Plutonium, weapons grade

The recycle weapons fuel cycle rehes on the reservoir of SWUs and yellow cake equivalents represented by the fissile materials in decommissioned nuclear weapons. This variation impacts the prereactor portion of the fuel cycle. The post-reactor portion can be either classical or throwaway. Because the avadabihty of weapons-grade fissile material for use as an energy source is a relatively recent phenomenon, it has not been fully implemented. As of early 1995 the United States had purchased highly enriched uranium from Russia, and France had initiated a modification and expansion of the breeder program to use plutonium as the primary fuel (3). AH U.S. reactor manufacturers were working on designs to use weapons-grade plutonium as fuel. 

Much of the world s separated plutonium has been used for nuclear weapons (Table 1). It is probable that 5 kg or less of Pu is used in most of the fission, fusion, and thermonuclear-boosted fission weapons (2). Weapons-grade plutonium requires a content of >95 wt% Pu for maximum efficiency. Much plutonium does not have this purity. 

Cost and Value of Plutonium. The cost of building all U.S. nuclear weapons has been estimated as 378 biUion in 1995 dollars (24). If half of this sum is attributed to U.S. weapons-grade plutonium production (- lOOt), the cost is 1.9 x 10 /kg of weapons-grade Pu. Some nuclear weapons materials (Be, enriched U, Pu) also have value as a clandestine or terrorist commodity. The economic value of reactor-grade plutonium as a fuel for electric power-producing reactors has depended in the past on the economic value of pure 235u... 

Now that much of the world has agreed to nuclear disarmament, scientists and world leaders are searching for uses for the surplus weapons-grade plutonium. Instead of pursuing disposal options, one option is the use of mixed-oxide (MOX) nuclear fuel. 

Other options for eliminating weapons-grade plutonium arc to seal it permanently in solid radioactive waste and dispose of it in waste repositories, and to use the plutonium to fuel fast neutron reactors (without reprocessing the plutonium into a MOX fuel). 

Irradiated Fuel A historically important and continuing mission at the Hanford site is to chemically process irradiated reactor fuel to recover and purify weapons-grade plutonium. Over the last 40 years, or so, several processes and plants— Bismuth Phosphate, REDOX, and PUREX—have been operated to accomplish this mission. Presently, only the Hanford PUREX Plant is operational, and although it has not been operated since the fall of 1972, it is scheduled to start up in the early 1980 s to process stored and currently produced Hanford -Reactor fuel. Of nine plutonium-production reactors built at the Hanford site, only the N-Reactor is still operating. 

Weapons-grade fissionable material (U-233) is harder to retrieve safely and clandestinely from the thorium reactor than plutonium is from the uranium breeder reactor. 

The plutonium fuel in a breeder reactor behaves differently than does uranium. Fast neutrons are required to split plutonium. For this reason water cannot be used in breeder reactors, as it moderates the neutrons. Liquid sodium is typically used in breeder reactors, and the term liquid metal fast breeder reactor (LMFBR) is used to describe it. One of the controversies associated with the breeder reactor is the production of weapon-grade plutonium and nuclear arms proliferation. 

Even when the analysis is being performed splendidly, the limitation of any measurement due to measurement uncertainty always leads to some doubt about the result. See chapter 6 for an example of uncertainty concerning the amount of weapons-grade plutonium in the world. 

Six plutonium containing particles stemming from soil (Marshall Island) were characterized by SIMS, SEM-EDX-WDX and sychrotron radiation by Jernstrom et al. AU the particles were identified as nuclear fuel fragments of exploded weapons components. Since they contained plutonium with a low °Pu/ Pu atomic ratio (less than 0.065), which corresponds to weapons grade plutonium or a detonation with low fission yield, the particles were identified as originating from the safety test and low yield tests conducted on Runit Island. ... 

Diakov, Anatoli S., The Cessation of Production of Weapons-Grade Plutonium in Russia, Science Global Security, Vol. 5, No. 1, 1994, pp. 33-35. 

Nuclear weapon— A bomb or other explosive that derives it explosive force from the release of nuclear energy. PlutoniumA heavy, rare natural element that undergoes fission in a nuclear bomb. It is produced artificially by bombarding uranium-238 with neutrons. The addition of one neutron to the nucleus of uranium-238 changes it into plutonium-239 which is called "weapons grade plutonium," the most efficient form for making weapons. 

Weapons-grade plutonium, dispersed at military accidents such as Thule in 1968 or as non-fissioned weapon particles after detonation of a Pu-bomb can be characterized by high Pu content relative to the other Pu-isotopes, while accidentally dispersed Pu from the previously widely used nuclear-powered satellites are characterized by high Pu content." The ratio of americium-241 to plutonium isotopes (as " Am is formed by the decay of Pu) is proportional to the initial " Pu concentration, thus it can also be used as an indicator to assess the origin of contamination. However, in most cases, as several sources may contribute to the transuranics content in environmental samples, mixing models applying several isotope ratios are required to assess the origin of possible contamination sources. 

The isotopic ratios of the investigated samples are shown in Figure 3-6. Typical isotope ratios of reactor-grade plutonium (Reactor GP ), weapons-grade plutonium (Weapon GP ) and global fallout values of the Northern Hemisphere" are also indicated. Note that Pu/ Pu and " Am/ Pu ratios are highly dependant on the decay time, while isotope ratios in reactor-grade plutonium depend on reactor-type and bum-up. ... 

Weapons-grade plutonium. This plutonium is 90% or more plutonium-239, the most suitable isotope for nuclear explosive. 

Separated reactor-grade plutonium. This plutonium has been produced as a by-product of commercial nuclear power plants, and normally contains much less than 90% plutonium-239. Reactor-grade plutonium can also be used to make nuclear explosives, but is much less suitable for this purpose than is weapons-grade plutonium. 

The primary use for plutonium (Pu) is in nuclear power reactors, nuclear weapons, and radioisotopic thermoelectric generators (RTGs). Pu is formed as a by-product in nuclear reactors when uranium nuclei absorb neutrons. Most of this Pu is burned (fissioned) in place, but a significant fraction remains in the spent nuclear fuel. The primary plutonium isotope formed in reactors is the fissile Pu-239, which has a half-life of 24 400 years. In some nuclear programs (in Europe and Japan), Pu is recovered and blended with uranium (U) for reuse as a nuclear fuel. Since Pu and U are in oxide form, this blend is called mixed oxide or MOX fuel. Plutonium used in nuclear weapons ( weapons-grade ) is metallic in form and made up primarily (>92%) of fissile Pu-239. The alpha decay of Pu-238 (half-life = 86 years) provides a heat source in RTGs, which are long-lived batteries used in some spacecraft, cardiac pacemakers, and other applications. 

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