The U.S. Nuclear Regulatory Commission (NRC) has completed its draft safety evaluation (SE) a month ahead of schedule—albeit with open items—for TerraPower’s Kemmerer Power Station Unit 1, a pioneering 345-MW sodium-cooled fast reactor (SFR) under development in Wyoming.
The NRC’s draft SE was initially expected by March 2025, but productive engagement between the regulatory agency and TerraPower’s subsidiary, US SFR Owner, LLC (USO), allowed for earlier-than-anticipated completion, the regulatory body said in a letter on Feb. 26. According to the NRC, the final SE is now targeted for June 2026, two months ahead of the previous August 2026 timeline. The environmental review remains separately on track for completion in May 2026. TerraPower has told POWER it anticipates receiving NRC approval in late 2026, which could allow nuclear construction to begin in early 2027—potentially sooner if processes move efficiently.
Kemmerer 1 is taking shape in Lincoln County, Wyoming, about 3 miles from PacifiCorp’s three-unit 604-MW coal and gas–fired Naughton Power Plant, furnished with up to $2 billion in authorized funding under the Department of Energy’s (DOE’s) Advanced Reactor Demonstration Program (ARDP). While the demonstration will be a fully functioning commercial power plant, it will showcase TerraPower’s first Natrium reactor, an 840 MWth pool-type Natrium SFR reactor. Kemmerer 1 will be a hybrid nuclear facility that will integrate the fourth generation reactor with a nitrate molten salt-based energy storage system that could boost the system’s output to between 100 MWe and 500 MWe of power for more than 5.5 hours when needed, ramping at 10% a minute.
While the NRC’s draft SE represents a crucial step in the licensing process—signaling the NRC’s thorough review of the Natrium reactor’s safety features and design—the agency has identified several outstanding issues that TerraPower must address. These include materials qualification for environmental compatibility, special treatment requirements for safety-significant structures, systems, and components, and the seismic/structural design approach for non-safety-related systems. The NRC has also requested additional documentation on the PRA’s use within the Licensing Modernization Project (LMP) and other licensing programs.
The LMP is designed to modernize the regulatory process for non-light water reactors by incorporating risk-informed approaches. The NRC’s request for further PRA documentation suggests that it is closely evaluating how TerraPower is applying risk insights to safety classifications and regulatory decision-making, a key factor in the licensing of first-of-a-kind (FOAK) reactors like Natrium.
When asked how the identified open items compare to issues typically encountered in licensing reviews for conventional nuclear plants, the NRC told POWER that open items are an expected part of draft safety evaluations, particularly for complex topics requiring additional analysis before final technical decisions. “The TerraPower application used the Licensing Modernization Project approach, which means some topics can apply to several review areas. When those topics are resolved, multiple parts of the evaluation will be addressed simultaneously. Issues such as materials qualification and PRA documentation have been open items in the past,” agency spokesperson Scott Burnell said.
The NRC noted the early draft evaluation stems from the agency’s extensive pre-application discussions and ongoing technical exchanges with TerraPower. Burnell added that the agency expects that lessons learned during this review will “lead to efficiency improvements down the road, whether for additional TerraPower applications or for other vendor submissions. For example, this continuous improvement effort bore significant results in completing review of the second Kairos construction permit application several months faster than the first Kairos review,” he said.
—Sonal Patel is a POWER senior editor (@sonalcpatel, @POWERmagazine).
Editor’s Note: This story is being actively updated. We encourage you to revisit this article or check our website for the latest updates.