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Kairos Power

Kairos Power

🇺🇸 Alameda, US · Founded 2016 · Active

Kairos Power is a US nuclear company founded in 2016 and headquartered in Alameda, California. It is developing the KP-FHR, a fluoride salt-cooled high-temperature reactor: the fuel is solid TRISO particles packed into pebbles, and a molten fluoride salt called Flibe carries the heat away at low pressure. Because the fuel is solid rather than dissolved in the salt, the design is distinct from reactors that use molten-salt fuel. In December 2023 it received a construction permit for the Hermes test reactor in Oak Ridge, Tennessee, the first the NRC had issued for a non-light-water reactor in about fifty years, and nuclear construction there began in May 2025. Permits for the two-unit Hermes 2 followed in November 2024. In 2024 Google agreed to buy power from a fleet of Kairos reactors of up to 500 MW by 2035.

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Sector
Fission
Technology
Fluoride salt-cooled high-temperature reactor
Fuel
High-assay low-enriched uranium, TRISO particle fuel
Role
Reactor developer

It is the operator of record for Hermes test reactor (under construction) and Hermes 2 test reactor facility (planned).

It also holds 3 awards or agreements with no cash figure, which are not added to any total.

4 regulatory milestones are tracked here, all anchored to a docket reference in the regulator's own record.

Terms

Fluoride salt-cooled high-temperature reactor
Molten salt COOLANT with solid fuel, typically TRISO, and a separate solid moderator, usually graphite. Kairos Power's KP-FHR is the reference example.
High-assay low-enriched uranium
High-assay low-enriched uranium: uranium enriched to between 5% and just under 20% uranium-235, as the US Department of Energy defines it. It is still formally low-enriched, because the international line for highly enriched uranium is 20%, which is why many designs specify 19.75%. The binding supply constraint for many advanced reactor designs. The 5 to 10% part, which carries lighter US physical-security requirements than material from 10% up, is also tagged as LEU+. A developer calling fuel in that band 'LEU' is making a labelling choice, not describing a different enrichment.
TRISO particle fuel
Fuel kernels about the size of a poppy seed, each wrapped in layers of carbon and silicon carbide, so every particle acts as a tiny containment for its own fission products. The US Department of Energy reports that irradiated particles came through more than 300 hours of testing at temperatures up to 1,800 °C with no to minimal damage. That record covers the particle designs, temperatures and burnups actually tested; a claim outside that envelope is not covered by it.

Funding

3
commitments with no cash figure
  1. 2025-08-18
    Offtake or power purchase agreement
    Power purchase agreement announced 18 August 2025: TVA to buy up to 50 MW from Kairos Power's Hermes 2 plant in Oak Ridge, Tennessee, with Google receiving the plant's clean-energy attributes through the TVA system. Term, start date and binding terms are not stated, so isBinding is left unset.
    Unpriced
  2. 2024-10-14
    Offtake or power purchase agreement
    Master Plant Development Agreement with Google, signed and announced 14 October 2024: a path to 500 MW of Kairos plants by 2035, first deployment targeted by 2030, with Kairos selling energy, ancillary services and attributes to Google under plant-level PPAs. The 500 MW is a framework target, not a signed capacity purchase; plant-level PPA terms are not disclosed, so isBinding is left unset. Capacity is a company target (planned), not a delivered figure.
    Unpriced
  3. 2024-02-21
    Milestone-based award
    DOE Technology Investment Agreement under the Advanced Reactor Demonstration Program, announced 21 February 2024: up to $303 million toward the Hermes demonstration reactor, paid as fixed payments on demonstrated milestones. No amount is recorded because $303 million is a ceiling, not cash received.
    Unpriced

Designs

Design Developer Approach Electrical output per unit Size class Licensing stage
KP-FHR Kairos Power Fluoride Salt-Cooled High-Temperature Reactor, KP-X Kairos Power Fluoride salt-cooled high-temperature reactor 75 MWe planned Small modular reactor No milestone recorded

Design values

Design values for devices operated by Kairos Power. These are what a machine was built to do, not results.
DeviceParameterValueUnitStatus
Hermes test reactorThermal capacity (rated)35MWdesign valueplanned

Devices

Hermes test reactorFHRUnder construction1 figure on recordHermes 2 test reactor facilityFHRPlannedNo figures yet

Licensing

  1. 2023-12-14achieved
    Construction permit issued
    NRC construction permit issued for Hermes test reactor · US Nuclear Regulatory Commission
    Construction Permit CPTR-6 · Docket 50-7513 · ADAMS ML23338A258
  2. 2024-11-21achieved
    Construction permit issued
    NRC construction permits issued for Hermes 2 test reactor facility (two units) · US Nuclear Regulatory Commission
    Construction Permits CPTR-7 (Docket 50-611) and CPTR-8 (Docket 50-612) · ADAMS ML24324A021, ML24324A022
  3. 2025-05achieved
    Construction start
    Hermes test reactor: safety-related construction begins · US Nuclear Regulatory Commission
    Docket 50-7513 · NRC EA/FONSI, FR Doc 2026-07700 (91 FR, 2026-04-21) · ADAMS ML26083A275 (request)
  4. 2029-04-30target
    Hermes test reactor — latest date for completion of construction under permit CPTR-6
    No regulatory stage recorded · US Nuclear Regulatory Commission
    CPTR-6 amendment order 2026-05-13 · Docket 50-7513 · ADAMS ML26083A275 (request), ML26085A103 (safety evaluation)

Related companies

Sources