In the small southwestern Wyoming town of Kemmerer, population roughly 2,600, a coal-fired power plant has anchored the local economy for decades. Now, on a site adjacent to PacifiCorp’s retiring Naughton coal station, the federal government has authorized construction of something the U.S. commercial nuclear industry has never built before: a sodium-cooled fast reactor designed to feed electricity to the grid.
The U.S. Nuclear Regulatory Commission issued construction permit CPAR-1 to US SFR Owner, LLC, a subsidiary of TerraPower, the advanced nuclear company founded by Bill Gates in 2008. The permit authorizes construction of Kemmerer Power Station Unit 1, and the Department of Energy has called it the first construction permit the NRC has ever granted for a commercial non-light-water power reactor. For an agency whose entire commercial licensing history has revolved around water-cooled designs, the decision breaks new regulatory ground.
What the Natrium reactor actually is
Every commercial power reactor operating in the United States today is a light-water reactor, a design that uses ordinary water both to cool the nuclear fuel and to moderate the chain reaction. The Natrium concept replaces water with liquid sodium, a metal that remains liquid at high temperatures and conducts heat far more efficiently. Because sodium does not need to be pressurized the way water does in a conventional reactor, the system operates near atmospheric pressure, which simplifies the containment structure and reduces certain accident risks.
The reactor core itself is rated at 345 megawatts electric, enough to power roughly 250,000 homes. But the design includes a feature no operating U.S. nuclear plant currently offers: an integrated molten salt energy storage system that can temporarily boost the plant’s output to 500 MWe. That storage capability is intended to let the plant ramp up when wind and solar generation drops and scale back when renewables are abundant, functioning more like a dispatchable battery than a traditional baseload generator.
TerraPower selected the Kemmerer site specifically because it sits next to the Naughton coal plant, which PacifiCorp has been phasing out. The location offers existing transmission infrastructure, a workforce experienced in power-plant operations, and a community already familiar with large-scale energy production. The logic is straightforward: retire coal, reuse the grid connection, and retrain workers for a plant that produces zero carbon emissions during operation.
How the permit came together
The regulatory path followed the NRC’s established two-track process. US SFR Owner, LLC filed its construction permit application on March 28, 2024. The NRC docketed the application for formal review, triggering parallel environmental and safety evaluations.
On the environmental side, NRC staff completed a Final Environmental Impact Statement, cataloged as NUREG-2268, which assessed the project’s potential effects on land use, water resources, ecology, cultural sites, and the local economy under the National Environmental Policy Act. Staff concluded that the environmental case supported issuing the permit, provided safety findings did not reveal disqualifying risks.
The Commission agreed. Under order CLI-26-5, it issued CPAR-1, authorizing construction of Kemmerer Power Station Unit 1. The project is backed by the Department of Energy’s Advanced Reactor Demonstration Program, a federal initiative that provides cost-shared funding to move next-generation nuclear technologies from concept to commercial reality. DOE has committed up to $2 billion in support for the Natrium demonstration.
A first, but with historical footnotes
The DOE’s characterization of CPAR-1 as the first NRC construction permit ever issued for a commercial non-light-water power reactor is significant, but it benefits from a bit of history. The closest precedent is the Clinch River Breeder Reactor, a sodium-cooled fast reactor proposed for Oak Ridge, Tennessee, in the 1970s. That project advanced through preliminary NRC review but never received a completed construction permit; Congress cut its funding in 1983 amid cost overruns and policy disputes over plutonium fuel cycles. The Associated Press, drawing on NRC context, framed the Natrium permit as the first such approval in more than 40 years, a characterization that likely references the Clinch River era.
Either way, the practical takeaway is the same: no sodium-cooled fast reactor has ever been licensed, built, and operated as a commercial power plant in the United States. Kemmerer would be the first.
What the permit does not cover
A construction permit is not permission to operate. Under the NRC’s two-step licensing framework, TerraPower must eventually file a separate operating license application demonstrating that the completed plant can run safely, that staffing and procedures meet regulatory standards, and that emergency preparedness plans are in place. Historically, that second stage has taken years and can surface issues that were not fully resolved during construction permitting.
Several practical questions also remain unanswered in the public record as of June 2026. No verified source provides a projected construction timeline, an estimated total project cost beyond the DOE’s cost-share commitment, or a target date for the reactor to begin generating electricity. TerraPower has previously indicated it aims to have the plant operational by the early 2030s, but the NRC’s regulatory filings do not lock in that schedule.
The safety case for sodium coolant also carries unique considerations. Sodium reacts vigorously with both water and air, which means the plant’s design must account for potential sodium leaks and fires in ways that water-cooled reactors do not face. The NRC’s safety evaluation addresses these scenarios, but the detailed technical analyses have not been fully synthesized in publicly accessible plain-language summaries. Independent nuclear engineers and watchdog organizations will likely scrutinize those documents closely as construction proceeds.
What Kemmerer is watching for
For residents of Lincoln County, Wyoming, the Natrium project is less about reactor physics than about paychecks and property values. The Naughton coal plant has been a major employer, and its phased retirement raises real questions about the local tax base and economic stability. TerraPower has said the Natrium plant would create hundreds of construction jobs and roughly 250 permanent positions, figures that would represent a substantial workforce in a county of fewer than 20,000 people.
Community sentiment, however, is not monolithic. NRC licensing proceedings allow for public comment and formal interventions, and concerns about nuclear waste storage, long-term site stewardship, and the novelty of the technology have surfaced in local and regional discussions. Tribal governments with historical ties to the area also have standing interests that the environmental review process is designed to address.
The broader energy picture adds another layer. Wyoming generates more electricity from coal than any other state, and its leaders have been vocal about wanting to transition on their own terms rather than through federal mandates. A successful Natrium demonstration could offer a model: replace coal plants with zero-carbon generation that preserves jobs, grid reliability, and tax revenue. A troubled or delayed project could reinforce skepticism about advanced nuclear technology’s readiness for commercial deployment.
Where the Natrium permit fits in the larger nuclear landscape
The Kemmerer permit arrives during a period of renewed interest in nuclear energy across the United States. Tech companies hungry for carbon-free electricity to power data centers have signed agreements with nuclear developers. Congress has passed bipartisan legislation streamlining parts of the NRC’s review process for advanced reactors. And the NRC itself is evaluating multiple other advanced designs, including small modular reactors and high-temperature gas-cooled concepts.
None of that guarantees the Natrium project will succeed on schedule or on budget. The U.S. nuclear industry’s recent track record on large construction projects is sobering: the Vogtle expansion in Georgia, the only new conventional reactors built in the country in decades, came in years late and billions over budget. TerraPower’s supporters argue that the Natrium design is simpler and smaller, making it less vulnerable to the cost escalation that plagued Vogtle. Critics counter that first-of-a-kind projects almost always encounter unforeseen problems.
What is not in dispute is that the NRC has now completed a full environmental review and issued a construction permit for a commercial reactor that operates on fundamentally different principles than anything in the existing U.S. fleet. The permit is documented, timestamped, and publicly accessible. Whether it leads to a functioning power plant on the Wyoming prairie, or becomes another chapter in the long history of advanced reactor ambitions that stalled short of the finish line, depends on decisions that have not yet been made and money that has not yet been spent. Kemmerer, and the rest of the country, will be watching.
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*This article was researched with the help of AI, with human editors creating the final content.
