X-energy, a Maryland-based nuclear technology firm, is betting that a reactor fueled by tiny, heat-resistant particles can eliminate the risk of a core meltdown entirely. That claim, if validated at commercial scale, would address the single greatest public fear about nuclear power and reshape how regulators, utilities, and investors evaluate the technology. But the path from laboratory milestone to grid-connected power plant runs through a thicket of licensing reviews, fuel production challenges, and competition from at least one other advanced reactor developer building in the same Tennessee city.
A Fuel That Cannot Melt
The core of X-energy’s safety argument rests on TRISO fuel, a particle roughly the size of a poppy seed encased in multiple layers of carbon and ceramic coatings. The U.S. Department of Energy characterizes this fuel as one that will not melt in the reactor design context, a statement that goes well beyond the usual engineering hedging about safety margins. X-energy’s design pairs TRISO particles with a pebble bed, high-temperature gas-cooled reactor architecture. Each fuel pebble contains thousands of coated particles, and the reactor uses helium rather than water as a coolant. Because the fuel retains fission products even at extreme temperatures, the design eliminates the failure mode that caused the Fukushima and Three Mile Island disasters: a loss of coolant leading to fuel damage and radioactive release.
The DOE has backed that technical promise with real dollars. X-energy completed a pebble bed reactor development effort, and a separate $40 million project advanced the high-temperature gas reactor design further. Dozens of U.S. companies are developing advanced reactor designs, according to the DOE, but X-energy’s focus on a fuel form that physically cannot reach melting temperatures under reactor conditions sets it apart from competitors still relying on conventional fuel assemblies with engineered safety systems layered on top. The company is positioning TRISO as a platform fuel that could, in principle, serve multiple reactor types, which helps justify the capital-intensive investment in a new fabrication facility.
Building the Fuel Supply in Oak Ridge
A reactor design means nothing without a reliable fuel supply, and that is where X-energy’s subsidiary TRISO-X enters the picture. The company applied for a special nuclear material license from the Nuclear Regulatory Commission to build a fuel fabrication facility, and the NRC accepted the application for docketing after receiving the required environmental report. Fuel production efforts are already taking shape in Oak Ridge, Tennessee, where TRISO fuel manufacturing work is underway. The NRC also extended the public comment period for the TX-1 fuel facility licensing action, a sign that the review is generating enough interest and complexity to warrant additional scrutiny.
This fuel pipeline matters for a practical reason most coverage overlooks. Even if X-energy’s reactor design clears every regulatory hurdle, it cannot operate without a domestic source of TRISO fuel produced at industrial scale. The United States currently has no commercial TRISO fuel production line, which means the licensing timeline for the fabrication facility is just as consequential as the reactor approval itself. Any delay in fuel licensing directly delays reactor deployment, creating a bottleneck that no amount of reactor engineering can solve. In that sense, TRISO-X’s Oak Ridge plant is as much a first-of-a-kind project as the reactor it is meant to serve, and its success or failure will shape whether TRISO becomes a mainstream nuclear fuel or remains a niche research material.
Kairos Power and the Parallel Track
X-energy is not the only firm racing toward a meltdown-resistant reactor in Oak Ridge. Kairos Power is building the Hermes non-power test reactor at the same Tennessee site, using a different but related approach. Hermes employs fluoride salt-cooled high-temperature reactor technology, designated KP-FHR, and also uses TRISO fuel along with high-assay low-enriched uranium, or HALEU. The NRC applies a “functional containment” concept to Hermes, meaning the layered barriers within the fuel itself serve as the primary containment rather than a massive reinforced concrete dome. Kairos submitted its construction permit application in September 2021, and the NRC issued Construction Permit No. CPTR-6 on December 14, 2023, after completing a safety evaluation in June of that year.
The permitting pace accelerated from there. The NRC issued construction permits CPTR-7 and CPTR-8 for Hermes 2 on November 21, 2024, authorized by Commission Order CLI-24-03. The agency also issued a final Environmental Assessment and Finding of No Significant Impact for Hermes 2, a separate review from the full Environmental Impact Statement (NUREG-2263) completed for the original Hermes reactor. The Department of Energy underscored the significance of this step when it highlighted that the NRC approved Hermes construction as a milestone for advanced reactors, signaling that non-light-water designs can clear the same regulatory bar as conventional plants. Kairos had already demonstrated operational credibility by completing 1,000 hours of pumped salt operation in its first molten salt system. That hardware milestone matters because it shows the coolant technology works outside a simulation, a step X-energy’s gas-cooled design must also demonstrate convincingly.
