Countries: United States

The United States is a nuclear weapon state member of the Non-Proliferation Treaty. In April 2015, the United States declared a stockpile of 4717 warheads as of the end of September 2014. This stockpile included about 1,900 strategic warheads deployed on about 800 missiles and bombers, 180 non-strategic warheads and approximately 2,600 warheads in reserve. Additional 2500 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 7,100 nuclear warheads.

The current stock of fissile materials in the United States is estimated to include 87.6 tonnes of plutonium and 599 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 has a HEU stockpile estimated to be about 600 tons, of which 253 tons are believed to be in weapons or available for weapons. The United States stockpile is falling as it continues to dispose of the 187 tons of HEU it has declared excess and to be downblended into low-enriched uranium. This amount includes 153 tons of HEU out of 175 tons declared excess in 1994 and 28 tons assigned for downblending from 200 tons of HEU declared excess in 2005, as well as 6 tons of other HEU, including U.S. origin HEU research reactor fuel that had been exported and has been returned as part of the effort to end the civilian use of such fuel. As of the end of December 2014, 146.6 tons of HEU had been down-blended or shipped for down-blending; of this total 146.1 tons had been down-blended and 0.5 tons had been shipped.

The United States has reserved 152 tons of HEU for naval fuel. This is material enriched to over 90 percent in uranium-235 and was previously in or available for weapons and in 2005 was declared excess for weapon purposes. Also, the United States as of the end of 2014 had about 31 tons of spent naval HEU fuel in storage at the Expended Core Facility at the Idaho National Laboratory. Naval spent fuel is to go to a geological repository.

There are several new commercial uranium enrichment facilities that are being built in the United States, none of wich will be producing highly-enriched uranium.

Weapon plutonium

According to the official plutonium balance released 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 2014 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 44.4 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 4.5 tonnes was disposed of as waste after 1994. Additional 0.2 tonnes of plutonium was lost to radioactive decay since 1994.

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 unirradiated plutonium is 87.6 tonnes (95.4 tonnes declared in 2009 minus 7.8 tonnes). However, this amount includes contaminated material, residuses and other forms.

Civilian plutonium

The United States has no separated civilian plutonium. At the end of 2014, an estimated 625 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.