Hermes
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.
| 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 |
| 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 |
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 |
| Idaho National Laboratory EBR-II downblending | not disclosed | 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 |
| General Matter | not disclosed | planned |
| Urenco Capenhurst HALEU line | not disclosed | planned |
Units announced with this design
5 units in the Global Nuclear Power Tracker carry the model name "KP-FHR", 1construction, 2pre construction, 2announced. Announcement is not permission; compare this against the regulatory position above.
| Unit | Country | Status | Gross MW |
|---|---|---|---|
| Hermes nuclear power plant 1 | United States | construction | 50 |
| Hermes nuclear power plant 2a | United States | pre construction | 25 |
| Hermes nuclear power plant 2b | United States | pre construction | 25 |
| Kairos Power Texas A&M nuclear power plant 1 | United States | announced | 75 |
| Kairos Power Texas A&M nuclear power plant 2 | United States | announced | 75 |
Sources
- US Nuclear Regulatory Commission · retrieved 2026-09-06
- Announced units: Global Nuclear Power Tracker, Global Energy Monitor, August 2026 release , CC BY 4.0
How these sources are used, including the corrections applied on top of them and what is deliberately left blank · download the underlying data