The US Nuclear Regulatory Commission (NRC) has authorised the staff to issue TerraPower’s subsidiary, US SFR Owner (USO), a construction permit for unit 1 of the company’s Kemmerer Power Station commercial nuclear power plant in Wyoming. “This is a historic step forward for advanced nuclear energy in the United States and reflects our commitment to delivering timely, predictable decisions grounded in a rigorous and independent safety review,” NRC Chairman Ho Nieh said.
This is the first commercial reactor the NRC has approved for construction in nearly a decade and the first approval for a non-light water reactor in more than 40 years. NRC staff finished their technical review of this new design in less than 18 months, following a streamlined mandatory hearing process. NRC authorised its Office of Nuclear Reactor Regulation to issue the permit, having found the staff’s review of the Kemmerer application adequate to make the necessary regulatory safety and environmental findings.
TerraPower filed the application in March 2024, requesting a permit to build the sodium-cooled, advanced reactor design at the Kemmerer site near an existing coal-fired power plant. The NRC staff accepted the application and began formal review in May 2024. The NRC staff issued its safety evaluation for the permit in December 2025, and the final environmental impact statement for the site in October 2025. USO would need to submit a separate operating licence application, and the NRC staff would need to approve it before the facility could operate. USO expects to complete construction by 28 February 2031 and apply for a future Class 103 operating licence for a 40-year period. USA is the primary “owner” of the reactor for licensing purposes, distinguishing it from the “energy island” (non-nuclear side) often managed in partnership with utilities such as PacifiCorp.
“Our team has worked relentlessly for over four years with the NRC staff to get to this moment,” said TerraPower’s President & CEO, Chris Levesque. “We had extensive pre-application engagement with the NRC; and we submitted a robust and thorough construction permit application almost 2 years ago. We have spent thousands of manpower hours working to achieve this momentous accomplishment. We plan to start construction on the Natrium plant in the coming weeks and look forward to bringing the first Natrium reactor and energy storage system to market in the great state of Wyoming.”
The project is supported by the US Department of Energy’s (DOE’s) Advanced Reactor Demonstration Program (ARDP) and is intended to demonstrate the Natrium sodium-cooled fast-reactor technology developed by TerraPower and General Electric (GE)-Hitachi. TerraPower has signed agreements with companies such as Meta to develop up to eight reactors and entered the UK Generic Design Assessment (GDA) process in February.
The 345 MWe (840 MWt) plant includes an energy storage system to temporarily boost output up to 500 MWe when needed. The reactor plant consists of a pool-type, metal-fuelled, sodium-cooled fast reactor (SFR) featuring a “compact and simple safety envelope” and utilising a molten salt energy storage system which will enable load-following. The design relies on passive safety systems and thermal convection for cooling. It uses HALEU (high-assay low-enriched uranium) metal fuel, containing between 5% and 20% uranium-235. It is designed to use 80% less nuclear-grade concrete per megawatt than traditional large-scale reactors.
The design draws from GE Hitachi’s PRISM reactor and TerraPower’s Traveling Wave Reactor concepts. As part of its “pool-type” configuration, the primary coolant pumps and heat exchangers are all submerged in a single large tank of sodium to prevent external leaks.
The construction permit for Kemmerer unit 1 allows TerraPower and Bechtel, the primary construction partner, to begin nuclear-island work including the reactor building and safety-related structures.
Work on the “energy island” (the non-nuclear portion containing the turbine and molten salt storage) began in June 2024. On-site facilities include the sodium Test and Fill Facility (TFF) which is nearing completion, with interior steel installed and outside sheathing scheduled for 2026. This facility will test the full sodium loop before it is introduced to the reactor core. Construction of the Kemmerer Training Center (KTC) began in August 2025 and will house the reactor’s simulator. Curtiss-Wright was awarded two major contracts in February 2025 to deliver the training simulator and the distributed control systems for both the nuclear and energy islands.
The Natrium reactor is not manufactured in a single factory. It is a global assembly project where major components are fabricated by specialised international partners and shipped to the Kemmerer site for final installation. TerraPower has awarded several contracts for the “reactor enclosure system” and other critical hardware. The reactor vessel is being manufactured by HD Hyundai Heavy Industries in South Korea and the core barrel & guard vessel are being supplied by South Korea’s Doosan Corporation.
Equipos Nucleares SA (ENSA) in Spain is producing the reactor head and Canada-US Marmen is manufacturing the rotating plug. The intermediate heat exchanger is designed by BWXT Canada, while the sodium-salt heat exchangers are fabricated by Thermal Engineering International (US). The sodium pumps are being designed and fabricated by Hayward Tyler in the US. A dedicated facility is located in Wilmington, North Carolina and operated in partnership with GE Hitachi will manufacture the HALEU metallic fuel assemblies. The first fuel cores are targeted for loading in 2027-28.
Framatome US Government Solutions is designing the ex-vessel fuel handling machine, while Teledyne Brown Engineering is responsible for the in-vessel transfer machine. A joint venture between TerraPower and GE Hitachi is constructing the Natrium Fuel Facility in Wilmington, North Carolina, to produce the required HALEU metallic fuel. AVANTech was contracted in July 2025 to design sodium processing modules and deliver the Cold Trap Skid for the TFF.
Since liquid sodium is highly corrosive and operates at 500°C, material science is also important. The reactor vessel & guard vessel will be constructed from 316FR stainless steel, optimised to resist creep (deformation under constant high heat) and fatigue over a 60-year lifespan.
The redan, which physically separates the hot pool of sodium from the cold pool within the single reactor, and upper internal structures use Type 304 and 316 stainless steels, which do not become as brittle as other metals when bombarded by the fast neutrons. The HALEU fuel pins are encased in HT9 ferritic-martensitic steel, which has extremely low swelling rates under intense radiation.
To deliver massive components to the high-desert plains of Kemmerer, Wyoming, TerraPower and Bechtel will have to navigate logistical complexities. Most heavy components (like the reactor vessel from South Korea or the head from Spain) will arrive at West Coast ports. From there, they will be moved via heavy-haul rail or specialised multi-axle road transporters. The reactor vessel is roughly 10 metres in diameter and 15 metres tall. To fit through mountain passes and under bridges, some components will have to be shipped in “sub-assemblies” to be welded on-site in the Nuclear Island Fabrication Shop – a massive temporary factory built specifically for the project.
Currently, the only commercially operating sodium-cooled fast reactors are in Russia. Development of these reactors took decades with full integrated government support. In the US and Europe research on fast reactors took place in the 1960s and 1970s but all the projects have been closed down. With Terrapower only now beginning construction of the nuclear island using components from a range of different companies and facing possible logistical delivery problems, launch of Kemmerer unit 1 in 2031 may be optimistic.
