Of-thec:'
compressor, in the compression ratio of .the air in the compressor, in 'the
throughput=of the:engine, and in the' power of the.,turbine;
feet the rotational speed of the propellers.'.
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115
,
S TAY AT
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? Ergines with 'steam or gas turbines.may.be cateerized as forming a second group
of atomic turboprop engines. Their design is similar to that of atomic ram-jet en-
gines:with motor-driven compressors,: as illustrated in Figs.39 and 40. Figure 46
d)
c)
through the condenser is negligible, since the air is heated to a comparatively
limited extent. However, the condenser of an atomic turboprop engine is essentially
a ram-jet.
Thus, the atomic turboprop engine with a steam turbine actually repre-
Fig.45 - Schematic Sketch of an Atomic Turboprop Engine with Separate
Drives for Compressor and Propellers
a) Propellers; b) Air compressor; c) Control rod; d) Reactor;
e) Air Turbine for compressor; f) Air turbine for propellers;
g) Jet nozzle; h) Reduction gear
presents the design of an atomic turboprop engine with a mercury turbine. The mer-
cury is heated in this engine b means of liquid sodium as the heat-transfer agent,
which is,circulated_by a pump._ The mercury vapors, produced in the heat exchanger,
are delivered to the turbine. The energy of the mercury vapor is converted to
mechanical energy in the turbine and is transmitted to the propellers by means of
.the-reduction gear. The used vapor proceeds to a condenser, and is there condensed
? to liquid mercury, which is recycled by pump to the heat exchanger. Heat is re-
moved from the mercury vapor in the condenser by air forced through the condenser
by a fan.
-..More,than:90%_of-the thrust of an atomic turboprop engine with a steam turbine
js created by the propellers. :The thrust created-by the.reaction'of the air passing -
i)
Fig.46 - Schematic Sketch of an Atomic Turboprop Engine with Intermediate
Heat-Transfer Agent
a) Propellers; b) Fan; c) Jet nozzle; d) Condenser; e) Mercury tUrbine;
f) Mercury pump; g) Reduction gear; h) Heat exchanger; i) Control rod;
j) Reactor; k) Pump for heat-transfer agent
cents two engines: a turboprop, and a ram-jet. This combination is quite in-
triguing. Thus, a turboprop engine operates efficiently at low flying speeds, andla
ram,-jet at highspeeds. The problem is that of making proper and full use of the ad-
vantages of both types of engines. At low speeds, the, main -engine is the turboprop
-
.STAT
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the consumption of nuclear fuel decreases, and the weight and sizel'or: the. reactor..
y
may be reduced.
- Thanks to the fact that the heat transfer in the, recovery-uilittS.kes place, tray
STAT STAT
and at high speeds, the ram-jet. In order to make more complete use of a turboprop
engine, it is desirable to install an auxiliary heat exchanger in the path of the
air downstream'of the condenser, similar to that illustrated in Fig.42,.and heat the
air to the highest possible temperature. As the flying speed increases above a given
level, the power of the steam turbine begins to drop due to a decrease in the dissi-
pation of heat in the condenser, and the share of the propellers in the production of
thrust begins to decline, while the share of the ram-jet engine starts to increase.
At a flying speed only 50% greater than the speed of sound, the condenser and its
auxiliary heat exchanger will develop one-half the thrust of the entire power plant,
even if special supersonic propellers are used whose efficiency decreases only in-
significantly with increasing flying speed. Thus, an atomic turboprop engine with
steam turbine is capable of self-regulation. As the flying speed increases, there
is a reduction in the power of the propellers accompanied by an increase in thrust
of the ram-jet engine.
The above statements on self-regulation are also valid for the atomic turboprop
engine using a gas turbine, whose design is presented in Fig.47.
However, as in the case of an ATJEMC, the gas turbine has to be several times
as powerful as a steam turbine of equal power. The dimensions of the gas turbocom-
pressor will be considerably greater than those of the mercury turbine and the mer-
cury pump. The advantage of an atomic turboprop engine with gas turbine is the lack
of the need for a heat exchanger and an intermediate heat-transfer agent, and the
possibility of heating the gas directly in the reactor. This is no small advantage,
since the presence of an intermediate heat-transfer agent-significantly complicates
the operation of an atomic power plant.
In order to increase the economy of modern power plants and engines using chem-
ical fuels, wide use is made of what is known as heat recovery. The principle of
heat recovery lies in the fact that a portion of the heat of the combustion product
is utilized to heat the air entering the furnace.
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?
?
Heat recovery may also be used in an atomic turboprop engine with a gas turbihe.
In addition to economizing nuclear fuel, heat recovery permits a significant reduc-
tion in the heat-exchange interface between working medium and air in the condenser.
d)
e)
q)
Ii)
-4111111
I NNW
a
LThiL_=_Th
Fig.47 - Schematic Sketch of an Atomic Turboprop Engine with Independent
Supplementary Heating Surface
a) Control rod; b) Reactor; c) Reduction gear; d) Propellers; e) Fan;
f)-Helium turbine; g) Helium compressor; h) Pump for heat-transfer agent;
i) Jet nozzle; j) Auxiliary heat exchanger; k) Heat exchanger.
Figure 48 gives a schematic sketch of a helium atomic turboprop engine with
heat recover. The helium from the turbine passes through the heat recovery unit,
where it surrenders a portion of its heat to the helium, jlriaceeaing,to the compres
-sor from the reactor, and is then delivered :to the condenser. The finally ,cooled
helium is compressed in the compressor and delivered-to the redetor..o0m,the:-Icay-to-2
' the reactor it undergoes preliminary heating in the recovery unit:' -.Consequently,:
.1
119
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helium to helium, the heat-exchanger,surface-in the recovery unit need only be a
fraction of that which would be required to remove the same amount of heat from
helium to air. As a result, the size and weight of the recovery unit can be rela-
tively small.
When a recovery unit is present, the quantity of heat-removed from helium to
air in the condenser will decrease, so that the dimensions and weight of the con-
b5
1)
)
Fig.48 - Schematic Sketch of a Helium-Driven Atomic Turboprop Engine
with Heat, Recovery
a) Propellers; b) Reduction gear; c) Fan; d) Control rod; e) Reactor;
.?
f) Heat recovery unit; g) Helium compressor; h) Heat exchanger;
i) Jet nozzle; j) Helium tui.bine
denser can also be reduced.
However, despite the above advantages, the bse or heat recovery maybe unprofit-
able. The point is that the temperature to which the air is heated in the condenser
is reduced in the presence of a, heat recovery unit. Consequently, .the role of the
condenser as,a ram-jet engine is diminished.
Let us describeone more design Of an atomic turboprop engine with -a Steam tur-
bine Using water vapor; -"produced in it oboiling-*ater",type of reactor. :This'deiigt
??
120
is presented in Fig.49. The "boiling-water" reactor-is a large vessel containing
ordinary or heavy water, into which uranium rod lattice encased in aluminum or zir-
conium cans is inserted. If the rods are of natural uranium, heavy water has to be
used; if the rod material is enriched uranium, ordinary water may be used. The
b) d)
Ili
'114111IuIpe rod?
