Milestones
- NRC construction permit for HermesDec 2023Complete.
- Groundbreaking in Oak RidgeJul 2024Complete.
- NRC construction permit for Hermes 2Nov 2024Complete.
- Construction of HermesNowCurrent milestone.
- Hermes operationTarget 2027Not yet reached.
Most important updates
- 16 Jul 2026
- 17 Apr 2026
- 18 Aug 2025
- May 2025
- 12 Dec 2023
Upcoming
- 2027Hermes operation (next)
- 2027Hermes test reactor start-up targeted
- 2030Hermes 2 due to begin supplying power to TVA's grid for Google
Current obstacles
- Beryllium and tritium in the saltThe FLiBe salt contains toxic beryllium and makes tritium when irradiated; both must be kept contained.
Physics limits
- The salt needs ultra-pure lithium-7Lithium-6 absorbs neutrons and makes tritium, so FLiBe must use lithium enriched above 99.99% lithium-7, a scarce, costly material; beryllium is also toxic.
- The salt freezes at 459 °CFLiBe is solid below about 459 °C, so every pipe and vessel must be kept hot, and cold spots can plug the loop.
- TRISO fuel is dilutedEach pebble is mostly graphite, so the uranium is thinly spread. Cores are large for their power and need HALEU enriched up to 19.75%.
How it works
Fuel in golf-ball-size pebbles
TRISO particles, uranium kernels wrapped in carbon and ceramic layers, are packed in pebbles that hold radioactivity to about 1,600 °C.
Molten salt at low pressure
FLiBe salt (lithium and beryllium fluorides) carries heat at about 550–650 °C but boils only above 1,400 °C, so no high pressure.
Pebbles float through the core
The pebbles are lighter than the salt, so they float up through the core, are removed at the top, checked and reinserted while running.
A test before power
Hermes (35 MW thermal) makes no electricity; it tests fuel, salt and safety for Hermes 2, a 50 MWe plant planned for TVA and Google.
Update log
Thu 16 Jul
- Minor: BlogTest
Fri 17 Apr
- Major: PressManufacturing
Fri 23 Jan
- Minor: PressCommercial
Mon 18 Aug 2025
- Major: BlogCommercial
May 2025
- Major: BlogManufacturing
Nov 2024
- Minor: PressRegulatory
Tue 12 Dec 2023
- Major: PressRegulatory
Wed 20 Jul 2022
- Minor: PressManufacturing
About Kairos Power
Kairos Power
Fluoride salt-cooled reactor, TRISO pebbles, Hermes
California company building a high-temperature reactor cooled by molten salt (FLiBe) and fuelled by TRISO pebbles. It is building Hermes test reactors in Oak Ridge, Tennessee, and has a deal with Google for up to 500 MW.
- Hermes got the first US permit in 50+ years for a reactor not cooled by ordinary water (Dec 2023).
- Google agreed in October 2024 to buy power from up to 500 MW of Kairos reactors.
- Builds non-nuclear test units in-house first, learning step by step before the nuclear reactor.
- Founded
- 201610 yrs
- Headquarters
- United States
- Status
- Private
- Valuation
- private
- Works in
- EnergyFission
- Coverage
- 1 program · 9 updateslatest 16 Jul 2026checked 25 Sep
- People
- Mike Laufer (opens kairospower.com)Co-founder & CEO