ORIG. RUSSIAN: HIGH PRESSURE VESSELS OF LIGHT-WATER AND MODERATED POWER REACTORS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP88-00904R000100100032-5
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 24
• Document Creation Date: December 22, 2016
• Document Release Date: August 12, 2009
• Sequence Number: 32
• Publication Date: May 1, 1964
• Content Type: STUDY

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' Third United Nations
International Conference
N on the Peaceful Uses
,~~Y
Confidential until official release during Conference
U:33R
May 1()6;1
Or i t;i rial : HUJJIAN'
HIGH PRESSURE VESSELS OF LIGHT-WATER COOLED
AND-MODERATED POWER REACTORS
Stekolnikov V.V., Khokhlatchev A.A., Denisov V.P.,
Vikhorev Ju.V., Prigorovskiy N . I. , Lugov F.A. ,
Kovalenko B.I., and Dobronravov V.B.
1. I N T R 0 D U C T I 0 N
The high pressure vessels of light-water cooled and mo-
derated high-power reactors have been designed in the USSR
for the New-Voronezh Atomic Power station, for the APS in
the German Democratic Republic and for the Ulyanovsk Expe-
rimental Industrial APS. In designing the reactor vessels
provision has been made for a complete cycle of vessel fab-
rication in order to only mounting and assembly works and
connecting of the communications to accomplish at site as
well as for transporting these vessels to the site of moun-
ting by railway heavy cars.
In accordance with specifications the life of these
vessels should be 20 years, that was the main problem of the
whole design and development works.
2. MAIN FEATURES OF HIGH PRESSURE VESSELS
Difficulties in designing and manufacturing the vessels
of large pressurised water power reactors operating under
high pressure has been dictated by the following specific
conditions:
- by the high operating pressure of the coolant, so that
it at higher diameter value results in significant thickness
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of the vessel walls. This condition has made the solution
of technological and welding problems more difficult; it is
associated with the increase of stresses caused by pressure
differences especially at variable duties;
- by the high temperature of the coolant; by a conside-
rable volume of the primary tircuit and consiquent ly by a
higher amount of the stored energy which may lead to a seri-
ous danger in case some damage takes place somewhere in the
vessel seal;
- by the presence of radiactive radiation causing some
additional temperature difference in the vessel wall at a le-
vel of the core and a change in physical and mecLanical pro-
perties of the metal during of operation, and consequently
by the necessity of periodic checking the change of these
properties;
- by vessel loading condition-F3 associated with the pe-
riodical change in the load induced by pressure and tempera-
ture.
The number of loading cycles for a culculated and expe-
rimental determination of the vessel material workability
within the above said period of life has been estimated with
the assumed following conditions:
1) with pressure fluctuations within ?5 kg per sq. cm
at a steady operating duty because of some non-ideality of
the automatic control system functioning at the . set power
level, i.e. by the value of 104;
2) with the same condition as the above mentioned but
with pressure fluctuation within -7 kg per sq.cm at transient
operating duties i.e. by the value of 103;
3) with pressure drop to the atmospheric level and
temperature drop to 60-70 0C at sheduled and emergency shut-
downs of the reactor with after-heat removal, i.e. b,-,- the
value of 200 cycles;
- by inaccessibility of the major part of the vessel
elements and joints for their repair and inspection after
the reactor operation is commenced;
These features of the high pressure vessels have ne-
cessitated to put forward additional requirements for their
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design, choice of steel, and technology of fabrication, the
requirements which are more strict than those of the Gostek-
hnadzorx) so far as in general the design of steam boilers
and vessels operating under pressure is displayed in the
USSR by rules and standards of the Gostekhnadzor.
As a metal for the fabrication of the reactor vessels
of high dimentions a standard boiler steel can be used as
well as a special steel having higher mechanical properties.
