The Nuclear Regulatory Commission (NRC) has taken a historic vote to issue construction permits to allow Kairos Power to build the 70-MWth Hermes 2, a "low power" advanced test facility comprising two 35-MWth test molten salt reactors. With the decision, "Hermes 2 has become the first electricity-producing Gen IV plant to be approved for construction in the U.S.," said Kairos Power.
Kairos plans to build Hermes 2 at the East Tennessee Technology Park Heritage Center (ETTP) in Oak Ridge, Tennessee. The site will also host the proposed single 35-MWth Hermes 1 test reactor, a non-nuclear engineering test unit, and potentially a Kairos Power fuel fabrication facility.
Construction on Hermes 1, a non-power demonstration reactor, began in July 2024 and is expected to be completed by 2027, making it Kairos Power's first nuclear project. If construction of Hermes 2 proceeds on schedule, the facility's two reactors -- capable of a combined electrical output of 20 MWe -- could begin operation by December 2027.
The NRC's issuance of the Hermes 2 construction permit represents a key milestone in the two-step CFR Part 50 licensing process. Kairos Power will need to apply for and secure an operating license before the plant can commence operations. Once operational, Hermes 2's two reactors are anticipated to have a licensed lifetime of 11 years.
The licensing milestone is another notch for the Alameda, California-headquartered engineering company, which has been developing and marketing nuclear power plant designs based on its fluoride salt-cooled, high-temperature reactor (KP-FHR) technology since its founding in 2016. The company is pursuing a notable "rapid iterative development approach," which involves using iterative hardware demonstrations and in-house manufacturing "to achieve disruptive cost reduction and provide true cost certainty for commercialization." Under the stepwise approach, Kairos is also looking to de-risk its technology and supply chain logistics and clear regulatory hurdles before scaling to full commercial deployment.
As POWER has reported, Kairos's KP-FHR 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 company's targeted commercial offerings will include the KP-X Commercial Demo Plant, a single-unit, 50-MWe fluoride salt-cooled high-temperature reactor designed to operate at 650C and near-atmospheric pressure, and KP-FHR Commercial Plant, a dual-unit, 150-MWe reactor configuration (2 x 75 MWe) designed for high efficiency with a 650C reactor outlet temperature. Kairos' designs will use 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%.
In October, notably, Kairos signed a landmark Master Plant Development Agreement with Google to develop a 500-MW fleet of molten salt small modular reactors (SMRs) by 2035 to power the tech giant's data centers, with the first reactor expected to be operational by 2030. Google said accelerating nuclear deployment is critical to meeting surging data center energy demands and achieving its 24/7 carbon-free energy goals by 2030. While Kairos confirmed to POWER it is planning one KP-X Commercial Demonstration Plant, it declined to reveal specifics about the individual plants to be deployed under the pioneering deal with Google.
As part of its unique iterative approach, Kairos has kicked development with a series of Engineering Test Units (ETUs), which are non-nuclear integrated tests designed to validate the performance of critical systems in a controlled environment. ETU 1.0, commissioned at the company's Albuquerque facility, operated for over 2,000 hours using 12 metric tons of molten fluoride salt (Flibe) to simulate coolant flow and heat transfer at temperatures up to 675C. Following its decommissioning following six months of operation in July 2023, Kairos initiated ETU 2.0 in Albuquerque. Its next steps will entail the development of ETU 3.0 in Oak Ridge to incorporate lessons learned from earlier iterations and refine modular construction techniques.
The Hermes reactors represent the next phase in the company's pathway. Hermes 1, a single-unit, non-power demonstration reactor, focuses on operational safety and system integration. Building on its design, Hermes 2 will feature two 35-MWth reactors sharing a Rankine Cycle power conversion system with a 20 MWe capacity. It will also add intermediate salt loops and steam superheaters.
"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 company said on Wednesday.
Finally, as part of its iterative approach, Kairos has marked numerous regulatory milestones. In December 2023, NRC granted Kairos a construction permit for its 35-MWth Hermes 1 "non-power" demonstration -- 25 months after it accepted Kairo's construction permit application under 10 CFR Part 50.21 (a class of licenses for medical therapy and research and development facilities) in November 2021. The NRC's approval for Hermes, notably, marked the federal regulator's first green light for the construction of a non-water-cooled reactor in more than 50 years.
Licensing for Hermes 2 has been even speedier. While the NRC formally accepted Kairos' CPA for Hermes 2 in June 2023, it issued its final safety evaluation for the permits in July 2024 and completed its Final Safety Evaluation Report (FSER) for Hermes 2 in August 2024 -- nearly four months ahead of schedule. In total, from CPA acceptance to the construction permit vote, the NRC process has taken 16 months. The timeframe is a staggering achievement for the regulator, which has been historically regarded as notoriously slow in its licensing processes -- particularly for new or novel reactor designs -- owing to its rigorous safety standards, detailed reviews, and public consultation requirements.
The NRC said the efficient review stemmed from a "new, streamlined mandatory hearing process" conducted via written documents. The commission "authorized the agency's 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," it noted. NRC staff "expects to issue the permits in the near future," it said.
"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 on Wednesday. "This shows we can rapidly apply relevant conclusions from earlier reviews to promptly reach decisions on new reactors."
Kairos on Wednesday suggested the rapid review and approval timeline stems from Kairos' extensive pre-application engagement with the NRC. Engagement dates "back to 2018, along with numerous process improvements piloted by the first Hermes CPA and the NRC's new simplified mandatory hearing process," it said. "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."
According to Peter Hastings, Kairos vice president of Regulatory Affairs & Quality, the licensing basis established by the Hermes 1 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."
Darrell Gardner, Kairos senior licensing director, described the company's experience working with the NRC as "positive." The company's applications served as "a testing ground for more efficient processes that will benefit the entire industry," he noted. " Kudos to the NRC and to the entire Kairos Power team for another job well done," he said.