Sellafield reprocessing plant at night. Sellafield (formerly Windscale) is a nuclear fuel reprocessing plant in Cumbria, UK. Sellafield comprises several reactors and reprocessing units of different ages. The dome at centre is the inoperative prototype Advanced Gas-cooled Reactor (AGR). At centre left are the chimneys of the Windscale Piles. These were the first two reactors to be used at Sellafield, and were part of a secret nuclear weapons programme. At far left are the cooling towers of Calder Hall, the UK's first commercial nuclear reactor. The buildings at right house the magnox fuel reprocessing plant. Sellafield opened in 1951.