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Stopping the Production of Fissile Materials for Weapons

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Stopping the Production of Fissile Materials for Weapons SCIENTIFIC Established 1845 AME RI CAN September 1985 Stopping the Production of Fissile Materials for Weapons 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 nu- clear 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 I NEUTRON I I I I I 'it I I / I I I FISSION / PRODUCTS I NEUTRON I ( I I / I I I / 39 I / / f:}~ I / 1/4 ~ "~ 0!J I / ELECTRON NEUTRINO I Np239~ I r? I "- /'/5 "~ e~ ELECTRON Q NEUTRINO 1/ ~ "~ V ~ 239~ B" . je../ ~ "~ 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 <l: actor, completed in 1964 at Hanford, 5: a: w => which generates electric power as well > 0 as producing plutonium.
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