' 11111
f)
???=0010
-
Fig.49 - Schematic Sketch of an Atomio Turboprop Engine with
"Boiling-Mater" Reactor
a) Propellers; b) Fan; c) Steam turbine; d). Condenser; e) Jet nozzle;
? 7
f) Reduction gear; g) Water pump; h) Water reactor with steam
separator; i) Control rod
-
water in the reactor acts as a moderator and, at the same time, serves to removes.ifie
heat from the uranium rods. The power, level of the reactor is so.regulatedthat the
-
revired.amountof steam will be produced each iecondi,-Theyeteamjrom the reactor
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proceeds to-the turbine which it rotates; the steam is then condensed in the con-
denser and is recycled to the reactor by pump. The power of the pump is about 2% of
the power of the turbine. The turbine is connected to coaxial propellers as in the
above-described design.
The advantages of this design are simplicity, reliability in operation, and its
relatively low cost. A "boiling-water" reactor has a self-protection from explosion
in case of breakdown if, for any reason the control rod mechanism fails. At the
instant of excessive liberation of heat, the water is .converted into steam which
latter is discharged into the atmosphere through a safety valve. The reactor now no
longer has a moderator, and any nuclear reaction instantly decays. To start the re-
actor again all that is needed is to refill it with water. It is easy to remove
from the water the uranium fission products, which are very strong neutron absorbers.
This makes it possible to reduce the reserve reactivity of the reactor and increase
the percent "combustion" of nuclear fuel.
The shortcomings of this design are the radioactivity of the water passing
through the turbine and the exceedingly low temperature of condensation of the water
vapor. The latter prevents efficient use of the condenser as a ram-jet engine.
The reader has no doubt become aware by now that, in all above designs of
atomic turboprop engines, a reduction gear is an essential component. The turbines
of modern turboprop engines rotate at 6000 - 15,000 rpm. The high rotational speeds
are necessary to hold down the dimensions of the high-power turbines. The propeller
operates most effictively when' it rotates at 'about 1000 rpm. Thus, the reduction -
gear serves the purpose of reducing the rpm to the level m6st advantageous for pro-
peller operation.
If two propellers are mounted On the engine, the reduction gear has the addi-
tional function of changing the direction of rotation of one of the propellers so
that they will rotate in opposite directions. This also increases the efficiency of
the propellers. Difficulties with the reduction gear are among the major causes for
122,
?
the limited usefulness of turboprop engines in modern aircraft. At present, trans-
missions with involute teeth are in wide use in.reduction gears. There are many
-
shortcomings inherent in this system (low contact strength, sensitivity to lack of
precision in manufacture and assembly, high friction losses leading to overheating
of the gears, etc.). The lightest and most reliable type of reduction gear is that
used in marine power plants. The weight of such reduction gear is about 1 kg per
horsepower.transmitted. The weight of modern aircraft reduction gears is
7 ? 10 times lower. This saving in weight is obtained at the expense of a sharp re-
duction in the service life of the gear. But even this weight level is excessive
for aircraft. Even if only 0.1 kg of reduction gear weight is required per traner_
nitted horsepower, the total weight of the transmission, for a 50,000 hp engine-will
be 5 tons,- and powers of 50,000 - 100,000 hp will be customary for-atomic power -
plants. Designers and scientists of all countries are making every attempt to
duce the weight of the reduction gear. There is reason to hope that, in the very
near future, the gearing invented by N.L.Novikov, will provide a means for inCreas=
ing the power transmitted by reduction gears without increasing their weight.
However, it would be desirable to completely eliminate the use .of a reduction
_ gear. Is this possible? Calculations show that a reduction gearymaybe_pliminated
completely if a mercury-turbine is-used. The.. possibility exists:of designing. a: ?
turbine in which the rotor will rotate in one direction and thehousing-in:another..
The rotor will be connected by shaft to the tractorpropellerand, the housing will be
connected to the pusher propeller over a hollow shaft which contains the second,
shaft. If the rotational speed,of.the rotor 'relative to the housing is4006TP1m,
then-each propeller will rotate at 2000 rpm. This rpm is satisfactori for specially-
designed supersonic propellers.' The design-difficulties encountered...in creating,,-.
such an engine without reduction gear will, of course, result in an increase
turbine weight, but this increase in weight. will. only a fractiokofLthe.weight:,
of a reduction gear. ,
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? ??
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Let us give an example of the project of an atomic aircraft power plant:con-
sisting of two atomic turboprop engines without reduction gear and using mercury
turbines. Mercury vapor, heated to a temperature of 800?C is delivered to the six-
stage turbines of 70,000 hp each, at a pressure of 112 atm. The'mercury vapor is
produced in a fast-neutron reactor. The power of-each turbine is distributed be-
tween two coaxial propellers (60,000 hp), with the fan forcing the air through the
condenser (9000 hp) and the pump recycling the liquid mercury to the reactor
(1000 hp). The weight of the entire power plant will be 20.5 tons. Of this, the
Weight of the two engines is 11.2 tons, the dry weight of the reactor (without
shielding) is-4.5 tons, and the weight of the mercury is 4.3 tons. At a flying
weight of 85 tons, an aircraft with this type of atomic power plant will-be able to
carry 3 tons of useful load and fly at a speed 2.5 times that of sound. The con-
sumption of nuclear fuel under these 'conditions will be 13 gm/hr.
Combination Power Plants with Nuclear and Chemical Fuels
We have already discussed the difficulties of designing a high-temperature re-
actor, the difficulties of shielding the aircraft from the reactor radiations, and
the lack of a clearly defined method for overcoming' these difficulties. The general
trend to travel a blazed trail has-resulted in the appearance in the press of opin-
ions to the effect that the first atomio power plants will include not only atomic,
but also conventional engines, and that after the air is heated in the reactor, it
will be heated further by the combustion of kerosene or gasoline in this air'.
Underlying some of the .Suggestions for' the development of power plants, ing1116-
ing 'both atomic and conventional engines to function throughout the flight, is the
effort to reduce the capacity of the-reactor so as to lower thedimensions and,
weight both of the reactor itself and of the radiation shielding. Other suggestions
along these-lines-are based on the effort to use -an' atomic engine as the main source
of energy-and to connect-the-conventional engine whenever necessary for a brief ??
124
period in order to increase. the power of the power plant, as for example, during ,
_ .
take-off, climb, etc. .Let us see what the real possibilities of such proposals-
might be.
. The compound power plant and its radiation shielding can make use 'of that por?
tion of the total weight of the aircraft which' is ordinarily taken up by the conven-
tional power plant and its fuel reserve in present-day aircraft.. If a' conventional
engine is retained in the compound installation, then the atomic engine and its ra-
diation shielding can be installed on the aircraft only at the expense of the fuel
'reserve, with the provision that a portion of this reserve must be set aside for op-
erating the conventional engines. This portion is so small that the possible op-'
erating.time.of the conventional engine may be ?calculated in minutes:. If this fuel
residue isidivided by the entire period of flight, the thrust of the conventionalF,.
engines would have to be so small that.no noticeable improvement in the-flight
characteristics of the aircraft could be expected from this operation. Thus, a com-
pound power plant, consisting of atomic and conventional engines, can hardly be con-
sidered realizable and is obviously not rational,
However,. _it is possible to- combine the use of nuclear and chemical energy.in-A-
siugle engine.. Figure 50 illustrates an engine of, this -type., This is an'atomiS._
turbojet-engine in which the air is heated in a separately-housed reactor.- Then-.,,-,
kerosene, is injected .into the ,air and, on: combustion, heats the.-airfurther.,?Ift
this engine- 'would: use a turbine with pooled ,blades, the temperature of:-.the-air up-
stream of the turbine could be raise4 to' 15009C. This, will resplt in increasing s,
specific and frontal, thrust and in reduping the engine 'weight. --Ifthe-engine -'is
?
limited to ptapArd.tenTeraturs aheadLof,tietturbine?(of the order,of-,800?C)then:'-
-
in an engine,built according to the ,design,shown,in Fig.5Q, the,tqmperature_Of,the
heating surface of thp reactor cap be redused compared. to that, of Ileatipespr
-face of the reactor ,in a, regular, atomic,
_
.?
