Steam-generating heavy water reactor
Steam Generating Heavy Water Reactor (SGHWR) is a United Kingdom design for commercial nuclear reactors. It is similar to the Canadian CANDU reactor designs in that it uses a low-pressure reactor vessel containing high-pressure piping for the coolant, which reduces construction costs and complexity.
SGHWR was a heavy water moderated reactor, which used ordinary (light) water as coolant, in contrast with earlier UK designs that used graphite moderators which led to very large reactor sizes. Unlike CANDU, the SGHWR uses slightly enriched uranium fuel, which allows for higher burnup and more economical fuel cycles. The modern CANDU ACR-1000 reactor design uses a similar concept, as does the Italian CIRENE, hosted at Latina Nuclear Power Plant.
Only a single SGHWR was ever built, the small 100 MW prototype reactor at Winfrith, often known simply as the "Winfrith Reactor". It was connected to the grid in 1967 and ceased operation in 1990 after 23 successful years.  It was owned by the United Kingdom Atomic Energy Authority. Decommissioning is now being carried out by Magnox Ltd on behalf of the Nuclear Decommissioning Authority.
A similar design was the Gentilly Nuclear Generating Station in Quebec, but this was not successful and shut down after a short lifetime.