Gas-cooled reactors have roots that reach way back to the development of early experimental reactors in the United States and Europe. In the United States, early experimental reactors at Oak Ridge and Brookhaven National Laboratories were air-cooled, as were early production reactors known as the “Windscale Piles” in the United Kingdom. Dragon, also located in the United Kingdon and operational from 1965 to 1976, used helium as the coolant and graphite as the moderator.

The Department of Energy and Idaho National Laboratory announced this week that the sixth major core overhaul of the Advanced Test Reactor (ATR) is complete, after an 11-month outage that began in April 2021. The ATR was built as a key piece of mission support for U.S. Navy programs and first reached full power in 1969. Today it remains “the world’s largest, most powerful and flexible materials test reactor,” in the words of INL—quite a feat for a reactor that was planned over 60 years ago.