With the need for a remote site obviated , it was decided to build the facility on the coast of Cumberland at a former Royal Ordnance Factory , ROF Drigg . This was soon switched to a more suitable site at the nearby former ROF Sellafield . To avoid any confusion with Springfields , the name was changed to Windscale . Construction began in September 1947 . The danger of the Wigner Effect was not overlooked . Walter Zinn visited Britain in 1948 and provided crucial information . New calculations based on this meant that the layout of the graphite blocks , which were already being machined , had to be changed . The two Windscale reactors became operational in October 1950 and June 1951 . Due to faulty calculations at the design stage , the reactors did not produce the expected output . As a result , extraordinary measures had to be taken to provide Penney with a first shipment of plutonium in June 1952 , and sufficient quantity for a core by the 1 August 1952 deadline . Improvements in the bomb design ultimately meant that he could get by with 15 per cent less plutonium . Starting in 1953 , the Windscale reactors were able to use slightly enriched uranium as a fuel . They were shut down after the Windscale fire in October 1957
Windscale fire
Windscale fire
High Explosive Research