Bill Gates-founded; Natrium sodium-cooled fast reactor under construction in Wyoming.
Four SMR units operate worldwide, all in Russia and China, and that count has not moved since 2023 — even as 2026 brought a construction permit, a modern licensing framework and four reactors reaching criticality in the US. A read of the gap between permits and power.
TerraPower named Hyundai Engineering & Construction its EPC contractor for up to eight future Natrium reactors, with completion, price and performance guarantees intended to make the fleet financeable on conventional commercial terms. A separate term sheet with SK Innovation covers Korea's first commercial Natrium plant.
TerraPower / UK ONR — TerraPower's Natrium design was accepted into the UK's Generic Design Assessment, with the Office for Nuclear Regulation, the Environment Agency and Natural Resources Wales beginning Step 1 in June 2026 — the sodium-cooled fast reactor's first overseas licensing push, following its US construction permit at Kemmerer. The same 345 MWe design with molten-salt storage boosting to 500 MW.
TerraPower / NRC — The NRC issued a construction permit for TerraPower's Natrium plant (Kemmerer, Wyoming) — the first US commercial advanced-reactor approval in ~a decade and the first non-light-water reactor approval in over 40 years. 345 MWe sodium-cooled fast reactor with molten-salt storage boosting to 500 MW; completion targeted 2030.
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Oklo 
NuScale Power