Kairos Power: First Advanced Reactor Construction Permit in US History
Kairos Power is the company that broke through. Founded in 2016 as a UC Berkeley spinout by Mike Laufer and Ed Blandford, Kairos developed the KP-FHR — a fluoride salt-cooled high-temperature reactor using TRISO pebble-bed fuel that operates at low pressure, eliminating the high-pressure rupture risks of conventional reactors. In December 2023, the NRC issued Kairos a construction permit for its Hermes test reactor at Oak Ridge, Tennessee — the first construction permit for an advanced (non-light water) reactor in United States history. In 2024, Google signed a power purchase agreement for up to 500 MW from future Kairos reactors, the largest corporate PPA for advanced nuclear ever announced. With over $600 million raised, DOE ARDP backing, and a stepping-stone development strategy from test reactor to commercial fleet, Kairos Power has become the fastest-moving advanced reactor company in America.
THE COMPLETE KAIROS POWER TIMELINE
Spun out of UC Berkeley research by co-founders Mike Laufer (CEO) and Ed Blandford (CTO). The company was built around the fluoride salt-cooled high-temperature reactor (FHR) concept, combining TRISO pebble-bed fuel with a molten fluoride salt coolant for a fundamentally different approach to nuclear energy.
Developed the KP-FHR design using TRISO pebble-bed fuel in fluoride salt coolant. The low-pressure operation of the FHR eliminates the risk of high-pressure rupture events common in pressurized water reactors. Built engineering test units to validate key components and material interactions with molten salt.
Selected for the DOE Advanced Reactor Demonstration Program (ARDP) Pathway 2 — risk reduction for the Hermes test reactor. Total project cost: $303 million, with 50% DOE cost share (~$150M). This federal backing validated the FHR technology approach and accelerated the Hermes development timeline.
Submitted construction permit application to the NRC for Hermes — a 35 MWth non-power test reactor to be built at Oak Ridge, Tennessee. Kairos chose the construction permit pathway instead of a full design certification, allowing faster regulatory progress while proving the technology at scale.
Raised cumulative funding of approximately $330 million. Hermes designed as a stepping stone — prove out FHR technology at scale before advancing to the commercial power-producing Hermes 2 (35 MWe) and full-scale KP-FHR units. Engineering Scale Test Unit (KRUSTY) operations validated salt chemistry and heat transfer.
NRC issued the construction permit for Hermes — the FIRST construction permit for an advanced (non-light water) reactor in the United States. A historic regulatory milestone that took approximately 2 years of NRC review. Site preparation began immediately at the Oak Ridge, Tennessee location adjacent to DOE facilities.
Google signed a power purchase agreement for up to 500 MW of electricity from future Kairos commercial reactors — the largest corporate PPA for advanced nuclear ever announced. Construction progressed at the Hermes site in Oak Ridge. The Google deal provided a committed demand signal and deep-pocketed anchor customer that validated the commercial pathway.
Nuclear concrete was poured on May 7, 2025 at the Hermes site in Oak Ridge, Tennessee — a major construction milestone marking the beginning of safety-related concrete placement. KP-FHR commercial-scale design (~140 MWe) advancing through pre-application engagement with NRC. Received second DOE ARDP award for Hermes 2 — a power-producing demonstration unit. Total funding raised exceeded $600 million.
HALEU fuel contract finalized with DOE (January 2026). Oak Ridge National Laboratory signed a $27M technical partnership (February 2026). Operating license application being prepared (February 2026). Molten salt production facility expected operational in 2026. Google deal driving commercial reactor pipeline for late 2020s through 2030s deployment. TVA partnership for Oak Ridge site support. Target operational: 2027.
WHY KAIROS MATTERS
Kairos Power represents a convergence of factors that the advanced nuclear industry has been waiting for: a genuinely novel reactor design, a historic regulatory achievement, a deep-pocketed corporate customer, and a disciplined stepping-stone development strategy. Here is why Kairos stands out.
