The steam generating heavy water prototype reactor at Win-frith has been in operation since 1967 and to date has produced a total of 2,250 million units of electricity. The operating performance of the reactor has been good. As well as acting as a power producer, it has served as an experimental facility to provide irradiation and engineering information for development of a commercial version of the reactor. The Atomic Energy Authority envisages that the Central Electricity Generating Board will continue to purchase electricity from the reactor in the foreseeable future.