The Sizewell nuclear site consists of two nuclear power stations, one of which is still operational, located near the small fishing village of Sizewell in Suffolk, England. Sizewell A, with two Magnox reactors, is now in the process of being decommissioned. Sizewell B has a single pressurised water reactor (PWR) and is the UK's newest nuclear power station. A third power station, to consist of twin EPR reactors, is planned to be built as Sizewell C.

Sizewell B was built and commissioned between 1987 and 1995, and first synchronised with the National Grid on 14 February 1995. The cost of Sizewell B has been quoted as £2 billion (1987 prices) with a quarter of that cost being related to civil engineering works.

The original rating was for a thermal power of 3,444 MW and gross electrical output of 1,250 MW, which after house load of 62 MW gave a net output to the grid of 1,188 MWe, equivalent to 8.7 TWh (31 PJ) in the year of 2005. It was uprated by 1% in 2013 with a thermal power of 3,479 MW and an electrical output of 1,195 MWe, though this is dependent on seawater temperature. Sizewell B is due to close in 2035, although EDF has announced that it is planning a 20 year life extension until 2055.