The UK’s worst nuclear accident, which occurred on 10 October 1957 at the Windscale nuclear power station at Sellafield. The first of two atomic piles, built in 1950 and 1951 as part of Britain’s atomic weapons project, caught fire releasing radioactive material into the environment. The 120-metre-high piles were solid graphite moderated and air cooled with horizontal channels within which uranium cartridges could be passed and exposed to neutron radiation to produce plutonium. After the accident, pile one was sealed and pile two was permanently shut down shortly after.