The US Nuclear Regulatory Commission (NRC) has directed staff to issue a construction permit to Kairos Power for the company’s proposed Hermes non-power test reactor to be built at the Heritage Center Industrial Park in Oak Ridge, Tennessee. The permit authorises Kairos to build a 35 MWt reactor that would use molten salt to cool the reactor core.

Following a mandatory hearing, NRC authorised the Office of Nuclear Reactor Regulation to issue the permit, having found the staff’s review of the Kairos application adequate to make the necessary regulatory safety and environmental findings. The staff expects to issue the permit by the end of the month.

Kairos submitted its construction permit application (CPA) for review in November 2021 to build the Hermes reactor in 2021. The test reactor, which will not generate electricity, is intended to provide operational data to support the development of a larger version for commercial power. NRC issued the final environmental impact statement for the site in August following the final safety evaluation for the permit in June. Kairos will have to submit a separate application for an operating licence.

Kairos Power said the entire process took just over two years to complete and involved dozens of technical and topical reports which were developed, in part, with support from the US Department of Energy (DOE). “Kairos Power is thrilled to have achieved this major regulatory milestone as we make final preparations to start construction at the Hermes site next year," said Kairos co-founder & CEO Mike Laufer. "We are excited for this next phase in the deployment of the Hermes reactor, and we remain committed to being a good community partner to our neighbours in Oak Ridge as we bring value to the region and build on its nuclear legacy."

US Assistant Secretary for Nuclear Energy Kathryn Huff said this is “a huge milestone for the nuclear energy sector”. She added: “NRC’s approval of the first ever CPA granted to a Generation IV reactor charts a path forward for future design applications as we work toward deploying new reactor technologies. This accomplishment is a testament to the collaborative work among Kairos, the NRC, DOE and all stakeholders involved in the project.”

The Hermes design is for a 35 MWt non-power version of the company's fluoride salt-cooled high temperature reactor, the KP-HFR. Kairos has also submitted a construction permit application for Hermes 2, a proposed two-unit demonstration plant that would build on the experience of Hermes and would produce electricity and demonstrate the complete architecture of future commercial plants. The Hermes demonstration reactors will help 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.

Hermes is one of several new reactor technologies DOE is supporting through its Advanced Reactor Demonstration Program. The low-power reactor uses a TRISO fuel pebble bed design with a molten fluoride salt coolant. The KP-FHR is based, in part, on DOE-sponsored Integrated Research Projects led by several universities, national labs, and international partners to advance fluoride salt-cooled high-temperature reactors.

Kairos Power is conducting salt operations at its first engineering test unit (ETU) in New Mexico. The ETU is a non-nuclear, full-scale mock-up of Hermes that will demonstrate key systems and components of the reactor, test the supply chain, and allow workers to gain operational experience. Kairos will build and operate a total of three ETU iterations before constructing Hermes.

Image: Artist's impression of the Hermes plant (courtesy of Kairos Power)