A former uranium enrichment plant site in Oak Ridge, Tennessee, is set to host the first Gen IV nuclear reactor in the U.S. Construction of the Hermes Low-Power Demonstration Reactor is now underway by Kairos Power.

The low-power reactor is the first non-light water design approved for construction by the U.S. Nuclear Regulatory Commission in more than 50 years. The fluoride salt-cooled high-temperature reactor, expected to be operational in 2027, will combine tri-structural isotropic (TRISO)-coated particle fuel with a molten lithium fluoride and beryllium fluoride salt coolant to demonstrate safe and clean heat production.

The TRISO pebble bed fuel will be produced in partnership with the U.S. Los Alamos National Laboratory. The facility is being built using modular construction techniques piloted at Kairos’s testing and manufacturing campus in Albuquerque, New Mexico, with reactor modules fabricated there and shipped to the Oak Ridge site for assembly.

Kairos Power is currently seeking a construction permit for Hermes 2 — a pair of 35 M thermal reactors that will be built at the Oak Ridge site with a shared turbine to demonstrate electricity generation. The factory-built small modular reactor design is expected to inform the commercialization of a 140 MWe fluoride salt–cooled, high-temperature reactor within the next decade.