The Steam Generating Heavy Water Reactor (SGHWR) was a United Kingdom design for commercial nuclear reactors. It uses heavy water as the neutron moderator and normal "light" water as the coolant. The coolant boils in the reactor, like a boiling water reactor, and drives the power-extraction steam turbines.
A single prototype of the design, the 100 MWe "Winfrith Reactor", was connected to the grid in 1967 and ran until 1990. A larger commercial design with a 650 MWe power rating was selected in 1974 as the basis for future reactor builds in the UK, but declining electricity use led to this decision being reversed in 1976 and no production models were ever built.
SGHWR was among a number of similar designs, which include the CANDU-derived Gentilly Nuclear Generating Station in Quebec, the Fugen Advanced Test Reactor in Japan, and the never-commissioned CIRENE reactor in Italy. These designs differ with the baseline CANDU design, which uses heavy water as the coolant as well as the moderator.