Pressurised water reactor (PWR) at Sizewell B nuclear power station. The reactor (grey, at lower centre) uses enriched uranium as a fuel. Energy is released as the atomic nuclei split (fission). This energy is used to heat pressurised water which then passes into the four steam generators (upper left and upper right). This water's energy is transferred across a heat exchanger in the steam generator to boil water into steam. This high-pressure steam then passes out of a pipe at the top of the steam generator and is used to drive electrical turbines (not seen here). Based on an American design and opened in 1995, Sizewell B is Britain's first PWR power station.