Stopping the Production of Fissile Materials for Weapons

SCIENTIFIC Established 1845 AME RI CAN September 1985

A halt in producing the essential ingredients of nuclear weapons would be easy to verify. It could therefore contribute to tighter control over the amount of weaponry in the superpowers' arsenals

Agreements on nuclear-arms con- Since fissile material is an essential for a cutoff were often linked to ef- ..n. trol based, like SALT II, on ingredient in all nuclear weapons, a forts to persuade nonnuclear states to verifiable counts of missiles and cutoff would place an ultimate limit support the Nonproliferation Treaty. other vehicles for delivering nuclear on the number of weapons that could That treaty came into force in 1970 weapons may soon be impossible to be prod uced.Proposals for a cutoff and has since been signed by more devise. The vulnerability of strategic of production of fissile materials have than 100 states.That the U.S. and weapons that has come with preci- therefore been on the international the U.S.S.R., the nations that devised sion guidance has stimulated a trend arms-control agenda virtually since the treaty, had not brought their arms toward small, mobile ballistic missiles, the invention of nuclear weapons. race under control resulted in increas- such as the proposed U.S. Midgetman, Between 1956and 1969 a cutoff was ingly strong expressions of dissatisfac- which may be exceptionally difficult repeatedly put forward by the U.S. as tion with the treaty on the part of the to detect. Cruise missiles and many of a separate arms-control proposal. The nonnuclear states at the review con- the other new weapon systems have Soviet responses were not encourag- ferences of 1975 and 1980. The issue been designed to carry either conven- ing, perhaps because at that time the can be expected to cause even greater tional or nuclear explosives, impeding U.S.S.R. had considerably fewer nu- difficulty at the third review confer- an accurate count of deliverable nuclear warheads than the U.S. By the ence, which will run from late August clear warheads. 1980's the two stockpiles were com- through mid-September of this year. Clearly a new approach is needed parable, however, and in 1982 Sovi- A superpower agreement to cut off to complement the delivery-vehicle et Foreign Minister Andrei Gromy- the prod uction of fissile materials for counting rules. We suggest a new look ko suggested that the "cessation of nuclear weapons would thus be in the at one of the oldest proposals for re- production of fissionable materials interests of nonproliferation as well as straining the growth of nuclear arse- for manufacturing nuclear weapons" superpower arms control. The purpose nals: an agreement to cut off any fur- could be made one of the initial stages of this article is to provide some of the ther prod uction of the fissile materials of a nuclear disarmament program. technical background req uired for a that are necessary for the construc- A cutoff would be a natural part of constructive public discussion about tion of nuclear weapons. any larger package of mutually re- the feasibility of a cutoff. Every nuclear weapon contains at inforcing arms-control and disarma- least a few kilograms of chain-reacting ment proposals. For example, to be art of the basis for any such discus- fissile material. Fission of about one meaningful any agreement to freeze or P sion is a description of the nature kilogram of uranium 235 demolished reduce the number of warheads would and availability of the fissile materials Hiroshima. Nagasaki was leveled by have to contain assurances that new themselves. Uranium 235 is the only the fission of one kilogram of plutoni- warheads were not being prod uced. fissile isotope that exists naturally in um 239 in another weapon.The devel- A cutoff would serve another pur- more than trace quantities. It is not opment of thermonuclear, or "hydro- pose as well. Continued production of found in a form that can be used di- gen," bombs in the early 1950's did fissile materials for nuclear weapons rectly in manufacturing nuclear weap- not eliminate the need for fissile ma- by the superpowers is severely under- ons, however. Only. 7 percent of a typ- terials, because such weapons require mining their efforts to discourage com- ical sample of natural uranium is U- a fission explosion to ignite the hydro- parable activities by other nations. In 235. The other 99.3 percent is uranium gen fusion reaction. the 1950's and 1960's U.S. proposals 238, a heavier isotope that cannot sus- SRlJRNNRH RIlJER PLRNT "N RUGUST 25.1981

