In the small ranching and coal town of Kemmerer, Wyoming, construction crews are reshaping the landscape next to a retiring coal plant, laying the foundation for a nuclear reactor unlike any that has operated commercially in the United States. TerraPower, the advanced nuclear company founded by Bill Gates, broke ground on the Natrium reactor after the Nuclear Regulatory Commission issued construction permit CPAR-1 to the project’s subsidiary, US SFR Owner, LLC. It is the first construction permit the NRC has granted for a new commercial reactor in over a decade and the first ever issued for an advanced, non-light-water design.
The permit authorizes construction of Kemmerer Power Station Unit 1 in Lincoln County but does not yet allow the company to load fuel or operate the plant. TerraPower submitted its application on March 28, 2024, and the commission authorized the permit through Order CLI-26-5, according to the NRC’s project page for the facility.
A reactor that runs on liquid sodium
The Natrium plant is a pool-type sodium fast reactor rated at 840 megawatts of thermal power. Instead of the pressurized water used in every operating U.S. commercial reactor, it circulates liquid sodium as its coolant. Sodium operates at atmospheric pressure and transfers heat far more efficiently than water, which simplifies some safety systems but introduces a different engineering challenge: sodium reacts violently with water and air. To manage that risk, the Natrium design separates the sodium coolant loop from the water-steam cycle with an intermediate heat-transfer layer, preventing direct contact between the two.
The core will run on metallic HALEU fuel, a higher-assay low-enriched uranium that allows a more compact reactor core and longer intervals between refueling than the fuel used in conventional plants. The Department of Energy has confirmed that the design targets 345 megawatts of electrical output at baseline. What sets Natrium apart from a traditional nuclear plant is an integrated molten salt energy storage system that can absorb excess reactor heat and dispatch it as additional electricity during peak demand, boosting output to 500 megawatts without changing the reactor’s thermal power. If the system works as designed, the plant could ramp its grid output up and down much like a natural gas peaker, complementing wind and solar rather than competing with them.
No commercial reactor has demonstrated this kind of flexible storage-coupled operation. There is no operational data from Kemmerer or any other Natrium facility to confirm the boost capability, cycling durability, or long-term maintenance demands of the molten salt system.
Federal dollars and the ARDP pipeline
Natrium is one of two flagship projects under the Department of Energy’s Advanced Reactor Demonstration Program, or ARDP, which pairs federal funding with private investment to push next-generation reactor designs from paper to operation on a compressed schedule. The other flagship is X-energy’s Xe-100 high-temperature gas reactor, planned for a site in Texas. Under ARDP, the federal government shares costs for design, licensing, and early construction work with the developers.
Before the NRC issued the construction permit, DOE completed a Draft Environmental Assessment (DOE/EA-2264) covering federal funding authorization for preconstruction activities at the Kemmerer site. That review, conducted under the National Environmental Policy Act, evaluated site preparation, early infrastructure installation, and associated environmental effects in Lincoln County. It concluded that the limited scope of those activities did not require a full environmental impact statement. A more comprehensive environmental review will accompany later licensing stages as the project moves toward an operating license.
The project’s estimated cost has been widely reported at up to $4 billion, a figure that reflects the original ARDP cost-sharing framework of roughly $2 billion in federal funds matched by private capital. TerraPower has not published a detailed, updated budget that accounts for inflation, supply chain shifts, or design changes that emerged during the permit review. First-of-a-kind nuclear projects have a stubborn history of cost escalation. The Vogtle Units 3 and 4 expansion in Georgia, the last new reactors built in the U.S., came online years late and billions over its original budget. That history does not dictate the outcome in Kemmerer, but it is the backdrop against which every cost and schedule claim will be measured.
The HALEU fuel bottleneck
One of the most closely watched risks for the Natrium timeline is the availability of HALEU fuel. Unlike the low-enriched uranium pellets used in conventional reactors, HALEU is enriched to between 5% and 20% uranium-235, and no commercial fuel fabrication pipeline existed in the United States when TerraPower began the project. For years, the only significant global supplier of HALEU was Russia’s Tenex, a supply chain that became politically untenable after the invasion of Ukraine.
Centrus Energy’s facility in Piketon, Ohio, began producing small quantities of HALEU under a DOE contract, but output remains limited. Scaling domestic HALEU production to the volumes Natrium will require is a prerequisite for fueling the reactor, and delays in that supply chain were a primary reason TerraPower pushed its operational target from 2028 to 2030. Whether Centrus and other emerging suppliers can deliver enough fuel on schedule remains one of the project’s most consequential unknowns.
What Kemmerer stands to gain and lose
Kemmerer, population roughly 2,600, grew up around coal mining and coal-fired power. The Natrium reactor is sited near PacifiCorp’s Naughton coal plant, which is being retired, allowing the project to reuse existing transmission lines and tap a local workforce experienced in large-scale energy operations. For a community watching its economic anchor disappear, the reactor represents a potential second act: construction jobs in the near term, permanent plant positions over the longer horizon, and a new source of property tax revenue for Lincoln County.
But the transition is not without tension. Some residents have raised questions about nuclear waste storage, the safety implications of sodium coolant, and whether a first-of-a-kind technology will deliver the stable employment that coal provided for generations. NRC licensing procedures include public comment periods and meeting opportunities, though comprehensive summaries of local input specific to the Kemmerer project have not yet been published in the regulatory record.
Wyoming’s state government has signaled strong support for the project, and PacifiCorp, the regional utility, is expected to be a key customer for the plant’s output. The alignment of state policy, utility interest, and federal funding has created favorable conditions, but the project’s ultimate success will depend on execution: whether construction stays close to its 2030 target, whether the HALEU supply materializes, and whether the reactor and its storage system perform as promised once they are built.
A test case for the next generation of nuclear power
What is happening in Kemmerer matters well beyond Lincoln County. If Natrium works, it will validate a class of advanced reactors that the U.S. nuclear industry and the federal government have spent billions trying to bring to market. It will demonstrate that a sodium-cooled reactor can be built, licensed, and operated commercially in the modern American regulatory environment, something no company has done. And it will show whether pairing a reactor with energy storage can make nuclear power flexible enough to thrive on a grid increasingly shaped by wind and solar.
If it stumbles, through cost overruns, fuel delays, or technical setbacks, the consequences will ripple through the broader advanced nuclear sector, reinforcing skepticism that has dogged the industry since the last wave of U.S. reactor construction stalled decades ago. For now, the NRC permit is real, the site work is underway, and the federal commitment is substantial. The harder questions will be answered in concrete, sodium, and molten salt over the years ahead.
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*This article was researched with the help of AI, with human editors creating the final content.
