The Long Mott Generating Station has received a US construction permit from the Nuclear Regulatory Commission, clearing four X-energy Xe-100 reactors for development at Dow’s UCC Seadrift Operations site in Calhoun County, Texas. The approval is the first construction permit for a high-temperature gas-cooled reactor in nearly 60 years and the NRC’s first approval of a multimodule advanced reactor facility. It also marks the first-ever pebble-bed HTGR approval, with safety resting on the passive physics of the Xe-100’s TRISO-X coated particle fuel.
The permit is a significant regulatory step, but it does not authorize operation. Long Mott Energy LLC, a wholly owned subsidiary of Dow, is the applicant and recipient. Before fuel can be loaded or the reactors started, the company must obtain a separate operating license from the NRC. The four units would produce 320 megawatts of electricity and 800 megawatts of thermal output in total, with each reactor rated at 80 megawatts electric and 200 megawatts of heat.
Long Mott Generating Station: Industrial heat at the center of the project
The proposed plant is designed primarily to generate high-temperature steam for industrial use at Seadrift, with excess electricity exported to the grid. X-energy said the four first-of-a-kind Xe-100s are expected to provide clean industrial power to the site for 60 years. Dow described the project as a way to replace existing energy and steam assets near the end of their useful lives.
X-energy said the review found that the Xe-100 design can be safely sited and constructed within an operating industrial site. Dow Business Vice President for Energy and Climate Edward Stones said the project would be evaluated through competitiveness, execution readiness and capital affordability before any construction decision. Dow is expected to consider a preliminary investment decision in 2027, while full-scale nuclear construction would begin only after a final investment decision by Dow’s board.
The timetable has been long by advanced nuclear standards. Dow submitted the construction permit application in March 2025, with X-energy serving as technical and licensing lead. The NRC docketed the application and set an 18-month review schedule in June 2025, then completed the review slightly ahead of that schedule. The Office of Advanced Reactors completed a final safety evaluation in October 2026, recommending that the Commission make findings under 10 CFR 50.35, 50.40 and 50.50. That staff evaluation did not commit the Commission to issue a permit.
How the Xe-100 differs from conventional reactors
The Xe-100 is a high-temperature gas-cooled reactor that sends helium gas over uranium-containing fuel pellets and relies on TRISO-X coated particle fuel. The US Department of Energy has described TRISO fuel as “the most robust nuclear fuel on earth.” X-energy says the design’s safety profile is expected to support a 400-meter emergency planning zone, compared with 10 miles for conventional light-water reactors, allowing generation to be sited closer to the point of demand.
TechCrunch reported that X-energy claims the reactor design is safer than many existing reactors. The Union of Concerned Scientists questioned that claim and the speed of the permit. Edwin Lyman, the group’s nuclear power safety director, said the NRC “only accomplished this feat by pushing consideration of critical safety questions to a later date,” issues that should have been resolved before construction was approved.
X-energy’s CEO J. Clay Sell tied the earlier-than-expected permit to the NRC’s review process, congressional reforms over the preceding six years and work by the X-energy and Dow teams. He said the milestone validates a regulatory approach that can be replicated across the company’s expanding commercial pipeline.
A broader commercial pipeline takes shape
The Long Mott Generating Station is the first advanced nuclear facility approved for an industrial site in the United States, a milestone achieved under the Department of Energy’s Advanced Reactor Demonstration Program, but X-energy’s commercial reach extends well beyond Texas. Since receiving the program award, the company says the Xe-100 has moved from concept to a pipeline exceeding 11 gigawatts, equal to 144 reactors. Projects include the Cascade Advanced Energy Facility with Amazon and Energy Northwest, a second Amazon project with AEP, and a Centrica partnership targeting approximately 6 gigawatts in the United Kingdom.
Amazon’s Climate Pledge Fund led X-energy’s 500 million dollar Series C-1 round, and Amazon has committed to buying 5 gigawatts of capacity from the nuclear startup. X-energy’s April initial public offering raised 1 billion dollars. The permit produced only a small rise in the company’s share price, enough to recover the previous week’s losses, while the shares trade at less than half their initial offering price.
That market reaction shows why the permit should not be mistaken for commercial proof. TechCrunch noted that no small modular reactor is currently operating in the United States, and X-energy says Dow’s reactors will not be operational until the early 2030s. Proponents argue that smaller reactor designs can accelerate construction and reduce costs, although those advantages have not yet been demonstrated.
Approved topical reports may speed the next projects
X-energy said its 14 NRC-approved topical reports apply to the Xe-100 design generically rather than only to Long Mott. Future applications can cite those approved methodologies without re-demonstrating the underlying technical basis, though each application still requires individual review. The company began pre-application engagement with the NRC in 2018, and Dow joined in 2023, producing more than a dozen approved topical reports that addressed complex safety questions before formal licensing began.
NRC Chairman Ho K. Nieh said: “Today, the new NRC is issuing America’s first construction permit for a high-temperature gas-cooled reactor in more than half a century.” He added that the agency “delivered on the 18-month schedule,” demonstrating that rigorous safety reviews can run on predictable timelines and move advanced nuclear technology from design to construction.
Principal Deputy Assistant Secretary for Nuclear Energy Mike Goff said the approval shows meaningful progress toward deploying reactors that can deliver reliable power and industrial heat. The milestone also comes with financial support, as X-energy has been informed that its Department of Energy award is intended to increase to 2.15 billion dollars in total for a first-of-a-kind commercial advanced nuclear plant and TRISO-X fuel fabrication facility.
What readers should watch next
The permit moves Long Mott into the next phase of project development, including design finalization, supply chain maturation for long-lead components and preparation of an operating license application. Full-scale nuclear construction still depends on Dow’s final investment decision, so the approval is not an immediate construction start. X-energy expects first delivery in the early 2030s, and the company views the permit as a reference point for future licensing, including in the United Kingdom, where the Xe-100 is in Generic Design Assessment.
For industrial energy users and nuclear investors, the test now shifts from licensing to execution. Dow must demonstrate that the design, equipment, materials and financing can mature before major site work begins. The NRC must still approve operation through a separate license. X-energy must deliver its first four reactors on a schedule that has yet to be proven, while the company tries to convert a pipeline of more than 11 gigawatts into operating assets. The Long Mott Generating Station has cleared its central regulatory hurdle, but whether it becomes a repeatable model for industrial nuclear power will be decided by what follows.