THERMAL INFRARED IMAGES would help to ensure compli- ange; the cooler background is rendered in blue and gray. The ance with a ban on production of fissile materials for weapons. The streams are about 100 meters wide until they flow into a swamp, images shown here reveal discharges of hot water from two U.S. where one spreads out into a delta 1,500 meters wide. These images plutonium-production reactors at Savannah River, S.C. In this were made from an airplane flying at an altitude of 1.2 kilometers. false·color representation the streams of hot water are red and or· Similar images made from satellites could detect hidden reactors. tain a chain reaction. To make a practi- stockpile arms beyond our needs or bombarded with neutrons in a nuclear cal weapon the uranium must be en- seek an excess of military power that reactor [see illustration below]. Plutoni- riched to contain at least 20 percent U- could be provocative as well as waste- um-production reactors are basically 235. U.S. weapon-grade uranium con- ful."Since then the U.S. uranium-en- no different from nuclear-power reac- tains more than 90 percent U-235. richment complex has produced main- tors, except that they are operated to One technology through which this ly the "low-enriched" uranium that is yield plutonium containing more than level of enrichment is achieved was used as fuel in most nuclear-power re- 93 percent of the isotope Pu-239. Such developed early in the history of the actors. Although highly enrich<:d ura- so-called weapon-grade plutonium is U.S. nuclear-weapon program. Called nium has been produced for use in not the only grade from which weap- gaseous diffusion, it involves diffusing naval reactors, research reactors, some ons can be made, but it is more desir- uranium hexafluoride (a gaseous, ura- plutonium-production reactors and a able than grades that contain high- nium-carrying compound) through a few power reactors, the U.S. has add- er percentages of heavier plutonium succession of thousands of porous bar- ed no highly enriched uranium to its isotopes. Pu-239 is preferred over U- riers. In the 1940's and 1950's the U.S. nuclear-weapon stockpile since 1964. 235 for modern, compact nuclear war- built three diffusion enrichment plants All the weapon-grade uranium used heads because a much smaller quan- in Tennessee~ Kentucky and Ohio. In in new warheads has come from the tity-only a few kilograms-is need- the early 1960's, at the peak of U.S. stockpile produced before 1964 or has ed to produce a fission explosion. prod uction, these facilities prod uced been recycled from retired weapons. During most of the period between about 80 tonnes (metric tons) of weap- Recently, however, because of the in- 1955 and 1964 the U.S. had 13 reactors on-grade uranium each year-enough creased demands associated with its producing plutonium.Eight reactors for the production of thousands of nu- nuclear-weapon buildup, the Reagan were at the Hanford site, near Rich- clear weapons. Administration has proposed resum- land, Wash., and five were at the Sa- By 1964 the U.S. had such a large ing the production of highly enriched vannah River site, near Aiken, S.C. To- supply of fissile material that President uranium for weapons. gether they produced more than six Lyndon B. Johnson decided to cut back Another fissile isotope, plutonium tonnes of plutonium each year, enough prod uctiori, explaining that "even in 239, is also used in nuclear weapons. for more than 1,000 warheads. the absence of agreement we must not To make Pu-239, a sample of U-238 is In the eight-year period following

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FISSION CHAIN REACTION produces plutonium 239 from ura- U-235 atom (2), sustaining the reaction. Another is absorbed by an nium 235. When an atom of U-235 is bombarded with a neutron atom of U-238, converting it into U-239 (3). The U-239 decays into (1), it yields intermediate-weight atoms, called fission products, and neptunium 239 by emitting an electron and a neutrino (4). Pu-239 two or three additional neutrons. One neutron bombards another is created when the Np-239 emits an electron and a neutrino (5). President Johnson's decision to cut 20 2 back U.S. production all the Hanford i=' z reactors were shut down and two of w 0 the five production reactors at Savan- (/) a: t: w nah River were mothballed. The other z e::. => 15 1.5 three have remained in operation, :.::: ::?: a: => along with a newer "dual purpose" re- 0 Z which generates electric power as well > 0 as producing plutonium. ~ w a: 10 I- Because of the Administration's ...wJ if Cl. plan to produce more than 10,000 W W (/) 0 LL new compact nuclear warheads, sev- LL 0 0 eral projects have been initiated that (/) I- would increase the rate at which the Z Z 0 5 0.5 w :::i...J I- U.S. stockpile of weapon-grade plu- Z ~ 0 tonium grows. These projects include 0 restarting one of the mothballed Sa- vannah River reactors and converting ~ into weapon-grade plutonium some of the 17 tons of fuel-grade and re- 1960 1965 1970 actor-grade plutonium owned by the FISCAL YEAR Department of Energy. HISTORY OF U.S. URANIUM ENRICHMENT helps to provide an estimate of the How much fissile material is in amount of fissile material in the U.S. stockpile. Enrichment activity (black) is measured in the U.S. and U.S.S.R. stockpiles? "separative work units" (SWU's). The number of SWU's is