A R T I C L E S

N O N T R A D I T I O N A L C O N C E P T S O F N U C L E A R P O W E R P L A N T S W I T H

INHERENT SAFETY ( N E W N U C L E A R T E C H N O L O G Y FOR THE NEXT

STAGE OF L A R G E - S C A L E P R O D U C T I O N O F N U C L E A R P O W E R ) *

V. V. Orlov, E. N. Avrorin, E. O. Adamov, A. P. Vasil'ev,

E. P. Velikhov, A. A. Vertmna, I. V. Gorynin, B. F. Gromov,

Yu. I. Zvezdin, V. A Ignatov, I. S. Slesarev, M. I. Solonin, V. I. Subbotin, and V. V. Khromov UDC 621.039.5

Atomic energy - the most important discovery of 20th century physics - has placed unprecedented power in human

hands. Nuclear weapons not only engendered the tragedy of Hiroshima and Nagasaki as well as the fear of nuclear annihilation,

but it also wrought a fundamental change in the military-political picture of the world: It has done away with large wars and

provided a real foundation for eliminating all weapons of mass destruction. Atomic energy also provides us with a virtually

inexhaustible source of heat, light, and the means for performing work and for transportation.

Nuclear fuel has certairf advantages over traditional (chemical) fuels that will not only make it possible to overcome the

dangers associated with chemical fuels but it will also provide significant ecological, economic, and benefits. These benefits

include the following:

the heat content of nuclear fuels is millions of times higher than that of chemical fuels and the volumes of material that

must be mined and transported are correspondingly smaller;

there are no dangerous chemical emissions (SO 2, NO2, CO2, etc.), oxygen combustion is eliminated, and the volumes of

radioactive wastes are insignificant, facilitating localization and disposal of wastes;

The most dangerous long-lived radioactive wastes - the actinides - can be burned up (fissioned) and due to radioactive

decay the period of time during which the rest of the wastes remain dangerous is shortened; and,

breeding of nuclear fuel is possible and feedbacks (Doppler effect, etc.) allow for stabilization and self-regulation of

nuclear burning.

On the basis of this and the fact that fossil-fuel resources are limited, more than 40 years ago, during the period of rapid

growth of power generation, oil exploration, and oil production, nuclear physicists began working on the the peaceful uses of

atomic energy.

The risk and efforts which society took on in order to assimilate this new unlimited but potentially dangerous source of

energy were justified by the possibility of achieving a drastic solution to the fuel and energy problems facing mankind. The

lounders of nuclear power saw this as its main goal, and work on it began only after E. Fermi in the USA and A. I. Leipunskii

in the USSR pointed out, back in the 1940s, a way to solve the problem of nuclear fuel resources for large-scale nuclear power

on the basis of fast reactors. "Atomic electricity" was first obtained in 1952 on the EBR-1 fast reactor [1.2 MW (heat)]

*This paper is a continuation of the discussion, initiated by A. A. Abagyan, G. L Biryukov, S. V. Bryunin, et al. in their paper

"Status and problems of the development of nuclear power in the USSR" (Atomnaya Ener~ya, 69, No. 2, 67-79, February, 1991),

of the prospects for further development of nuclear power. It is the hope of the editorial staff that discussions of this important

subject will continue.

NIKIt~T VNIITF, I. V. Kurchatov Institute of Atomic Energy, Central Scientific-Research Institute of Machine-Building

Technology, TsNIIKM, Ft~I, VNIINM im. A. A. Bochvara. Moscow Engineering Physics Institute. Translated from Atomnaya

t~nergiya, Vol. 72, No. 4, pp. 317-329, April, 1992. Original article submitted August 28, 1991.

1063-4258/92/7204-0287512.50 ©1992 Plenum Publishing Corporation 287

But the development of nuclear power at the first stage, which is now approaching completion, proceeded along a

different path - the development of thermal reactors, primarily light-water reactors, which were adopted in military nuclear

technology and, at that time, were simpler to build. At this stage, nuclear power developed into an autonomous branch of the

power production industry, replacing --5% of fossil fuels in the world fuel balance (3% in our country); it accumulated extensive

experience; and it demonstrated on the example of long-time operation of hundreds of nuclear power plant s that it is capable of

generating electricity in an economical and ecologically beneficial manner. But the plans for rapid development and creation,

even in this century, of large-scale nuclear power production encountered two large obstacles in the 1970s-1980s:

contrary to expectations, the oil problems of the 1970s did not increase the demand for atomic energy; they were

successfully solved by energy conservation measures which reduced (by =1/3) the energy intensiveness of production as well as

the need for power-generation capacity, including also nuclear capacity;

the large accidents at the Three Mile Island (USA) and Chernobyl nuclear power plants indicated that nuclear power is

not ready for such rapid growth and that the extant scale of power production is not matched with the level of safety.

