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164 | Section 4 Nuclear Weapons, Terrorism, and Nonproliferation Managing the NuclearWeapons Legacy Written by Michael R. Greenberg, based in part on an interview with David S. Kosson, with comments by Richard L. Garwin Background Tens of thousands of nuclear weapons have been built, primarily by the United States and the former Soviet Union. The U.S. government began nuclear weapons production under the Manhattan Project and has now moved to the stage of decommissioning many of the weapons and managing the by-products. This brief is about U.S. government efforts to manage its usable nuclear materials from decommissioned and surplus weapons. Nuclear Weapons U.S. nuclear weapons are complex devices designed to explode only when authorized , with extensive safeguards to prevent accidental or malicious detonation . There are two basic types of nuclear weapons. An “atomic bomb” uses high-grade conventional explosives and uranium that has been enriched to the extent that it is fissile (a far greater extent of enrichment is required to support a nuclear detonation than is required for nuclear fuel for power production). The high-grade explosives are used to trigger fission of the enriched uranium, that is, the enriched uranium atoms split apart. All U.S. nuclear weapons and many of the others in the world use the artificial element plutonium rather than highly enriched uranium. In either case, the explosives “assemble” a metal shell to become a sphere, or momentarily compress a ball of fissionable material sufficiently to reduce the neutron leakage so that the neutrons released during fission may generate a “chain reaction” that produce more neutrons in each successive generation. (See Walker, 2005, for a well-written account of the creation of the first atomic weapons.) Managing the Nuclear Weapons Legacy | 165 Current nuclear weapons are “thermonuclear “devices. These weapons use conventional high-grade explosives to trigger fission, which, in turn triggers fusion of heavy hydrogen atoms in tritium gas, that is, atoms are fused together rather than split apart. For context, fusion is what powers our sun. Each of these fusion reactions produces a neutron, and the sudden release of a pulse of neutrons “boosts” the fission reaction to a higher level and multiplies the energy release of the fission bomb by a substantial factor. A “thermonuclear” weapon uses a fission device or a boosted fission device to prepare a large amount of thermonuclear fuel—usually solid lithium deuteride (LiD) at high compression and temperature to provoke fusion among the heavy hydrogen (deuterium) atoms and between the deuterium and the tritium that is made from the capture of fusion neutrons in lithium. In a thermonuclear weapon, typically half of the energy release comes from fusion and half from fission. Both forms of nuclear weapons are entirely different from “dirty” bombs and nuclear power plants. A dirty bomb (or radiological dispersal device) uses explosives, like dynamite, to spread radioactive materials. People can be injured or killed by the explosion and debris, and by the spread of radionuclides by a dirty bomb detonation. The dispersal of radionuclides also may cause extensive public fear, even if the levels are low such that there is no immediate health risk. But there is no fission or fusion, and therefore no nuclear blast, and hence the effects of a dirty bomb should be restricted to radiological contamination, though the effects can be damaging to people and property in the local area. (See “Dirty Bombs.”) A nuclear power plant uses enriched uranium (with a lower enrichment level than used for weapons) to create controlled fission that produces heat that is used to turn a turbine, which, in turn, creates electricity. (See “Sustainability .”) Nuclear power plants are designed with extensive safeguards so that they cannot explode. They are not bombs but they can have accidents that under worst conditions can liberate much of the radioactivity that has accumulated in the reactor, which would probably be contained in the concrete protective structure. (See “Nuclear Power Plant Safety Systems.”) Managing Surplus Nuclear Weapons Grade Materials Nuclear power can be part of the solution for managing the nuclear weapons legacy. The tens of thousands of nuclear weapons that are no longer part of the U.S. arsenal must be taken apart so that they no longer can be used as weapons. Each weapon has thousands of components. The vast majority of these are complex electronics. The actual bomb material, the “physics package,” has only several hundred components. The fissionable material, consisting of highly [3.15.156.140] Project MUSE (2024-04-19...

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