roughly proportional to the amount of energy spent sorting U-235 from U-238. These figures, taken with the percent- Enough information is publicly avail- age of the "depleted uranium" (material left over after sorting out most of the U-235) that able to allow reasonable estimates of was U-235 (color), suggest the U.S. could have produced about 750 tonnes (metric tons) of the U.S. stockpile, but public informa- highly enriched uranium before the 1964 cutoff of production. The increase in enrichment tion about the Soviet weapon-produc- activity that began in the early 1970's was due not to production of highly enriched urani- tion complex is much sparser. It allows um for weapons but to increased production of low-enriched uranium for power plants. only a rough estimate of the size of their plutonium stockpile and yields no clues to the size of their stockpile of output is directly proportional to the been made by Wolfgang Weiss, Al- weapon-grade uranium. amount of U-235 that has been fis- bert Sittkus, Helmut Stockburger and According to the records of the De- sioned in these reactors, which in turn Hartmut Sartorius of the Max Plank partment of Energy, the U.S. has since is directly proportional to the quanti- Institute for Nuclear Physics in Frei- 1944 bought approximately 250,000 ty of plutonium they have produced. berg. By estimating the amount of tonnes of natural uranium, containing (Approximately .9 kilogram of pluto- Kr-85 released in weapon tests world- about 1,800 tonnes of U-235. The best nium is produced for each kilogram of wide and in fuel reprocessing outside way to estimate how much of this U- U-235 that is fissioned.) On this ba- the U.S.S.R. and then subtracting the 235 went into weapons is to examine sis we conclude that the U.S. weapon amount from the total amount of Kr- the Government reports that list the stockpile contains about 100 tonnes of 85 released into the atmosphere, it is annual amounts of "separative work," plutonium. Once again Cochran and possible to estimate how much has or enrichment, done in the U.S. urani- Hoenig have made a similar estimate. been released into the atmosphere by um-enrichment complex and the asso- Data relating to the amounts of plu- the U.S.S.R. [see illustration on page ciated percentages of U-235 that were tonium and highly enriched uranium 45]. By this method we estimate that left in the "depleted uranium" by- produced for weapons by the U.S.S.R. through 1984 the U.S.S.R. had re- product of the enrichment process. We have not been made available by that leased about as much Kr-85 into the estimate using these data that the U.S. government or by the U.S., but Soviet atmosphere as the U.S. If, as in the could have produced up to about 750 plutonium production can be gauged U.S., most of the Kr-85 was released tonnes of highly enriched uranium for from the amount of radioactive kryp- in reprocessing fuel from reactors that weapons prior to the 1964 cutoff of ton 85 that has accumulated in the produce plutonium, then the amounts production. After estimating the non- atmosphere. This isotope, which is of plutonium in the two coun-tries' weapon-related demands for uranium produced by fission, is released by fa- stockpiles, like their estimated num- enrichment through 1964 and subse- cilities that reprocess nuclear fuel. bers of nuclear warheads, are roughly quent demands for highly enriched Relatively small amounts are also re- comparable. The current rate of pluto- uranium, we conclude that there are leased by tests of nuclear weapons nium production in the U.S.S.R. ap- still at least 500 tonnes of weapon- and by leakage from reactor fuel. Be- pears to be considerably higher than grade uranium remaining in the U.S. cause it is chemically unreactive, Kr- that in the U.S., however. weapon stockpile. Thomas B. Coch- 85 accumulates in the atmosphere, ran and Milton M. Hoenig of the Nat- where its distribution is nearly uni- uppose the two superpowers agreed ural Resources Defense Council have form because of its long radioactive S to cut off production of fissile ma- reached a similar conclusion. half-life (approximately 11 years). terials for weapons. Could one country The amount of plutonium in the Since about 1954 various groups adequately verify that the other had U.S. weapon stockpile can be estimat- of investigators throughout the world not violated the agreement? For the ed from data that have recently been have made periodic measurements of purpose of this discussion we shall de- released by the Department of Energy the atmospheric concentration of Kr- fine adequate verification as the ability on the heat outputs of its plutonium- 85. The most comprehensive and ac- to detect within a few years any set of production reactors since 1951. Heat curate published measurements have clandestine activities large enough to increase one of the superpower stock- ternational Atomic Energy Agency uranium is significant. Because the nu- piles at a rate greater than I percent (IAEA), which would use techniques clear arsenals of the superpowers are per year. This would be a significant similar to those it employs in safe- already huge, diversions of nuclear restraint; it represents a rate of pro- guarding fissile materials in states that material would have to be 1,000 times duction about one-tenth as large as have signed the Nonproliferation Trea- larger than that to have any poten- the peak production rates of the past. ty and have committed themselves to tial strategic significance. There is lit- The strategic significance of smaller not building nuclear weapons. tle doubt that the diversion of much violations would be so minor that it Indeed, as part of its campaign for less material could be detected. The is doubtful either superpower would the Nonproliferation Treaty the U.S. IAEA safeguards should be able to de- consider the gains to be worth the offered to put all its own nuclear facili- tect diversions of less than 1 percent of risks of detection. ties except those "with direct national the fissile material flowing through a For example, taking our estimates of security significance" under IAEA safe- . nation's nuclear-reactor fuel system. the U.S. stockpiles as a yardstick, a guards. An agreement between the In comparison, 5 percent of the flow growth rate of 1 percent per year cor- U.S. and the JAEA making it possible to through the U.S. nuclear-power sys- responds to production of about five implement the offer went into effect in tem or 15 percent of that through the tonnes of weapon-grade uranium or 1980. The Soviet Union made no simi- smaller Soviet system would have one tonne of plutonium.Undetected lar move until 1982, when Gromyko to be diverted before the diversion violations below this level would still announced that the U.S.S.R. would amounted to five tonnes of U-235 or provide the wherewithal to produce be willing to place some of its peace- one tonne of plutonium per year. hundreds of warheads per year and ful nuclear installations under the con- The task of the JAEA safeguards is to would therefore be quite significant in trol of the JAEA. A very limited initial confirm, within a specified accuracy, absolute terms, but with respect to agreement was concluded this March, that any fissile material delivered to the existing stockpiles such violations under which the IAEA will be able to or produced at a facility is either still would be insignificant. safeguard one of the two main classes there, has been fissioned or has been The problem of verifying a cutoff of Soviet power reactors. Unfortu- delivered to another safeguarded loca- can be divided into two subsidiary nately, however, the class of reactors tion. In this respect the problem of problems. The first is ensuring that sig- that was offered for safeguarding is not safeguards is similar to the problem of nificant quantities of fissile material the one that could most easily be oper- currency safeguards that challenges a are not diverted to weapons from legit- ated as dual-purpose reactors (like the bank inspector. Visiting IAEA inspec- imate activities; the second is ensuring Hanford reactor that produces both tors periodically check the consistency that there are no significant clandestine power and weapon-grade plutonium). between actual and reported invento- prod uction facilities. ries. Measurements of radiation are The U.S. has always assumed that a he JAEA safeguards are hundreds used along with other nondestructive cutoff agreement would include a sys- T of times more stringent than those measurements on randomly selected tem of oncsite inspections of facilities that would be required to verify a nuclear-fuel assemblies to check that that process fissile materials for pur- superpower cutoff agreement: they there has been no substitution of poses other than weapon production, are designed to detect within days or "counterfeit" fuel. in order to ensure that no significant months the diversion of enough mate- Where fissile material is in inactive amounts of material were being di- rial to make a single nuclear weapon. storage the JAEA simplifies its task by verted. Since about 1965 official U.S. The JAEA has specified that the diver- applying tamperproof seals to the con- statements have suggested that the in- sion of only eight kilograms of plutoni- tainers and storage vaults involved so spection could be assigned to the In- um or 25 kilograms of weapon-grade that their contents need not be checked on each visit. Storage areas that cannot be sealed are monitored for suspi- cious activities by tamperproof cam- ,eras. Systems have been developed that make it possible, if necessary, to monitor the pictures being collected (j) by such cameras remotely in real time. a: (2 10 The fuel cycle that is currently most () common in U.S. and U.S.S.R. pow-