Measures for increasing the safety of nuclear power plants made it possible to continue building such plants, but there

are virtually no orders for new nuclear power plants. Nuclear power-generation capacity in the world will increase in the next

10-15 years by scarcely more than 15%. Seeking to justify their previous large investments in this field, firms that build reactors

are preparing designs of improved nuclear power plants in the hope that the situation will change during this period or there

will be orders from some developing countries. In our country, besides a sharp increase in the opposition to nuclear power as a

result of the accident at Chernobyl, a deep crisis - not an energy crisis - is impeding the development of nuclear power (in our

country the per capita consumption of energy is higher than in many of the most developed countries but the standard of living

is many times lower). The way out of this crisis and the institution of an efficient market economy will require a long time and

great effort. In the process, there will appear opportunities for adopting the energy conservation technology developed in the

west. For this reason, there are no grounds for counting on a large energy program, either nuclear or nonnuclear, in the next

15-20 years; this would be impossible and there is no need for it. However, a limited program of construction of nuclear power

plants, based on improved designs and as people become convinced of the safety of these plants, would be useful both for

replacing many old thermoelectric power plants, which have exhausted their service life, and for maintaining both the industrial,

scientific, and engineering knowledge of nuclear power production which was gained with great effort and will be needed in the

future.

In our country it is especially important that in the near term the construction of nuclear power plants can be based on

existing fuel and machine-building industries using existing fuel resources, which are significant. There are three points of view

regarding the fate of nuclear power and, correspondingly, three fundamental directions:

1. Nuclear power does not justify the risk, effort, stress, and fears associated with it, and it is not a deciding factor in the

economics of most countries (France is an exception). It is simpler to "shut it down" and to direct efforts toward improving the

traditional and developing new energy technologies (renewable sources, thermonuclear schemes not involving neutrons and

tritium, etc.). The main problem is gradual dismantling of nuclear power plants and disposal of radioactive wastes.

2. Most nuclear-power specialists have adopted an evolutionary view, oriented toward limited development of nuclear

power in the foreseeable future, preserving the place of nuclear power in power generation, even on the basis of traditional

nuclear technology (light- and heavy-water reactors and possibly fast and high-temperature gas-cooled reactors). If the need for

large-scale nuclear power and the associated problem of the cheap uranium resources arise in the more distant future, then they

will be solved on the basis of the evolution of the traditional concept of fast reactors. From this standpoint, the efforts should be

concentrated on the evolutionary improvement of traditional nuclear technology (primarily light-water reactors); new concepts

should be studied at the scientific research level. This is probably the point of view of the authors of the paper "Status and

problems of the development of nuclear power in the USSR" (Atomnaya ff~nergiya, 69, No. 2, 67-79, February, 1990). It is also

obvious to us that existing nuclear power plants must be safe and the new plants, though limited, must be improved, and

methods must be developed for dismantling nuclear power plants and disposing of the radioactive wastes.

3. But we would like to justify here the point of view that the most immediate and important problem, together with the

problems indicated above, is to develop and demonstrate to society a new nuclear technology, capable of completely solving the

fuel-energy problems of the next century which are confronting the entire world, including our own country.

Summarizing the outgoing century, we must acknowledge that its energy problems turned out to be solvable without the

large-scale involvement of nuclear power and that the main goals of nuclear power, which made the work worthwhile, remain in

the future, in the next century.

288

The possibilities of energy conservation are limited, and an increase in energy production in the next century is unavoid-

able due to population growth and increased cost of raw materials and preservation of the environment, especially in connection

with the increasing number of developing countries which are becoming industrialized (at the present time these countries now

consume five to ten times less energy than the developed countries).

Growth of energy production based on traditional chemical fuels presents a host of problems which are constantly

getting worse: resource, international, ecological, transport, and social. The last three are especially important for our country.

The power generation industry is extremely slow to adopt new technology and new fuels; many decades are needed to

develop and adopt them in standard energy production. Advanced preparation is required. New renewable sources, just as

thermonuclear fusion, still cannot be considered a realistic base for energy production in the next century, in any case during the

first half of the next century. On the basis of extensive practical experience, fusion energy, though not the only imaginable

source, is the only realistic path for solving efficiently the problems indicated above, assuming, of course, that safety questions

are completely resolved. But this is accessible only to nuclear power on a scale ten times larger than the current scale, replacing

at least 20-30%. and not 3-10%, of the fossil fuels. Stabilization at the current level and then reduction of production and

consumption of chemical fuel for energy production by development of large-scale nuclear power is the goal and the content of

the next stage of development of nuclear power - "the second nuclear era." By not demonstrating to society the reality of this

prospect and by limiting ourselves only to the solving current problems, we shall also harm its present development and possibly

eliminate the main argument. After all, present-day nuclear power is important not only and even not so much in itself, but

rather it is a step toward large-scale nuclear power.

