Another Fourth-Generation Nuclear Reactor Begins Construction in the U.S.
Construction of Hermes, Kairos Power’s 35-MWth iterative non-power demonstration molten salt nuclear reactor, has officially kicked off in Oak Ridge, Tennessee. The effort marks another major step for the burgeoning advanced nuclear industry, which celebrated the groundbreaking of TerraPower’s Kemmerer 1, a pioneering sodium-cooled fast reactor demonstration, in June.
Site work and excavation for the Hermes demonstration commenced earlier this month at the East Tennessee Technology Park Heritage Center (ETTP) site in Oak Ridge, spearheaded by heavy civil construction firm Barnard Construction Co., Kairos, announced on July 30.
When completed as anticipated in 2027, Hermes will become Kairos Power’s first nuclear build. The demonstration molten salt reactor is part of the Alameda, California–based engineering company’s notable “rapid iterative development approach” to developing and marketing nuclear power plant designs based on its fluoride salt-cooled, high-temperature reactor (KP-FHR) technology.
Architect’s rendering of the Hermes Low-Power Demonstration Reactor facility
Architect’s rendering of the Hermes Low-Power Demonstration Reactor facility (July 2024) Courtesy: Kairos Power
From ETUs to Hermes: Testing to Pave the Way for Commercial Deployment
Kairos anticipates a KP-FHR commercial reactor could become operational in the early 2030s. As POWER has reported, Kairos’s KP-FHR features a graphite-moderated, “randomly packed” pebble‐bed reactor with molten fluoride salt coolant (a molten fluoride salt mixture of 2LiF:BeF2 [Flibe] enriched in Li‐7). The KP-FHR is designed to operate at high temperatures and near‐atmospheric pressure, using tri-structural ISOtropic (TRISO) particle fuel in pebble form with a carbonaceous‐matrix coated particle design.
The reactor coolant, a chemically stable, low-pressure molten fluoride salt mixture, has a boiling point of 1,430C, notably lower than 1,600C, and yet functionally very high, Kairos has noted. “The fundamental concept is the combination of [TRISO] particle fuel coupled with a molten fluoride salt coolant,” Peter Hastings, Kairos vice president of Regulatory Affairs and Quality, said in recent testimony filed with the NRC.
“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. The intrinsic low pressure of the reactor and associated piping, along with the fission product retention provided by the TRISO fuel, enhances safety and eliminates the need for low‐leakage, pressure retaining containment structures,” he explained. Additionally, the design “relies on passive decay heat removal and does not need an emergency core cooling system for decay heat removal or replacement of coolant inventory. The major plant systems are the reactor system (RS), the primary heat transport system (PHTS), and the decay heat removal system (DHRS),” he said.
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Kairos has so far made substantial progress on a series of Engineering Test Units (ETUs), which are non-nuclear, unenriched Flibe-wetted and isothermal integrated tests at the company’s KP-Southwest research and development facility in Albuquerque, New Mexico. The company is also 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.
On July 1, ETU 1.0 began decommissioning after six months—more than 2,000 hours—of pumped salt operations using 12 metric tons of Flibe. The learnings from the test unit will inform the design, construction, and operation of the Hermes reactor and future deployments, the company said. Recently, it also kicked off ETU 2.0 in Albuquerque, which will demonstrate modular construction. Work to build the final ETU iteration, ETU 3.0 has also begun under a collaboration between Barnard and Kairos, the company confirmed on Tuesday.
ETU 3.0 will be built at the ETTP site in Oak Ridge, where the Hermes demonstration reactor is now under construction.The engineering test unit “will generate supply chain, construction, and operational experience to inform the Hermes project,” said Kairos. “This iterative approach will allow lessons learned from ETU 3.0 civil construction to transfer seamlessly to the Hermes facility.”
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), is pursuing a pathway that addresses technical and regulatory risks. Courtesy: Kairos
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), is pursuing a pathway that addresses technical and regulatory risks. Courtesy: Kairos
Hermes’ primary objective “will be to demonstrate Kairos Power’s ability to produce affordable nuclear heat. Hermes will not produce electricity,” Kairos noted. However, Hermes, a 35-MWth thermal reactor, will, like the KP-FHR, use TRISO containing high assay low-enriched uranium (HALEU), configured as a pebble bed with molten fluoride salt coolant. The test reactor is intended to provide operational data to support the development of a larger version for commercial deployment.
Kairos has meanwhile embarked on developing the next iteration, Hermes 2, a two-unit demonstration that will comprise two 35-MWth test reactors. Like Hermes, Hermes 2 will use TRISO-fueled pebbles in Flibe, but it will produce a combined electrical output of 20 MWe via an integrated steam-powered (Rankine Cycle) conversion system. Hermes 2, set to be deployed in Oak Ridge on the same site as the first Hermes demonstration, will “further de-risk technology, construction, supply chain, and licensing for a multi-reactor plant,” Kairos has said.