, sign this type,..of :reactor.. This is, tjip.,, point, generally, emphasized ,in;statement,8 _
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the effect that combination systems will be developed before purely atomic systems.
However, it is quite doubtful whether the range of flight with such a combination
engine will exceed the range of an aircraft with conventional engines of today.
They may, however, serve as experimental installations for gathering experience in
the operation of power plants with nuclear reactors.
It is much more probable that atomic jet engines with kerosene afterburners
d)
Fig.50 ? Schematic Sketch of a Combination Turbojet Engine Using
Nuclear and Chemical Fuels
a) Nose cone; b) Compressor; c) Control rod; d) Reactor; e) Kerosene
injectors; f) Combustion chamber; g) Turbine; h) Jet .nozzle
will come into practical use. Such engines will have a standard afterburner chamber
between the turbine and the jet nozzle. In this chamber the air will undergo sup?
plementary heating by combustion of kerosene. The afterburner chamber will be
turned on for brief periods: on take?off, in climb, during acceleration, and for
brief boosts of maximum flying speed. Atomic turbojet engines with afterburners
will first be used in military aircraft so as to provide air superiority in tactical
flight characteristics. In passenger and transport aircraft, it might be more de?
sirable to save the weight of kerosene required for such boosters, in favor of in?
creasing the payload, the number of passengers to be parried, etc.; in addition,
126
4
?
the possibility of improving the tactical flight characteristics of a given aircraft
by increasing the power of the atomic power plant itself should not be forgotten.
If a more powerful atomic turbojet engine were installed on an aircraft, whose-weight.
would equal that of an atomic jet engine with booster and supplementary fuel, it
could well be that the thrust would be no less than that of the atomic jet engine
with its booster operating. If this proves to be the case, it is obvious that there
will be no gain by using an atomic turbojet engine and booster.
MNpm the above statements on combination power plants, it would follow that
their application, if at all, will be only for experimental purposes.
Probable Designs of Atomic Power Plants for Aircraft
The basic shortcoming of all atomic ram?jet engines is the very method of heat?
ing air in the engine by heat?transfer from the heating surface of the reactor or
the heat exchanger. In the first place, this method of heating results in increased
friction losses. In the second place, the heating of the air by heat transfer re?
quires a temperature of the heating surface at least 500 ? 1000C higher than the
temperature of the already hot air. When kerosene is burned in conventional en?
gines, the liberation of heat occurs throughout the entire volume of the combustion
chamber, and the temperature of the combustion products.is usually considerably .
higher than the temperature of the combustion?chamber walls, cooled by forced cur?
rents of cold air.
We-know that the mechanical strength of metals is reduced at increasing temper?
atures.. If the structural materials of the reactor and the combustion chamber can
withstand equally high temperatures, the temperature to which the air has to be
'heated in an atomic engine will be less than in a conventional engine, which along
with the increased friction losses, will result in a reduction in the specific
thrust of the engine, and in an increase in its specific weight. Thus, the very
principle of transferring heat to air by heat liberation in atomic engines faced the
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-problem of, lower specific parameters than those in conventional jet engines. Now,
if we could only cause the heating to take place throughout the entire volume of the
air instead of only in a thin layer adjacent to the heating surface!
Let us examine a design of an atomic ram-jet engine, as illustrated in Fig.51.
A gaseous, liquid, or powdered nuclear fuel is injected into the air, compressed by
the velocity head. On entering the reactor chamber, this nuclear fuel is subjected
to the effects of a neutron flux, with a result that a portion of the nuclei under-
a)
b
c)
e)
Fig.51 - Schematic Sketch of an Atomic Ram-Jet Engine with Gaseous
Nuclear Fuel
Nose cone; b) Reactor; c).Jet nozzle; d) Reactor cooling;
e) Gaseous nuclear fuel
goes fission. In this case, the liberation of heat occurs throughout the entire
volume of air, with the result that the contact area between. air and reactor can be
reduced by hundreds of times. This leads to a significant reduction in friction
losses. Heated air, as before, enters the jet nozzle, and is ejected at high
velocity.
?The function of the reactor in this design is different from that in all atomic
engine designs we have discussed up to now. There the reactor was a source of heat,
. .
here the reactor is used_as a neutron source. However, the prOduction of neareni
128
LI
during the nuclear reaction is accompanied by the liberation of large quantities of
heat. A heat-transfer agent must be circulated through the reactor in order to dis-
sipate this heat. The heat removed from the reactor maybe used for operating a -
steam or gas turbine of another engine or for heating air in an atomic turbojet en-
gine heat exchanger, used in combination with the atomic ram-jets discussed above.
An analysis of the practicability of the engine illustrated in Fig.51, shows
that the decisive factor is the high concentration of nuclear fuel injected into the
air, i.e., in the final analysis a large rate of consumption of this fuel. More-
over, in order to increase the probability that neutrons will collide with fuel
-
nuclei, the density of the neutron flux must be considerably increased. To attain
the necessary rates of consumption of the injected 'nuclear fuel, it is necessary, as
we learn from calculations, to increase the density of the neutron flux of the reac-
tor by thousands and hundreds of thousands of times, relative to the maximum at-
tained to this date in stationary systems. An increase in the density of the neu-
tron flux will, in turn, lead to an increase in heat liberation in the reactor it-
self which will require a higher rate of heat dissipation, etc. All of this makes
realization of the design in Fig.51 improbable.
If it is impossible at present to solve the problem of attaining a high density
of neutron flux, might it not be possible to provide for trapping the powdered nu--
clear fuel? An atomic turbojet engine operating on this principle is illustrated in
Fig.52. Into air compressed by the compressor, a mixture of powdered atomic fuel
and air is injected (or taken in by suction). The nuclear fuel is more or less uni-
formly mixed with the air and enters the channels honeycombing the reactor. It is
here that the nuclear 7-Action occurs and the air is heated, from where it enters
the turbine which in turn rotates the compressor. From the turbine the air emerges
in a spiral stream, rotating about the axis of the engine. The heavy particles of
nuclear fuel are hurled toward the outer surface and are sucked out along with a
- , - ; -=? -
small quantity of air, again to be mixed with the air at the reactor input.
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129
STAT
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Certain authors propose a complete elimination of a reactor in the conventional
meaning of -the term. They propose that atomized nuclear fuel be introduced at the
compressor input. In the air compressed by the compressor, the concentration of nu-
clear fuel increases; as soon as this air enters a duct surrounded by a neutron re-
flector, a nuclear reaction is initiated and the air is heated. Downstream of the
9
Fig.52 - Schematic Sketch of an Atomic Turbojet Engine with Atomized
Nuclear Fuel
a) Nose cone; b) Compressor; c) Reactor; d) Reactor cooling;
e) Turbine; f) Jet nozzle; g) Duct for recycling the atomized
nuclear fuel
turbine, the nuclear fuel is trapped, as in the engine,(Fig.52). The cooling of the
reflector-is much easier for the cooling of the reactor. However, the realizability
of such a design is rather dubious. The dimensions of the duct in the reflector
must be quite large in order for a nondecaying nuclear reaction to occur, in the nu-
clear fuel, atomized in the air. As the concentration of nuclear fuel' in the air
increases, the dimensions of the channel may be reduced. However, this would lead
to a decrease in engine thrust, due to the fact that an excessively large share of
the air will be tapped downstream of the turbine, along with the nuclear fuel. An
increase in concentration by increasing the compression ratio of 'the compressor is
not possible above a fixed level since, in the course of compression, the air be- .