nder a cutoff U-235 would still be U used as fuel not only in nuclear-power reactors but also in naval- TOTAL (FROM ATMOSPHERIC propulsion reactors. The U.S. and Kr85 CONCENTRATIONS) I the U.S.S.R. each have more than 120 100 ships propelled by nuclear reac- (jJ tors. U.S. naval reactors are fueled by w weapon-grade uranium and are cur- a: rently supplied with about five tonnes =:J 0« of U-23 5 per year. Since the total esti- ~ REMAINDER w (FROM U.S.S.R.) I mated shaft horsepower of the Soviet E- 80 trJ nuclear navy is about the same as that to of the U.S., and since Soviet ships are Z at sea a much smaller percentage of 12c.. >- the time, it is likely the Soviet navy's a: demand for U-235 is smaller. ~ Neither navy is likely to allow international inspectors in its ships or in 40 the facilities that produce fuel for naval reactors. One possible arrangement would be for the superpowers to agree on the amount of U-235 each would be allowed to produce for use in its naval reactors. Under this arrangement the U-235 would be produced entire- ly at safeguarded plants and an equivalent amount of irradiated enriched uranium would have to be turned in ATMOSPHERICKRYPTON 8S gives an indication of the size of the U.S.S.R. plutonium stockpile. This isotope is released primarily by nuclear-fuel reprocessing facilities and re- at another safeguarded facility within mains in the atmosphere because it is chemically unreactive. The upper curve, which is a certain period of time. These meas- based on historical measurements of atmospheric Kr-8S (corrected for radioactive decay), ures would prevent the cumulative di- shows the total amount of Kr-8S released to the atmosphere worldwide. The lower curves version of significant quantities of na- give the authors' estimates of the contributions to this total originating in weapon tests val U-235 for use in weapons. worldwide and in reprocessing facilities outside the U.S.S.R. The remainder (color) repre- The U.S. has about as many research sents an estimate of the amount of Kr-8S released by reprocessing facilities inside the reactors as it has naval power reactors, U.S.S.R. It is comparable to the amount released by those in the U.S. Most releases from but their total demand for U-235 is the U.S. and the U.S.S.R. were probably from facilities producing plutonium for weapons, about one-tenth as large. We have no suggesting that the superpowers' stockpiles of weapon plutonium are also comparable. reason to think the corresponding demand in the Soviet Union is much larger. This is a small flow of materi- Savannah River reactors. Such a reac- come possible to subject the exterior al (about half a tonne per year) com- tor, like any other, could be safe- of every structure on the earth's sur- pared with the amount that constitutes guarded against clandestine prod uc- face to detailed inspection. a significant violation. In any case, the tion of fissile materials for weapons. Today indications of the energy in- IAEA has developed thorough safe- tensity of hidden activities can be ob- guards to detect diversions from re- f legitimate reactors and their fuel tained as well, by telescopes that are search reactors. Icycles can be safeguarded against sensitive to the infrared radiation emit- The final class of reactors whose fuel significant diversion of materials to ted by warm surfaces. When the data cycles must be safeguarded are triti- nuclear weapons, what are the pros- from such satellite surveillance are um-production reactors. Tritium pro- pects of one side's successfully con- analyzed in combination with infor- vides the neutrons that initiate the fis- structing a clandestine production fa- mation culled from internal reports, sion chain reaction and "boost" the cility? Under early U.S. proposals for a from intercepted radio and microwave fission efficiencies in U.S. nuclear cutoff of production of fissile materi- transmission and from interviews with weapons. It is also the source of most als, each superpower would have de- emigres, the integrated product is stun- of the neutrons produced by the "neu- ployed roving teams of inspectors to ning. This has been demonstrated con- tron bomb." Tritium is produced by search the other's territory. That ap- vincingly in the Department of De- allowing lithium 6 to absorb neutrons proach was unacceptable to the Soviet fense's annual publication on Soviet in the same type of reactor that pro- Union. It was therefore highly signifi- military power. duces plutonium when U-238 is made cant when, in 1969, the U.S. complete- It is unlikely that either superpower to absorb neutrons. ly dropped the demand. What brought could conceal from such scrutiny the Because of its 12-year radioactive about such a major change in position? existence of a program large enough to half-life, tritium must be replenished Part of the answer is that surveil- produce one tonne of plutonium or even if stockpiles are frozen. This lance satellites had given the U.S. five tonnes of highly enriched urani- would not call for a very large-scale Government confidence that it could um per year. There would be many effort, however. An amount of triti- detect large-scale