1. minimizing the risk that weapons or fissile materials could be reintroduced into the arsenals from which they came, halting or reversing the arms reduction process; and

  2. strengthening the national and international arms control mechanisms and incentives designed to assure continued arms reductions and prevent the spread of nuclear weapons.

In pursuit of these objectives, the U.S. and Russian governments have agreed that the United States will buy 500 tons of excess Russian HEU, which will be "blended down" to low-enriched uranium (LEU)2 so that it can be used for nuclear reactors but not for weapons. The United States will later resell the material to fulfill demand for nuclear fuel on the domestic and world market.

Plutonium, though it can be used as a fuel in either current or future reactor designs, does not lend itself to the commercial approach being taken with HEU for two reasons: (1) plutonium cannot be isotopically diluted so that it cannot be used in weapons; and (2) it costs more to use as fuel in current light-water reactors than LEU, even if the plutonium is available free while the uranium must be mined, processed, and enriched. Plutonium's toxicity and the need to safeguard it from diversion and theft3 require special handling procedures that greatly increase the costs of its use.

Accordingly, in 1992 the U.S. government asked the Committee on International Security and Arms Control (CISAC) of the National Academy of Sciences (NAS) to identify and evaluate the approaches that could be used for the disposition of plutonium from excess nuclear weapons. The Panel on Reactor-Related Options for the Disposition of Excess Weapons Plutonium was formed by the NAS in November 1992 to support CISAC's study. The panel consists of three members of CISAC (Richard Garwin, John Holdren, and Michael May) and four additional members selected for their relevant expertise on issues related to reactors and reactor wastes (John Ahearne, Robert Budnitz, Thomas Pigford, and John Taylor) (see list of panel members on p. iii).


Natural uranium includes only 0.7 percent of the fissile isotope uranium-235 (U-235), with almost all of the remaining 99.3 percent being U-238. (Isotopes are different forms of the same chemical element having differing numbers of neutrons—235 neutrons and protons together in the case of U-235, and 238 in the case of U-238.) To be usable in a weapon, the concentration of U-235 must be greatly increased from its level in natural uranium, a process known as enrichment. Typical weapons-grade uranium contains more than 90 percent U-235. Because the various isotopes of an element are chemically indistinguishable, enrichment requires physical separation techniques. These are costly and time-consuming, and the relevant technology is not widely available—a set of circumstances that has constituted one of the primary technical barriers to proliferation of nuclear weapons. Some types of nuclear reactors, by contrast, can operate with natural uranium, though most of the world's power reactors use LEU containing 3-5 percent U-235. HEU can easily be blended with natural or depleted uranium to produce LEU.


We follow the Committee on International Security and Arms Control report (NAS 1994, p. 6) in using the term "diversion" for cases in which the state that owns the material returns it to weapon use and the term "theft" for cases in which the material is illicitly obtained by other parties.

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