Title: Weapon Materials Basics | Union of Concerned Scientists
Headings: Weapon Materials Basics
Weapon Materials Basics
Fissile materials basics
How much is needed to build a bomb?
Downloads

Content: In addition, the continued use of HEU for both civilian research and naval propulsion reactors increases the risk of terrorist access to this material. Plutonium. Plutonium occurs only in trace amounts in nature. It is produced as a matter of course in power reactors when the uranium-238 in reactor fuel absorbs neutrons. Countries producing plutonium for weapons have generally operated their reactors to maximize the production of plutonium-239—the isotope most useful for nuclear weapons—and to minimize the production of other plutonium isotopes such as plutonium-240. Weapon-grade plutonium contains less than 7 percent plutonium-240. Under normal nuclear power plant operation, the plutonium in spent reactor fuel contains roughly 24 percent plutonium-240; such plutonium is often referred to as "reactor-grade." However, essentially all isotopic mixtures of plutonium—including reactor-grade plutonium—can be used for nuclear weapons. In order to use plutonium in nuclear weapons or nuclear fuel, however, it must be separated from the rest of the spent fuel in a reprocessing facility.