130
comes heated and may reach the maximum temperature permissible for strength con-
siderations. Thereafter, further heating becomes impossible, so that the turbine
will be unable to rotate the compressor, not to mention the fact that the engine
will develop no thrust.
There have been proposals to heat the air in the engine by an electric arc.
However, this method of air heating has its drawbacks. For example, it is difficult
to develop a reliable electric arc of such extraordinary power, that will function
for the relatively long period during which the engine is expected to operate with-
out interruption. In addition, the system for producing electric energy will be
bulky and heavy and most likely will cancel the gain obtained by the absence of a
heat exchanger.
Vast perspectives will open before the aircraft designer when science is able
to control thermonuclear reactions. The rapid development of nuclear physics in
recent years testifies to the fact that the major difficulties in creating a con-
trolled thermonuclear reaction will be overcome and a thermonuclear engine will be
developed. The application of thermonuclear engines to aviation will result in
further advancement in aircraft design, and will make aircraft less earth-bound,
enabling 'it to fly in the upper layers of the atmosphere at colossal speeds.
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CHAPTER IV
AIRCRAFT WITH ATOMIC ENGINES
The Problem of Radiation Shielding
The development of aircraft with atomic engines involves the necessity of over-
coming the radiation hazards due to the emission of various types of radiation
having a detrimental effect upon the human organism.
The first concepts as to radiation hazards and the difficulties of shielding
human beings from the radiations of atomic engines appeared simultaneously with thi.
first ideas on atomic aircraft. As far back as the beginning of 1935, the Soviet
scientist, 0.Petrarskiy, advanced the idea of an atomic train of stratoships (Fig-
ure 53), in which the protection of the passengers from the effects of radiation
would be attained by housing the crew and passengers at a considerable distance
from the atomic, or subatomic, engine. These ideas, advanced more than twenty years
ago, are still of interest today. Therefore, we will quote an excerpt from
0.Petrovekiyls article* in which he discusses an atom...: train of stratoliners:
"This train will consist of two units. The first travels, as a rule, without human
beings aboard and is equipped with subatomic engines. This unit will tow a second
aircraft by means of cables approximately 1000m in length. The second aircraft
will 'be designed, more or less, along the lines of a glider without 'engines. Con-
* The article "An Isotope Gun" was published in the journal TekhnikalMolodezhi
(Technics for Youth), No1' 1, January 1935.
? ,4 "-, - ? .;1n 4 ?
132
tralwill be exerted from this second aircraft.
"The reason for the separation of this stratoplane train into two separate-ma-
chines is chiefly the fact that the powerful radioactive decay in the engine is ac-
Fig.53 - Schematic Sketch of an Atomic Train of Stratoplanes
from the Journal "Tekhnika Molodezhi", No.1, 1935
The train of stratoplanes with subatomic engines will consist
of two units. The subatomic engines will be installed on the
first, while crew and control mechanism will be carried on
the second.
a) Engine stratoplane (no crew); b) Fuselage with groups of
isotope guns; c) Towing cables of 1000 m length; d) bagineleis
stratoglider with crew (towed by cable)
companied by a no less powerful radiation.
"For protection from this radiation, which is extremely harmful to the,bUman
organism, no means other than removal to a considerable distance exist at_present."L
Today;' the Problem' Of ProteCtion fram 'fadiation by other Mian; for ikample '
shields; is no longer as hopeless ea it had been then; however, even' noW"thii-is-
ST:fAT.
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CHAPTER IV
AIRCRAFT WITH ATOMIC ENGINES
The Problem of Radiation Shielding
The development of aircraft with atomic engines involves the necessity of over-
coming the radiation hazards due to the emission of various types of radiation
having a detrimental effect upon the human organism.
The first concepts as to radiation hazards and the difficulties of shielding
human beings from the radiations of atomic engines appeared simultaneously with thi-
first ideas on atomic aircraft. As far back as the beginning of 1935, the Soviet
scientist, 0.Petrovskiy, advanced the idea of an atomic train of stratoships (Fig-
ure 53), in which the protection of the passengers from the effects of radiation
would be attained by housing the crew and passengers at a considerable distance
from the atomic, or subatomic, engine. These ideas, advanced more than twenty years
ago, are still of interest today. Therefore, we will quote an excerpt from
O.Petrovskiy's article* in which he discusses an atom.,?: train of Itratoliners:
"This train consist of two units. The first travels, as a rule, without human
beings aboard and is equipped with subatomic engines. This unit will tow a second
aircraft by means of cables approximately 1000 m in length. The second airCraft
will be designed, more or less, along the lines of a glider without engines. Con-
* The article "An Isotope Gun." was pdblished in the journal Tekhnika Molodezhi
(Technics for Youth), N.g.l, January 1935..
132
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trol will be exerted from this second aircraft.
"The reason for the separation of this stratoplane train into two separate ma-
chines is chiefly the fact that the powerful radioactive decay in the engine is ac-
Fig.53 - Schematic Sketch of an Atomic Train of Stratoplanes
from the Journal "Tekhnika Molodezhi", No.1, 1935
The train of stratoplanes with subatomic engines will consist
of two units. The subatomic engines will be installed on the.
first, while crew and control mechanism will be carried on
the second.
a) Engine stratoplane (no crew); b) Fuselage with groups of
isotope guns; c) Towing cables of Ippio m length; d) Engineleia
0 ,
stratoglider with crew (towed by cable)
companied by a no less powerful radiation.
"For protection from this radiation, which is,eXtremely harmful to.theChnian
organism, no means other than removal to a considerable distance exist at_ireaent.":
Today, the problem of protection from radiation by Other Miani, for ex.an
shields, is no longer as hopeless as it had been then; however, even now this is
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one of the most complex problems in the development of atomic aircraft equipped to
carry hUMan beings. During the last 10 - 15 years, scientists have made a careful
study of the properties of various types of radiation produced in the operation of
atomic power plants, and have discovered the most effective materials for shields.
They have also developed the basic principles for shielding systems. Let us briefly
treat these problems:
The radiation emitted during the operation of atomic power plants include the
following that are harmful to the human organism: alpha rays,- beta rays, gamma rays,
and neutrons.
Aloha Rays represent a stream of positively charged particles: helium nuclei.
Their penetrating power is quite insignificant. In air, for example, they travel
no more than 10 cm from the radiation source and in metals only hundredths of a
millimeter. Virtually the sole source of alpha particles in an atomic power plant
is the nuclear fuel (uranium and plutonium), which is naturally radioactive. Alpha
particles are completely absorbed in the metal cans in which nuclear fuel is usu-
ally encased and, therefore, require no further consideration on our part.
Beta Rays represent a stream of electrons. The major source of beta radiation
are the fission "fragments" Of the fuel nuclei. EMission of beta rays also results
from the absorption of neutrons by nuclei of most of the chemical elements com-
prising the moderator, the heat-transfer agents, the structural materials, other
materials used. The penetrating power of beta rays is greater than that of alpha
rays, but still comparatively small; in air, beta particles can travel up to 20 m
and in metals a few millimeters.