Since it has been decided to fabricate the reactor vessels
at the plant, because this provides better quality, reduces
their weight, and makes their transportation to the site
easier, the alloyed steel proposed by prof. Pashkov and
engineer Teplova has been chosen; the use of this steel
enables to reduce a vessel weight twice. As for welding the-
re have been taken the materials proposed by two engineers,
namely: Molchanova and Ivanova. The chosen chromium-molyb-
denum-vanadium steel posesses high strength and plastic
properties. For example, its yield limit at the operating
temperature 50 kg per sq. cm, the strength limit 70-80 kg
per sq cm at relative extention 20%, and shock viscosity is
not less than 10 kg per so.em. In this connection it is the
chemical composition that has made it possible to obtain ho-
mogenous mechanical properties throughout the whole cross-
-section of t-} vessel. Besides of these high mechanical
and plastic ?~rorerties this steel po_;:-ssos high heat-resis-
tiviiy at the operating temperature and allows overheating
up to 4500C. The steel also has all the required technologi-
cal properties, i.e. weldability, a good ability of being
plated with a layer of the other metal and it enables to
make forgings up to 100 tons and heavier as thick as 600 mm.
In designing the reactor vessels a number of specific
requirements have been observed.
The ring-shaped portions or simply ring portions of the
vessel are made as forged without longitudinal seams.
x)
the state agency which works out and issue rules for the
design and construction of the industrial istallations
and exercises inspection of their operating conditions.
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thick and 3350 mm in diameter. It has 55 throughout perfo-
rations, 90-2000 mm in diameter, on which the tubes hou-
sing monitoring and measuring devices are positioned. The-
se tubes are made as double "bells", one inside the other,
and their welded seams connecting them with the cover are
shif led aside from the zone of maximal concentration i.e.
placed at some distance from thepe perforation contour.
The internal surface of the vessel is covered with
the anti-corrosion welded metal made by the austenitic
electrodes manually or automatically by bands. The welded me-
tal is around 20 mm thick.
The fabrication, test assembly and hydro-test have
been accomplished entirely at the manufacturing plant.
In developing the reactor vessel the attention was
payed to make it reliable in operation, that is why a se-
ries of measures controlling the vessel behaviour in ope-
ration conditions have been provided. Among them the
installation of 24 channels in the vessel for loading
test samples made of the same material of what the vessel
details are made. It is possible to extract periodically
these samples checking on a change in mechanical and plas-
tic properties of the vessel metal and a shift of the cri-
tical temperature of imbrittleness.
There are several tensometers installed at the points
the most sensitive to the change of the temperature condi-
tion to control the stressed state o4' the vessel.
These points are at the stud steam and welded joints
between the flange and the ring portion of the middle zone.
The tensometers positioned on the studs are connected
to the instruments provided with self-recorders and sound
signals. There is a special monitoring system provided to
control the thrust ring heating-cooling, this system le-
vels the temperature difference of the flange and the
thrust ring thus lessening aLditional stresses in the studs
at transient operating conditions the reactor start-up and
shut-down).
The use of this system enables then necessary faster
heatup or cooldown the reactor than it is stipulated by
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the operating instruction.
The ways of solving the problems acossiated with the
construction of large vessels being shown in the descrip-
tion of the New-Voronezh APS are universal only in their
principal part.
Considering each-reactor being specific in its cha-
racter seperate elements of the vessel may differ by their
constructional make up or by way of designing some units.
For example, it is due to relatively law stressed state
of the vessel at the New-Voronezh and ('l; ?:.. ovsk Atomic Po-
wer Stations the flat easy-fabricated cover is used, but
the cover for the reactor supplied to the German llemocra-
tic Republic is made as spherical one (Fig. 4. ). It is cau-
sed by the fact, that the reactor in the GDR was design to
allow recharging without taking the cover off; that made
it necessary to enlarge the diameter of cover perforations.
The spherical cover allows to make recharging maintaining
a lower level of stresses.
The reactor designed for the Ulyanovsk APS is a boil-
ing water reactor, that is why at mounting work it has been
provided by additional measures to make the vessel nozzles
with heat protection.
