Having completed its review of the construction permit application for Kairos Power’s Hermes test reactor, the US Nuclear Regulatory Commission’s (NRC’s) Advisory Committee on Reactor Safeguards (ACRS) has submitted its conclusions to the agency, recommending approval. California–based Kairos submitted its application to build a demonstration reactor at the East Tennessee Technology Park in Oak Ridge, Tennessee in September 2021 and NRC accepted the application for review two months later.

“Key attributes of the Hermes design include low thermal power of the reactor, use of TRISO fuel and FLiBe [a eutectic mixture of lithium fluoride and beryllium fluoride] coolant as an effective functional containment, and passive heat removal capability,” ACRS stated in its letter to NRC chair Christopher Hanson. “The overall design results in projected dose consequences with large margins to regulatory siting criteria… A scaled demonstration plant like Hermes will be valuable to test key technical elements, design features, safety functions, and equipment performance for this technology. There is confidence that the facility can be constructed in accordance with relevant regulations and the design bases outlined in the preliminary safety analysis report. The construction permit for Hermes should be approved.”

Hermes is a 35-MWt fluoride salt–cooled high-temperature reactor. The proposed unit is intended to demonstrate complete nuclear systems, advance Kairos’s manufacturing capabilities for critical components, test the supply chain, and facilitate licensing certainty for the technology. The company expects Hermes to be operational in 2026 and to lead to the development of a commercial-scale, 140-MWe version dubbed the KP-X.

In December 2020, Kairos received a US Department of Energy (DOE) Advanced Reactor Demonstration Program award for risk-reduction funding to support the development, construction, and commissioning of Hermes in collaboration with Oak Ridge National Laboratory, Idaho National Laboratory, Materion Corporation, and the Electric Power Research Institute. The total award value is $629m over seven years, with the DOE contributing $303m. Kairos has also established a cooperative development agreement with the Tennessee Valley Authority to provide defined engineering, operations, and licensing services for Hermes.

Image: A rendering of the Hermes low-power demonstration reactor (courtesy of Kairos Power)