Kairos' Hermes Secures First NRC Green Light for Advanced Nuclear Non-LWR Reactor
The Nuclear Regulatory Commission (NRC) has approved a construction permit for Kairos Power’s 35-MWth Hermes molten salt “non-power” demonstration reactor, which the firm has proposed to build at the East Tennessee Technology Park Heritage Center (ETTP) site in Oak Ridge.
The NRC on Dec. 12 directed staff to issue the construction permit for the test reactor and expects the permit to be issued by the end of the month. The NRC accepted Kairos’s construction permit application (CPA) for Hermes submitted under 10 CFR Part 50.21 (a class of licenses for medical therapy and research and development facilities) in November 2021. A vote on Tuesday follows a mandatory hearing on Oct. 19, during which the commission authorized the NRC’s Office of Nuclear Reactor Regulation to issue the permit. The NRC, notably, wrapped up its final safety evaluation for the demonstration reactor within 18 months, well ahead of schedule.
A Historic Approval
The approval is a major boost for Alameda, California–headquartered Kairos Power, a privately owned nuclear engineering, design, and manufacturing company that says it is “singularly focused” on the commercialization of its fluoride salt-cooled high-temperature reactor (KP-FHR). “Hermes is the first non-water-cooled reactor to be approved for construction in the U.S. in over 50 years,” noted Peter Hastings, Kairos vice president of Regulatory Affairs & Quality.
While the NRC has a long history of regulating non-light water reactors (LWRs), the regulator’s last non-LWR construction permit, issued in 1968, went to Fort Saint Vrain, a high-temperature gas-cooled reactor that operated until 1989 in Colorado. Clinch River Breeder Reactor, a 350-MWe reactor proposed by the Tennessee Valley Authority (TVA) and Commonwealth Edison, was expected to receive a construction permit in 1983, but work stopped when the project was canceled that year. The NRC marked more progress when medical isotope producer SHINE Medical Technologies in 2016 received a construction permit for a medical isotope manufacturing facility in Wisconsin. However, along with Kairos, the NRC is reviewing non-LWR applications from only one other entity—Abilene Christian University, for a 1-MWth non-power molten salt research reactor in Texas.
For Kairos, the “historic achievement is a testament to the concerted effort by the entire Kairos Power team aligned with our iterative approach to licensing KP-FHR technology,” Hastings said. “Our successful pre-application engagement and application review have established a solid foundation on which to build.”
A Novel Iterative Approach
Kairos, a 2016-founded firm, is uniquely pursuing a new approach to nuclear development inspired by the success of space exploration technologies firm SpaceX. Kairos’s approach involves using iterative hardware demonstrations and in-house manufacturing “to achieve disruptive cost reduction and provide true cost certainty for commercialization.”
The firm targets costs “set to be competitive with natural gas in the U.S. electricity market.” The approach, which targets a U.S. commercial demonstration by 2030 or earlier—and a rapid deployment ramp in the 2030s—also involves a nuanced strategy to address regulatory risks.
While Hermes, a scaled advanced reactor demonstration plant, will not produce power, it will support development of Kairos’s KP-FHR, a 140-MWe advanced reactor technology that uses a flexible steam cycle to produce and then convert heat from fission into power. Kairos’s KP-FHR essentially comprises a graphite-moderated, “randomly packed” pebble‐bed reactor with molten fluoride salt coolant (a chemically stable molten fluoride salt mixture of 2LiF:BeF2 [Flibe] enriched in Li‐7), operating at high temperature and near‐atmospheric pressure.
The fuel in the KP-FHR is based on tri-structural ISOtropic (TRISO) particle fuel in pebble form with a carbonaceous‐matrix coated particle design. The fuel will contain high-assay low-enriched uranium (HALEU) enriched at 19.74%. “The fuel kernel and some of the coatings on the particle fuel provide retention of fission products. TRISO particles are dispersed within the graphite matrix of fuel pebble’s fuel layer,” the company has said.
Hermes, located within the ETTP—on the building site of a former Department of Energy gaseous diffusion plant (K-33)—will produce 35 MWth and feature coolant operating temperatures of between 550C and 650C. The demonstration’s key objective is to “prove Kairos Power’s capability to deliver low-cost nuclear heat,” but it will also help shed more light on cost and a supply chain, along with reducing risks through testing and a licensing approach, the company said. Kairos Power also notably has a cooperative development agreement with the TVA to provide defined engineering, operations, and licensing services for Hermes.
Integrating a Commercialization Plan
To prepare for the construction and operation of Hermes—Kairos’ first nuclear iteration—the company is making headway on the Engineering Test Unit (ETU), a non-nuclear, unenriched Flibe-wetted, and isothermal integrated test, at Kairos’s KP-Southwest research and development facility in Albuquerque, New Mexico.