The future scales of nuclear power also impose new requirements on nuclear technology, the main ones being as follows:

drastically improved safety of all elements;

fuel balance, reduction of specific consumption of natural uranium approximately by a factor of ten by switching to a

closed fuel cycle and breeding; and,

economics, preservation, with all this, of the economic advantages of nuclear power.

Experience shows that the traditional nuclear technology, founded 40 years ago on the basis of the limited experience of

military nuclear technology, has inherent contradictions in meeting these requirements. They are based on the previously

prevailing confidence in the omnipotence of engineering safety methods and they inherently contain the potential danger of

accidents leading to radiation emission: uncontrollable reactor runaway (reactivity margin for burnup, poisoning, and power

effects Ak >> t3); coolant losses accompanying rupture of the reactor loop, boiling of the coolant, malfunction of emergency

cooling; fires, explosions. These potential dangers were realized in the accidents at the Three Mile Island and Chernobyl nuclear

power plants, and they shook the confidence in the omnipotence of engineering methods. Nonetheless, nuclear power plants are

being improved, primarily by adding such means, imposing extraordinary requirements on the quality of equipment, control

systems, as well as operating personnel in order to reduce the probability of accidents. This makes nuclear power plants more

expensive and more complicated. The new nuclear power plants have achieved great success in this direction and this has made

it possible to continue building them, but this path has almost reached its technical and economic limits. The only proof of

safety of the future large-scale nuclear power, which will have to operate for 100 times more reactor-years than present-day

nuclear power, is a long extrapolation of present experience with the help of recently developed probability theory. But this

theory is based on unreliable data, especially data on low-probability events and correlations of events. In addition, it cannot be

checked experimentally and for this reason it is not a convincing proof of safety.

In the last few years significant progress has been made in the technology of handling radioactive wastes, but in the case

of large-scale nuclear power and 100 times more wastes, there is some doubt in the safety of long-distance transportation of

highly active wastes and underground storage of these wastes, especially actinides, based on the reliability of engineering

structures and long-term geological predictions.

Our contemporaries are not convinced either by the arguments of the economic risk theory (according to which a

probability of a large accident of 10 .5 per year is acceptable, though this means several such accidents in the next century) or by

comparing with the number of deaths due to automobile accidents, chemical emissions or earthquakes, since they require a

drastic increase in the safety of all new technology, nuclear and nonnuclear.

Light-water reactors, just as high-temperature gas-cooled reactors, cannot give the required reduction of the specific

consumption of uranium. Modern fast reactors, which can solve this problem, are expensive, even compared with the much more

complicated and expensive light-water reactors, and their safety has its own Achilles heet - the burning and boiling of sodium.

Nuclear power based on the traditional technology does not have a consistent and convincing concept, which would be convinc-

ing for society, of its future, and this has a negative effect on its present situation.

289

M, tons ~

°F 1 I I l I I I 0 200 ~-00 600 dO0 ~ yr

Fig. 1. Mass of natural uranium (in equilibrium with its decay

products) equivalent (with respect to radiation danger) to one

ton of fission products as a function of the holding time with

0.1% U, Pu, 1% Np, Am and Cm (1), 0.01% U, Pu, 0.1% Np,

Am and Cm (2), 0.01% U, Pu, 0.1% Np, Am and Cm remain-

ing in the fission products after radiochemical processing and

extraction of 1%, Cs and 0.1% Sr (3), specific consumption of

natural uranium (tons of uranium per ton of fission products)

(4).

We must give clear answers to these questions and doubts, first to ourselves and then to society, whose opinion will

ultimately determine the fate of nuclear power.

A. Wienberg and others understood the inadequacy of the engineering philosophy of safety already after the accident at

Three Mile Island. Weinberg introduced the concept of "inherent safety" (in the wide sense of the term), which are the key words

of the new philosophy of safety, consisting in maximum use of the fundamental physical and chemical properties and laws

inherent to nuclear fuel, heat-transfer agents, radioactive wastes, and other components. This path can be counted on to achieve

a very high degree of safety by simplifying and not complicating the construction, and it will permit solving the economic

probIem. Breeding, as one of the fundamental properties of nuclear fuel which can solve the problem of fuel resources, must be

used for safety purposes. Thus inherent (in other words, natural) safety opens the path to new nuclear technology, combining

harmoniously the qualities of safety, breeding, and economic efficiency. In addition, this approach must be extended to both

reactors and nuclear power plants as well as other components of the nuclear system, including handling of radioactive wastes.

