US-based Kairos Power has poured first concrete for the Hermes Low-Power Demonstration Reactor, marking the start of “nuclear construction” on the project in Oak Ridge, Tennessee. Kairos Power first broke ground at the Hermes site in July 2024 and completed excavation in October.
Hermes is a scaled demonstration of Kairos Power’s fluoride salt-cooled high-temperature reactor technology and is the first advanced nuclear reactor to receive a construction permit from the US Nuclear Regulatory Commission (NRC).
Safety-related construction activities, which are subject to oversight by NRC and can only be performed with a construction permit, have begun with a focus on the building’s foundation. To ensure structural soundness, Hermes will have 51 six-foot-diameter drilled piers extending approximately 40 feet below grade to anchor the building to bedrock.
The first safety-related concrete pour was the culmination of several months of preparation. Two earlier projects at the Oak Ridge site served as proving grounds to test the drilled pier installation process and refine Kairos Power’s nuclear quality assurance programme.
In February, Kairos Power completed design, construction, and installation of the reactor vessel for its second non-nuclear Engineering Test Unit (ETU 2.0). The reactor vessel is a central component of the ETU, which Kairos Power is building to advance the iterative development of its Fluoride Salt-Cooled High-Temperature Reactor (KP-FHR) technology. ETU 2.0 will demonstrate KP-FHR system integration in an optimised, fully modular design, building on lessons learned from ETU 1.0. The ETU programme is intended to mature Kairos Power’s internal manufacturing capabilities, mitigating supply chain risk for the Hermes demonstration reactor series and Kairos Power’s commercial fleet.
The construction team, led by Barnard Construction Company, completed a full-scale test pier in November (Pier 52) to demonstrate the process before drilling 70 piers for ETU 3.0 over four months. The team became highly proficient, installing as many as six piers in a single day using quality control checklists similar to those that will be used for Hermes.
“The first safety-related concrete pour for a US advanced reactor under an NRC construction permit is a major milestone and a significant accomplishment for the Kairos Power team and our construction partners,” said Kairos Power CEO & co-founder Mike Laufer. “This achievement reflects the value of our iterative development process to meet the necessary nuclear quality standards and provide crucial real cost information that gives confidence to our customers. It is a testament to the hard work of our dedicated team and represents an enormous amount of learning and progress.”
Kairos Power Chief Technology Officer & co-founder Edward Blandford said: “Working with our partners and in close communication with the NRC, we are committed to maintaining the highest standards of quality and safety to ensure the success of this project.”
The Hermes reactor will leverage proven technologies that originated in Oak Ridge – a combination of TRISO coated particle fuel and FLiBe (a eutectic mixture of lithium fluoride and beryllium fluoride) molten fluoride salt coolant. Hermes is supported by risk reduction funding from the US Department of Energy’s (DOE’s) Advanced Reactor Demonstration Program.
