Sodium-Cooled Fast Reactors (SFRs) use liquid sodium metal as the primary coolant, taking advantage of sodium's excellent heat transfer properties, high boiling point (883 degrees Celsius at atmospheric pressure), and transparency to fast neutrons. By operating in the fast neutron spectrum, SFRs can achieve significantly higher fuel utilization than thermal reactors, including the ability to breed new fissile material from fertile uranium-238 and transmute long-lived radioactive waste isotopes into shorter-lived elements. The technology has decades of operating experience from demonstration plants including the Experimental Breeder Reactor-II (EBR-II) at Idaho National Laboratory, France's Phenix and Superphenix, Japan's Monju, and Russia's BN-600 and BN-800.
TerraPower's Natrium is the most advanced SFR in the current deployment pipeline and among the highest-profile nuclear projects globally. Founded by Bill Gates, TerraPower's 345 MWe Natrium design incorporates an integrated molten salt energy storage system that enables peak output of 500 MWe, decoupling reactor thermal output from grid electrical delivery. The Natrium plant in Kemmerer, Wyoming received its NRC construction permit in 2025, with DOE cost-sharing of up to $2 billion of the estimated $4 billion total project cost. Construction is underway with 1,600 workers expected at peak, targeting completion in 2030. In January 2026, Meta announced an agreement for up to 8 Natrium plants totaling 2.8 GW baseload plus 1.2 GW storage, with the first two units by 2032 and six more by 2035. KHNP of South Korea secured a stake in TerraPower in January 2026.
Oklo Inc. (NYSE: OKLO) is developing the Aurora powerhouse, a compact sodium-cooled fast reactor targeting 15-75 MWe, with the first deployment at Idaho National Laboratory where ground was broken in September 2025. Despite an earlier NRC application rejection, Oklo redesigned and is preparing its COLA Phase 1 submission for 2026. With a market capitalization of approximately $12.9 billion, Oklo is the largest SMR company by valuation, bolstered by a 1.2 GW power campus agreement with Meta in Pike County, Ohio. ARC Clean Technology's ARC-100 (100 MWe) completed CNSC Phase 2 Vendor Design Review in July 2025, becoming the first sodium-cooled fast reactor to complete Canada's regulatory pre-licensing process, with deployment planned at Point Lepreau, New Brunswick.