Elements of inherent safety have been used in the past. In the last few years they have been increasingly elaborated in

new designs of nuclear power plants of the traditional type (passive shielding and shut-down cooling, self-regulation effects, etc.).

But traditional reactor concepts cannot systematically realize inherent safety, ~ince the potential dangers are already inherent in

their initial conceptualization.

The aim of the new nuclear technology is to achieve systematically, starting at the conceptual level, inherent safety,

thereby eliminating a host of dangerous accidents. To do this, reactor physics and technology have an arsenal of tools which have

not yet been fully utilized:

lowering the reactivity margin to Ak < fl (elimination of poisoning, achievement of a breeding factor --1 in the active

zone, etc.);

elimination of the dangerous effects of reactivity (void, etc.), full involvement of the self-regulation properties of the

reactor via feedbacks (for example, as in the PRISM design (USA));

prolonged shut-down cooling with air (this is now done in modular designs of high-temperature gas-cooled reactors, the

PRISM design, but it can also be achieved in other types of large reactors);

use of low-pressure, nonburning heat-transfer agents with high boiling points together with high natural circulation and

thermal inertia; and, implementation of measures which eliminate dangerous radiation consequences of external perturbations, both natural

ones (hurricanes, earthquakes, etc.) and those associated with technogenic accidents (airplane collision, explosions during

transportation), terrorism, and rocket attack.

International guarantees of nonproliferation of nuclear weapons are a necessary condition for wide development of

nuclear power, but they must be supported by physical and technical measures in nuclear fuel cycle technology.

290

The expansion of long distance transportation of fissioning and highly active materials could become one of the main

obstacles to the development of large-scale nuclear power. Closure of the nuclear fuel cycle of a nuclear power plant will

completely solve this problem; this solution is based in modern technology (liquid-salt reactors, concept of a fast reactor IFR).

The safety in handling and final storage of radioactive wastes is greatly enhanced by returning the wastes into the reactor and

burning up all actinides. This opens up the possibility of storing the rest of the wastes without disrupting the background

radiation equilibrium after prolonged (200-400 yr) holding in small maintained cooled storage areas at the nuclear power plant

(Fig. 1).

If the problems of breeding nuclear fuel, safety of nuclear power plants, and handling of radioactive wastes are solved,

then there are no resource or ecological limits on the duration of the "nuclear era." This involves the concept of renovation of

carefully selected nuclear power plant sites and repeated use of these sites together with the developed infrastructure in the

construction of new nuclear reactors to replace reactors which have been shut down.

Looking at the long-term future, we must also take into account the possibility that there will appear a new energy

technology (renewable resources, thermonuclear fusion) that could be preferable to nuclear power with respect to economic,

ecological, or other qualities. For this reason, in discussing the concept of large-scale nuclear power one must imagine and

present to society its last stage, requiring burnup of all accumulated nuclear fuel and disposal of radioactive wastes. This stage

may turn out to be long (exceeding a century), since large quantities of accumulated 238U, contaminated 232U, and much more

slowly burning plutonium will have to be burned up and other wastes will have to be stored for a long period of time.

Large-scale nuclear power can be developed only if society assimilates the knowledge and radiation culture in the

manner that electricity was assimulated in the 19th century. In this case, radiation technology with utilization of radionuclides

will be widely disseminated in industry, agriculture, and medicine. The dissemination of such culture in society, starting with

school, is an important problem facing nuclear power engineers, as is the development of new nuclear technology - both power

generation and other applications. The development and choice of new nuclear technology for the large-scale nuclear power of

the future also require new approaches to the choice of criteria, safety being the primary one. In the developed countries,

society, having provided itself with sufficient food and other life necessities, and having developed the basis for further scientif-

ic-technical progress, raises the problems not so much of continuing quantitative growth of production as increasing the quality

of life, including safety and preservation of the environment. Although quality requires considerable material inputs, the main

results are achieved by searching for and developing new approaches and technologies. The subjective criteria of a society which

no longer has to worry about daily bread, ,of course, are adjusted in time by technical and economic possibilities, but they

increasingly determine the direction of progress, narrowing the objective criteria. To technologists, bemoaning the incompetence

and excessiveness of the demands of society, which will cost too much, society often retorts that it can wait until they or other

scientists find new, safer, and at the same time not very expensive solutions. The most recent and striking example, demonstrat-

ing that these expectations are not in vain, are the successes achieved in energy conservation, whose effect in the fossil-fuel

economy and for the environment has turned out to be much greater than that of nuclear power. The well-known steps taken by

OPEC served only as an excuse for implementing ripe ideas and technology already developed by technical progress.

