Countries: United Kingdom

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United Kingdom is a nuclear weapon state member of the Nuclear Non-proliferation Treaty. It has officially declared that its nuclear arsenal includes fewer than 120 operationally deployed nuclear warheads and that the total size of the arsenal does not exceed 215 nuclear warheads.

The U.K. stock of fissile materials is estimated to be 3.2 tonnes of military plutonium and 19.8 tonnes of military HEU. The HEU stock also includes 1,400 kg of HEU that is reported as civilian in an annual declaration submitted to IAEA. Based on the IAEA declaration, the United Kingdom owned 103.3 tonnes of separated reactor-grade plutonium as of December 31, 2014.

Highly enriched uranium

The United Kingdom produced its military HEU at the Capenhurst Gaseous Diffusion Plant. The plant was producing HEU between 1952 and 1962. After that it continued to operate until 1982, producing LEU for power reactors. In addition to domestic production, the United Kingdom received about 13 tons of uranium-235 in HEU from the United States.

According to the official HEU balance, released in 2006, the total audited stock of military HEU was reported to be 21.86 tonnes as of March 31, 2002. The average enrichment of the material was not given.

Since the 2002 audit, an estimated 2.1 tonnes of HEU were further removed from the stockpile, so the HEU stock as of the end of 2014 is estimated to be 19.8 tonnes. In addition, 1,400 kg is reported to be civilian HEU.

The United Kingdom operates a gaseous centrifuge uranium enrichment plant in Capenhurst. This facility is part of the URENCO consortium and has been placed under safeguards.

Military plutonium

The main production site for UK military plutonium was the Sellafield complex, which hosted a total of six production reactors: the two Windscale Piles and the four Calder Hall reactors, and all reprocessing operations. The United Kingdom operated four additional dual-use reactors at Chapelcross, whose fuel was also sent to Sellafield for reprocessing. The first discharges of spent fuel from five nominally civilian Magnox reactors was also put towards the military stockpile.The two air-cooled graphite-moderated "Windscale Piles" were shut down after a graphite fire in 1957. The Calder Hall reactors were used to produce military plutonium until 1989. The Chapelcross reactors were used to produce plutonium until 1964 and tritium thereafter. Both sets of reactors were dual-purpose, that is, they also produced electric power. The two groups of reactors were shut down in 2003 and 2004 respectively.

In addition to its own production, the United Kingdom also exchanged some plutonium with the United States.

In 1998, the United Kingdom declared a stockpile of 7.6 tonnes of military plutonium. Subsequently, 4.1 tonnes of non-weapon grade plutonium and 0.3 tonnes of weapon-grade plutonium were declared as excess to military requirements and to civilian custody. This leaves 3.2 tonnes of weapon-grade plutonium that is either in weapons or available to weapons.

Civilian plutonium

The United Kingdom has separated large quantities of reactor-grade plutonium produced both by its commercial power plants and its fleet of dual-use reactors (Calder Hall and Chapelcross) when they were operated in civilian-mode. It also took ownership of some foreign-origin plutonium stored in the country. As of December 31, 2014, the amount of separated reactor-grade plutonium owned by the United Kingdom was 103.3 tonnes. This amount includes 4.4 tonnes of military-origin plutonium declared excess.

The United Kingdom currently has two reprocessing plants, located at Sellafield. The B-205 plant reprocesses metal natural-uranium fuel from first-generation "Magnox" reactors, the last of which was shut down in 2015. THORP reprocesses oxide fuel from British Advanced Graphite Reactors and foreign LWR reactors.