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 a departure from previous UK designs, which had used graphite as the moderator and carbon dioxide gas as the coolant.
As part of this program, a 100 megawatt electrical (MWe) prototype of the SGHWR was built at Winfrith in the 1960s and was connected to the grid in 1967.
In 1976 this decision was reversed due to the combination of a predicted sharp drop in electricity demand, higher than expected costs, and the lack of obvious export potential in a shrinking nuclear market.
Given the limited number of new reactors expected in the future, modified versions of the AGR were selected over SGHWR as no further development effort was needed.
The ability to run on natural uranium was considered a major benefit in the 1960s as it appeared the demand for enrichment would outstrip the supply.
The last attempt to use this basic design was the modern Advanced CANDU Reactor of the early 2000s, but development ended without an example being built.