Our contemporaries will hardly agree to any criterion with respect to nuclear power other than elimination of large

radioactive emissions in accidents at nuclear power plants or leakage during handling, including storage of radioactive wastes. In

a world operating according to the laws of probability, this means not absolute safety but reducing the probability of such

emissions to negligibly small values. For the large-scale nuclear power of the next century with production of about 106 reac-

tor-years this can be a probability of 10 - s per year. This value can be adopted for the new nuclear technology. But probability

estimates are acceptable as a safety criterion only if they are reliable or are known to be the maximum estimates, which cannot

be said about modern methods of probability analysis of safety. Systematic implementation of the principle of inherent safety will

make it possible to eliminate deterministically the most dangerous accidents in most cases, including low-probability ones.

Apparently, even here it will be possible to find a chain of events leading to dangerous states, and it is only to these cases that

it will be necessary to apply the maximum probability estimates. We shall have to consider any possible situation which we or

others can imagine, including situations which are now hypothetical or projected. But the only cases and processes that need be

considered are those allowed by the laws of nature and the capabilities of people and technology. This, seemingly obvious,

condition should be kept in mind, since there is a real danger of arbitrariness, which is inadmissible in specific developments.

Safety criteria must, of course, be considered in connection with economics. But inherent safety presupposes that it can

be achieved economically. In time, the price of energy will go up, following fuel and more stringent ecological requirements, and

this will create economically more favorable conditions for nuclear power. However, we have grounds for demanding of the new

nuclear technology that the costs of producing energy not exceed significantly the costs ~n terms of modern tight-water reactors.

291

6 r 7 • ~ ~ / /

I 18,90 2000 2010 2020 2030 20#0 2050

y ea~[

Fig. 2. Total energy consumption (1), electricity consumption

(2), and consumption of electricity generated by nuclear

means (3) according to 1984 ( ) and 1991 ( . . . . . )

forecasts.

600

""71- -30L ;990 2000 20;'0. 2020 2030 2040 2050 2005 207020;'5 2025 2035 20#5

Year Year

Fig. 3 Fig. 4

Fig. 3. Forecast of nuclear-power growth up to 2050 (the power of a nuclear heat generating plant is converted

to equivalent electric power; the efficiency is 0.4, the materials utilization factor is 0.8). 1, 2, 3) total power of

fast and thermal reactors, respectively.

Fig. 4. Demand for replenishment with plutonium accumulated up to 2005 (1); 2, 3, 4) fuel without 235U and

fuel with 10 and 20% of the plutonium replaced with 235U, respectively.

NUCLEAR POWER IN THIS COUNTRY. NEXT STAGE

The sovereign states comprising the USSR, irrespective of changes in political status, are closely bound together by many

economic and other ties. This allows us to consider, at least in the most general features, long-term growth of energy production,

which for the first half of the century can be approximately represented by the curves in Fig. 2 on the basis of the following

assumptions: primary energy production stabilizes in the next 20 years; energy consumption increases in the next 40 years by

approximately a factor of 1.5 (from 2.2 to 3.3 billion tons of reference fuel per year); electricity production grows predominately,

from 0.6 to 1.7 billion tons of reference fuel per year with the fraction of electricity increasing in the fuel-energy balance

approximately from 1/4 to 1/2 as a result of a decrease in the fraction contributed by the direct use of heat.

The main economic goal of the development of nuclear power is to stabilize the production, transportation, and burning

of nuclear fuel, and later also reduction of the use of nuclear fuel for energy production. The scenarios of development of

nuclear power (Figs. 3-6) start from this and the following assumptions:

Nuclear power plants (some nuclear heat-generating plants) with overall electric power capacity up to 40 GW, mainly

based on traditional reactors (BBER and MKER (modular channel power reactor)) with inherent safety, will come on line in the

next 20 years;

292

30

2O

1590

1

I I I I I 2000 2010 2020 2030 2040 2050

Year

Fig. 5

:4~000

~000

~o zOO0

Ioo0 C~

A 0 ~ I 2010 2010 2020 Z030 2040 2050

Year

Fig. 6

Fig. 5. Yearly demand for natural uranium for nuclear power: 1) total demand with 10% plutonium replaced

with 235U; 2) demand for thermal reactors. Total demand for natural uranium for fast reactors is 170,000 tons;

the demand for plutonium is 300 tons; the demand for natural uranium for thermal reactors during the same

period is 1,020,000 tons.