“ETU 1.0 is commissioned and hot functional testing is currently underway,” Kairos told POWER on Thursday. In October, Kairos reported it began loading 14 tons of the molten fluoride salt coolant into the ETU, “initiating the largest Flibe transfer since the Molten Salt Reactor Experiment in 1969.” Over the last three weeks, “the team has begun circulating Flibe in the ETU vessel, initiated pebble handling operations, and exercised the Reactivity Control System, in addition to other tests. ETU 1.0 will be put in layup over the holidays, with testing scheduled to resume in January,” Kairos added. “We expect to complete testing and begin the process of decommissioning ETU 1.0 in the first part of 2024.”
Kairos, notably, is already producing Flibe for the ETU program at its June 2022–commissioned Molten Salt Purification Plant (MSPP) at specialty materials company Materion’s campus in Elmore, Ohio. Chemically stable and capable of operating at low pressure, the liquid fluoride salts will be used to cool several major hardware demonstrations that Kairos Power has planned as part of its pathway to commercialize the commercial-scale, 140-MWe KP-FHR version, dubbed the KP-X.
A ‘Wealth of Lessons’
The effort to build the first U.S. plant to produce Flibe at an industrial scale “has generated a wealth of lessons that will help de-risk salt production for future iterations,” Kairos noted. “Further, as we commence Flibe testing with the ETU, our team at KP Southwest benefits from extensive knowledge about molten salt behavior and beryllium handling protocols gained from over a year of Flibe operations with MSPP.”
Meanwhile, the ETU is designed to demonstrate the “integration of principal systems, structures, and components,” Kairos has noted. “Lessons learned from ETU will be integrated into Hermes and future iterations on the path to commercializing KP-FHR technology.”
Once all 14 tons of Flibe are circulating in ETU, Kairos expects to embark on “a multi-month testing program that will continue to provide learnings and data until the system is decommissioned to make way for the next iteration—ETU 2.0,” it said.
ETU 2.0, slated to demonstrate modular construction, involves building each subsystem as a modular skid. “This will enable us to advance ETU 2.0 construction while ETU 1.0 operations and decommissioning are still in progress,” it said. “This summer, the team began construction on the Modular Systems Facility, which will support ETU 2.0 subsystem development,” it noted.
In August 2023, Kairos announced that the third ETU iteration—ETU 3.0—will be built on land owned by Kairos Power adjacent to the Hermes site at Heritage Center Industrial Park. “The strategic decision to build ETU 3.0 in Oak Ridge will accelerate our civil construction experience locally, building relationships and generating learnings that will transfer directly to the Hermes project,” Kairos said. “It’s one more way that we can leverage experience from the ETU series to take risk off the table prior to our first nuclear build.”
Hermes Will Be Followed by Power-Producing, Two-Unit Hermes 2
For now, Kairos plans to break ground on Hermes at the Heritage Center in 2024. However, it must first secure a separate approval for an NRC operating license before it can begin operating the Hermes demonstration to comply with the two-step, 10 CFR Part 50 licensing process. Because the firm is working with a $303 million federal award under the Department of Energy’s (DOE’s) Advanced Reactor Demonstration Program (ARDP) risk reduction pathway, Kairos has targeted mid-2026 as an initial commissioning date for Hermes.
This summer, notably, the NRC also formally accepted for review a CPA for a new iteration, Hermes 2, a two-unit demonstration that would produce “low-power” electricity. Hermes 2 will be deployed in Oak Ridge on the same site as the first Hermes reactor “to further de-risk technology, construction, supply chain, and licensing for a multi-reactor plant,” Kairos said.
The Hermes 2 CPA builds on Kairos’s successful Hermes CPA “with many sections in common, given its similar siting considerations and the same fundamental KP-FHR safety case,” the company noted. Among key differences is that each Hermes 2 unit will have a licensed lifetime of 11 years and use an intermediate salt loop to exchange heat from the primary salt to the common power generation system.
Kairos CEO Mike Laufer in July noted a “a few important details must fall into place before we can fully commit to building it.” He added, however, that “Hermes 2 presents a unique opportunity to accelerate commercial deployment of KP-FHR technology while bringing value to the local community over the long term.”
On Tuesday, Laufer lauded the company’s latest regulatory milestone. “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 neighbors in Oak Ridge as we bring value to the region and build on its nuclear legacy,” he said. “With the Hermes construction permit now approved, Kairos Power is demonstrating our leadership in developing advanced nuclear reactors, and we have made a big step forward on our path to deploying clean, safe, reliable, and affordable energy in East Tennessee and beyond.”
—Sonal Patel is a POWER senior associate editor (@sonalcpatel, @POWERmagazine).
Updated (Dec. 14): Adds details from Kairos