Federal regulators approve TerraPower’s Natrium reactor in Wyoming, a first for non-water-cooled nuclear

KEMMERER, Wyo. — In a high desert town long defined by coal, federal regulators have approved a very different kind of power plant.

The U.S. Nuclear Regulatory Commission has authorized a construction permit for TerraPower’s Natrium reactor near Kemmerer, clearing the way for what the company says will be the first commercial U.S. power plant that does not rely on water to cool its nuclear core.

The March 4 decision is the first time the NRC has signed off on construction of a commercial non–light-water reactor and the first approval for any new commercial reactor in nearly a decade. The project, backed by a company founded by Bill Gates, is the centerpiece of a federal push to demonstrate “advanced” nuclear designs while helping coal communities navigate the energy transition.

“This is a historic step forward for advanced nuclear energy in the United States,” NRC Chair Ho Nieh said in a statement. He said the decision reflects the agency’s commitment to “timely, predictable decisions grounded in a rigorous and independent safety review.”

The permit allows TerraPower’s subsidiary, US SFR Owner LLC, to begin building Kemmerer Power Station Unit 1, a 345-megawatt-electric sodium-cooled fast reactor that will sit near the retiring Naughton coal plant. The design includes a molten-salt thermal storage system that can boost power output to 500 megawatts for several hours when demand peaks.

TerraPower must still secure a separate operating license before the plant can produce electricity.

A first-of-its-kind approval

The NRC said its staff completed the technical review of TerraPower’s construction permit application in less than 18 months, after the agency formally accepted the application in May 2024. The review included a safety evaluation report completed in December and a final environmental impact statement issued in October for the Kemmerer site.

Federal officials are casting the permit as a milestone for both technology and climate policy. In a March 9 article, the Department of Energy highlighted the decision as “the first construction permit ever issued by the NRC for a commercial non-light-water power reactor,” emphasizing that the project is part of the agency’s Advanced Reactor Demonstration Program.

That program, created under the Energy Act of 2020, is designed to help bring at least two advanced reactors online by the early 2030s. TerraPower’s Natrium and X-energy’s Xe-100 high-temperature gas-cooled reactor were chosen as flagship demonstrations, with the federal government agreeing to cover up to half the cost.

DOE has committed as much as $2 billion in cost-shared funding for the Natrium project, with TerraPower and its partners expected to match that amount. Public and company estimates put the total cost of the Kemmerer plant at around $4 billion.

How Natrium differs

Unlike the United States’ existing commercial fleet, which uses light water to cool uranium fuel in high-pressure reactors, Natrium is a pool-type sodium-cooled fast reactor.

Liquid sodium circulates through the core at atmospheric pressure, drawing heat from metallic fuel made with high-assay low-enriched uranium (HALEU), which is enriched to between 5% and 20% uranium-235. The primary coolant then transfers heat to a separate molten-salt loop, which feeds a conventional steam turbine in what TerraPower calls the plant’s “energy island.”

The molten salt can store roughly a gigawatt-hour of thermal energy, allowing the plant to run its nuclear island steadily around 345 megawatts while ramping electric output up or down to follow changes in the grid.

TerraPower and its technology partner, GE Hitachi Nuclear Energy, say this separation between the nuclear and non-nuclear systems should simplify safety analysis and reduce the amount of equipment that must meet stringent nuclear construction standards.

Supporters argue that sodium’s high boiling point allows the reactor to operate at lower pressure than water-cooled designs, enabling passive heat removal through natural convection if active systems fail. They also point to negative reactivity feedbacks in the core that can dampen power increases in off-normal conditions.

Critics counter that sodium brings its own hazards. The metal burns when exposed to air and reacts violently with water, raising the risk of fires or sodium-water reactions in the event of leaks or steam-generator failures. The Union of Concerned Scientists has warned that sodium-cooled fast reactors can exhibit potentially dangerous behavior if not carefully designed.

In a statement responding to the NRC’s decision, UCS nuclear safety expert Edwin Lyman called Natrium an “experimental nuclear reactor” whose coolant “can catch fire” and said fast reactor designs “have inherent instabilities that can rapidly increase power” if coolant voids are not properly controlled.