clandestine prod uc- opportunities to discover such a pro- um equal to that in the U.S. stockpile tion from space. Routine surveillance gram. For example, the construction could probably be maintained by a re- of the Soviet Union by satellites be- of plutonium-producing reactors and actor with the capacity of one of the gan in 1961, and by 1969 it had be- their associated fuel-reprocessing facilities would be the equivalent of mul- destine production program could be an amount is about eq ual to the heat tibillion-dollar enterprises. In view of supplied for years with uranium from generated by a U.S. city of 300,000 the many thousands of workers who a previously established stockpile. The people. It would be hard to dispose of would be involved, it would be ex- U.S. has built up a stockpile of hun- so much heat without detection-sen- tremely difficult to conceal the nature dreds of tonnes of U-235 in depleted, sors exist that can detect from space of an effort on this scale. natural and low-enriched uranium. the presence or absence of ceiling in- A great deal of uranium, rough- Similar stockpiles probably exist in the sulation in a single-family house. ly 1,000 tonnes of natural uranium, U.S.S.R. It is all too easy to imagine The illustration on page 41 shows a would be needed as well. Although this that a stockpile of uranium containing thermal infrared image, made from an is not a physically large amount of ma- up to perhaps 100 tonnes of U-235 airplane, of the outflow of hot water terial, it does correspond to a signifi- could be hidden before a cutoff agree- from the Savannah River production cant fraction of the projected uranium ment went into effect. reactors, each of which has an average flow in either of the superpowers' nu- Another way to detect clandestine heat output of about 1.5 million kilo- clear-power systems. It is likely that production plants would be to search watts each. Similar images could be ob- the diversion of so much newly mined for emissions characteristic of their tained at satellite altitudes. Although uranium would be difficult to hide, operation. The best example of such attempts could be made to reduce the particularly if uranium mills were sub- an emission is the enormous amount thermal infrared emissions from hot ject to some level of on-site safeguards. of heat generated by plutonium-pro- water by, for example, thoroughly duction reactors. A set of clandestine mixing it into a large river, the conceal- he detection of clandestine produc- reactors capable of producing one ment problem would be acute, and T t(on facilities through their associ- tonne of plutonium per year would the efforts at concealment themselves ated mining and milling activities has have an average output of about three would provide clues to the nature of limitations, however, because a clan- million kilowatts of waste heat. Such the enterprise. The least conspicuous facilities that are currently able to produce weapon- grade fissile materials are probably the so-called centrifuge enrichment plants. This technology, which is just coming into commercial use, involves spinning cylinders of uranium-carrying gas in centrifuges. Considerably fewer stages are needed in order to reach a given level of enrichment in a ceijtrifuge plant than in a diffusion planf. In addition centrifuge plants are smaller and consume less energy. The appearance of gas-centrifuge plants is much less distinctive than that of diffusion plants, and it might not be possible to identify them from satellite photographs alone. The larger intelligence effort would probably be able to identify them, however, by picking up indications of the enormous effort required to manufacture ------, and install the great number of centri- I I fuges needed to produce five tonnes I I of highly enriched uranium per year I I [see illustration on opposite page]. The Department of Energy recently TRITIUM- i PRODUCTION I announced that its future uranium- REACTORS t enrichment facilities would employ a new technique called laser isotope sep- I I aration. This technology exploits the I fact that the atomic energy levels of U- I I 235 and V-238 electrons are slightly I I different because of the difference in I the masses of the atoms' nuclei. To I _f------I separate the isotopes a set of lasers ___9 -?