Kairos is building the Hermes Low-Power Demonstration Reactor – known as Hermes 1 – in Oak Ridge, Tennessee. It was one of the first round of companies conditionally selected by the Department of Energy (DOE) last year to receive high-assay low-enriched uranium (HALEU) under a programme enabling nuclear developers to request HALEU from DOE sources including the National Nuclear Security Administration.
Kairos said it has now successfully completed negotiations to secure the HALEU required for the Hermes 1 programme. It will use the material to produce HALEU TRISO (tri-structural isotropic) fuel pebbles for the reactor, in partnership with Los Alamos National Laboratory, using manufacturing processes it has developed and optimised in its own labs.
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Hermes 1 is under construction in Tennessee (Image: Kairos)
Hermes 1, a scaled demonstration of Kairos’ KP-FHR fluoride salt-cooled high-temperature reactor technology, is the first non-light-water reactor to be approved for construction by the US Nuclear Regulatory Commission. Kairos Power broke ground at the Hermes 1 site in Oak Ridge in July 2024 and began nuclear safety-related construction in May 2025. It will not produce electricity – Kairos’s iterative development approach will see lessons learned from the project feeding into the Hermes 2 commercial-scale demonstration plant – a two 35 MWt-unit plant for which the US Nuclear Regulatory Commission issued a construction permit in November 2024. Hermes 2 will include a power generation system.
HALEU – uranium enriched to contain between 5% and 20% uranium-235 – will be used to fuel many advanced reactors. The DOE’s HALEU Availability Program was established in 2020 to secure a domestic supply of the material for civilian domestic research, development, demonstration, and commercial use. Allocating nuclear developers HALEU material from DOE sources, including material from the National Nuclear Security Administration, is a way of bridging a HALEU availability gap with existing material as the supply chain builds up.
“We are pleased to secure the HALEU we need to demonstrate our technology with Hermes 1,” said Kairos Power Chief Technology Officer and co-founder Edward Blandford. “The US Department of Energy has been a vital partner on the Hermes project, with its ongoing risk reduction investment through the Advanced Reactor Demonstration Program. The allocation of HALEU will enable continued progress on Kairos Power’s path to delivering affordable advanced reactors at scale.”
The DOE is investing up to USD303 million in the Hermes project through the Advanced Reactor Demonstration Program.