4. RESEARCH WORK
Together with a high amount of design and calculation
work the adopted research program to study the stressed sta-
te of the vessel under stationary and non-stationary opera-
ting duties, to study the strength of the base and welding
materials chosen for the vessel fabrication as well as to
check on the sealing ability of the joint between the cover
and the vessel flange has been cerried out.
The whole program is phased as follows:
1. Checking on the stressed state of the vessel on
plastic models by tensometers and on the resin models by
an optical method.
2. Checking on the stressed state of the vessel on
steel models under operating conditions with simulating non-
-stationary conditions of the vessel operation.
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that with a rather complicated shape of the vessels, with
details of high thickness and different cross-section to be
connected considerable stresses may occur at startup or
shuttdown reactor with subsequent cooling it down. To check
stressed condition the steel model 1:4,5 (Fig. 6.) was made
and subjected to various tests. It was pressurized to 100
kg per sq.cm and heated by an electric heater. After heating
the contained water to 275?C, it was discharged with simul-
taneous introducing the cold water in from a buffer tank;
this resulted in mixing the both waters at the inlet. The
rates of cooling the water in the model were chosen as tho-
se proportional to the square value of the scale, i.e.
bin = bn x m2, where:
bm; bn - are water cooling rates in the model and in the
full size vessel correspondingly;
m is the model scale.
Heat-resistant tensometers with 10 mm base were used to
register stresses. They were positioned both inside the mo-
del and on the outside in special protective casings. Data
was recorded by potentiometers with 2 sec. interval.
The analyses of the data obtained shows that the stress-
es at the vessel nozzles are decreasing at cooling the model
vessel, down,that the chosen cooling rate of 30?C per hour
is permissible for a given vessel design because it does
not induce stresses exceeding the yield limit of the base
metal and bending moments of the cover exceeding the per-
missibile moments caused by the control system mechanisms
installed on the cover.
Also they prove to the fact that the model seal opera-
tes well enough despite its sealing surfaces intershift per-
ceptibly one upon the other.
Strength Test of Chosen Materials under Operating
Conditions
The number of possible operating duties as well as
those of emergency at which vessels are being effected by
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their internal pressure, level of power and heat lord. at
the maximal degree and at the same time has. been determined
on the basis of a given period of life of the vessel. The
task set to investigate the strength of materials has been
solved in the aspect of:
- testing standard samples of the base material, of the
welded metal surface cover and welded joints for strength;
- testing material samples having been irradiated in the
channels of the experimental. reactor;
- repeated-statical testing small dimentional samprlesl
- repeated-statical testing the samples corresponding
in size to the actual details of the vessel up to 500 mm in
thickness (Pig. 7. ) ;
- testing samples to determine the critical temperature
of inbrittlement and the shift of this temperature depending
on the size of a detail, and the degree of irradiation;
- testing samples with the welded metal cover for heat
shock with 300?C temperature drop;
As a result of the programme carried out it is _found that
the materials accepted for the design Possess sufficient heat
resistivity and slightly change their properties being irra-
diated by an integral neutron flu..u: which corresponds to the
material wear during the 20 year ,period of vessel operation.
The repeated statical tests have shown, that the exis-
ti.n level of st,'lsses in the ve s;, `.:, with their concentra-
ti oo. considered is permissible .or- the given period of ope-
ration with 10--fold. margine of ,zfety estimated in the num-
ber of the reactor cyc le-shut -down.
Investigating the significance of critical temperature
of inbrittlement, it has been found that the most thick
details, i.e. the cover and the flange cause some limit in
the vessel performance because their critical temperature of
imbrittlement is within +50 - 80?C at their initial state.
The same materials have been studied under irradiation; their
critical temperature of inbrittlement is growing to 100-
-120?C with an increase of their integral dose of irradiation.
Since the ability of the vessel to carry high pressure
has not been lessened, what is proved by the results of in-
vestigations, the vessels have been tested hydraulically by
cold water and at the site by water heated to 80-90?C. For
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the future it is aeclci.ea to raise the pressure also with
the warm water in the circuit.
