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TerraPower has received the U.S. Nuclear Regulatory Commission’s construction permit for its 345-megawatt-electric Natrium plant near Kemmerer, Wyoming. The approval is historic but narrower than the headline “first-ever U.S. permit” suggests: it is the NRC’s first construction permit for a commercial non-light-water power reactor. It does not let TerraPower load fuel or generate electricity; a separate operating license is still required.
What the NRC approved
The permit applies to Kemmerer Power Station Unit 1, formally licensed to US SFR Owner, LLC, a wholly owned TerraPower subsidiary. TerraPower submitted its construction-permit application on March 28, 2024, and the NRC completed acceptance and docketing on May 21, 2024. The agency finished its final environmental impact statement in October 2025 and its safety evaluation in December 2025.
On March 4, 2026, the NRC Commission authorized staff to issue the permit. Staff issued construction permit CPAR-1 on March 9. Keeping those dates separate matters: the Commission’s authorization and the formal permit issuance were related but distinct regulatory actions. The NRC says the approval is the first construction permit for a commercial non-light-water reactor, the first commercial-reactor construction approval from the agency in nearly a decade, and its first approval for a commercial reactor of this type in more than 40 years. It is not the first nuclear-reactor construction permit ever issued in the United States.
Why a construction permit is not permission to operate
A construction permit authorizes building the nuclear facility under the approved design, permit conditions, inspections and other NRC requirements. It does not authorize fuel loading, reactor startup or electricity production.
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TerraPower must submit a separate operating-license application. The NRC must review and approve that application before commissioning, fuel loading and operation can begin. TerraPower’s current target is to submit the application in 2028; that is a project plan, not an operating date guaranteed by CPAR-1.
How the Natrium reactor works
Sodium-cooled fast reactor
Natrium is a pool-type sodium fast reactor rated at 840 megawatts thermal and 345 megawatts electric. Its primary coolant is liquid sodium, not water. The reactor uses metallic uranium-zirconium fuel designed for high-assay low-enriched uranium (HALEU).
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Because sodium boils at a much higher temperature than water, the primary system can operate at atmospheric pressure rather than the high pressures associated with many light-water reactors. TerraPower also describes passive heat-removal features that use natural forces during shutdown or accident conditions. Those are design claims and features evaluated through the NRC process, not a guarantee that the plant is risk-free. Sodium’s chemistry creates different engineering requirements, including management of its reactions with air and water, leak detection and fire protection.
Molten-salt storage is separate from the reactor
Natrium is not a molten-salt reactor. Its molten-salt system is thermal storage integrated with the plant’s energy island. The reactor can provide heat continuously while the storage system holds some of that energy and releases it when demand rises.
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| Figure | What it means |
|---|---|
| 345 MWe | The reactor’s nominal electrical output. |
| Up to 500 MWe | Temporary plant output when reactor heat is supplemented by stored thermal energy; this is not the reactor’s nameplate rating. |
TerraPower and the Associated Press have compared the peak output with electricity demand from roughly 400,000 homes. That is an estimate whose result varies with regional household consumption.
Where the project is being built
The project is planned for Lincoln County, near Kemmerer, Wyoming, adjacent to an existing coal-fired power site. The location connects an advanced-nuclear demonstration with a region long associated with coal and other energy production.
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The site includes a nuclear island containing the reactor systems and an energy island containing storage, heat-transfer and power-conversion equipment. Non-nuclear site preparation began in June 2024. TerraPower announced the official start of construction on the plant itself on April 23, 2026. That distinction explains why accounts can cite both 2024 and 2026 as the start of “construction.”
What must happen before electricity reaches the grid
- Build both islands: TerraPower and its contractors must complete the nuclear and energy facilities, supporting systems and site infrastructure.
- Qualify the fuel: The metallic uranium-zirconium HALEU fuel must be developed, manufactured and qualified, with supporting fuel-fabrication and test facilities.
- Secure the fuel supply: HALEU contains more than 5% and less than 20% uranium-235. A dependable domestic supply and qualified manufacturing chain remain essential project dependencies.
- Obtain the operating license: TerraPower expects to submit its application in 2028, after which the NRC must conduct its operating review.
- Commission the plant: The project must complete testing, receive authorization for fuel loading and startup, connect to the grid and demonstrate reliable commercial power delivery.
Bill Gates’ role and the ownership question
TerraPower was founded by Bill Gates and other investors, and Gates is a major backer and prominent advocate. The NRC permit, however, was issued to US SFR Owner, LLC—not to Gates personally. TerraPower and its project partners are responsible for development, licensing and construction.
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Funding, cost and commercial risk
The project is supported by the U.S. Department of Energy’s Advanced Reactor Demonstration Program, a public-private partnership. TerraPower says the program provides for up to $2 billion in federal support under a 50/50 cost-share arrangement, with TerraPower and its partners matching the federal contribution.
The Associated Press has described the project as costing up to $4 billion. That figure includes first-of-a-kind work such as licensing, design methods and codes, fuel development and qualification, a sodium test facility and a fuel-fabrication facility. It should not be treated as the proven overnight cost of a mature, repeat-build reactor.
For investors and taxpayers, the central uncertainty is execution. The first plant must manage new technology, HALEU availability, sodium systems, storage interfaces, supply chains, construction quality, licensing and schedule control. A successful demonstration could provide a reference design for later plants, but it would not by itself prove that a wider fleet can be built at lower cost or on time.
Why the permit matters beyond Wyoming
The approval reduces a major regulatory uncertainty for developers of advanced reactors that do not use conventional light-water designs. It also offers a potential model for dispatchable nuclear generation: steady reactor operation combined with short-duration output flexibility from thermal storage.
That precedent is not a guarantee of an advanced-nuclear boom. The decisive tests are still ahead: completing the plant, producing qualified HALEU fuel, winning the operating license, controlling first-of-a-kind costs and demonstrating dependable operation.
Quick Recap
Key dates and status
| Date or target | Event |
|---|---|
| March 28, 2024 | Construction-permit application submitted. |
| May 21, 2024 | NRC acceptance and docketing completed. |
| June 2024 | Earlier non-nuclear site work began. |
| October 2025 | NRC final environmental impact statement completed. |
| December 2025 | NRC safety evaluation completed. |
| March 4, 2026 | Commission authorized permit issuance. |
| March 9, 2026 | NRC staff issued construction permit CPAR-1. |
| April 23, 2026 | TerraPower announced official plant-construction start. |
| 2028 target | TerraPower expects to submit its operating-license application. |
| 2030 expectation | DOE and project materials cite expected completion; the date is not guaranteed. |
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