In total, only a few dozen reactors of this type were constructed, most of them in the UK from the 1950s to the 1970s, with very few exported to other countries. The first magnox reactor to come online was Calder Hall (at the Sellafield site) in 1956, frequently regarded as the "first commercial-scale electricity producing reactor in the world", while the last in Britain to shut down was Reactor 1 in Wylfa (on Ynys Môn) in 2015. , North Korea remains the only operator to continue using Magnox style reactors, at the Yongbyon Nuclear Scientific Research Center. The Magnox design was superseded by the Advanced Gas-cooled Reactor, which is similarly cooled but includes changes to improve its economic performance.