Engineer and advanced nuclear power developer Kairos Power LLC has begun construction of the Hermes low-power demonstration reactor, what it says is the first and only next-generation nuclear reactor that the U.S. Nuclear Regulatory Commission has okayed to build and the first using non-light-water technology to be permitted in the U.S. in more than 50 years. 

The demonstration molten salt reactor is part of the Alameda, Calif., firm's “rapid iterative development approach” to develop and market nuclear power plant designs based on fluoride salt-cooled, high-temperature reactor technology, it said. Hermes, a 35-MWth thermal reactor, is set to “demonstrate Kairos Power’s ability to produce affordable nuclear heat,” said the developer, noting it will not initially produce electricity.

Barnard Construction Co. Inc., Bozeman, Mont., has begun construction in Oak Ridge, Tenn., for the developer that aims to complete the project by 2027 as a “critical step” to commercialize its technology. 

Kairos Power, founded in 2016, anticipates a commercial reactor could operate in the early 2030s.  

The firm noted its investment of about $100 million in the plant and supporting infrastructure, and an infusion last year by the U.S. Energy Dept. of up to $300 million. ENR could not confirm by posting time if the total project cost was higher and whether it had additional investment sources. 

The agency will pay Kairos in installments for the demonstration project, set up under a technology investment agreement, which will be based on milestones such as construction progress and application for a future federal operating license.

Barnard and Kairos Power also are collaborating to build a third engineering test unit in Oak Ridge, what the developer says is a “non-nuclear” facility “that will generate supply chain, construction and operational experience to inform the Hermes project.” Two other test units have been built at research and testing locations operated by Kairos Power in Albuquerque, N.M., and Elmore, Ohio, the firm said will "inform design, construction and operation of the Hermes reactor."

Both will be built using modular construction techniques, with reactor modules fabricated at the Albuquerque site and shipped to Oak Ridge for assembly, “demonstrating the potential of a factory-built small modular reactor design to transform conventional nuclear construction,” Kairos Power said.

Kairos Power was the first to apply to the federal nuclear regulator for a proof of concept for its technology, the company said, adding that it seeks to reduce technical risk “through a novel approach to test iteration that often is lacking in the nuclear space.” 

The facility is designed to operate at high temperatures and near‐atmospheric pressure, using a special particle fuel coupled with a molten fluoride salt coolant, the company told the commission in a 2023 filing. “The combination of extremely high‐temperature‐tolerant fuel and low‐pressure, single‐phase, chemically stable reactor coolant removes entire classes of potential fuel‐damage scenarios, greatly simplifying the design and reducing the number of safety systems," said Peter Hastings, Kairos Power vice president of regulatory affairs and quality.

"This historic initiative presents a critical opportunity to transform the way we generate power in the U.S., as well as an opportunity to expand economic and employment opportunities for the greater Tennessee area,” said Quincy Anderson, Barnard vice president and operating manager.

The firm also plans to develop the next iteration, Hermes 2, also at Oak Ridge, which will comprise two 35-MWh test reactors. It will use the same fuel but is set to produce a combined electrical output of 20 MWe via an integrated steam-powered conversion system, Kairos Power said, adding that the project will “further de-risk technology, construction, supply chain and licensing for a multi-reactor plant.”

In July, the commission completed its final safety evaluation for Hermes 2, “nearly four months ahead of schedule," the regulator noted. 

Tennessee Valley Authority now is preparing a a construction permit application for a GE Hitachi BWRX-300 small modular nuclear reactor at its 935-acre Clinch River site, located near Oak Ridge, and is weighing added sites in its large service area for other possible deployments.