As it was shown above, design vessel nozzles in assem-
bly with austenitic steel sleeves having their linear coef-
ficient of extension 1 ?.10-6 1/?C, and a nozzle itself is
made of steel with 12.10-6 1/?C linear coefficient of exten-
sion.
The check up of the nozzles of this type for strength,
has been exercised at a special experimental plant where a
nozzle of actual size has been subjected to the periodical
change of temperature simultaneously carrying stresses in-
duced by internal pressure.
Investigation of Cover Seal Performance
Checking on the seal, the instruments and mechanisms of
the stud tightening system, and those of monitoring system
was exercised at the experimental plant the scheme of which
is shown in Fig. 8. The experimental plant is constructed
from details of the actual size and provided with all neces-
sary tensometric equipment enabling to watch stressed sta-
tes and temperature at various points of the structure when
tested.
There were two phases of testing; at first, 50 cycles
of raising the pressure up to 100 kg per sq.czn and dropping
it down to 0 were done, then the experimental plant was re-
peatedly heated and cooled again with subsequent shortening
the time of transition from one cycle to the other.
During these tests it was established that:
- the sealing unit assembly should be done precisely, the
non-alignment of the cover and the flange should be within
0,1 - 0.2 mm;
-- the sealing gasket can be used repeatedly several times;
- the monitoring cool-heat system of the thrust fling
decreases a stud bending moment and when necessary can main-
tain them at a level of stationary operating duty;
the sealed joint between the cover and the flange per-
forms well at all the conditions created up to one at which
it was being cooled at the rate of 120?C per hour;
- the stressed state of the units and details of the
vessel upper part under various conditions is determined.
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It is found that the rate of cooling provided by the design
with regard to vessel strength is permissible;
- a degree of stud tightening providing complete impermeabi-
lity of the joint being equal to 0,7 - 0,9 min, measured by
the indicator, or was equivalent to the total Y
tightening'
_1 , 5 Phydraulic, where
Ptightening - the total force of tightening of
all 60 studs;
Phydraulic - the force effecting the cover caused
by the internal pressure.
Control Checking of Vessel State at Manufacturing Plant
For primary reactor vessels as a necessary test at their hyd-
raulic testing tensometric measurements should be done, their
accounting results are to be included into a test report
and accepted by the Gostekhnadzor services. From the view-
point of using this data for subsequent operational purpo-
ses they can be very helpful at making a final decision
where to position tensometers by means of which the operatio-
nal personnel control the reactor duties at starting it up
and shutting it down.
At the hydraulic test of the vessel stress measure-
ments have been done at those points where by technical rea-
sons it is not possible to measure them on the model or at
the experimental plant. The total number of tensometers does
not exceed 100.
5- FABRICATION AND QUALITY CHECKING
ORGANIZATION OF INVESTIGATION WORK ON TECHNOLOGY
Initiating the investigation work on checking the tech-
nology of the chosen metal the decision was made that the
development of fabrication technology of ingots, forgings
and plates, the development of welding and welding material
technology as well as working out the technique of quality
control should be displayed at the manufacturing plant on
standard size details and units at close cooperation with
the research institutes and designing agencies.
The problems of fabricating forgings and plates as thick
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as 600 mm with insignificant distribution of mechanical proper-
ties throughout their thickness, and choosing a reliable tech-
nique to check their quality were to be solved. For welding
work it was necessary to develop the technique of manual and
automatic welding of the ring portions from alloyed steel with
welded metal cover as well as the technique of defected
weld repair. In the field of thermal treatment such conditions
were to attain which would provide the given mechanical pro-
perties of the base metal and welded joints with an insigni-
ficant guaranteed level of residual stresses in the structure
at the same time. In the field of checking it was necessary
to show the significance of various defects, their influence
on the structure strength, and to accumulate statistical data
in order that on this basis to work out standards of the
structure quality estimation. The program of this research
work was the most expensive and overwhelming.
