The Fort St. Vrain Generating Station in Colorado, USA, operated a 330 MWe High-temperature Gas-cooled Reactor (HTGR) from 1979 to 1989.

Modern High Temperature Gas-cooled Reactors (HTGRs) can achieve high thermal-to-electric conversion efficiencies of around 40%. Today, HTGR technology is represented mainly by experimental and demonstration reactors. China’s commercial demonstration HTR-PM reactor at the Shidao Bay Nuclear Power Plant entered full commercial operation in 2023.

The fuel consists of TRISO particles containing uranium oxide or uranium oxycarbide. Each fuel kernel, approximately 0.5 mm in diameter, is surrounded by several protective layers of pyrolytic carbon and silicon carbide. After coating, the particles are about 1 mm in diameter and are embedded in graphite fuel elements. In pebble-bed reactors, these take the form of graphite spheres about the size of a tennis ball, known as fuel pebbles. The fuel is continuously loaded into the reactor from above and removed from the bottom after passing through the core. Another design uses hexagonal graphite blocks containing the fuel, an arrangement used particularly in American reactor designs.