Gamma Revs are an electromagnetic radiation similar to x-rays but of shorter
wavelength. About 95% of the total flux of gamma rays emitted by a reactor is due
to fission of the fuel nuclei. In addition, such rays are generated on absorption
of neutrons by the nuclei of certain, chemical elements that go into the makeup, of a
nuclear reactor.
134
Neutrons are particles of neutral ,charge, representing a constituent of atomic
nuclei. These are emitted on fission of the fuel nuclei. The absence of an elec-
tric charge explains their high.penetrating power. Fast neutrons have an excep-
tionally high penetrating power. The absorption of neutrons by nuclei usually re-
sults in artificial or induced radioactivity. In other words the nuclei of a ma-
jority of elements themselves become sources of radioactive radiation as they absorb
neutrons.
The above types of radiation cause a specific disease in man: radiation sick-
ness. The degree of damage to the organism depends upon the quantity of radiant en-
ergy absorbed or, as it is called, the radiation dose, The magnitude of the dose
received is greater, the greater the intensity of radiation and the longer the time
during which the human being is exposed. A special unit called the roentgen is
used for measuring the size of the dose.
A single irradiation at a dose of up to 50 roentgens produces no observable
changes in the human organism, and the subjective feeling of well-being is no way
impaired. A dose of 50 - 100 rcentgens induces insignificant changes in the blood,
which rapidly disappear without leaving a trace.
If irradiation is repeated periodically, then even at a small daily dose ra-
diation Sickness may occur since the effect of radiation is cumulative., At present,
it is believed that the maximum dose for a human being daily exposed to irradiation
over a period of years should not exceed 0.3 roentgen.
The main source of radiation in an atomic aircraft is the nuclear reactor. The
intensity of radiation is greater, the greater the power of the reactor. When the
reactor is turned off, the intensity of radiation diminishes greatly, but a rather
significant radiation continues for a long period, since certain artificially ra-
dioactive substances formed during operation of the reactor decay very. slowly.
Special shelters and shields are only necessary for biological protection from
gamma radiation and neutrons. In view of the small penetrating power of beta rays,
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these will be absorbed completely in the shields.
In view of the fact that 'gamma rays react primarily with electrons, the best
shielding material is a substance with a large number of electrons per atom. Iron,
steel, lead, and bismuth find practical application as materials capable of weak-
ening the flaw of gamma rays. As a rule, the greater the density of the substance;
the smaller will be the thickness of the layer of substance required for obtaining
a given reduction in the intensity of gamma radiation. For example, in order to re-
duce the intensity of gamma radiation by one-half, a layer of steel of about 2 cm
thickness is required. The thickness of a layer of 'lead for the same purpose is
1,3 cm.
The neutron flux of a reactor includes neutrons of widely varying energies:
from thermal to fast neutrons. Since high7-energy neutrons are weakly absorbed by
various materials, one of the main functions of neutron shielding is to retard ?
these neutrons. In practice, protection from neutrons may take the form either of
single-layer or double-layer shields. When using a two-layer shield, the first
shield facing away from the reactor is made of a good moderator, and the second of
a good absorber of neutrons. Minium shield thickness is obtained when ordinary
water is used as the moderator. However, the use of water for shielding an air-
craft reactor is hardly within-the realm of possibilities. In terms of operational
realities, the best moderator for neutron protection aboard an aircraft is graphite.
Graphite, however, has a draliback,of'its own: The thickness and weight of the pro-
tective shield is greater than for .water.
. If the shield. is of,a single layer, its structural material mast simultaneously
be able to moderate and absorb neutrons. To accomplish this end, the reactors of
stationary power plants are surrounded. by thick layers of ordinary water and col*-
erste, -with graphite or boron added. To improve the shielding qualities of the
concrete, the water content in the cement mix is sometimes increased-and added
cadmium-or boron' is used, or 'graphite-with added boron, or even pure boron. If ,?
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pure boron is used, the shield is thinner and lighter than a concrete shield or a
shield in which' graphite is used.
The difficulties 'in developing an atomic aircraft, with respect to 'radiation
hazards, lie in the fact that even if the best materials presently known Are used
for shielding purposes, the weight and dimensions of the shield are quite consid=
erable. The distances to which the crew and passenger quarters can be removed from
the reactor in an-aircraft is comparatively small and, for practical purposes, not
more than 20 - 30 14 In this connection, a considerable portion of the required
degree of. moderation of the reactor radiation is taken up by the protective thields
When an aircraft reactor is operating at maxbmim output, the shields must reduce
the intensity of radiation by a factor of 10 million. To reduce the 'intensity of
gamma radiation by a factor of 10-million we need a lead shield of approximately
35 am thickness. The weight of one square meter-of such a shield is four tons.
The American scientist, R.Murray (Bib1.14), in an investigation of several -
possibilities of application of atomic energy in aviation, gave, as-a typical em-
ample, the calculation of a shield for the' B-47 bomber if that aircraft were
equipped with atomic' engines. The purpose of the calculation was to show' the re-
lationship between the weight of the shield and the payload-of the aircraft for a -..
given condition of flight:.altitudell km, speed'800-km/hr. The -initial. weight ,=
data 'of ---the aircraft were-as follows: empty weight, 62.5 tone; weight with.con7en-%
tional fuel plus payload, 92.5 tons. lit order to attain these flight character--
istice,-the engine has to develop a total thrust of about 6.4 tons uhich, at a
speed-of 800 km/hr, corresponds to an engine power of about 18,000 hp. 'If 'it is
considered-that the total-efficiency of an atomic- power plant is 15%, then the
thermalimwer'or-the nuclear reactor required would be'approximatolv90,000.kw; or
-Protection-fram gamma radiation And neutronsp-as-suggeste&by-the
author;,?zwouldtake;the-form-of,two-sPherical-thieldt: the,first'ot-lead-and the z, -
seCond of water. '-The diaMeter-arthwaUclear reactor, spherical in shape's :would 'be-
STA-1AT
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-Icifir4 t nalZed Coov ArIDrov
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0.9 m. When the reactor is removed 15 m from the crew quarters, the necessary
thickness of the lead shield will be 35 cm and that of the water shield 1.67 m.
total weight of such a shield (total weight of lead and water) was calculated as
172.5 tons, i.e., greater than the total flying weight of the aircraft.
In the next stage of his calculations, the author no longer used a closed
spherical shell as basis. He now proposed a shield in the form of a sector of a
sphere, placed between the reactor and the cockpit, and weighing only one fifth as
much as a complete sphere, i.e., 34.5 tons. Using a reactor weight of 7 tons as
basis, the author arrives at a flying weight of the aircraft of 104 tons, i.e., 12%
greater than the normal flying weight of a B1-47. If the flying weight is increased,
the required conditions of flight, necessitate an increase in engine thrust and
thus in reactor power. This, in turn, involves an increase in the weight of the
shielding. On the basis of these calculations, the author draws the conclusion
that "A vicious circle is thus created: The increased weight of the shielding re-
quires an increase in engine power, and an increase in power requires an increase
in weight of the shielding, and so forth".
We are not in agreement with this disoriented kind of conclusion. If the
author had" carriedhis calculations slightly further, he would have become con-
vinced that in reality no "vicious circle" exists at all. An increase in flying
weight by 12% certainly does require an increase in the reactor power and conse-
quently an increase in the weight of the shielding. However, Murray's awn calcu-
lations show, that the weight of the neutron-radiation shielding incases by ap-
proximately one ton, i.e., by about 3% relative to its previous weight. Let us as-
sume that we have increased the .weight of the-shielding by one ton. Then the
flying weight of the aircraft will increase by that same sum. However, this in-
crease is now only 1% and requires (in view of a certain increase in the necessary
reactor power) an increase in the weight of the neutron shielding by only two or
three-tenths of a percent. Analogous results are obtained by calculation of
The
138
shields for gamma radiation.
