Natrium
Natrium is a liquid sodium-cooled reactor design from TerraPower rated at 345 MWe. A construction permit has been issued; construction has not begun. It requires HALEU fuel.
The first commercial Generation IV reactor approved under the NRC's Part 50 framework, permitted in March 2026. Pairs a sodium fast reactor with molten salt heat storage so the plant can follow load without changing reactor power. Non-nuclear construction started in 2024 ahead of the permit. Its schedule has already slipped once over HALEU: the design assumed Russian supply.
| Tier | Permitted |
|---|---|
| Regulator | US NRC |
| Application type | Construction permit (10 CFR Part 50) |
| Docket / reference | NRC Docket 50-7505, US SFR Owner LLC |
| Application date | 2024-03 |
| Review phase | Construction permit issued March 2026 |
| Decision expected | not stated |
| Coolant | Liquid sodium |
|---|---|
| Reactor family | Fast reactor (FBR) |
| Electrical output | 345MWe |
| Thermal output | not disclosed |
| Fuel | Metallic uranium |
| Enrichment | HALEUUp to 19.75% U-235 |
| First site | Kemmerer, Wyoming |
| Offtakers | PacifiCorp |
This design needs HALEU — uranium enriched above 5% and below 20%. That is not the fuel any commercial Western power reactor uses today, and it is the single most common reason an advanced reactor timeline slips. Every Western facility that can make it or turn it into fuel:
| Facility | Capacity | Status |
|---|---|---|
| TRISO-X Fuel Facility (TX-1), Oak Ridge | not disclosed | construction |
| American Centrifuge Plant, Piketon | 900kg HALEU/yr | operating |
| Nuclear Fuel Services, Erwin | not disclosed | operating |
| Savannah River Site HEU downblending | 3,100kg HALEU total | operating |
| BWXT TRISO facility, Gillette | not disclosed | planned |
| Urenco Capenhurst HALEU line | not disclosed | planned |
Sources
- US Department of Energy and TerraPower · retrieved 2026-09-06