Fig. 6. Predicted demand for nuclear power for reprocessing spent fuel from fast (1) and thermal (2) reactors.

in subsequent years inherently safe nuclear power plants will be constructed at moderate rates (with a doubling time T 2

of about 20 years);

for supplying electricity and heat primarily to remote regions - construction of small improved nuclear heat and electric

power, heat, and steam plants operating on thermal neutrons (light-water, high-temperature gas-cooled, or other type); their

relative contribution to nuclear power is of the order of 20%; and,

toward the end of the period nuclear power should contribute approximately one-half of electricity production and about

1/3 of the fuel-energy balance.

The fuel balance for thermal reactors was calculated using the characteristics of modern reactors with return of 235U and

transfer of the plutonium into fast reactors; fast reactors with a breeding ratio of 1.3 and plutonium doubling time of 22 years

(the period of the external fuel cycle is three years) were analyzed as nuclear power plants of the new generation.

The results of the calculations lead to the following conclusions:

the adopted scenario of the growth of nuclear power can be realized without significant expansion of uranium produc-

tion approximately up to 20,000 tons per year and uranium enrichment plants for production of fuel for thermal reactors with

consumption of approximately one-half of known (2 million tons) uranium resources;

the deficiency of plutonium for fast reactors with low breeding rate can be made up by using weakly enriched uranium

(2-4%) with a small increase in the demand for uranium and, possibly, by using military stores of plutonium;

excess plutonium appears in the period following the one considered and this will make it possible to reduce the

consumption of natural uranium; and,

at the beginning of the 21st century it will be necessary to build a plant, having a capacity of -~2000 tons per year, for

chemical reprocessing of fuel from thermal reactors. The production work of the fuel cycle (reprocessing, preparation of fuel,

holding of wastes) for the new-generation nuclear power plants will be performed at the plants.

The consideration of fast reactors here as the basis for large-scale nuclear power reflects the fact that such reactors are

preferable for the fuel balance and for achieving inherent safety. But we do not yet have a fast reactor whose possibilities are

fully realized; concepts of thermal reactors capable of providing the required fuel balance and safety must also be investigated.

REQUIREMENTS FOR NUCLEAR TECHNOLOGY WITH INHERENT SAFETY

Modern safety requirements and standards were based on the experience of traditional nuclear technology, primarily

light-water reactors. The requirements for the new nuclear technology can now be formulated only in a general form and will be

refined and adjusted as experience accumulates. In their most general form, they consist of eliminating accidents leading to

inadmissible radiation emissions. All possible situations involving equipment malfunction, errors made by personnel, or external

293

TABLE 1. Measures for Eliminating or Reducing the Consequences of Some Accidents

No. Class of accident Possible measures for eliminating the accident

1 2 3

i.

2.

3.

5.

6.

7.

8.

9.

I0.

Runaway on prompt neutrons: accident or control error

deformation of the active zone

accidental change in the composition of the active zone

formation of secondary critical mass

Damage to the active zone

Loss of coolant: leak in or damage to the first loop, boiling of coolant

Loss of cooling of the active zone: blocking of flow through fuel assembly; boiling of coolant, stoppage of pumps

Blockage of the coolant circulation channel

Loss of cooling from the second loop or means for removing residual heat

Other accidents in which the tem- perature, loads, and pressures reach levels which are critical for the fuel, coolant, and other components: equipment malfunction

control errors

Fires and explosions:

accidental contact of fuel, coolant, and moderator with air, water, or steam; formation of hy- drogen in dangerous con- centrations

steam explosion

Accidents in transportation, reproeessing, fabrication, and storage of fuel and radio- active wastes

Spreading of radioactive wastes from the storage location: damage to engineered structures in burial grounds, migration

External actions: natural (earthquakes, etc.) terrorism, rocket attack (nonnuclear)

Total reactivity margin gk < ~ ; Akbu < ~; active-zone breeding ratio = i; depleting absorber (Gd); frequent over- loads; elimination of poisoning (fast reactor, circulating fuel, eta.)

Construction of the active zone elimi- nating increase in reactivity with Ak > ~ accompanying deformation of the zone

Void and other effects ~k < ~; elimi- nation of boiling, entry of vapor, gas, etc. in dangerous quantities into the active zone

Temperature and other margins; elimina- tion or low rate of compactio n of fuel; low enrichment of fuel; depleting absorbers

Large margins for the determing para- meters up to the limiting values; low energy margin, etc.

