Following the decision taken in January 1947 for the UK to have an independent nuclear deterent [2], Sellafield was chosen as the location of the plutonium production plant [3], with the initial fuel load into the Windscale Piles commencing July 1950 [4]. By July of 1952 the separation plant was being used to separate plutonium and uranium from spent fuel.

Unlike the early US reactors at Hanford, which consisted of a graphite core cooled by water, the Windscale Piles consisted of a graphite core cooled by air. Each pile contained almost 2000 tonnes of graphite, and measured over 24 feet high by 50 feet in diameter. Fuel for the reactor consisted of rods of uranium metal, approximately 1 foot long by one inch in diameter, and clad in Aluminium [5].

The Piles themselves are currently being decommissioned.