Countries: United States

The United States is a nuclear weapon state member of the Non-Proliferation Treaty. In May 2010, the United States declared a stockpile of 5113 warheads as of the end of September 2009. This stockpile included almost 2000 strategic warheads deployed on about 800 missiles and bombers, 500 non-strategic warheads and 2,600 warheads in reserve. Additional 3500-4500 warheads are awaiting dismantlement. Taking into account the warheads in the dismantlement queue, the size of the U.S. weapon arsenal is estimated to be 9,400 nuclear warheads.

The current stock of fissile materials in the United States is estimated to include 94.8 tonnes of plutonium (80.7 tonnes of which is weapon-grade) and 686.6 tonnes of highly-enriched uranium (some of which is in irradiated naval fuel).  Of these amounts, 49.3 tonnes of separated plutonium and 194 tonnes of HEU have been declared as excess to military requirements. The United States has no separated civilian plutonium.

The United States is not producing fissile materials for weapons. Production of HEU for weapons ended in 1964. Additional HEU was produced for naval-reactor fuel through 1992. All U.S. production reactors were shut down in 1987.

Highly-enriched uranium

The United States was the first country to produce enriched uranium. During 1945-47, a little over a tonne of HEU was produced by electromagnetic separation at the Manhattan Project's Y-12 plant near Oak Ridge, Tennessee. Then the HEU production shifted to two large gaseous diffusion plants, one at Oak Ridge, Tennessee, and one at Portsmouth, Ohio.

The Oak Ridge gaseous diffusion plant produced HEU for weapons during 1945-1964 and thereafter produced only low-enriched uranium for nuclear power-plant fuel until 1985. The Portsmouth plant started production in 1956 and also produced HEU for weapons until 1964. Then it shifted to producing mostly low-enriched uranium for power-reactor fuel and HEU enriched to an average of 97.4 %, for naval-propulsion reactor fuel. There are several new commercial uranium enrichment facilities that are being built in the United States (see Facilities: Uranium enrichment). None of them will be producing highly-enriched uranium.

Cumulatively, the United States acquired 751.9 tonnes of uranium-235 (835 tonnes of 90% HEU equivalent). As of the end of September 2004, about 180 tonnes of HEU had been consumed in nuclear reactor fuel, nuclear tests, transfers to foreign countries, and down-blending to low-enriched uranium (LEU). The measured HEU inventory was declared as 590.5 tonnes of U-235 in 686.6 tonnes of HEU as of September 2004 (656 tonnes 90% HEU equivalent). By the end of 2012, with about 141 tons of material either downblended or sent for downblending, the United States had a remaining stockpile of 604 tonnes of HEU.

Of the total HEU stock, about 100 tonnes had been fabricated into naval fuel that is to be disposed of in a geological repository after use. Another 159 tonnes have been designated for the naval-fuel reserve, and  20 tonnes have been reserved for use in space and research reactors.

Weapon plutonium

The first significant amounts of plutonium produced in the United States were used in the nuclear explosive that was tested in New Mexico on 16 July 1945 and then the bomb based on that design that was detonated over the Japanese city of Nagasaki on 9 August 1945. This plutonium was produced by the first three graphite-moderated, water-cooled reactors built on the U.S. Department of Energy's (DOE's) Hanford site on the Columbia River in Washington State. Later, an additional six such production reactors were built at Hanford and another five, moderated and cooled by heavy water, were built on the DOE's Savannah River Site in South Carolina. The primary mission of the Savannah River reactors was to produce tritium for U.S. nuclear weapons but they produced a great deal of weapon-grade plutonium as well.

U.S. production of weapon-grade plutonium peaked in the 1950's and early 1960's. During the 1960s, nine of the fourteen U.S. production reactors were shut down. Five continued to operate into the 1980s, primarily to produce tritium. All U.S. production reactors were finally shut down in 1987.

According to the official plutonium balance reselased by DoE in 2009, the United States produced and acquired 111.7 tonnes of plutonium. As of the end of September 2009, the United States had used and otherwise removed 14.0 tonnes of this plutonium. Measured inventory in 2009 was declared to be 95.4 tonnes, leaving 2.4 tonnes as inventory difference. Of the 95.4 tonnes, 81.3 tonnes is weapon-grade plutonium, 12.7 tonnes is fuel-grade, and 1.4 tonnes is power-reactor grade plutonium. These numbers do not include 3.8 tonnes of weapon-grade plutonium that had been disposed of as waste as of 2009.

In its 2011 INFCIRC/549 declaration, the United States reported that 61.5 tonnes of government owned plutonium has beed declared as excess for national security needs. This amount includes 44.7 tonnes of separated plutonium, 4.6 tonnes of plutonium in unirradiated MOX fuel, and less than 0.05 tonnes held in the fuel fabrication process. In addition, 7.8 tonnes of the plutonium declared as excess is in irradiated fuel and 4.4 tonnes was disposed of as waste.

Taking into account that 7.8 tonnes of the plutonium inventory is in irradiated fuel and the 4.4 tonnes has beed disposed of as waste, the amount of separated plutonium is 87.0 tonnes (95.4 tonnes declared in 2009 minus 7.8 tonnes and minus additional 0.6 tonnes disposed of as waste between 2009 and 2011). However, this amount includes contaminated material, residuses and other forms.  

Civilian plutonium

The United States has no separated civilian plutonium. At the end of 2011, an estimated 546 tonnes of plutonium was contained in spent fuel stored at civilian reactor sites and 12 tonnes of plutonium in spent fuel stored elsewhere. These 12 tonnes include the 7.8 tonnes of government owned plutonium that was declared as excess to national security needs that is accounted for in the weapon plutonium section.