US-based TerraPower has announced the start of construction of its Natrium plant, Kemmerer unit 1, in Kemmerer, Wyoming after the Nuclear Regulatory Commission (NRC) granted the first-ever construction permit for a commercial-scale advanced NPP in March.
The plant features a 345 MWe sodium-cooled fast reactor integrated with a molten salt-based energy storage system. The storage technology allows the facility to temporarily boost its power output to 500 MWe for over five hours, enabling it to follow daily electricity load changes and integrate with renewable energy sources. Construction is expected to involve approximately 1,600 workers, with 250 full-time staff required for operations.
Completion is targeted for 2030. The total project cost is estimated at $4bn, with the Department of Energy (DOE) providing half through its Advanced Reactor Demonstration Program (ARDP). The project has been under active development since TerraPower broke ground on the greenfield site in June 2024 and began construction on non-nuclear support facilities.
“This is the moment our industry has been working toward for a generation. We’re not just breaking new ground on a first-of-a-kind nuclear plant in Wyoming; we’re building the next generation of America’s energy infrastructure,” said TerraPower President & CEO Chris Levesque. “The Natrium plant will deliver reliable and dispatchable power to the grid and Kemmerer unit 1 serve as a commercial blueprint to mobilise a fleet of Natrium plants across the country and around the world.”
Dr Rian Bahran, Deputy Assistant Secretary for DOE’s Office of Nuclear Energy noted: “Today’s construction milestone is a testament to the Department of Energy’s investment in American innovation and helping companies like TerraPower deliver the next generation of advanced nuclear technologies. The Natrium reactor shows that when government and private industry work together, we can build a bright future for our country powered by nuclear.”
Dena Volovar, President of Bechtel’s Nuclear, Security & Environmental business said Bechtel is proud to partner with TerraPower as the engineering, procurement and construction contractor on the project. “The start of construction at Kemmerer Unit 1 marks an important step forward for the project and for the next generation of US nuclear energy. By combining TerraPower’s reactor innovation with Bechtel’s processes, experience and execution model we will deliver these nuclear projects consistently, safely and at scale. By applying the latest digital tools and project delivery systems, Bechtel is uniquely positioned to deliver the nation’s first Natrium plant with efficiency and execution certainty.”
TerraPower is already signing customers. In January, the company reached a deal with Meta to build up to eight Natrium reactors in the US with the first two targeted to come online by 2032. If the full order is fulfilled, the additional reactors will be operating by 2035. The company also has memorandums of understanding with government agencies in Utah and Kansas to explore potential sites in those states.
While the project has now legally and physically moved from “site preparation” into the “nuclear construction”, a construction permit is not a final stamp of approval on a finished design, but rather a green light to proceed with a specific, proposed design that the regulator has deemed safe enough to start building.
Under the 10 CFR Part 50 licensing pathway TerraPower is using, the design and construction phases overlap. This two-step process allows construction to begin on the “nuclear island” while the final details of the design are still being refined for the eventual operating licence.
When NRC issued the permit in March, it explicitly stated that this “does not constitute approval of the design”. Instead, it confirms that their rigorous safety evaluation, completed in December 2025, found no issues that would preclude building the facility as described in the application.
TerraPower still has to submit a separate Operating Licence application, currently targeted for 2027. At that stage, the NRC will perform a second, even more exhaustive review of the final “as-built” design to ensure it meets all safety and performance requirements before any fuel can be loaded.
While construction at the Kemmerer site is only now transitioning into the “nuclear island” phase, several critical, long-lead reactor components have been under active manufacture off-site since late 2024. The manufacturing focuses on the complex, first-of-a-kind (FOAK) systems.
In December 2024, TerraPower awarded major contracts for the fabrication of the reactor enclosure system. These include the reactor vessel; the vessel internals – structural supports for the fuel assemblies, control rod mechanisms, and internal instrumentation; and primary cooling loops – parts for the primary sodium circuit, which operates at atmospheric pressure.
Because the reactor’s heat must be transferred safely to the non-nuclear “energy island”, specialised exchangers and pumps are under manufacture. These include: intermediate heat exchangers (IHX) -critical sodium-to-sodium exchangers that sit within the primary vessel; sodium-to-salt heat exchangers (SHX) – large-scale units that transfer heat from the intermediate sodium loop to the molten salt storage system; and electromagnetic pumps – these use magnetic fields to move the electrically conductive liquid sodium, eliminating the need for mechanical moving parts in contact with the coolant.
