Kairos Power began construction on its Hermes non-powered demonstration reactor in Oak Ridge, Tennessee in July 2024, targeting activation in mid-2026. Hermes is a 35 MWe fluoride salt-cooled high-temperature reactor — the non-nuclear portion of which has been completed. The NRC approved Kairos's Hermes construction permit in December 2023, and the NRC also approved plans for Hermes 2. Hermes uses TRISO pebble fuel in a molten lithium-fluoride beryllium-fluoride salt coolant, operating at atmospheric pressure. The first activation is one of the most anticipated milestones in US advanced nuclear in 2026.