The simplest calculations will show that, at any required condition of flight,
the relative weight of the shielding system decreases with increasing flying weight.
Reliable shielding from radiation in atomic aircraft, not inferior in speed and
ceiling to the best modern aircraft using chemical fuel engines, is completely re-
alizable. It is true that, for the present methods of radiation shielding, this
will hold only for the heaviest types of aircraft, whose all-up weight is not less
than 100 - 120 tons.
It would be advantageous if it were possible to design a shielding system as
suggested by Murray, i.e., to place both shields only on one side of the reactor.
In reality, the matter is somewhat more complicated. In order to reduce the neu-
tron radiation, the reactor must be encased in shields on all sides. Otherwise,
the structural materials of the aircraft, adjacent to the unshielded portions of
the reactor, will be permeated by a powerful neutron flux. The degree of induced
radioactivity will be so great that it will be impossible to approach the aircraft
for long periods, even after the reactor has been removed. True, the weight of the
shell on the sides of the reactor not directly facing the crew quarters can be re-
duced by making this portion of the shell thinner.
The shell, while reducing the intensity of neutron radiation to a nondangerous
level, will not reduce the gm-ray faux to the required degree. For, protection
from gamma radiation, a supplementary steel or lead shield is required. To do this
_
in the form of a,closed shell around the reactor is not believed possible because
of the excessive weight that would result. Protection from gamma radiation can
only be a partial or, as it is sometimes termed, shadow protection. The protective
shield is mounted only on the side of the reactor directly facing the cockpit.
Since the gamma rays will for the most part, move in straight lines, the location
,
of the crew and passengers on an atomic aircraft will be within the shell, as., it
were. Except for a small spherical sector, all the remaining space around the re-
S
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actor will be permeated by a gamma-ray flux og high intensity. Presence of human
beings near an atomic aircraft while the nuclear reactor is operating and for a long
Fig. 54 - Schematic Sketch of "Shell" Shielding of Passengers and
Crew of an Atomic Aircraft
a) Neutron shield; b) Safe zone; c) Gamma-ray shields; d) Reactor
time thereafter will be impossible.
Figure 54 gives a schematic sketch of one of the variants of reactor shielding
within the fuselage of an aircraft. The region of very high-intensity radiation is
shown by solid lines, while the broken lines indicate the region with somewhat re-
duced intensity due to the first shield; however, only past the second shield do we,
find a danger-free zone for human. beings during the entire flight.
It should be noted that the need for heavy shields is eliminated for the case
of single pilotless devices, to be used only once i.e., long-range rockets, flying
bombs, and radio-controlled bombers. The tendency to convert to pilotless means of
aerial warfare exists today, independent of the introduction of atomic aircraft en-
gines. Once atomic engines are produced, this tendency will become even stronger,
.since the problem'of protection fran radiation in unmanned devices consists prima-
in a protection of ground personnel, so that the specific weight of an atomic
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140
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power plant relative to the total weight of the object can be considerably reduced.
Recently, proposals with calculations appeared, for transport or passenger air-
craft with atomic engines: aircraft to be used for peaceful purposes. It is true
that the design of biological shielding for passenger-carrying atomic aircraft is an
even more difficult problem than for military aircraft. The weight of the shielding
would be excessive, on the basis of the first approximate calculations. For
ex-
ample, for a passenger aircraft with a 15-ton payload, approximate calculations
show that shielding of about 100 tons weight is needed to protect the passengers and
crew from radiation. Shielding of this weight, quite obviously, will tip; the scales
against atomic aircraft. At one time, the thought was advanced that an atomic air-
craft would become possible only when the total weight of the engine and the reactor
plus the shielding would be less or equal to the weight of conventional aircraft en-
gines plus the full load of chemical fuel (kerosene or gasoline).
This type of ratio is attainable only for the heaviest types of aircraft with
an all-up Weight of 120 - 200 tons, in which the weight of the engines and fuel
would be 60 - 140 tons. It is already possible today to think of a combined weight
of reactor, power plant, and shielding that would be in this weight category. In
addition it should be remembered that, in view of the enormous advantage of atomic
aircraft in terms of range of flight, a minor impairment in flying characteristics
of the first atomic aircraft compared to conventional aircraft is entirely per-
missible. Even at reduced speed and ceiling and tolerating a certain excessive-
weight of the atomic power plant, the atomic aircraft will, have certain indisputable
advantages over conventional aircraft with respect to range of flight.
Svecial Design Features of Aircraft with Atomic Engines
To describe a design of atomic aircraft actually in existence is impossible
since no such aircraft exists. But both in the press of our and other countries,
-
a series of proposals as to design and general layout of a,passenger-carrying
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atomic aircraft has already been published. The major concern has been that of re-
liable protection of crew and passengers.
In the first place, considering that the intensity of direct gamma radiation
from the reactor declines in inverse proportion to the square of the distance there-
from, the tendency is to move the reactor as far as possible from the passenger corn-
..
IlLAnLA: Alb . : _1 ? wimm N4104: '
:C11111111111W
Fig.55 - Canard-Type Atomic Passenger Aircraft
a) Atomic power plant; b) Shieldings; c) Cargo; d) Trucks; e) Passengers;
f) Crew; g) Landing gear
'partment. For ,example, it is proposed to place the reactor in the tail of the fuse-
lage or at the wing tips. Such a location of the reactor would compel a change in
design and even in the conventional external shape of an aircraft.
In 1955, Professor G.I.Pokrovakiy proposed to design an atomic passenger air-
craft of rather unusual appearance (Fig.55). The aircraft would have an excep-
tionally long fuselage whose tail section would contain the atomic engine, while
the passenger compartment would be carried far forward. The abandonment of the con-
ventional design with rearward location of the empennage is due to the fact that an
atomic power plant represents a highly concentrated weight Which should be as close
142
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Fig.56 - Possible Variant of Atomic Transport Aircraft
Fig. 57 - Proposed Variant of Atomic Air:ci-aft with a Single
Reactor and Spherical Radiation Protection
a) Shielding; b) Reactor; a) Ehgines
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to the center of the fuselage as possible. When shifted to the rear, this concen-
trated weight disrupts the aerodynamic balance, and the aircraft, with the center of
gravity shifted to the rear, will tend to point its nose upward or, as the.-.phrase
goes, will pitch. Moreover the tail assembly of such an aircraft would be close to
the center of gravity, the cables by which the aerodynamic forces of the controls
are applied would be short, and the controls .would have little effect. In order to
eliminate these undesirable phenomena, G.I.Pokrovskiy proposed instead to use the
canard design of aircraft, i.e., one in which the control surfaces are forward of .
the wing, since he believed this design best suited to the proposed purpose.
Interest in this type of design of an atomic aircraft has been displayed both
here and abroad. However, certain doubts have been raised. The canard design was
used in the early days of aircraft and was abandoned because of difficulties with
the controls: an aircraft with its control surfaces forward of the wing has inade-
quate stability and ii difficult to control on take-off and landing. The possi-
bility is not excluded that, as time passes, the difficulties wdll. be overcome and
some atomic aircraft will adopt the canard design. There has been a story in the
press to the effect that a'canard7type aircraft has already been planned in England.