Hermes 2 will comprise two units producing 35 MWth and “low” power. It is slated to 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. Courtesy: Kairos
The ETTP site will host Hermes, a 35-MWth non-power demonstration, Hermes 2 (two units producing 35 MWth and 20 MWe of power), and ETU 3.0, a test iteration designed to “generate supply chain, construction, and operational experience,” Kairos said. Courtesy: Kairos Power
Permits for First Non-Water-Cooled Reactor in Decades
As part of its iterative approach, Kairos has marked numerous regulatory milestones. In December 2023, the NRC granted Kairos a construction permit for its 35-MWth Hermes “non-power” demonstration. 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. The NRC accepted Kairos’ construction permit application for Hermes 1 in November 2021. Kairos is now awaiting 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.
In June 2023, meanwhile, the NRC formally accepted for review a construction permit application (CPA) for the next iteration, Hermes 2, the two-unit demonstration that would produce “low-power” electricity. The NRC last week wrapped up its final safety evaluation for Hermes 2, “nearly four months ahead of schedule, and using about 60% fewer resources than expected,” the regulatory body noted.
Kairos is notably also pioneering a novel performance-based, fixed-price milestone funding approach to support the design, construction, and commissioning of its 35-MWth Hermes demonstration. In February 2024, the firm secured a $303 million funding agreement from the Department of Energy (DOE), where the company will receive fixed payments upon achieving significant project milestones. The strategy will be implemented under a Technology Investment Agreement (TIA) between Kairos and the DOE as part of the DOE’s Advanced Reactor Demonstration Program (ARDP) risk reduction award. Announced in December 2020, the ARDP award’s total value for the Hermes project over seven years is $629 million, with $303 million, or about 48%, coming from the DOE.
A Collaborative Effort
Kairos has developed Hermes as part of a substantial collaborative effort, with partners that include Hermes is a joint effort by Kairos Power and its partners, including Oak Ridge National Laboratory, Idaho National Laboratory, EPRI, and Materion Corp. “In addition, Kairos Power is partnering with Los Alamos National Laboratory to produce TRISO pebble fuel for Hermes in the lab’s Low-Enriched Fuel Fabrication Facility. Kairos Power has also established a cooperative development agreement with the Tennessee Valley Authority (TVA) to provide engineering, operations, and licensing support for Hermes,” the company noted on Tuesday.
Big milestone for advanced nuclear in the US. Congratulations Kairos Power! This is a key step on the path towards commercializing the technology. Advanced nuclear technology is what America’s clean energy future looks like. https://t.co/wbhPwDfCeR
— Tennessee Valley Authority (@TVAnews) July 30, 2024
The milestone is also especially notable amid considerable new enthusiasm for the future of nuclear power. As POWER has reported, the sector has celebrated solid support around the world for its potential to provide carbon-free power and heat.
In June, Bellevue, Washington, headquartered TerraPower broke ground on the non-nuclear portion of Kemmerer Unit 1, a 345-MW Natrium sodium-cooled fast reactor (SFR) power plant, at a site about miles from PacifiCorp’s three-unit 604-MW coal and gas–fired Naughton Power Plant. TerraPower, a Bill Gates nuclear innovation startup, and GE Hitachi Nuclear Energy (GEH) unveiled the Natrium design in September 2020. TerraPower submitted a construction permit application (CPA) to the NRC in March 2024 (through a wholly owned subsidiary US SFR Owner, and the NRC accepted the CPA on May 21. While the NRC is now working on establishing a review schedule for the CPA, TerraPower says it anticipates submitting the operating license in 2027, allowing it to begin construction on the nuclear island in 2026 and complete the plant “this decade.”
Construction start of Hermes is illustrative of another rapid development journey for advanced nuclear that began less than four years ago. Kairos, founded in 2016, first announced it would deploy a test reactor at the ETTP in Oak Ridge in December 2020, pending completion of due diligence and discussions with state and local officials. The 2,200-acre ETTP site, which formerly hosted the K-33 gaseous diffusion plant site for 40 years, is now a private industrial park.
TVA’s 935-acre Clinch River site in Roane County, near Oak Ridge, Tennessee—for which the utility holds the nation’s only early site permit (ESP) from the NRC—is notably located about 6 miles away. TVA last year confirmed it is preparing a construction permit application for a GE Hitachi BWRX-300 at the Clinch River site and exploring additional sites in the TVA service area for potential SMR deployments.
“We’re thrilled to start building in the historic East Tennessee Technology Park,” said Edward Blandford, Kairos Power’s chief technology officer and co-founder. “The City of Oak Ridge, the Department of Energy and its contractors, and the Barnard team have all been excellent partners in helping us repurpose this brownfield site. Barnard’s strong track record and people-centered culture are a great match for Kairos Power, and we look forward to working together over the long term to realize the future of clean nuclear energy,” he said.
—Sonal Patel is a POWER senior editor (@sonalcpatel, @POWERmagazine).
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