- ..JI are tuned to produce energy that can 81 DISPOSAL I be absorbed by U-235 atoms (each of which loses an electron in the process) but not by U-238. An electric field ACTIVITIES TOBE SAFEGUARDED to ensure compliance with a cutoff begin when then separates the charged U-235 ions uranium leaves the mill where uranium oxide is extracted from raw uranium ore (1). At a from the uncharged U-238 atoms. conversion'plant (2) the uranium oxide is converted into a gas (uranium fluoride) so that it can be enriched (3). Then it is converted back into an oxide or a metal (4) and fabricated An enrichment plant based on laser into reactor fuel (5). After it has been used (6) the spent fuel is stored at the reactor site isotope separation would be smaller (7). From there it can be shipped to a radioactive-waste depository (8) or to a reprocessing than a centrifuge plant; it would there- plant (9), where any fissile uranium and plutonium it contains can be recovered and recycled. fore be even more difficult to identify CENTRIFUGE ENRICHMENT PLANT enriches uranium by ment;; it also has a much less distinctive appearance. Nevertheless, passing it through a "cascade" of centrifuges. Each of the centri- construction o( a clandestine centrifuge enrichment plant could fuges shown (cylinders) is roughly the height of a person. This is the probably !J.e detected by a thorough intelligence effort. To produce least conspicuous type of uranium-enrichment facility now in com- five tonnes of' weapon-grade uranium each year (the quantity de- mercial use. It is smaller and consumes less energy than a diffusion fined by the authors as representing a significant violation of a cut- enrichment plant and requires considerably fewer stages of enrich- off agreement) would require approximately 100,000 centrifuges. from satellite photographs. Neverthe- prehensive Nuclear Test Ban Treaty grade plutonium would have to be dis- less, a laser enrichment plant capable in 1980. Systematic obstruction of ef- posed of with greater care, since there of producing five tonnes of weapon- forts to obtain answers to legitimate is no natural isotopic denaturant for grade uranium per year would still queries would, of course, bring into plutonium. One method would be to cost the equivalent of hundreds of question the continuation of the cut- use the plutonium as fuel in a relative- millions of dollars to construct and off agreement. ly few heavily safeguarded reactors would incorporate unusual, high-pow- The reward for successful conceal- operated in a "once through" mode ered, rapidly pulsed lasers. These fea- ment of a clandestine production pro- (that is, without reprocessing the fuel). tures and others would facilitate the gram would hardly be spectacular; it Ten large reactors could in this way detection of such a plant by the larger would be a small increase in the size of dispose of all the plutonium currently intelligence effort. a stockpile of fissile material that is in U.S. or Soviet weapons in a decade. Although each of the means of de- already unnecessarily large. Since the superpowers can probably tection we have discussed could in the- estimate each other's stockpiles of fis- ory be el uded, the clandestine prod uc- fthe superpoWers are able to reach sile materials reasonably well, there is tion of fissile materials would require I an agreement banning further pro- no obvious reason they could not, on that the construction and operation duction of fissile materials for nuclear the basis of these estimates, negotiate of all major facilities involved be con- weapons, it will be natural to try to red uctions of 50 percent or so in their cealed successfully for a period of sev- extend the ban to include the other weapon stockpiles. When stockpiles eral years. The detection of one suspi- states with nuclear-weapon capability had been reduced, small violations cious facility by any of the available and to persuade those states without would be more important, and so a means of surveillance and intelligence nuclear-weapon capability who have greater exchange of information and would threaten the entire enterprise. not signed the Nonproliferation Trea- more refined analyses would be neces- Ambiguous evidence of clandestine ty to do so. A verifiable production sary in order to lay the basis for fur- production activities could be brought cutoff would also lay the basis for veri- ther reduction agreements. to a body organized along the lines fiable reductions in the quantities of There is no reason, however, to de- of the Standing Consultative Commis- fissile materials already in the arsenals lay the actions that could be taken im- sion, which was originally established of the nuclear-weapon states. mediately. If the superpowers are will- to discuss questions concerning com- The obvious way to dispose of fissile ing to accept inspections and other pliance with the 1972 SALT I treaty. In materials would be to "burn" them in safeguards on their nuclear activities the absence of satisfactory explana- existing nuclear-power reactors. The that are not related to weapons, both tions on-site inspections could be re- weapon-grade uranium would be use- a cutoff in production of fissile mate- quested, as was agreed by the U.S., the less for nuclear weapons after it was rial for nuclear weapons and substan- U.S.S.R. and the u.K. in the case of diluted with depleted or natural urani- tial reductions in the quantities of fis- underground nuclear tests, before the um down to the level used in power-re- sile materials already in the stockpiles suspension of negotiations of a Com- actor fuel. The stockpiles of weapon- could be satisfactorily verified.