Another variant of atomic passenger aircraft design (Fig.56) envisages the
placement of the engines in the wing tips and vertical tail surfaces. In this case,
the general design is very similar to that of conventional aircraft, except that
'the engines arealso carried far back,. at the- greatest ,possible distance from the*
passenger cabin. The stability of such' an aircraft may better, but the removal
of heavy atomic engines from the center of gravity and placing them on long thin
wing cantilevers and on the control surfaces raises doubt as to the, reliability of
'the entire design.
The question as to which arrangement' of the power 'plantis the more ,desirable?,
;has hot-yet.been answered.. Some designers believe-that it is 'best. to have one
:single reactor for all engines and to place Was closet as possible to, the center of
144
gravity of the aircraft, as illustrated in Fig.57. 'in this variant, it is easier to
provide shielding for both passengers and ground personnel. In addition, the major
concentrated load (reactor plus shielding) is in a more desirable location as far as
stability and controllability are concerned., The shortcoming of this variant is the
large weight of the all-around shielding of the reactor.
The weight factor in an atomic aircraft would be improved if the gamma-ray
were designed not as a single shield but as a number of separate shields (Pig.93).
Fig. 58 - Method for Incorporating the Shielding System in the
Stress Pattern of the Aircraft
a) Compartments; b) Shielding; c) Engines; d) Reactor
It would be desirable to arrange the shielding material so as, to be of greatest
benefit to the design, permitting optimum balance of the aircraft and minimum
stress on the stressed members of the glider. This would make, it possible to use
lighter shielding while providing adequate protection to thecrew,,to avoid exces7?:,,
sive point loads, and to compel the shielding material to function in,,. conjunction'
with the other stressed elements of the aircraft!. structure.. It is true that, ,in
this case, lead mould not be as suitable for.gamma,shielding material, and would
have to be replaced by stronger.materials-such as aircraftstrUctural
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In this case, however, there would be no significant gain as far as the weight of
the shield is concerned. Calculations show that the weight of a steel shield is not
more than 5% greater than that of a lead one, and that a steel shield may be de-
signed as part of the structure of the aircraft, which in the long run would result
in a reduction of the weight of an aircraft with steel shields by comparison to that
of an aircraft with lead shields.
At'present, persistent efforts are being made to find means of reducing the
weight of the shielding. The foreign press carries reports to the effect that in
the United States and Britain, shielding materials have been discovered permitting
the weight of the shielding to be reduced by a factor of 5 - 6 and that a plan for
an atomic aircraft with a flying weight of only 42 tons has already been drawn. No
confirmation of these reports has been received and it is not possible to vouch for
their veracity.
At the same time, there are many interesting and in some cases quite shrewd
and bold proposals to reduce the weight of the shielding and to create suitable con-
ditions for passengers and service personnel of an atomic aircraft. One thing, how-
ever, is certain: the problem of biological protection has not been solved.
Abroad, many specialists believe that the first aircraft to be built will be
an atomic bomber, in view of the fact that it is easier to provide radiation
shielding since a crew of onlY 3 - 5 members will have to be protected. A trans-
port modification of the atomic aircraft will follow ,some years later. Neverthe-
less, preliminary calculations of the cost of an atomic passenger aircraft and the
cost of its operation were made in other countries as early as 1953 - 1954. As ex-
amples for this purpose, a plan was studied for an atomic aircraft with a 15-ton
payload, designed to carry 180 passengers at 1600 km/hr for =unlimited distance'.
The cost of an aircraft with. these characteristics was estimated at 9 billion
francs, while the cost of the large Comet-3 passenger aircraft was Only
700,000,000 francs. However, if the reduction in operating cost, the savings in
146
cost of chemical fuel, and similar factors are taken into consideration it is felt
that a saving of 5 billion francs would be made annually for each atomic aircraft. -
This permits the hope that atomic aircraft will rapidly amortize their manufacturing
cost.
Special Take-Off and Landing Features of Aircraft with Atomic Ermines
The difficulties involved in using atomic power plants in aviation also in-
clude the fact that while today's heavy aircraft lose almost 50% in weight before
landing due to the fuel consumption in flight which improves their landing charac-
teristics, nothing of the kind can be expected of atomic aircraft which means that
landing must be made at the same weight as that for take-off. This will, of course,
increase the landing speed, the length of the landing run, and in general will com-
plicate landing, making it more difficult and dangerous. The high landing speed of
atomic aircraft will compel a lengthening of the runways, construction of stronger
landing gear, etc.
However, a careful examination of this problem of the hazards connected with
landing an atomic aircraft shows that they are not as insurmountable as might seem.
The designers of modern high-speed aircraft were always faced with the task of re-
ducing impermissibly high landing speeds and excessive landing runs. The landing
speed and, consequently, the length of the landing run of an atomic aircraft may be
reduced by the same means applied or being developed today for modern high-speed
aircraft. These include, primarily, an efficient active mechanization of the wing
and fuselage for take-off and landing: slots, flaps, and other devices for in-
creasing the lift of the aircraft at law speed. At present, special devices are
being developed to control the boundary layer of the air flawing round the wings.
In landing, special pumps are used for removal of the boundary layer by suc--
tion from the upper surface of the wing. It would be even 'better if. this air could
.
then be used to "blow away''', the eddies forming at the wing at high landing angles,..
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147 STAT-
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of attack. Moreover, there are interesting proposals to develop special "air flaps"
for increasing the coefficient of lift of a wing on take-off and landing. Measures
of this type would make it possible to increase the lift of the wing of an atomic
aircraft during landing by several times, meaning that the landing could take place
at speeds so law as to be safe. The length of the landing run can be reduced to a
minimum by using brake parachutes, by reversing the thrust of the engine (i.e., by
creating thrust in the opposite direction) and by a number of other measures, such
as "braking" devices on the runway.
In view of the problem of landing difficulties, it seams desirable first to
plan and build large atomic hydroplanes which will take off and land at sea, where
the landing strip is of whatever length required. In the United States, such a
plan has been under development since 1955, and at present the first variant of an
atomic hydroplane is under construction. The advantages claimed for this variant
are the presence of water, which prevents radioactive contamination of the locality
during landing and take-off and the absence of restrictions as far as take-off and
landing distances are concerned. The first test flights may be performed over the
ocean wastes. This also simplifies the problem of shielding.
The landing and take-off characteristics of atomic aircraft assume a com-
pletely different aspect if vertical take-off aircraft are considered (Figs.59a,
.59b).. This type of aircraft has been, given particular attention during recent
years. An aircraft with vertical take-off and landing coMbines the highly desirable
properties of high flying speed and possibility of basing not only on airfields but
also on relatively small natural fields. The difficulties in creating an atomic
!vertical take-off aircraft are great, since this requires the development of a.
+power plant that will be able to produce a sea-level thrust 3Q - 40% greater than
the weight of theraircraft. . Such thrusts and capacities are within the realm of
'possibilities, but here a lightweight and advanced shielding is particularly neces-
sary, so as to obtain the necessary ratio of shielding weight to aircraft weight,.
148
cellaSanitized Coov AriDrov
Fig.59a -,Vertical Take-Off Aircraft
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Fig.59b - Schematic Sketch of rez?-?tiC'ai. Taiet-Oif Vert4Olifiandii4 o
'AierAft with'Turbo:Proi &gine ?' '
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149,
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in view of the enormous reactor power required.