Low pressure, limitation of coolant leakage

Rejection of dense casings for fuel assem- blies; large margins up to boiling; high level of natural circulation of the coolant; self-regulation of the reaction with feedbacks; thermal inertia of the loop

Several cooling channels, elimination of freezing of the heat exchanger, elimina- tion of dumping of cold water

Reduction of reactor power due to feed- backs, thermal inertia, prolonged passive shut-down cooling with water and air, including through the reac- tor housing and reactor pit

Same measures as in 3) and 4); large margins up to critical values of parameters

Large margins up to critical values of the parameters

Simplification of control with maximum (total) automation

Elimination of combustible materials; intermediate loop

Elimination of hydrogen formation in dangerous quantities due to radiolysis and chemical reactions

Intermediate loop; rupture of membranes for dumping steam and reducing pressure; hydraulic scheme preventing damage to the active zone and leakage of steam in dangerous quantities into the active zone

Closure of nuclear fuel cycle at the nuclear power plant, institution of saftey measures

Return of actinides into reactors and burn-up of actinides

Holding of wastes in maintained storage areas, decay to the activity level of natural uranium. Radiation equivalent storage of radioactive wastes and physicochemical forms of wastes so as to prevent migration

Engineering methods of shielding Burial of radiatively dangerous objects

294

natural or other perturbations are considered. In order to exclude from analysis any situation it is necessary to prove that this

situation is prohibited by natural laws, technological possibilities, and human capabilities. If such proof is available, these

situations are not taken into account in the designs and in justifying the safety of the designs. The word "elimination" is under-

stood deterministically in all cases, except, perhaps, separate chains of events, whose probability is negligibly small. This probabil-

ity is taken to be 10 -8 reactor-years, if its calculation is reliable or is reliably known to be maximum. Table 1 gives a list of

classes of accidents occurring at nuclear power plants and in the handling of radioactive wastes as well as possible measures for

eliminating such accidents. Protective devices - both active and passive with indirect action - having limited reliability are

neglected.

The indicated measures are, in principle, simple and well known, and many of them are employed in present-day nuclear

technology. The problem of developing a new nuclear technology consists of eliminating not some but all dangerous accidents.

Other radiation safety measures, besides those indicated above, must also be adopted:

further reduction of the dose loads on personnel, automation of maintenance and repair work and dismantling of

equipment;

reduction of regular radioactive emissions and reduction of the volume of wastes with low and medium activity by at

least an order of magnitude;

reduction of radioactivity of wastes produced in the mining of uranium and coextraction of long-lived products of

uranium decay (thorium, radium, etc.), and reduction of uranium railings to a minimum; and;

utilization of useful radionuclides from wastes (especially cesium and strontium).

The new nuclear technology must meet the following general requirements:

the cost of energy production must be comparable to that of modern light-water reactors;

the specific demand for uranium must be 5-10 times lower than in present-day reactors;

the electrical efficiency must be of the order of 40%;

dispossessed lands must be reduced, thermal emissions must be reduced below that of modern nuclear power plants, and

waste heat from nuclear power plants must be utilized;

designs must take into account the requirements for dismantling of reactors and renovation of nuclear power plants, and

reactor lifetime must be increased to 50-60 years; and,

every nuclear power plant must have a center for teaching and training of personnel and for providing public informa-

tion, education, and instruction of school children.

EXAMPLE OF A REACTOR WITH INHERENT SAFETY

Inherent safety can be achieved without substantially exceeding the limits of the technology which has been assimilated

in reactor practice. This is illustrated by the example of a fast reactor with lead as the coolant, proposed several years ago at the

I. V. Kurchatov Institute of Atomic Energy and studied at the conceptual level by a group of specialists from NIKIt~T, Special

Office of Construction "Gidropress," Ft~I, VNIINM ira. A. A. Bochvara, TsNIIKM, VNIITF, PNITI, and the Central Scien-

tific-Research Institute of Machine-Building Technology. The investigations showed that the development of such a reactor can

be based on the technology, materials, knowledge, and experience accumulated for fast reactors and reactors cooled with the

heavy liquid metal PbBi, which is similar to lead. For this reason, it can be built within a limited time (10-12 years) and form the

foundation for the development of large-scale nuclear power production.

Reactors with electric power capacity of 300-1000 mW and two- and three-loop schemes using both dense U N - P u N fuel

and a heterogeneous oxide-carbide composition, which make it possible to achieve a breeding ratio of --1.3, active-zone breeding

ratio -1 , and reactivity effect Ak </3, were considered. The low moderation and absorption of neutrons by lead make it possible

to increase sharply, as compared with sodium, the volume ratio of coolant and fuel (approximately from 0.8 to 2.5), and this

reduces the lead velocity (2 m/sec), the power required to pump the lead, and simultaneously the heating (--110 ° C), and it gives

a high level of natural circulation (15-20% of the nominal circulation). With initial lead temperature of 420°C (the melting

point is 327°C) the maximum temperature (hot point) of the casings of the fuel cells is less than 650°C, and the maximum

temperature on the pipes of the stream generator is 530°C, which makes it possible to use standard steel. Experiments per-

formed on loops with lead (so far a total of 5000 h) using the anticorrosion technology assimilated for PbBi show that the

corrosion problem can be solved in this case also.

