The 1998 Strategic Defence Review declared the UK’s total stockpile of fissile material as part of its commitment to the control of fissile material. This comprised 7.6 tonnes of plutonium; 21.9 tonnes of highly enriched uranium; and 15,000 tonnes of other forms of uranium.
The Review stated that 4.4 tons of plutonium, including 0.3 tons of weapons-grade plutonium, and over 9,000 tonnes of non-highly enriched uranium were no longer required for defence purposes and would be now be placed under European Atomic Energy Community (EURATOM) safeguards and made liable to inspection by the International Atomic Energy Agency (IAEA). Moreover, the UK would cease exercising its right to withdraw fissile material from safeguarded stocks for nuclear weapons. The 4.4 tons of fissile material surplus to defence requirements, including 0.3 tonnes of weapons-grade plutonium, was transferred to the UK’s civilian plutonium stockpile.
The Review also stated that “All stocks of highly enriched uranium will, however, be retained outside safeguards, since material no longer needed for nuclear weapons will be used for the naval propulsion programme. We have considered whether further disaggregation of these totals at this time would be compatible with our continuing, if reduced, security requirement. We have concluded that it would not.”
The ‘Historical Accounting for UK Defence Highly Enriched Uranium’ published by the Ministry of Defence in 2006 reiterated that “MoD HEU is held outside international safeguards for defence purposes, but is subject to a strict materials accountancy regime”.
The UK confirmed in 2010 that this material was under European Atomic Energy Community (EURATOM) safeguards and liable to inspection by the International Atomic Energy Agency. The material is stored at the Sellafield nuclear site.