International Panel on Fissile Materials

The United States is a nuclear weapon state member of the Non-Proliferation Treaty. In January 2021, U.S. nuclear weapon stockpile was estimated to include 5,550 warheads. Of these, about 3,800 weapons are in active stockpile and about 1,750 weapons are awaiting dismantlement. The active stockpile includes 1,800 deployed warheads, assigned to strategic and non-strategic delivery systems, and an estimated 2,000 warheads in reserve.

The current stock of fissile materials in the United States is estimated to include 87.8 tonnes of plutonium and 495 tonnes of unirradiated highly-enriched uranium. The United States has no separated plutonium produced by a civilian program.

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 495 tons as of the beginning of 2020. In 2016 it declared that as of 30 September 2013 its HEU inventory was 585.6 tons, of which 499.4 tons was declared to be for "national security or non-national security programs including nuclear weapons, naval propulsion, nuclear energy, and science." This material was estimated to include about 360.9 MT of HEU in weapons and available for weapons, 121.1 tonnes of HEU reserved for naval fuel and 17.3 MT of HEU reserved for research reactors. The remaining 86.2 tonnes of the 2013 declaration was composed of 41.6 tonnes 'available for potential down-blend to low enriched uranium or, if not possible, disposal as low-level waste', and 44.6 tonnes in spent reactor fuel.

As of the end of 2020, the amount available for use had been reduced to about 472.1 tonnes, which is estimated to include 361 MT in weapons or avaiable for weapons, 96 MT of HEU in naval reserve and 15.2 MT reserved for research reactors. The material in these two categories is covered by an obligation not to use if for weapons. Together with the material awaiting downblending, currently estimated to be 23 MT, it consitutes the 134 tonnes of unirradiated HEU not available for weapons.

Separated plutonium

According to the most recent official plutonium balance, in 2009 the United States measured inventory was 95.4 tons. According to U.S. INFICRC/549 declarations, since 2009 the United States disposed of additional 0.2 tons of plutonium in WIPP and lost 0.1 tons to radioactive decay. It also added 0.4 tons of research reactor plutonium transferred from abroad. Taking into account that the plutonium stock includes 7.8 tons of irradiated plutonium, the amount of separated plutonium is 87.8 tons.

Of the total amount of 87.8 tons of unirradiated plutonium, 79.7 tons are considered military stock. Even though the United States reports 49.4 tons of separated unirradited plutonium in its INFCIRC/549 declaration, most of this material is in weapons or weapon components or other weapon-origin material that retains classified attributes. Some of this material (4.6 MT) is in unirradiated MOX fuel. While all this material is covered by a pledge not to use it for military purposes, only 3 MT of separated plutonium is safeguarded. These are 3 tons of plutonium at the Savannah River Site that are placed under IAEA safeguards.