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Kairos Power is promising, but it has not yet proved that it can deliver affordable commercial nuclear electricity. The U.S. company is developing a fluoride salt-cooled, high-temperature reactor that combines molten-salt cooling with solid TRISO fuel. Its progress is unusually substantial for an advanced-nuclear startup: the Nuclear Regulatory Commission has issued construction permits for its Hermes and Hermes 2 projects, Hermes construction is underway, and Google has committed to support a potential fleet of Kairos reactors.
That progress should not be confused with an operating commercial reactor. Kairos still must complete construction, obtain permission to operate, qualify and secure fuel, demonstrate reliable electricity generation, and show that its manufacturing model can reduce costs across multiple units.
The short version
- Kairos Power, founded in 2016, is developing the KP-FHR: a fluoride salt-cooled, high-temperature reactor.
- The design uses solid TRISO fuel in pebble-shaped fuel elements, not fuel dissolved in liquid salt.
- Hermes is a low-power demonstration reactor in Oak Ridge, Tennessee.
- Hermes 2 consists of two 35-MWth test reactors and is intended to be a commercial-scale demonstration.
- Google is targeting up to 500 MW of new Kairos nuclear capacity by 2035, while a Google-Kairos-Tennessee Valley Authority arrangement associates Hermes 2 with 50 MW of nuclear energy for the TVA grid and a 2030 target.
- The commercial case remains unproven until the reactors operate reliably and their costs are demonstrated.
What Kairos Power is building
Kairos is a U.S. nuclear technology, engineering and manufacturing company focused on commercializing one main reactor concept rather than pursuing several unrelated designs. Its stated strategy combines reactor development with in-house manufacturing, prefabrication and successive hardware demonstrations.
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The company argues that building and testing hardware repeatedly can expose engineering problems earlier, improve construction methods and reduce cost and schedule uncertainty before a larger commercial rollout. That is an important part of the investment and climate-tech story: Kairos is trying to solve not only a reactor-physics problem, but also the nuclear industry’s difficult construction and delivery problem.
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The strategy is supported by meaningful milestones. The NRC issued a construction permit for Hermes in December 2023. The Department of Energy reported that construction began in 2024, while Kairos says nuclear-safety-related construction began in May 2025. The NRC issued construction permits for Hermes 2 on November 21, 2024, and Kairos announced groundbreaking on April 17, 2026.
Those milestones demonstrate progress beyond a paper design. They do not, however, establish that Kairos has a commercially operating reactor or a proven low-cost power plant.
How the KP-FHR reactor works
KP-FHR stands for fluoride salt-cooled, high-temperature reactor. Its key design choices are easier to understand when separated:
- TRISO fuel produces heat. Small fuel particles are coated with multiple layers of ceramic and carbon materials. The particles are embedded in a carbon matrix and assembled into pebble-like fuel elements.
- Molten fluoride salt carries the heat. The salt circulates through the reactor and transfers heat without serving as the fuel itself.
- A heat exchanger transfers energy to water. The NRC describes Hermes 2 as using a shared Rankine-cycle steam system.
- Steam drives a turbine. The turbine-generator converts thermal energy into electricity for the grid.
Google describes Kairos’s design as combining molten-salt cooling with ceramic pebble fuel and a low-pressure operating concept. Compared with conventional water-cooled reactors, molten salt can carry heat without the same high coolant pressures. Kairos and its supporters see that as a route to simpler systems and passive-safety features.
These are design objectives and claimed advantages, not verified evidence that the plant will produce cheaper electricity. A low-pressure coolant system does not remove the need to manage heat, radiation, materials, pumps, valves, heat exchangers, fuel handling and other plant systems.
Key terms
- FHR
- Fluoride salt-cooled, high-temperature reactor.
- TRISO
- Small fuel particles surrounded by multiple protective layers and embedded in a carbon-based fuel element.
- HALEU
- High-assay low-enriched uranium. The NRC identifies HALEU-based TRISO fuel as the fuel basis for Hermes 2.
- MWth
- Megawatts of thermal output from the reactor.
- MWe
- Megawatts of electrical generating capacity. Thermal output and electrical output are not interchangeable.
- SMR
- Small modular reactor. The term describes a commercial deployment category, but it does not mean every Kairos project is a conventional grid-scale SMR.
Why TRISO fuel matters
TRISO fuel is designed to retain fission products within its layered particle structure under specified accident conditions. The NRC describes the fuel as HALEU TRISO particles embedded in a carbon-matrix pebble and identifies the high-temperature particles as the principal functional-containment feature for Hermes 2.
