Nuclear warheads, plutonium

We all share a national security interest in working with Russia to assure that material removed from nuclear warheads is removed from weapons applications. Of course, there is no simple blending operation that will convert weapons plutonium into material that cannot be used for weapons without major effort... 

An amount of 3.7 kg plutonium is also reported as typical for pits in U.S. and USSR devices. Corroborating evidence is given in a Russian report on early tests (Dubasov et al., 1995) for example, which describes many devices with 3-4 kg of plutonium, and in press reports that refer to nearly 3 kg of plutonium in each of 32 USSR nuclear warheads in a sunken submarine east of Bermuda. Similar values have been reported for the two torpedoes that sank with the Russian submarine Komsomolets north of Norway in 1989, and for the U.S. weapons involved in the air crashes at Thule and Palomares in the 1960s. 

In March, 1997, the fourth workshop was held in Amarillo, Texas, with the broadened topic of nuclear materials safety management. This subject was considered in the context of the entire nuclear fuel cycle. The focus was on the non-reactor segments with emphasis on the disposition of weapons plutonium from disassembled nuclear warheads. It was recognized that an accident in either country could considerably delay and possibly disrupt the efforts to disposition fissile weapons... 

The proposed program has two major components (1) nuclear facility (Lab-to-Lab or site-to-site) technical projects and training initiatives and (2) academic exchanges, curriculum and degree program development, and joint research to provide an enhanced safety focus. The objective of the NMS program is to improve the operational safety in the nuclear materials facilities and operations used for the storage and disposition of excess HEU and plutonium (Pu) from dismantled nuclear warheads and thereby enhance public and worker safety. 

No one knows for certain how much plutonium has been made—probably in excess of several million kilograms. Most of this amount has been used to make nuclear warheads by the United States, the former Soviet Union, and the other nuclear nations including the United Kingdom, France, China, Israel, India, and North Korea. 

Disassembly and disposal of nuclear weapons has also led to environmental contantination. The primary site for the disassembly of U.S. nuclear weapons is the Ptmtex Plant, located 17 miles northeast of Amarillo in the Texas panhandle. The United States has dismantled about 60,000 nuclear warheads since the 1940s. More than 12,000 plutonimn pits (hollow shells of plutonium encased in steel or other metal that are essential components of nuclear weapons) are stored in containers at Pantex. Plutonium, an element first produced in Manhattan Project reactors in 1942, has a half-Ufe of 24,000 years. 

At present there are large stocks of plutonium in several countries. These have arisen from two sources. Firstly commercial thermal power reactors have produced large amounts of plutonium. In some countries this plutonium lies in the unreprocessed fuel in spent fuel stores in others, where the spent fuel has been reprocessed, it has been separated and stored. Secondly significant quantities of plutonium have been released by the decommissioning of nuclear weapons. The relaxation of the "cold war" in the last decade has seen a substantial reduction in the stockpiles of nuclear warheads held by nuclear weapons states, particularly the USA and the former USSR. The fissile material from these warheads is now also in store. 

The critical mass of plutonium-239 necessary to fashion a nuclear warhead is less than the critical mass of uranium-235 that is necessary therefore, smaller warheads can be made. 

One of the many problems of nuclear power is the availability of fuel uranium-235 reserves are only about 0.7% those of the nonfissile uranium-238, and the separation of the isotopes is costly (Section 17.12). One solution is to synthesize fissile nuclides from other elements. In a breeder reactor, a reactor that is used to create nuclear fuel, the neutrons are not moderated. Their high speeds result in the formation of not only uranium-235 but also some fissile plutonium-239, which can be used as fuel (or for warheads). However, breeder reactors are more hazardous to operate than nuclear power plants. They run very hot, and the fast reactions require more careful control than a reactor used for nuclear power generation. Because of safety concerns, their use is still controversial. 

The partial elimination of nuclear weapons has created an additional disposal problem. The thousands of weapons being dismantled contain thousands of kilograms of plutonium. Some of it is suitable for use in nuclear power plants. However, the less useful low-grade plutonium must be disposed of in a way that would not allow its use in weapons. One strategy being investigated is first to convert the plutonium into a hydride, which would allow its separation from other elements in the warhead or bomb. The hydride would then be converted to an oxide, which could be incorporated into a ceramic material containing neutron absorbers to stabilize the material further. 

In addition to the amounts of civil plutonium, plutonium is being released from dismantled warheads. Under the START-I and -II Treaties, many thousands of US and Russian nuclear war-heads are slated to be retired within the next decade. As a result, at least 50 tonnes of plutonium from each side are expected to be removed from military programmes. 

The test programme, carried out with American co-operation at Nevada, is called for not only in its own right but also in order to maintain our scientific collaboration with the Americans in nuclear weapons development... Normally these tests are research tests but last year one of them was an experiment to determine whether a useful saving could be made in the amount of plutonium to be used in the Polaris warheads. .. 

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