nuclear reactor facility and plutonium production plant in the county of Cumberland (now part of Cumbria), in northwestern England, that in 1957 was the site of the United Kingdom's most serious nuclear power (nuclear energy) accident. The Windscale plant consisted of two gas-cooled nuclear reactors. The accident occurred on Oct. 8, 1957, when a routine heating of the No. 1 reactor's graphite control blocks got out of control, causing adjacent uranium cartridges to rupture. The uranium thus released began to oxidize, releasing radioactivity and causing a fire that burned for 16 hours before it was put out. The fire left about 10 tons of radioactive fuel melted in the reactor core. The fire also caused the release of sizable amounts of radioactive iodine into the atmosphere. As a consequence, the government banned the sale of milk produced in a 200-square-mile (500-square-kilometre) area around the reactor site for several weeks. At the time the British government released only sketchy details of the accident and in general tried to minimize its seriousness. The contaminated Windscale reactor was subsequently sealed until a cleanup of it was begun in the late 1980s.