That does not mean a TRISO-fueled reactor is impossible to damage or that a meltdown is impossible. Fuel-particle performance is only one part of overall plant safety. Regulators and operators must also address the reactor vessel, salt chemistry, heat-removal systems, fuel handling, power-conversion equipment, radioactive materials and emergency procedures.
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The relevant question is therefore not whether TRISO makes the reactor unconditionally safe. It is whether the fuel, reactor design and complete plant can meet their safety requirements under the conditions examined in the applicable licensing analyses.
Hermes versus Hermes 2
| Project | Status | What it is intended to show |
|---|---|---|
| Hermes | Construction underway in Oak Ridge, Tennessee. NRC construction permit issued in December 2023. DOE reported a projected operating date of 2027. | A low-power nuclear demonstration reactor intended to demonstrate the technology and produce clean heat rather than operate as a full commercial power station. |
| Hermes 2 | NRC construction permits issued November 21, 2024. Groundbreaking announced April 17, 2026. | Two 35-MWth low-power test reactors with a shared Rankine-cycle steam system. It is designed as a commercially oriented, power-producing demonstration. |
| Future commercial KP-FHR fleet | Not an operating fleet. Google agreement targets up to 500 MW by 2035. | Repeatable commercial deployment of standardized Kairos reactors. |
The distinction matters because coverage often compresses all of these projects into “the Kairos reactor.” Hermes is not the same as a future commercial fleet, and Hermes 2 is not yet an operating commercial nuclear station.
Kairos calls Hermes 2 its first commercial-scale reactor and first power-producing project. The NRC, however, describes it as an advanced test-reactor facility. Both descriptions can be accurate when used carefully: Hermes 2 has commercial-scale intent, but its regulatory status remains that of a test-reactor project.
What Google and TVA add to the story
In October 2024, Google announced an agreement to support development of multiple Kairos reactors, targeting up to 500 MW of new nuclear capacity by 2035, with the first unit targeted for 2030. The agreement gives Kairos an unusually strong early customer signal at a time when data-center electricity demand is increasing interest in firm, low-carbon power.
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In August 2025, Google, Kairos and TVA announced an arrangement associated with Hermes 2. The announcement linked 50 MW of nuclear energy to the TVA grid and set a 2030 target for operations. Google’s role involves procuring clean-energy attributes through TVA; this should not be described as Google directly owning or operating the reactors.
The arrangement creates a three-party commercialization model:
- Kairos develops and builds the reactor technology.
- TVA provides utility and grid context.
- Google provides demand and a potential anchor customer for clean, firm electricity.
That structure can help share first-of-a-kind project risk. It is not the same as guaranteed revenue, completed construction, bankable commercial economics or proof that the fleet will reach 500 MW.
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What Kairos has actually achieved
- Founded in 2016.
- Received an NRC construction permit for Hermes in December 2023.
- Started Hermes construction, with DOE reporting construction activity in 2024.
- Received NRC construction permits for Hermes 2 on November 21, 2024.
- Received up to $303 million in DOE support for Hermes through the Advanced Reactor Demonstration Program.
- Secured a Google agreement targeting up to 500 MW of advanced nuclear capacity by 2035.
- Announced a Google-Kairos-TVA Hermes 2 deployment arrangement tied to 50 MW on the TVA grid and a 2030 target.
- Broke ground on Hermes 2 on April 17, 2026.
Kairos also says it has three approved NRC construction permits and 14 approved topical reports supporting KP-FHR licensing. Those figures are company-reported measures of regulatory and technical progress, not independently audited proof of commercial readiness.
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It has moved from concept to hardware and construction
Many advanced-reactor concepts remain at the design, funding or licensing stage. Kairos has progressed through engineering demonstrations, permitted nuclear projects and physical construction. That makes its execution record more consequential than a concept illustration or preliminary announcement.
It is testing a different risk profile
The combination of molten-salt cooling, solid TRISO fuel and low-pressure operation is intended to provide a different safety and engineering profile from conventional large water-cooled reactors. The potential benefits include lower coolant pressure and passive heat-removal characteristics. Whether those features translate into lower construction and operating costs remains to be proven.
It is treating manufacturing as part of the reactor technology
Kairos’s thesis depends on factory-style production, prefabrication and standardized designs. The company is attempting to reduce the uncertainty associated with building large bespoke nuclear projects by learning from smaller successive units.
