Hermes
Output
35MWt
Hermes is a fluoride salt-cooled reactor design from Kairos Power rated at 35 MWt. Nuclear construction has begun. It requires HALEU fuel.
The first US construction permit issued for a non-light-water reactor, granted December 2023. Hermes is a demonstration unit, not a power reactor — it produces heat, not electricity — but it is the first new reactor technology to clear NRC construction licensing in decades.
Regulatory position
| Tier | Under construction |
|---|---|
| Regulator | US NRC |
| Application type | Construction permit (non-power reactor) |
| Docket / reference | NRC Docket 50-7513 |
| Application date | 2021-09 |
| Review phase | Under construction |
| Decision expected | not stated |
Design
| Coolant | Fluoride salt |
|---|---|
| Reactor family | High-temperature gas reactor (HTGR) |
| Electrical output | not disclosed |
| Thermal output | 35MWt |
| Fuel | TRISO pebbles |
| Enrichment | HALEUUp to 19.75% U-235 |
| First site | Oak Ridge, Tennessee |
| Offtakers | none announced |
Fuel supply for this design
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 Nuclear Regulatory Commission · retrieved 2026-09-06