In 1942 the Sellafield Industrial centre was chosen to house a second Royal Ordnance Factory and throughout World War Two the factory produced highly explosive propellants. The factory was closed following the surrender of Japan in 1945.
After the war the site was designated by the government to produce plutonium for nuclear weapons. In 1947 work began on the site, renamed Windscale, to make it suitable for nuclear development. Around 5,000 workers were involved in the construction project. The first reactor, named Windscale Pile 1 was opened in 1950 and a second reactor, Windscale Pile 2 was opened the following year.
In 1954 the United Kingdom Atomic Energy Authority was created and this new body became the owner of the Windscale site. The first of four nuclear reactors were created on the site, now renamed Windscale and Calder Works, in 1956. Officially opened by Queen Elizabeth II on 17th October Calder Hall Nuclear Reactor was the first commercial site dedicated to producing nuclear energy.
In 1971 the United Kingdom Atomic Energy Authority was split into a research division, which retained the name Atomic Energy Authority and a production division which was named British Nuclear Fuels Limited. The Windscale and Calder Hall reactors were overseen by the production division.
In 1981 British Nuclear Fuels Limited, as part of a major reorganisation, renamed the Windscale and Calder Hall site Sellafield.
Sellafield today, covers an area of around two square miles and is primarily used to store nuclear waste. However, the site is under consideration for the building of a new nuclear reactor.