The Open-pool Australian lightwater reactor (OPAL) is a 20 megawatt (MW) swimming pool nuclear research reactor. Officially opened in April 2007, it replaced the High Flux Australian Reactor as Australia's only nuclear reactor, and is located at the Australian Nuclear Science and Technology Organisation (ANSTO) Research Establishment in Lucas Heights, New South Wales, a suburb of Sydney. Both OPAL and its predecessor have been known simply as the Lucas Heights reactor.