In the small southwestern Wyoming town of Kemmerer, population roughly 2,600, construction crews are preparing to build something the United States hasn’t attempted in over a decade: a brand-new commercial nuclear reactor. But this one won’t look like any nuclear plant currently operating in the country.
The Nuclear Regulatory Commission has issued construction permit CPAR-1 to US SFR Owner, LLC, a subsidiary of TerraPower, authorizing construction of the Natrium reactor at the Kemmerer Power Station site. It is the first construction permit the NRC has granted for a commercial nuclear reactor since the Vogtle expansion in Georgia in 2012, and the first ever issued for an advanced, non-light-water reactor design. TerraPower, the nuclear energy company Bill Gates founded in 2008, plans to have the plant generating electricity by 2031.
The 345-megawatt reactor will rise on land adjacent to PacifiCorp’s Naughton Power Plant, a coal-fired facility whose units have been retiring in stages. The project carries an estimated price tag of roughly $4 billion and is partially funded through the Department of Energy’s Advanced Reactor Demonstration Program, which has committed up to approximately $2 billion in cost-sharing support. If the reactor meets its targets, TerraPower says it could produce enough electricity to power around 500,000 homes.
What makes the Natrium design different
Every commercial nuclear plant currently operating in the United States uses light-water reactor technology, a design lineage dating to the 1950s. These plants use ordinary water both to cool the reactor core and to moderate the nuclear chain reaction. The Natrium reactor breaks from that model in two fundamental ways.
First, it uses liquid sodium instead of water as its primary coolant. Sodium absorbs heat far more efficiently than water and operates at atmospheric pressure, which eliminates the need for the massive, high-pressure containment vessels that define conventional nuclear plants. The tradeoff is that sodium reacts violently with water and burns on contact with air, requiring careful engineering of every system boundary. TerraPower’s design addresses this by placing an intermediate sodium loop between the reactor and the power-generation system, so the radioactive sodium in the core never comes in direct contact with water or the outside environment.
Second, and perhaps more consequentially for the electricity market, the Natrium system pairs the reactor with a molten salt energy storage system. The reactor generates a steady 345 megawatts of thermal-to-electric output, but the storage system can bank excess heat and then discharge it during periods of peak demand, temporarily boosting the plant’s electrical output to 500 megawatts. That peak capacity is what underpins TerraPower’s claim about powering 500,000 homes. At the base output of 345 MWe running at a typical nuclear capacity factor above 90%, the plant would generate enough electricity for roughly 250,000 to 270,000 average U.S. households. The storage system pushes that figure higher during peak hours.
This flexibility is designed to complement wind and solar generation, which produce power intermittently. A reactor that can ramp its electrical output up and down without changing its core thermal output could fill gaps on the grid that renewables leave behind, a role currently served mostly by natural gas plants.
The regulatory path that got it here
TerraPower’s subsidiary submitted its construction permit application to the NRC on March 28, 2024. The agency accepted the application for review in May 2024 and completed its final safety evaluation by December 2025, concluding that no unresolved safety issues would prevent the permit from being granted. The full application docket is publicly available through the NRC’s records system.
That timeline is remarkably fast by nuclear regulatory standards. The NRC’s review of the Vogtle Units 3 and 4 combined license application took roughly four years. TerraPower’s construction permit review was completed in under two years, though the comparison is imperfect: a construction permit is a narrower authorization than a combined license, and TerraPower will still need to apply for and receive a separate operating license before the reactor can load fuel and connect to the grid.
The operating license process will involve additional safety reviews, updated environmental assessments, and public comment periods. That second round of regulatory scrutiny is where many of the remaining technical and safety questions will be formally adjudicated.
Why Kemmerer, and why now
The site selection was deliberate. Kemmerer sits in Lincoln County, a community whose economy has been tied to coal mining and coal-fired power generation for generations. PacifiCorp’s Naughton plant has been shedding capacity as the utility shifts toward cleaner energy sources under regulatory and market pressure. By building on adjacent land, TerraPower can potentially reuse existing high-voltage transmission lines, water infrastructure, and some of the skilled workforce that kept the coal plant running.
For Wyoming, the project represents something more than a single power plant. The state produces more coal than any other in the nation and has watched its dominant industry shrink for over a decade. State legislators and the governor’s office have publicly supported the Natrium project as a way to retain energy-sector jobs and tax revenue while diversifying Wyoming’s generation portfolio. Whether the reactor actually delivers on those promises will depend on hiring practices, local procurement decisions, and long-term operational economics that are not yet detailed in public filings.
The timing also reflects a broader shift in federal energy policy. The DOE’s Advanced Reactor Demonstration Program, created during the Trump administration and expanded under the Biden administration, was designed to push advanced nuclear designs past the prototype stage and into commercial deployment. TerraPower’s Natrium reactor and X-energy’s Xe-100 pebble-bed reactor were the program’s two flagship selections. The Natrium project has now reached the construction permit stage first, a significant lead in a field where the previous frontrunner, NuScale Power’s small modular reactor project in Idaho, was canceled in November 2023 after costs ballooned and utility partners withdrew.
What the permit does and does not guarantee
A construction permit authorizes TerraPower to build the reactor and associated facilities at the Kemmerer site under conditions specified by the NRC. It does not guarantee the plant will be completed on schedule, stay within budget, or ever generate commercial electricity. The NRC retains authority to impose additional requirements during construction, and the agency must independently verify that the finished plant meets all safety and environmental standards before issuing an operating license.
The $4 billion cost estimate, reported by the Associated Press and other outlets, has not been broken down in public filings. How much comes from the DOE cost-share, how much from Gates’s personal investment and other private capital, and what mechanisms exist to handle cost overruns are all questions without clear public answers as of June 2026. Advanced nuclear projects worldwide have a troubled history with cost discipline. France’s Flamanville EPR reactor, originally budgeted at 3.3 billion euros, ultimately cost more than 13 billion. The Vogtle expansion in Georgia came in at roughly $35 billion, more than double initial projections.
TerraPower’s 2031 operational target also carries risk. The company originally aimed to have the reactor running by 2028 but pushed the date back after delays in obtaining high-assay low-enriched uranium (HALEU) fuel, which the Natrium reactor requires and which was initially sourced primarily from Russian suppliers. The DOE has since funded domestic HALEU production through Centrus Energy’s facility in Piketon, Ohio, but the supply chain remains nascent.
What Kemmerer is watching for next
For residents of Lincoln County and energy workers across Wyoming, the construction permit marks the transition from regulatory paperwork to physical activity on the ground. Site preparation and early construction work are expected to begin in the coming months, bringing an initial wave of construction jobs to a community that has been bracing for the coal plant’s full retirement.
The next major regulatory milestone will be TerraPower’s application for an operating license, which must be filed and approved before the reactor can load fuel. That application will contain detailed technical specifications, updated safety analyses, and environmental reviews that go well beyond what the construction permit required. It will also trigger a new round of public comment, giving local residents, environmental groups, and other stakeholders a formal opportunity to raise concerns.
Until that process plays out, the Natrium project occupies an unusual position in American energy: a genuinely novel reactor design with real federal backing and a real construction permit, but with its ultimate cost, timeline, and community impact still unresolved. The permit is the furthest any advanced reactor company has gotten in this generation of nuclear development. Whether TerraPower can turn that regulatory achievement into a working power plant will determine not just Kemmerer’s economic future, but the credibility of advanced nuclear energy as a practical tool for replacing fossil fuels across the United States.
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*This article was researched with the help of AI, with human editors creating the final content.