More within reach at present may be the creation of an atomic helicopter of
large carrying capacity (Fig.60). In this design, vertical take-off and landing
Fig.60 - Probable Aspect of a Heavy Helicopter with an Atomic
Power Plant
could be ensured with a reactor of considerably less power than in a regular air-
craft with vertical take-off. The rotors of a helicopter, rotating at law speed,
develop a sea-level thrust exceeding the weight of the helicopter with engines of a
power below that of the rapidly rotating propellers of regular aircraft with ver-
tical take-off. It is true that the extremely large lifting rotor interferes with
high speeds in horizontal flight. When the rotating rotor is in the streamline
flaw of the ambient air around the rotating rotor in horizontal flight, the con-
siderable difference in the speeds of the blade which, at the given moment, is
moving against the airflow (forward) and that of the blade moving with the flaw
(rearward) causes a helicopter to begin losing stability at a speed of about
300,kmihr and creates the risk of nose-over and crash. The speed at which sta-
bility is lost is known as the critical speed of a helicopter; at present, it is
impossible to exceed this speed.
150
Despite the comparatively law horizontal flying speeds and the limited critical
speeds, helicopters built in the USSR have been widely applied thanks to their ad-
vantages on take-off and landing. The ceiling and range of modern helicopters with
chemical fuels are small. The development of a helicopter with an atomic power
plant will permit a significant increase in =nits and to extend the area of useful-
ness of helicopters in general. Heavy atomic helicopters will make it possible to
carry freight and passengers over enormous distances, without need to refuel at
airfields and, for that.matter, without the need for airfields at all.
Even more attractive is the concept of an atomic convertiplane (Fig.61). This
is a combined type of aircraft capable of taking off and landing vertically on
small areas. In flight, the engines are able to rotate from the vertical to the
horizontal position, and the convertiplane is able to develop significantly greater
speeds in horizontal flight than the customary type of helicopter. The installa-
tion of atomic turboprop engines will make it possible for a convertiplane to fly
any desired distance and to land at any point on the surface of the earth. It
would be within the power of such an aircraft to carryan expedition from Moscow to
the Antarctic or any other distant point on the surface of the earth within a
single day, to fly around the world within 24 hours, and rapidly to transport pas-
sengers, emergency freight, mail, etc. to any desired distance. Moreover, this
will require no intermediate landing fields, bases, or fuel depots, nor will the
vast expenditures for the construction of intermediate landing fields be necessary
or the cost of delivering hundreds and thousands of tons of chemical fuels to such
airfields.
Sioecial-Features of Grounci Servicing of Atomic Aircraft
The difficulties encountered in designing atomic aircraft are exceedingly
great, and some have not been overcome to. this day. However, in addition to the
difficulties in designing the aircraft themselves, there are difficulties ix oper-
153.
sT)?:rAT
ilAaMearl.
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152
?
ation and servicing such ships.
The special features of operating atomic aircraft are due primarily to the ra-
diation hazard which complicates the work done in flight, and also inspection; ad-
justment, and repair work both to the atomic power plant and to the atomic aircraft
as a whole. A number of operations will be performable only by means of automatic,
remote-controlled equipment which will have to be available at the time at which the
first atomic aircraft is built and, as a matter of fact, somewhat earlier.
The organization of flight servicing aboard atomic aircraft will have to be at
an absolutely strict and even higher level than the organization of the operation of
conventional aircraft:
The servicing of an aircraft in flight will primarily have to provide for con-
stant and precise control of the radiation level aboard the aircraft and at the
parking apron on the ground. Each member of the service crew will have to have ex-
act knowledge of his responsibilities both during normal work and in case of emer-
gency. The skill of the engineering and technical personnel of the group will have
to be beyond reproach so that each member will be able to make a conscious and ac-
curate evaluation of every step he takes, will know the possible consequences, and
will be able to take the necessary precautionary measures in this connection. As
far as possible, every step must be reversible. This means that any devide, once
started, must have been provided in advance with means for stopping it (if neces-
sary, very rapidly).
The above statements prove that an atomic engine and aircraft must be designed
with consideration not only of its flying characteristics but also of its major
operating characteristics, in order to provide convenience and safety for service
in flight and on the ground. Calculations show that, in an atomic aircraft capable
of flying at supersonic speeds, nshadown shielding will provide normal conditions
of work only for the crew compartment; outside this zone, the safe distance in the
r
case, of a reactor operating at full pager will be not less than 1000 - 1500 m or
153
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100 - 200 m after the reactor has been turned off. Consequently, to provide for
safety .of ground servicing, the atomic power plant must IA so designed that the're-
Fig.62 - One of the Proposed Variants of an Atomic Aircraft and
Inside Design of a Service Hangar
1) Location of reactor; 2) Reactor; 3) Television camera; 4) Well; 5) Shield-
ing walls; 6) Bomb bays; 7) Radiation counters; 8) Lead glass window; 9) Tele-
vision antenna; 10) Periscope; 11) Control room; 12) Television control panel;
13) Cockpit shielding; 14) Tunnel for crew; 15) Rail trolley for moving air-
craft; 16) Reactor cover; 17) Immersed reactor; 18) Well into which reactor
is immersed
actor can be readily removed from the aircraft after landing. Moreover, when using
an atomic engine with a liquid heat-transfer agent, special measures must be pro-
vided for damping this agent after the flight, since it will also be radioactive.
When using an atomic turbojet engine with direct heating of the air in the reactor,
of the type illustrated in Fig.33, the entire engine will,be radioactive, which
means that the entire engine nacelle will have to be readily dismountable.
?
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154
4.
4
.4)
- These specific features of design and operation of aircraft with atomic power
plants dictate the necessity for special equipment at landing areas, airfields, and
hangars for atomic aircraft, particularly for the first experimental models. The
airfield must have special storage provisions and underground laboratories for re-
actors, for the heat-transfer agents, and other radioactive materials and assemblies.
A foreign journal carried a drawing (Fig.62) showing a proposed design variant for
an atomic aircraft hangar.
'In addition to developing special hangars it is also necessary to provide com-
plete mechanization and automation of all work involving reactors, radioactive heat-
transfer agents,
tionary reactors
of manipulation,
ations, by means
and in some cases the engine as a whole. Experience with sta-
has shown that modern technology, in addition to the simplest types
has also made possible complex, laborious, and very precise oper-
of sensitive instruments and so-called "mechanical hands". For
modern science and engineering, the development of ground equipment for transport
of highly active reactors, for installation and removal of reactors by remote con-
trol, for connecting and filling the cooling systems with liquid or gaseous heat-
transfer agents presents no great difficulty.
In addition to the mechanization means, airfields 'for atomic aircraft with
"shadow" shielding must be equipped with shelters and comfortable air ierminals
with underground installations for passengers and service personnel. In the first
atomic aircraft, it may well be that such special devices will also be required for
entering the aircraft and particularly for leaving it after landing, before the re-
actor has been removed.
- The need for much of this ground equipment will naturally be eliminated as
soon as i reliable integral radiation shielding for aircraft'reactors"will have been
developed. When this is the case, ground servicing will become simpler' and safe;
however, for the time being this is a matter for the future (Fig. 63).
The preparations for starting and the actual startup of an atomic power plant
STATAT
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, on an aircraft will involve certain dif-
ficulties with respect to preliminary
heating of the heat-transfer agent and
initiation of its circulation in the sys-
tem, for agents*nich.are in a. solid or
viscous state at ambient, temperatures.
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.)reduce .the radiation hazard on take-off
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