This is potentially important for investors and policymakers. A reactor that works technically but takes too long or costs too much to build will struggle to scale. Kairos must show that its manufacturing and construction model can be repeated after the first highly supported projects.
The hard questions that remain
1. Will the projects meet their target dates?
DOE reported a projected 2027 operating date for Hermes, and Google and TVA identified 2030 for Hermes 2. These are targets, not guarantees. Construction, commissioning, fuel loading, testing and operating authorization can all affect schedules.
2. What does the construction permit allow?
A construction permit authorizes construction under the applicable regulatory framework; it is not an operating license. Kairos must still satisfy the requirements for fuel handling, testing, commissioning and operation before the project can function as a nuclear power facility.
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3. Can Kairos secure HALEU and TRISO fuel?
Hermes 2 is specified to use HALEU-based TRISO fuel. Commercialization therefore depends on fuel availability, qualification, fabrication capacity, transportation and long-term supply. The cited sources confirm the fuel basis but do not establish Kairos’s complete long-term commercial fuel-supply position.
4. Can molten-salt systems be maintained economically?
Important engineering questions include corrosion and material compatibility, salt purification and chemistry control, tritium management, pump and valve performance, heat-exchanger maintenance, inspection and repair methods, fuel-pebble handling and spent-fuel management. These are not necessarily failures; they are areas where operating evidence will matter.
5. What will the first commercial unit cost?
The public sources cited here do not establish a verified construction cost, levelized cost of electricity, tariff or final power price for Hermes 2. Claims that Kairos electricity will be cheaper than conventional nuclear should therefore be treated as commercial goals, not established results.
6. Can first-of-a-kind success become fleet-scale repetition?
A first project can benefit from exceptional government support, customer patience and engineering attention. The commercial test is whether Kairos can deliver multiple standardized units with predictable schedules, qualified suppliers, trained workers and acceptable financing requirements.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How Kairos compares with other advanced-nuclear developers
Kairos operates in a crowded U.S. advanced-nuclear field that includes TerraPower, X-energy, NuScale, GE Vernova Hitachi and Oklo. These companies do not offer interchangeable products. They differ in reactor type, coolant, fuel, output, licensing status, construction progress, commercial model and target customers.
For example, Kairos’s design uses molten fluoride salt as coolant and TRISO pebble fuel. Other developers may use sodium, gas or water cooling, different fuel forms or different plant configurations. A comparison based only on “advanced nuclear” or “SMR” can conceal more than it explains.
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The useful comparison is execution-based: Which companies have secured the relevant permits? Which have begun construction? Which have fuel and supply-chain plans? Which have credible customers? Which have demonstrated a path from a first plant to repeatable, financeable projects?
What this means for climate-tech and investment watchers
Kairos is a company to watch because it combines a distinctive reactor design with regulatory progress, federal support, construction activity and a major technology-company customer. Those are stronger signals than a long-term concept alone.
But the risks are also substantial. Kairos remains dependent on successful licensing, construction, fuel supply, materials performance, utility integration, workforce development and cost control. Google’s agreement increases demand visibility, but it does not eliminate those risks. Nor does it establish that Kairos will earn attractive returns or that its electricity will compete on price.
For readers evaluating the company or the broader sector, the most important future milestones are:
- Completion and commissioning of Hermes.
- Evidence that Hermes meets its safety and performance objectives.
- Progress on Hermes 2 construction and operating approvals.
- Reliable HALEU and TRISO fuel supply.
- Actual construction and operating-cost data.
- Evidence that the manufacturing process can be repeated across multiple units.
- Clear demonstration that customers will pay for firm, low-carbon electricity.
Bottom line
Kairos Power deserves serious attention because it has moved unusually far for an advanced-reactor startup and has connected its technology to real construction, federal support, regulatory milestones and prospective demand from Google and TVA. Its KP-FHR design could become an important source of firm, low-carbon power if the company executes.
However, Kairos is still demonstrating technology and project delivery. Hermes and Hermes 2 must be completed, fueled, licensed to operate and shown to generate electricity reliably at an acceptable cost. Until then, Kairos is a high-potential commercialization story—not a proven commercial nuclear fleet.
Sources: NRC Hermes 2 project page; NRC Hermes project page; Department of Energy on Hermes construction; Kairos technology overview; Kairos Hermes 2 groundbreaking announcement; Google-Kairos agreement; Google-Kairos-TVA announcement.
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