The Nuclear Regulatory Commission voted on March 4 to issue the first construction permit ever awarded for a commercial non-light-water reactor, approving TerraPower’s 345 MWe Natrium sodium-cooled fast reactor at Kemmerer, Wyoming. The NRC completed its safety review in December 2025, one month ahead of schedule and 11% under budget. Construction officially commenced April 23, 2026, with a grid commissioning target of 2030-2031.
The Natrium design differs from conventional light-water reactors in three ways that matter for investors: it runs on molten sodium coolant rather than water, operates at atmospheric pressure rather than high pressure, and incorporates a molten salt thermal storage system that allows output to flex between 345 MWe base and 500 MWe peak burst capability. That dispatchability feature positions Natrium explicitly as a load-following complement to variable renewables, not just a baseload replacement.
TerraPower’s project is backed by the DOE Advanced Reactor Demonstration Program, which co-funds the capital cost alongside private investment from Bill Gates and others. The Kemmerer site was chosen partly for its proximity to the retiring Naughton coal plant, enabling workforce and grid-infrastructure continuity. The NRC permit is significant beyond TerraPower: it establishes that the NRC can review and license advanced non-LWR designs on a commercially relevant timeline, which every other advanced reactor developer needed to see demonstrated before committing to NRC licensing pathways.