The NRC said its environmental and safety reviews included analyses of sodium-fire scenarios, seismic and structural performance, emergency planning and spent fuel management. The agency concluded that, with mitigation measures and oversight, the project meets its regulatory requirements for public and environmental protection.

A coal town’s new bet

For Kemmerer, a city of roughly 2,400 people near the Utah border, the Natrium plant represents a potential lifeline.

For decades the local economy has depended on the Naughton power station and nearby coal mines. PacifiCorp, which owns Naughton, has retired some units and is converting others to natural gas, part of a broader shift away from coal across the West. Census data show Kemmerer’s population declining over the past decade as fossil fuel jobs dimmed.

TerraPower announced in 2021 that it had selected a site near Naughton for its demonstration plant, framing the choice as a “coal-to-nuclear” transition. Since then, local officials say, interest in new housing, commercial development and infrastructure has picked up.

City leaders have said they expect 1,600 to 2,000 workers at peak construction and roughly 250 to 300 permanent jobs once the plant is operating — substantial numbers in a community of Kemmerer’s size. The company has already begun non-nuclear construction on parts of the site, such as earthworks and structures for the energy island.

The influx also brings strain. Regional planners and residents have voiced concerns about housing shortages, rising rents and pressure on schools and health services as the workforce grows. At public meetings, some locals have questioned emergency preparedness and the long-term handling of nuclear waste.

Union labor on the project

The plant will be built under a project labor agreement between engineering and construction firm Bechtel and North America’s Building Trades Unions, an alliance representing millions of construction workers.

NABTU President Sean McGarvey said the NRC’s decision secures “the nation’s first construction permit for advanced nuclear reactor development under a Project Labor Agreement with major industry leaders like Bechtel Corporation.”

In a March 5 statement, he called the move “a massive win for our nation’s energy security and its working people,” saying the project will create “middle-class, family-sustaining careers” and demonstrate “what is possible when innovation is paired with the most highly trained, highly experienced building trades workforce.”

The backing underscores a broader shift by some unions toward supporting certain clean energy projects, particularly those that guarantee prevailing wages and apprenticeship opportunities.

Fuel and timing uncertainties

Even with a construction permit in hand, Natrium faces obstacles unrelated to concrete and steel.

The reactor’s HALEU fuel is not yet produced at commercial scale in the United States. For years, the only significant supplier was Russia’s state-owned nuclear company. Since the invasion of Ukraine, policymakers and companies have moved to reduce reliance on Russian nuclear fuel.

TerraPower has signed an agreement with Centrus Energy to help develop domestic HALEU production. DOE is funding early efforts to establish a U.S. supply chain, but industry analysts have warned that scaling up enrichment and fabrication facilities will take time.

TerraPower has already pushed back its target completion date for the Kemmerer plant from 2028 to 2030, citing HALEU availability as one factor. If fuel production lags, the schedule could slip further, affecting other advanced reactor projects that also plan to use HALEU.

A test for advanced nuclear

The Kemmerer project joins a small but growing list of U.S. advanced reactor efforts. NuScale Power won NRC certification for its small modular light-water reactor design but has struggled with costs and project cancellations. X-energy aims to build a high-temperature gas-cooled reactor in Washington state under the same federal demonstration program that supports Natrium.

Energy officials and some grid planners see advanced reactors as a way to provide steady, low-carbon electricity that can ramp up and down to complement large amounts of wind and solar power. Skeptics argue that renewables paired with batteries and other storage will prove cheaper and faster to deploy, and that new reactor types introduce additional safety and waste questions.

For the NRC, the Natrium permit marks a rare move into unfamiliar territory after decades spent licensing variations of light-water technology. For Kemmerer, it marks the start of another boom, with no guarantee of how long it will last.

Over the next several years, as sodium pipes are welded, molten-salt tanks rise and fuel plants try to catch up, the Wyoming project will offer one of the clearest tests yet of whether advanced nuclear can move from promise to practice — and whether a community built on coal can secure its future with a new kind of atom.