The Windscale fire of 10 October 1957 was the worst nuclear accident in Great Britain's history, ranked in severity at level 5 on the 7-point International Nuclear Event Scale. The fire took place in Unit 1 of the two-pile Windscale facility on the northwest coast of England in Cumberland (now Sellafield, Cumbria). The two piles had been built as part of the British atomic bomb project. Windscale Pile No. 1 was operational in October 1950 followed by Pile No.