The US Nuclear Regulatory Commission (NRC) agreed to issue construction permits to Kairos Power for the Hermes 2 Demonstration Plant to be built at the Heritage Centre Industrial Park in Oak Ridge, Tennessee. Hermes 2 will build on experience from the Hermes Low-Power Demonstration Reactor, which was the first US Generation IV reactor to receive an NRC construction permit in December 2023. Kairos says Hermes 2 is now the first power-producing Gen IV plant to be approved for construction in the US.
The Hermes series represents a major step on Kairos Power’s iterative path to commercialising fluoride salt-cooled, high-temperature reactor (KP-FHR) technology. According to Kairos, Hermes 2 will demonstrate complete plant architecture at a reduced scale and supply clean electricity to the grid, further advancing technology, licensing, supply chain, and construction certainty for Kairos Power’s commercial deployments.
The Hermes design is for a 35 MWt non-power version of the KP-HFR. The permits authorise Kairos to build a facility with two 35 MWt test reactors that would use molten salt to cool the reactor cores. Kairos says the Hermes demonstration reactors will help to mitigate technology, licensing, supply chain, and construction risk to achieve cost certainty for KP-HFR technology. Kairos is targeting commercial deployments in the early 2030s. The Hermes 2 facility will include the two reactors and a shared power generation system. The facility is intended to provide operational data to support the development of the larger KP-HFR.
“While keeping safety at the forefront, the permitting process was quite efficient, and we issued these permits in less than 18 months,” said NRC Chair Christopher Hanson. “This shows we can rapidly apply relevant conclusions from earlier reviews to promptly reach decisions on new reactors.”
Following a new, streamlined mandatory hearing process conducted using written documents, the Commission authorised its Office of Nuclear Reactor Regulation to issue the permits, “having found the staff’s review of the Hermes 2 application adequate to make the necessary regulatory safety and environmental findings”.
NRC will need to review and approve any future application from Kairos before operating licences for the Hermes 2 facility can be issued. Kairos submitted its application to build Hermes 2 in July 2023. NRC issued its final safety evaluation for the permits in July 2024, and the final environmental assessment for the site in August.
NRC’s approval of the Hermes 2 construction permits follows a thorough review of Kairos Power’s application, which was completed on an accelerated schedule of just over one year. The rapid review and approval timeline was made possible by Kairos Power’s extensive pre-application engagement with NRC dating back to 2018, along with numerous process improvements piloted by the first Hermes CPA and the NRC’s new simplified mandatory hearing process. Additional efficiencies were created by the similarities and co-location of the two Hermes iterations, which allowed the Hermes 2 application to leverage work already done for Hermes.
“The NRC’s mission to protect people and the environment aligns closely with Kairos Power’s,” said Peter Hastings, Vice President of Regulatory Affairs & Quality. “The licensing basis established with both the Hermes and Hermes 2 construction permits will carry forward to future license applications, ensuring the safety of Kairos Power’s deployments while supporting continued innovation and efficiency in the review process.”
The Hermes 2 plant will be built on land that Kairos Power purchased in 2021 adjacent to the Hermes reactor, currently under construction. Kairos Power will now apply for an operating licence for Hermes 2, which must be approved by NRC before the plant can start up.
Kairos broke ground in October on a Salt Production Facility to be constructed at the company’s Manufacturing Development Campus at Mesa del Sol in Albuquerque, New Mexico. The facility will produce high-purity, molten salt coolant for the planned reactors, starting with the Hermes Low-Power Demonstration Reactor in Oak Ridge.
The coolant is a chemically stable mixture of lithium fluoride and beryllium fluoride salts known as “Flibe”. The Salt Production Facility will build upon lessons learned from the company’s Molten Salt Purification Plant in Ohio, which produced 14 tonnes of unenriched Flibe for the non-nuclear Engineering Test Unit (ETU 1.0) demonstration in Albuquerque in 2023.
ETU 1.0 is now undergoing decommissioning. Kairos Power’s “rapid iterative development” means designing, building, and testing multiple prototypes, learning lessons, and improving processes along the way. ETU 1.0 was a full-scale, electrically heated prototype of Hermes. The next iteration, ETU 2.0, already underway in Albuquerque, will focus on demonstrating the modular design of the reactor. After that, ETU 3.0 will be built in Oak Ridge, Tennessee adjacent to the eventual site of the Hermes reactor.
