ORIG. RUSSIAN: NUCLEAR SAFETY REGULATIONS FOR POWER REACTORS IN THE USSR

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP88-00904R000100110027-0
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 8
• Document Creation Date: December 22, 2016
• Document Release Date: August 26, 2009
• Sequence Number: 27
• Publication Date: May 1, 1964
• Content Type: STUDY

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Third United Nations
International Conference
on the Peaceful Uses
of Atomic Energy
Confidential until official release during Conference
A/CUN1.28/1'/38()
U 231i
May 1y(,i;
Uvit;lnal : X. 'J'-31-AN
NUCLWA.R SAFETY REGULATIONS FOR POWER REACTORS IN THE USSR
G.A.Gladkov,G.A.Bat,B.A.Buinitsky,Y.G.Nikola jev,
V.A.Sidorenko
INTRODUCTION
Research and power reactors of various types are operating
at present in the USSR. The new reactors that are being developed
and built in our country like-wise differ widely in types and in
specific design features. Evidently, the variety of reactor types
will increase in the future. In this connection an urgent need
arose for elaboration of general requirements which have to be
accomplished in designing reactors and in selecting their
operating conditions to provide maximum safety of reactor operati-.1.
On the other hand, whenever these requirements are deviated from
(which is allowed as an exception only) special safety measures
have to be taken, certain operating modes prohibited, etc. One of
the most important problem that confronts the designers of nuclear
reactor is the provision of nuclear safety, i.e. elaboration of a
code of obligatory requirements and measures which would guarantee
prevention of excessively quick or uncontrolled power excursion in
a reactor.
Elaboration of such general requirements was entrusted to the
authors of this paper who prepared a draft of "Nuclear Safety Regula-
tions For Power Reactors in the USSR". This paper contains these
Regulations and a brief discussion.
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II. Nuclear Safety Regulations for Power Reactors in
the USSR
1. Provision of nuclear safety implies specific measures
aimed at prevention of a quick or uncontrolled power runaway in
a reactor.
2. These Regulations are not valid for critical assemblies and
pulsed reactors.
3. In considering emergency situations account must be taken
of the possible coincidence of two accidents one of which requires
a long time (over an hour) to be explained or liquidated (such as
cooling of the reactor).
4. Regardless of their nature the accidents including the
melting of the reactor must not result in reactor runaway. The
shape, composition and quantity of the fissionable material must
ensure double supply before criticality is attained.
5. Changing of the reactor orientation in space, including
tipping of mobile and transportable reactors (in transit) as well
as sinking of a ship must in no way interfere with the operation
of the units which shut down chain reaction.
6. The effectiveness of the reactor safety units must be de-
termined on the basis of the following considerations:
a) if only one reactivity compensation element is provided,
the safety elements, minus one, together with one half of the
automatic regulator must cover the entire range of reactivity
variation from the operating point to the point corresponding
to the maximum reactivity on the reactivity versus temperature
curves
b) if the number of the reactivity compensation elements with
an operating time shorter than the emergency cooling time is more
than one, the safety elements, minus one, must cover reactivity
variation between the operating point and the temperature which the
coolant has at the inlet to the reactor by the moment when further
reactivity control can be effectively ensured by other control
elements. In this case, the entire reactivity supply for the
complete shut-down of the reactor must be provided by the reac-
tion shut-down elements minus any one of them;
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c) not less than two safety elements must be available.
7. The safety system muct provide safety signalling for the
power increase period at least during the start-up and transition
to power operation. The operating ranges of the safety system with
respect to power and period must overlap. The circuits of the power
and period safety systems must contain at least two monitoring
channels.
8. It is forbidden to start up a reactor without at least two
safety elements in the ready-to-operate position, the effective-
ness of the safety elements must be not below ; the effecti-
veness of the safety system, minus one safety element, not below
,d/2. This requirement must be fulfilled no matter how the re-
activity control system is displaced during operation after the
reactor start-up, which includes the formation of local piles and
xenon waves. The subcriticality of the reactor after the safety
elements mentiou(:d above and half of the automatic regulator are
placed in. the ready-tooperate position mast be at least 0,5% of Rc'.
y. The safety elements must not depend for their operation on
the provision of external power supplies. When two channels are
used, signals from either channel must cause the safety system to
operate. Not less than two properly operating safety channels must
be provided at all times.
10. The safety system must have provisions for checking the
condition of the emergency signalling circuits - from the pick-ur
to the actuator drives - during power operation without shutting
down the reaction. The pick-up circuits must contain current or
current unbalance indicators.
11. The effectiveness of the automatic regulation rod must
comply with one of the two requirements stated below:
a) Par .41 41?
b) at Par' the speed of the rod must be such that
the reactivity /9 is inserted at a uniform rate for a time period
not smaller than 20 sec. At the same time, the following condition
must be fulfilled: ~-~ ar` /Oss of the safety system elements minus
one of them.
Conditions (a) and (b) are not obligatory when there is a
non-inertial effect (as compared to the travel time of the red)
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which covers the effectiveness of the automatic regulator.
12. For reactor riding up with periods corresponding to the
operating speeds of the automatic regulator (second periods) the
derivative cTt (t - temperature) must remain negative within a
sufficiently large interval above and below the operating point.
When the temperature coefficient within some temperature range
is positive the maximum rate at which reactivity is inserted du-
ring start-up or heat- up must be below the rate at which reactivi-
ty is decreased by the motion of the automatic regulator. This
limits the power during the heat-up. At the same time the safety
elements, minus one of them, must cover the entire positive tempe-
rature effect of reactivity variation. In case the reactivity
control elements are inserted into the core in emergency situations
(during the heat-up) they may be included for compensation of the
positive temperature effect.
