The Nuclear Regulatory Commission has issued a construction permit for TerraPower’s Natrium reactor in Kemmerer, Wyoming, completing its safety review in 18 months and finishing nine months ahead of the agency’s own projected schedule. It is the first construction permit the NRC has granted for a commercial advanced nuclear reactor in the history of the U.S. licensing program, and it clears the way for physical construction to begin at a site where a retiring coal plant once powered the regional grid.
The permit, designated CPAR-1, was issued to US SFR Owner, a TerraPower subsidiary, following Commission order CLI-26-5. NRC staff said the review was completed “under budget and in 18 months” after finding no safety issues that would block the permit. The agency’s original milestone schedule, published in June 2024, had targeted a construction permit decision for March 9, 2026.
TerraPower founder Bill Gates and CEO Chris Levesque have described the Kemmerer project as a proof point for whether advanced nuclear power can be built on a commercially viable timeline in the United States. The Natrium design is a 345-megawatt sodium-cooled fast reactor paired with a molten salt energy storage system that can temporarily boost output to 500 megawatts during periods of peak electricity demand. No sodium-cooled commercial reactor has operated in the U.S. before.
A regulatory timeline that outran its own schedule
TerraPower filed its construction permit application on March 28, 2024, becoming the first developer to submit a commercial application for an advanced reactor design. The NRC accepted and docketed the application on May 21, 2024, and published a review schedule on June 12, 2024. That schedule projected a final safety evaluation by December 2025, a mandatory hearing on March 4, 2026, and a permit decision five days later.
Staff finished the safety evaluation ahead of the December target and concluded that the application met all regulatory requirements. The Commission then authorized the permit through order CLI-26-5. Whether the mandatory hearing was held on the originally scheduled date, consolidated into an earlier proceeding, or handled through written submissions has not been detailed in available NRC records.
The Department of Energy, which is co-funding the project through its Advanced Reactor Demonstration Program, separately confirmed the milestone. The DOE had already completed its own environmental review of federally funded site preparation work under NEPA designation DOE/EA-2264, issuing a finding of no significant impact for preliminary activities at the Kemmerer location.
What the Natrium reactor is and why Kemmerer
The Natrium design uses liquid sodium rather than water as its primary coolant, allowing the reactor to operate at higher temperatures and lower pressures than conventional light-water plants. The integrated molten salt storage system acts like a thermal battery, absorbing excess heat and releasing it to generate additional electricity when the grid needs it most. TerraPower has pitched this flexibility as a complement to wind and solar generation, which produce power on nature’s schedule rather than the grid operator’s.
Kemmerer, a town of roughly 2,600 people in southwestern Wyoming’s Lincoln County, was chosen in part because PacifiCorp’s Naughton coal-fired power station is retiring there. The site offers existing transmission infrastructure, a workforce with energy-sector experience, and a community that has publicly supported the transition. Wyoming Governor Mark Gordon has backed the project as a way to preserve energy jobs in a state whose economy has long depended on fossil fuel extraction.
What the permit does not settle
A construction permit allows TerraPower to break ground and build the physical plant, but it does not authorize the company to load fuel or generate electricity. A separate operating license review will follow, and that process carries its own timeline and technical requirements. First-of-a-kind reactor construction projects have historically run over schedule and over budget globally, from the Vogtle expansion in Georgia to the Olkiluoto 3 project in Finland.
The NRC’s claim that the review came in “under budget” has not been accompanied by any public accounting. No dollar figure for the projected review cost or the actual cost has appeared in agency records, making the claim an institutional assertion that cannot be independently verified. Similarly, no dissenting opinions from NRC commissioners have surfaced in available documents, though the absence of public dissent does not necessarily mean the review was uncontested internally.
Federal funding details for the next phase also remain unclear. The DOE’s Advanced Reactor Demonstration Program has committed significant public dollars to the Natrium project, but no primary source has specified what disbursements are triggered by the construction permit or on what timeline they will flow. The project’s total cost, estimated in earlier reporting at roughly $4 billion, depends on a mix of federal funds, private investment, and utility commitments.
Critics of sodium-cooled reactor technology have raised longstanding concerns about the chemical reactivity of liquid sodium, which ignites on contact with air and reacts violently with water. TerraPower’s design isolates the sodium loops from the steam cycle using an intermediate heat exchange system, but the technology has never been proven at commercial scale in the United States. The NRC’s safety evaluation addressed these design features, though the full technical basis for the staff’s conclusions has not yet been published in a publicly accessible format.
What the 18-month benchmark means for the nuclear industry
For developers considering their own advanced reactor applications, the Natrium review sets a concrete precedent. The NRC processed a construction permit for an entirely new reactor technology in roughly half the time that many industry observers had assumed the agency would need. If that pace holds for future applicants, it compresses one of the longest and least predictable phases of nuclear project development and changes the financial calculus for investors who have historically priced years of regulatory uncertainty into their models.
The timing also coincides with surging electricity demand from artificial intelligence data centers and a broader political consensus, rare in energy policy, that the U.S. grid needs more firm, low-carbon generation capacity. The Inflation Reduction Act’s production tax credits for nuclear power and bipartisan support for the ADVANCE Act, which directed the NRC to modernize its licensing framework, have created a policy environment more favorable to new nuclear construction than any period since the 1970s.
None of that guarantees the Kemmerer plant will be built on time, on budget, or at all. But the regulatory phase, long treated as the most daunting obstacle to new nuclear in America, just proved it can move faster than almost anyone expected. The next test is whether construction can do the same.
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*This article was researched with the help of AI, with human editors creating the final content.