The NRC construction permit for Hermes in December 2023 was the first ever issued for a non-light water reactor in the United States. This broke a regulatory barrier that had stalled advanced nuclear for decades. It proved that novel reactor designs can navigate the NRC licensing process to a construction-ready milestone.
The KP-FHR design uses fluoride salt coolant (Flibe) that operates at near-atmospheric pressure, eliminating the massive pressure vessels and containment structures required by pressurized water reactors. Combined with TRISO pebble-bed fuel — ceramic-coated uranium particles that can withstand extreme temperatures — the design offers inherent passive safety without the high-pressure rupture risks of conventional nuclear.
Google signing a 500 MW power purchase agreement was not just a contract — it was the strongest demand signal the advanced nuclear industry has ever received from a corporate buyer. It validates that hyperscalers need 24/7 carbon-free baseload power that renewables alone cannot provide, and they are willing to commit to advanced nuclear at scale to get it.
Unlike companies that pursued full NRC design certification before building anything, Kairos chose to build a non-power test reactor (Hermes) first to prove the technology, then advance to a power-producing demo (Hermes 2), then scale to commercial units (~140 MWe). This reduces technical risk at each stage and builds a track record of construction and operation before committing to a commercial fleet.
KAIROS POWER TODAY: BUILDING HERMES
As of May 2026, Kairos Power is in active construction of the Hermes test reactor at Oak Ridge, Tennessee, with nuclear concrete poured in May 2025. The NRC approved a 28-month construction permit deadline extension in April 2026, adjusting the completion target to 2027-2028 to accommodate engineering refinements and supply chain challenges typical for first-of-a-kind reactors. The company finalized a HALEU fuel contract with DOE in January 2026, signed a $27M partnership with Oak Ridge National Laboratory in February 2026, and is preparing its operating license application. A molten salt production facility is expected to become operational in 2026. The company is simultaneously advancing the design for Hermes 2 (a 35 MWe power-producing demonstration reactor) and its commercial-scale KP-FHR units at approximately 140 MWe each. The Google 500 MW PPA is driving the commercial pipeline, with multiple reactor deployments planned from the late 2020s through the 2030s.
Non-power demonstration. NRC construction permit issued Dec 2023. Nuclear concrete poured May 2025. NRC approved 28-month CP deadline extension (Apr 2026). HALEU fuel contract finalized Jan 2026. ORNL $27M partnership signed Feb 2026. Operating license application in preparation. Target operational: 2027-2028.
Power-producing demonstration unit. Second DOE ARDP award. Expected late 2020s. Will validate commercial electricity generation.
Commercial-scale units for Google PPA and other customers. NRC pre-application engagement underway. 2030s deployment target.
Google (500 MW PPA), Tennessee Valley Authority (TVA) for Oak Ridge site support, US Department of Energy (ARDP funding and HALEU fuel contract), and Oak Ridge National Laboratory ($27M technical partnership signed February 2026). Kairos has built a coalition of government, national lab, and corporate partners that de-risks the development pathway.
BOTTOM LINE
Kairos Power has done what no other advanced reactor company has accomplished: secured an NRC construction permit and started building. While the Hermes test reactor is not a commercial power plant, it represents the critical first step in a deliberate development strategy — prove the technology works before scaling it. The Google 500 MW PPA provides the demand anchor that NuScale never had, and the DOE ARDP backing provides federal cost-sharing that reduces private capital risk. The April 2026 NRC construction permit deadline extension (28 months) is not a setback — it reflects the reality of first-of-a-kind reactor construction and is normal for FOAK projects globally. The question is whether Hermes can be built on schedule and on budget by 2027-2028, and whether the KP-FHR design can scale to commercial economics. The stepping-stone approach — test reactor, demo reactor, commercial fleet — is the most disciplined development path in the advanced nuclear industry.