England - Dragon -1964 to 1976 – This helium-cooled test reactor provided early successful demonstration of the high temperature gas-cooled reactor and water-particle fuel.

Germany - AVR - 1966 to 1988 – This prototype helium reactor operated successfully for over 20 years and provided demonstration of 1740° F gas outlet temperature and key safety features, including safe shutdown with total loss of coolant circulation and without control rod insertion.

U.S. - Peach Bottom - 1967 to 1974 – This prototype helium reactor achieved a remarkable 86% availability during the electricity production phase.

U.S. - Fort St. Vrain - 1979 to 1989 – This reactor used water-lubricated circulator bearings which resulted in frequent water ingress into the reactor system and caused significant down time. In spite of a poor operating record, the Fort St. Vrain coated-particle fuel and reactor core worked extremely well. Because of the non-corrosive nature of helium, workers were exposed to radiation doses only about 1% that of average water reactors. Fort St. Vrain generated about 5 billion kWh.

Germany - Oberhausen 2 - 1975 to 1987 – This 50 MW electric turbine plant represented the evolutionary step from fossil-fired gas turbines with air as the working fluid towards the realization of nuclear powered helium gas turbines. Helium was used as the working fluid in a closed-cycle process for electricity and heat production. The plant incorporated heat exchangers (recuperator, precooler, intercooler) of comparable size to those required for a 600 MW thermal GT-MHR.

Germany - THTR - 1985 to 1988 – This helium-cooled nuclear power plant generated about 3 billion kWh. Political resistance in the post-Chernobyl era precipitated early shutdown.

Russia – Various successful demonstrations of fuel fabrication and fuel irradiation performance.

Japan – The Japanese are actively engaged in gas-cooled reactor research and development and have recently constructed and commissioned the High Temperature Test Reactor. (HTTR).

South Africa – The South African utility ESKOM is actively developing a design similar to the GT-MHR, but with a reactor core consisting of pebble-type fuel elements.