Regulatory Speed as Competitive Advantage
The real race here is not just about physics or engineering. It is about which company can move through the NRC’s licensing process fast enough to attract utility contracts and private capital before the current political window for nuclear energy closes. The NRC reached a milestone in its Part 53 advanced reactor licensing rulemaking, an effort to create a more flexible regulatory framework tailored to designs that differ fundamentally from the light-water reactors that dominate the existing fleet. That framework is intended to accommodate concepts like functional containment, high-temperature operation, and alternative coolants, all of which feature prominently in both X-energy’s and Kairos Power’s offerings. Yet until the final rule is in place and applied to real applications, developers must navigate a hybrid landscape of legacy requirements and emerging guidance.
For X-energy, the risk is that delays in either the fuel facility or the reactor license could allow competitors to claim the mantle of first commercial advanced reactor in the United States. For Kairos, the challenge is proving that a non-power test reactor like Hermes can translate quickly into a grid-connected plant that earns revenue, rather than remaining a demonstration perched on the edge of commercialization. Both companies are effectively testing whether the NRC can scale its review processes for advanced reactors without sacrificing rigor, and their timelines will inform how investors view the bankability of next-generation nuclear projects. Speed, in this context, is not about cutting corners but about reducing uncertainty, which is often more important to financiers than any single technical parameter.
Federal Support and the Broader Ecosystem
Behind the headlines about individual companies lies a broader federal ecosystem trying to make advanced nuclear a realistic option for decarbonizing the power sector. The Department of Energy has created multiple pathways for cost-shared demonstrations, fuel development, and infrastructure upgrades, many of which intersect with the Oak Ridge projects. Developers can tap competitive funding opportunities cataloged in portals such as the DOE Genesis site, which aggregates open solicitations and program information across the department. That visibility matters for smaller firms and suppliers that might contribute components, modeling tools, or specialized services to projects like X-energy’s TRISO-X plant or Kairos’s Hermes reactors.
Technical underpinnings for these efforts often trace back to decades of government-sponsored research. The Office of Scientific and Technical Information maintains a vast archive of reports, data sets, and journal articles through the OSTI database, including historical work on gas-cooled reactors, molten salt systems, and coated-particle fuels. Access to that corpus allows current developers to build on prior experiments rather than repeat them, shortening design cycles and informing safety analyses submitted to the NRC. At the same time, new infrastructure needs, from upgraded transmission lines to specialized manufacturing capacity, are beginning to surface on platforms like the Infrastructure Exchange, which connects energy projects to financing tools and stakeholders interested in long-lived assets.
Targeted innovation programs are also shaping which technologies reach the starting line. The Advanced Research Projects Agency (ARPA) Energy uses its program portfolio to push high-risk, high-reward concepts that might later feed into commercial designs, including materials that can survive extreme temperatures and coolants that improve thermal efficiency. While ARPA‑E awards are typically modest compared with full-scale reactor budgets, they can de-risk key components that otherwise would be too speculative for private investors. In parallel, DOE’s Nuclear Energy office has supported early design work and testing for both TRISO fuel and molten salt systems, creating a pipeline from laboratory-scale experiments to first-of-a-kind plants like those in Oak Ridge.
Taken together, these funding streams, research archives, and infrastructure tools form the scaffolding around which X-energy, Kairos Power, and their peers are building. The question now is whether that scaffolding can support the leap from demonstration to deployment quickly enough to matter for climate goals and grid reliability. If X-energy can prove that its TRISO-fueled reactor truly cannot melt down, and if TRISO-X can supply that fuel reliably from Oak Ridge, the company could redefine public expectations about nuclear safety. If Kairos can show that salt-cooled reactors with functional containment can be licensed and operated on schedule, it may open a parallel path that emphasizes thermal efficiency and compact plant footprints. Either way, the outcome in Tennessee will reverberate far beyond one city, shaping how the next generation of nuclear power plants is financed, regulated, and ultimately judged by the communities that host them.
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*This article was researched with the help of AI, with human editors creating the final content.