13. No faults in the circuits and drives of the reactivity
control system must cause the reactivity to increase at a rate
exceeding that specified in Point 10,b. Moreover, provisions must
be made to stop insertion of reactivity whatever fault occurs in
the circuits of the reactor reactivity control system.
14. The projects and the operating instructions for the ope-
rating reactors must always contain sections on nuclear safety
measures to be taken while carrying out maintenance and reloading
of the reactor.
15. To enable the comparison of the data relating to reactors
of various types, the effectiveness of control and safety elements
as well as the effectiveness of all physical processes taking place
in the reactor must be calculated in terms of reactivity /? . The
reactivity is found from the formula 1) 0 r?) = 9t1. ( 1 l
The formula (1) must be used to calculate the full reactivity
supply of the reactor /0 and all individual effects ? i. The
reactivity balance must be drawn up according to the formula
r,71 (lp) - I p (2)
16. In each specific case, the scientific advisor and the chief
designer of the reactor installation must submit well-grounded
reasons for all deviations from the rules set forth in these Regu-
lations; all such deviations must be approved by the State Commi-
ssion for the Utilization of Atomic Energy.
386
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Note: /P denotes here the portion of the delayed neutrons
for the given core.
III. Discussion
In accordance with their contents the Regulations can be
divided into three unequal parts. The majority of the Points re-
fer to the reactivity control system of a reactor and particu-
larly to the safety system (Points 5 through 13). Besides, the
Regulations specify the requirements to the reactor system proper
(Points k,5) and, finally, judicial and administrative points
(1,2,14,15,1b). We will discuss each group in turn.
Before starting the discussion of the problems connected
with the reactivity control system we would like to emphasize
Point 3 which stipulates the number of accidents in the reactor
system. It is supposed that there may be two accidents simulta-
neously, one of them being of a lengthy nature such as damage
of the hermetic sealing of the reactor vessel or failure of some
essential mechanism and the other, a short-time one, such as the
failure of some control system or short-time interruption of power
supply of some mechanism. It is assumed that emergency situations
where several accidents occur simultaneously, which are more
difficult and complicated than those described in Point 3 are
practically non-existant and, therefore, should not be considered
in designing reactors. This general assumption is also evident
in paragraphs dealing with the reactivity control system of the
reactor which consider the possibility that one absorbing rod or
a group of absorbing rods actuated by a common drive may fail to
operate to perform their immediate function.
A high degree of reliability is required of the elements
which shut down chain reaction. Therefore, Points 5 and 13 contain a
a number of very stiff requirements which are quite self-explana-
tory. It should be only noted that the second part of Point 13
requires the provision of facilities which would enable the ope-
rator controlling the installation to stop the increase of the
reactivity whatever faults may appear in various systems. Point 9
which calls for duplication of control stipulates a similar require-
ment for the safety system.
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Points 6 and 8 determine the required effectiveness of the
safety system. It is assumed here that after the safety system
operates the temperature of the coolant in the core will quickly
settle at a value close to coolant temperature at the inlet to
the core in power operation. Therefore, quick-acting devices,
such as safety elements, are needed to compensate the additional
reactivity. Further variation of the temperature in the core and
the corresponding variation of the reactivity proceed much slower
and can be compensated by the reactivity control elements having
considerably slower speed of action. Besides, Point 8 stipulates
that at any time during reactor operation provisions must be
available to quickly decrease the system reactivity be an amount
approximately equal to 16 , should the reactivity suddenly
increase at start-up or during operation. Attenti r)n is drawn to
the fact that the effectiveness of the safety system is liable to
be considerably affected by improper arrangement of the absorbers
in the core or by the appearance of xenon oscillations. The Regu-
lations stipulate the reactivity margin to be available until cri-
ticality is reached after the safety elements are raised so as to
mi 'Imize the dangerous effect of errors in preliminary evaluation
of the system reactivity prior to the reactor start-up. Points 7
and 10 formulate additional requirements to the safety system.
The requirements of Point 10 stem from the fact that separate
drives used for the safety system are not checked for condition
during long periods of time. All control circuits of the safety
system either do not have any objective indications which would
characterize their performance during operation of the reactor.
Therefore, measures are defined which make it possible, at least
partially, to remove this uncertainty - to check the control circui-
ts of the safety system with the reactor operating.
Point 11 indicates how the effectiveness of the automatic
regulator must be selected so as to avoid quick power growth in
the reactor at any displacement of the automatic regulation rods.
When the reactor reactivity is increased by an amount fi for
a period of 20 sec at a uniform rate, the reactor power doubles
after 9 sec. This gives sufficient time margin for the operator
and for actuation of the safety system.
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Point 12 stipulates the necessity for self regulation of
the core within the range of its operating temperatures and
prescribes the procedure for starting the system and bringing it
to normal operation when self-regulation is absent somewhere out-
side the operating temperature range of the core.
Of great importance for designing the reactors is Point 4
which stipulates that the reactor design must ensure a 200%
margin until the reactor goes critical as a result of core
meltdown. In some cases this places considerable limitations on
the construction of the lower reflector of the core and the spaces
below it.
We will not dwell on the judicial and administrative points
which define the scope of application of the Regulations, re-
quirements to record-keeping, etc. It should be only noted that
the sole purpose of Point 15 is to ensure uniformity in evaluation
of reactivity margin of various systems.
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