Fabrication of half-finished products
To attain the required mechanical properties forgings and
relates were hardened with a subsequent temper-hardening. At
welding the vessel steel it became clear that in order to at-
tain good quality of welded joints with the required mechanical
properties of the weld, to weld with post- annealing of over-
hardened zone, and to releave stresses, repeated annealing
was necessary. That is why at the initial state the base metal
(forgings, plates) had increased volumes of its yield limit
and strength limit, so that post-annealing could provide the
required properties.
Fabrication of vessel details
All the main vessel details and units, i.e. the flange,
the strengthening ring, the ring portions of the nozzle zone and
the middle vessel part, the thrust ring, the cover fastenings,
nozzles, are made from forgings. The vessel bottom is fabrica-
ted of two plates, each 120 mm thick, welded one to the other
by electric slag welding with a subsequent press forging.
Thermally nontreated plates were used as blanks for the vessel
bottom. Prior to welding the plates were carefully checked
for the absence of flakes. After electric slag welding, the
blank was treated thermally (hardening and annealing) to
attain uniform mechanical properties of the base metal and
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welded seam, then it was carefully checked ultrasonically from
on the whole surface. On the forged bottom only bevels for
welding with the cylindrical vessel portion were machined.
The ring portions of the middle vessel parts the same of
the nozzle zone, the flange, also the strengthening ring and
the thrust ring were fabricated from one forging each by means
of mechanical machining.
After machining every blank was tested by ultrasound for
the absence of flakes and other defects.
Welding work
At the fabrication the vessel was devided into three
technological units: the bottom with the ring portion, two
ring portions of the middle part, and the two ring portions
of the flange zone with the flange. Welding the details in
each unit, as well as welding the units, was made with the
accompanying heating the details at the place of welding by
means of special machines with welding and heating devices.The
se lding work was done mainly by machines. Having we ldiDd ring
joi'__:.s the unit was thermally treated (annealed) in the fur-
nace to provide the required for the welded joint properties.
All around welded joints and the zones ajoining to the
welded details after welding and thermal treating were careful-
ly checked by X-rays and ultrasonically.
Before welding vessel units each to other the internal
surface of every unit was covered with protective welded stain-
less metal. In order to provide high quality welded metal layer
prior to commencing the work on covering the surface with the
metal, the selection of electrodes and welding materials with
required properties was finished as well as the preliminary wor-
king out of welding conditions and quality testing on samples.
All internal surface was covered with welded metal except the spa-
ce ajoining to bevels to be welded after. This space was welded
when the unit welding had been already made. The check of mecha-
nical properties of butt welds was depplayed by testing the samp-
les cut out from the control plates welded simultaneously with
the make up of control welds using same initial materials, wel-
ding technique, conditions and thermal treatment.
To provide necessary accuracy of geometrical dimentions
of the vessel the details and the units of the vessel were fi-
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nally machined as a rule after welding and heat-treat ing.Much
attention was bayed to each detail and unit aiming at the accu-
racy of dimentions provided. As a result the alignment of the
vessel along the vertical axis was not more than 8 mm at a
length of 11 m.
Strengthening ring setting; other checks
Setting the strengthening ring on the flange of the fi-
nished welded and tested vessel was done with 1,5 mm strain per
side. Prior to setting the strengthening ring was heated in
the furnace. Due to a very accurate machining of the sitting
places of the ring and the flange after setting the ring the
vessel neck had an insignificant ellipticity of 0,2 mm over
the cover diameter.
In fabricating the vessel cover , thrust ring, fastenings,
nozzles, etc. a careful check was exercised at every stage of
the fabrication especially for flakes and some other hidden de-
fects.
The fabricated vessel when a control assembly was subjec-
ted to a hydraulic test at the manufacturing plant with a si-
multaneous check of the stressed state of all major elements
of the vessel by means of tensometers.
6. C O N C L U S I O N
The experience of the fabrication has shown that the reac-
tor vessel made at the plant provides for sufficient reliabili-
ty of operation proved by the technological tests and the de-
sign and the investigation on samples, models, natural scale
stand and other fabricated articles.
R E R E R E N C E S
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