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One of the characteristic features of lead-cooled fast reactors is the low power effect of the reactivity: 0.15%. This not

only makes it possible to limit the total reactivity margin to values not exceeding the effective fraction of delayed neutrons, but

it also makes it possible to employ for self-regulation of the reactor other negative effects of reactivity, which are small in

absolute magnitude. It is important that these effects also depend nonlinearly on the temperature and other parameters of the

active zone, such that they would have a much stronger stabilizing effect when the determining reactor parameters exceed

admissible limits.

Hardening of the lead in the steam generator as a result of deviations from the regular cooling regime in the second

loop can be prevented by increasing the temperature of the feed water up to 350°C and installing buffer vessels in front of the

steam generator. This corresponds to transcritical water pressure and net efficiency >40%. A cycle at lower pressure was also

considered for a three-loop scheme, but there are significant advantages to the simplicity of the two-loop scheme.

The chemical inertness of lead with respect to water and air makes it possible to do away with the intermediate loop and

the containment structure, which are required for reactors with sodium, as well to simplify the steam generator (control system

and leak protection system) and the emergency shut-down cooling system, in particular, by using also for a high-power reactor

highly reliable passive shut down cooling with water and air through the reactor pit. Shut-down cooling is also maintained in the

case of rupture of the containment structure and even if cracks appear in the pit (solidification of lead). Burning of the coolant

in the cases when the loop ruptures is eliminated.

The pressure of a column of lead at the level of the active zone (exceeding 1 MPa) and the vertical pressure drop

prevent dangerous volumes of gas or steam from entering the active zone. The margin up to boiling of lead (the boiling point is

1740°C as compared with 900°C for sodium), expressed in units of the heating, is equal to about 10 instead of 1.5-2 for sodium.

This, together with the large margins up to melting of the fuel, destruction of the fuel casings (owing to external pressure, they

are unloaded, cr = 2 kg/mm2), natural circulation, and self-regulation with feedbacks, simplify the reactor control system, and this

creates the prerequisites for automating the reactor and eliminating accidents caused by operator error. The requirements on the

construction of the reactor building and the fuel reloading systems are also reduced; this, combined with the other improvements

described above and the increased safety, creates the prerequisites for reducing the cost of nuclear power plants with lead

coolant below that of a sodium fast reactor.

Switching from sodium to lead reduces the energy intensiveness, the increase in volume of the active zone, the plutoni-

um load (more than 4 tons/GW), and the doubling time (T 2 > 20 yr with an external fuel cycle of about three years). At the

present time no one is counting on high rates of growth of energy, including nuclear energy, while a decrease in energy intensity

is only good for safety and has virtually no effect on economics.

Lead is not activated much by neutrons. This, together with corresponding removal of impurities from the lead, simplify

maintenance and makes possible repeated use with no increase in radioactive wastes after a reactor is dismantled. Reducing the

penetrating fluxes of fast neutrons, lead decreases activation of and radiation damage to the structures in the reactor and pit; this

prolongs reactor life reactor and makes it simpler to dismantle and renovate the reactor, and it reduces the volumes of radioac-

tive wastes. Finally, as in any fast reactor, here the actinides, including also 238U, can be efficiently burned.

It is evident even from the qualitative discussion of the results of the investigations that the use of lead opens up,

primarily thanks to its chemical inertness and high boiling point, the road to a nuclear technology that systematically implements

the principle of inherent safety. But this must be confirmed by detailed calculations and experiments at the next stages of design

and in the operation of the reactor. In this respect the proposition made at VNIIFT to build an experimental reactor on the

Semipalatinsk test area for perfecting the reactor and demonstrating its qualities, including stability with respect to specially

provoked worst-case accidents, is attractive.

The example considered above is probably not the only possible approach to the ideal of inherent safety.

Once again, nuclear power needs, as it did 30-40 years ago, fresh concepts and competition of ideas. This is just as

necessary as work on improvement of traditional types of reactors, and it should not be interpreted by specialists as interference

in their work.

Here, however, we encounter a dramatic contradiction: no country, not even the richest one, can develop several designs

of this scale. The only way out is to develop a new inherently safe nuclear technology by the combined efforts of the nuclear

countries which are equally interested in it. Russia, as the successor of the USSR, is one of the two countries with the most

powerful nuclear potential and has extensive and in many ways unique experience. We are responsible for Chernobyl and we are

suffering most acutely the problems of nuclear safety. It is thus justifiable and natural for our country to take the initiative in the

development of the safest possible nuclear technology.

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