To speed up the site construction, many of the structural modules for the nuclear island are also being prefabricated off-site. These include pre-cast shielding – large concrete and steel modular sections for the reactor building foundations and safety walls; and support steel – heavy-duty structural frames designed to meet seismic and nuclear safety standards.
TerraPower has assembled a global network of specialised partners to manufacture these components. The reactor pressure vessel is being manufactured by HD Hyundai Heavy Industries in South Korea. The core barrel & guard vessel is being produced by Doosan Enerbility (formerly Doosan Heavy Industries) in South Korea. The reactor head is being fabricated by Equipos Nucleares SA (ENSA) in Spain. The rotating plug is being manufactured by Marmen (a Canada-US joint venture).
IHX are being designed and fabricated by BWXT Canada Ltd. The sodium pumps are being designed and built by Hayward Tyler in the US. SHX are being fabricated by Thermal Engineering International (TEi) in the US.
The reactor protection system is being developed by Curtiss-Wright Flow Control Service. The engineering simulator is being developed by Western Service Corporation (WSC) to provide simulation-assisted engineering for the design.
Transporting and assembling the components for Kemmerer 1 involves a complex logistical operation that bridges international manufacturing with on-site modular assembly. Because many of the reactor’s largest components are fabricated abroad, getting them to the high-desert plains of Wyoming is a major undertaking.
Massive components like the reactor vessel (from South Korea) and the reactor head (from Spain) will arrive at major West Coast ports. From the ports, these oversized loads, some roughly 10 metres in diameter and 15 metres tall, will be moved to Kemmerer via specialised multi-axle road transporters or heavy-haul rail. To navigate mountain passes and bridges, some components are shipped as “sub-assemblies” rather than fully finished units to ensure they meet transport clearance requirements.
TerraPower and Bechtel are utilising a “factory-to-site” modular approach to streamline construction. A massive, 66,000-square-foot on-site Reactor Fabrication Building (RFB) serves as a dedicated assembly facility. It allows for the final welding and integration of the reactor vessel and guard vessel components in a controlled environment before they are moved to their permanent position in the Reactor Building.
In early 2026, Konecranes was contracted to supply five advanced cranes, including a 125-tonne high-capacity crane specifically for the RFB to handle these heavy modules.
By pre-assembling components in the RFB and using modular civil engineering parts, the team can perform many “manufacturing” activities directly at the plant. The plant’s design “decouples” the nuclear island from the energy island. This allows the non-nuclear energy storage and turbine systems to be built using standard industrial practices, while the highly regulated nuclear assembly happens concurrently in the specialised RFB.
However, integrating FOAK components from across the globe is a massive logistical and engineering gamble. This was a factor in the problems faced by the Westinghouse Vogtle and VC Summer projects in the US.
TerraPower is attempting to manage these risks through three specific strategies. Before a single piece of steel was cut, TerraPower and Bechtel built a complete digital twin of the plant. Every component from HD Hyundai (Korea) or ENSA (Spain) is modelled down to the millimetre. This allows engineers to “assemble” the plant virtually to ensure that a pipe from a US supplier lines up with a pump from a UK supplier before they ever meet in Wyoming.
The RFB acts as a “buffer.” It allows disparate parts to be inspected for manufacturing deviations, and performs the high-precision integration in a clean, weather-protected hanger. Sub-systems (such as the sodium pumps and heat exchangers) can be tested as a unit before dropping them into the final reactor building.
One of the biggest “obstacles” in nuclear builds is that if a non-critical part (a steam turbine) is late, it can stall the entire nuclear-certified workforce. By separating the Energy Island (molten salt and turbines) from the Nuclear Island, TerraPower can use standard industrial contractors for the majority of the plant. If there is a delay in the specialised Spanish reactor head, it will not stop US crews from finishing the energy storage system.
Nevertheless, despite these strategies, the obstacles are very real. Suppliers are making these parts for the first time. Hidden defects or “design-to-manufacturing” translation errors (especially with international standards like ASME and ISO) are common. A strike at a South Korean port or a specialised steel shortage in Europe could halt the entire Wyoming assembly line. NRC has to inspect these components at the source. If an international manufacturer misses a specific quality-assurance step, the part can be rejected upon arrival,
Development of the high-assay low-enriched uranium (HALEU) fuel needed for the reactor is a separate manufacturing effort. The Natrium Fuel Fabrication Facility in Wilmington, North Carolina, operated in partnership with GE Hitachi Nuclear Energy. Framatome US Government Solutions is designing the ex-vessel handling machine, while Teledyne Brown Engineering is responsible for the in-vessel transfer machine. James Fisher Technologies is building the injection casting furnace to demonstrate the metallic fuel casting process.
