Kairos Power has begun construction on its Hermes 2 demonstration reactor in Oak Ridge, Tennessee, moving forward on a project that could shape how the tech industry sources carbon-free electricity for the next generation of artificial intelligence infrastructure. The two-unit facility, authorized by the U.S. Nuclear Regulatory Commission in November 2024, represents one of the first advanced reactor construction projects approved by federal regulators in decades.
The groundbreaking follows Kairos’s October 2024 agreement with Google to develop up to 500 megawatts of nuclear power by 2035, a deal that signaled Big Tech’s growing appetite for round-the-clock clean energy to run sprawling data center campuses. While Hermes 2 itself is a smaller-scale demonstration plant rather than a commercial power station, it serves as the proving ground for the reactor technology Kairos plans to deploy at scale under that partnership.
What Hermes 2 actually is
Hermes 2 consists of two reactor units, each rated at 35 megawatts of thermal output, sited adjacent to the Hermes 1 test reactor already under construction in Oak Ridge. Neither unit is designed to feed electricity directly into the grid. Instead, the facility will validate Kairos’s molten-salt-cooled design at a meaningful scale before the company commits to full commercial builds.
The reactors use TRISO fuel, a type of uranium particle encased in multiple ceramic and carbon layers that act as miniature containment systems. Each particle can withstand extreme temperatures without releasing radioactive material, which is a core safety feature of the design. The fuel requires high-assay low-enriched uranium, or HALEU, a specialized material enriched beyond what conventional reactors use but well below weapons-grade levels.
Unlike the pressurized water reactors that make up most of the U.S. nuclear fleet, Kairos’s design circulates molten fluoride salt rather than water as its primary coolant. The salt operates at low pressure and high temperature, which simplifies some safety systems and, in theory, reduces construction costs. Hermes 2 is where that theory meets physical reality.
The regulatory path that got it here
The NRC issued construction permits for both Hermes 2 units on November 21, 2024, tracked under docket numbers 50-611 and 50-612. The approval followed a formal safety evaluation, a preliminary safety analysis report submitted by Kairos, and an environmental review that concluded with a Finding of No Significant Impact, meaning the agency determined construction would not cause meaningful environmental harm.
The full regulatory record, including Commission hearing documents, Federal Register notices, and Kairos’s own technical submissions, is available through the NRC’s public docket index. That paper trail matters because it allows independent analysts, journalists, and the public to trace exactly how the agency reached its decision.
The Hermes 1 reactor, a single-unit predecessor, received its own construction permit in December 2023, making it the first new non-power test reactor authorized by the NRC in roughly 50 years. Hermes 2’s approval extended that precedent to a multi-unit configuration, giving Kairos and the broader advanced nuclear industry a second data point for how novel reactor designs can navigate federal licensing.
Where Google fits in
Google announced its agreement with Kairos Power in October 2024, describing it as the world’s first corporate deal to purchase nuclear energy from an advanced small modular reactor developer. Under the reported terms, Kairos would deploy multiple commercial reactors capable of delivering up to 500 megawatts of power to support Google’s data center operations, with the first units expected online by 2030 and full capacity reached by 2035.
The arrangement reflects a broader pattern across the tech sector. Microsoft signed a 20-year power purchase agreement with Constellation Energy to restart a unit at Three Mile Island. Amazon acquired a data center campus adjacent to a Pennsylvania nuclear plant operated by Talen Energy. Meta issued a request for proposals seeking up to 4 gigawatts of new nuclear capacity. In each case, the driving force is the same: AI workloads demand enormous, uninterrupted electricity supplies, and intermittent renewables alone cannot guarantee that.
Hermes 2 does not directly supply Google with power. Its role is to demonstrate that Kairos’s reactor technology works reliably at a scale large enough to justify the commercial commitments both companies have made. If the demonstration succeeds, it strengthens the case for the larger deployments Google is counting on. If it encounters significant technical setbacks, the commercial timeline could slip.
Open questions that will define the project’s future
Construction authorization is not the same as an operating license. Before either Hermes 2 unit can run, Kairos must submit a separate operating license application and clear another round of NRC safety and environmental reviews. That process introduces its own uncertainties, particularly if the agency identifies design issues during construction or if regulatory standards evolve in the interim.
Fuel supply remains a practical concern. HALEU production in the United States has been limited, with Centrus Energy’s facility in Piketon, Ohio, operating under a Department of Energy contract to produce demonstration quantities. The DOE has invested in expanding domestic HALEU capacity, but whether supply will keep pace with demand from Hermes 2 and a growing roster of advanced reactor projects is not guaranteed. Any shortfall could delay fueling and startup even if construction finishes on schedule.
Project costs have not been disclosed in NRC filings or public financial statements. The NRC reviews safety and environmental compliance, not budgets, so the permits contain no spending figures. Without transparent cost data, it is difficult to judge whether the Hermes 2 design can eventually compete on price with natural gas, solar-plus-storage, or conventional nuclear plants.
Security and grid-planning questions also loom. Siting reactors to serve data center clusters introduces considerations around physical security, cybersecurity, and local grid reliability that differ from traditional utility-scale nuclear plants. These issues are not addressed in the construction permits, which focus narrowly on the proposed site, but they will surface as the industry moves toward commercial deployment.
What the construction start actually signals
Kairos breaking ground on Hermes 2 does not, by itself, prove that advanced nuclear reactors will power the AI boom. The gap between a construction site and a functioning power plant is measured in years, billions of dollars, and regulatory milestones that have historically tripped up nuclear projects of all sizes.
What it does confirm is that a federal agency completed a full safety and environmental review of a novel reactor design and found it acceptable under existing rules. That outcome gives future applicants a concrete template for structuring their own submissions. It gives investors a signal that the licensing process, long considered the most unpredictable obstacle for advanced nuclear, can be navigated on a reasonable timeline. And it gives the tech industry’s nuclear ambitions something they have lacked until now: steel and concrete in the ground.
The unanswered questions about fuel, financing, and long-term performance will determine whether Hermes 2 becomes a footnote or a turning point. For now, construction is underway, and the clock is running.
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*This article was researched with the help of AI, with human editors creating the final content.
