Abstract
The most likely source of fissile material for future nuclear proliferators is the enormous stockpile of weapon-and commercial-grade plutonium that exists worldwide. But how much plutonium is there, where is it, and what form is it in? The Nuclear Control Institute, the Institute for Science and International Security, and the Natural Resources Defense Council have all produced estimates of plutonium inventories. We now know that those estimates closely resemble those of the U.S. government.
In the July 9, 1999 Washington Times, journalist Bill Gertz published the U.S. government's estimates of world plutonium stockpiles, which he obtained from leaked Energy Department documents. Space constraints prevented Gertz from presenting a full account, but he later provided Nuclear Notebook with estimates of weapon-and commercial-grade stockpiles in 15 countries.
The first-ever gram amounts of plutonium were provided to Manhattan Project scientists in 1944, and the initial six-plus kilograms produced in the B reactor at Hanford were used in the Manhattan Project's Trinity test on July 16, 1945. The next six-plus kilograms went into the bomb dropped on Nagasaki on August 9, 1945. Since World War II, more than 1,200 metric tons of plutonium have been produced in nuclear reactors. Of those 1,200 metric tons, approximately 260 are weapon-grade plutonium, defined as containing less than 7 percent (typically 5-6 percent) plutonium 240, an isotope with a high rate of spontaneous fission. Commercial-grade inventories presumably are composed of a combination of fuel-grade plutonium (7 to 18 percent 240) and reactor-grade (more than 19 percent 240). (Despite its high plutonium 240 content, nuclear weapons can be made with reactor-grade plutonium.)
Throughout the 1950s and 1960s, weapon designers worked to reduce the amount of plutonium needed to produce a yield in the 10- to 20-kiloton range, roughly in the range of the Hiroshima and Nagasaki bombs. Modern U.S. warheads use two to four kilograms of weapon-grade plutonium per warhead. At an average of three kilograms per warhead, the world's approximately 260 tons of weapon-grade plutonium produced since 1945 would be enough for more than 85,000 warheads.
While the inventory of weapon-grade plutonium is unlikely to increase, the operation of the world's 400 power reactors means that the amount of reactor-grade plutonium will continue to grow. Most of this civilian plutonium remains in spent fuel rods that have been removed from reactors. However, more than 200 tons of civil plutonium have been separated, just as weapon-grade plutonium is obtained by chemically separating it from irradiated fuel.
Plutonium stockpiles, 1999
Describing Kazakhstan's plutonium as “weapon grade” is an Energy Department misclassification. It was produced in a breeder reactor and it is therefore civil plutonium that would require reprocessing.
Eighteen to 20 countries have nuclear reactors–and spent fuel. Five countries are engaged in commercial reprocessing: France, Britain, Russia, India, and Japan. Japan has about 21 tons of separated plutonium that could be used in a weapons program if Japan ever decided to exercise that option.
Not surprisingly, the U.S. plutonium inventory is the one we know the most about. Of its 85 tons, about 64 are used in current weapons or stored as intact weapon pits. The remaining 21 tons are stored in the form of solutions, scrap, and waste material at Rocky Flats and other Energy Department sites.
On March 1, 1995, President Clinton announced that 200 tons of fissile material would be permanently withdrawn from the stockpile. These 200 tons include 38 tons of weapon-grade plutonium–20 tons in the form of scrap and waste, and the rest in more than 6,000 intact pits stored at the Pantex plant.