Hermes 2
Output
70MWt
Hermes 2 is a fluoride salt-cooled reactor design from Kairos Power rated at 70 MWt. A construction permit has been issued; construction has not begun. It requires HALEU fuel.
A two-unit follow-on to Hermes that will generate electricity, with TVA taking the output. Kairos is deliberately iterating through demonstration hardware rather than attempting a first-of-a-kind commercial plant.
Regulatory position
| Tier | Permitted |
|---|---|
| Regulator | US NRC |
| Application type | Construction permit |
| Docket / reference | NRC Dockets 50-7514 and 50-7515 |
| Application date | — |
| Review phase | Construction permit issued November 2024 |
| Decision expected | not stated |
Design
| Coolant | Fluoride salt |
|---|---|
| Reactor family | High-temperature gas reactor (HTGR) |
| Electrical output | not disclosed |
| Thermal output | 70MWt |
| Fuel | TRISO pebbles |
| Enrichment | HALEUUp to 19.75% U-235 |
| First site | Oak Ridge, Tennessee |
| Offtakers | Tennessee Valley Authority |
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