On Nov. 9, the Nuclear Regulatory Commission issued a construction permit for the Long Mott Generating Station in Calhoun County, Texas, a plant built around four X-energy Xe-100 reactors that will mainly supply high-temperature steam to Dow’s Seadrift operations. The agency called it the first construction permit for a high-temperature gas-cooled reactor in nearly 60 years. Excess electricity is meant for the grid.
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Chairman Ho K. Nieh said the NRC delivered on its 18-month review schedule, which he framed as evidence that rigorous safety reviews can run on predictable timelines. The permit is the third advanced-reactor construction permit the agency has issued this year.
Four Xe-100 modules at Seadrift
The NRC’s Nov. 9 release describes a multimodule facility of four Xe-100 reactors, a pebble-bed design with online refueling. Trade coverage of the earlier environmental review put the combined rating at 320 megawatts electric and 800 megawatts thermal. POWER magazine’s account adds that the site covers 1,537 acres and that the design uses helium coolant, air-cooled condensers, and no cooling towers or water intake structures.
The applicant is Long Mott Energy, a wholly owned subsidiary of Dow Chemical, while X-energy designed the reactors. Nuclear Engineering International reports a project cost of $2.4 billion under the Department of Energy’s Advanced Reactor Demonstration Program, which shares costs 50/50 up to that amount, and says the plant would feed Dow’s 4,700-acre Seadrift complex with up to 800 megawatts of thermal power.
Dow’s Seadrift complex, by Nuclear Engineering International’s description, supports production of more than 4 billion pounds of materials a year, which explains why the plant is designed around steam first and electricity second. Edward Stones, Dow’s business vice president for energy and climate, called the earlier environmental clearance a significant milestone for the Long Mott Energy project.
The firsts the NRC claimed
Beyond the nearly-60-year gap, the NRC listed several regulatory firsts: its first approval of a multimodule advanced reactor facility, of a pebble-bed core, and of a design with online refueling. It was also the first review of a high-temperature gas-cooled reactor under the agency’s Licensing Modernization Project framework, a risk-informed approach meant to speed advanced designs.
The NRC release does not name the earlier project that sets the nearly-60-year baseline, and the agency’s wording is specific to high-temperature gas-cooled reactors. It should not be read as the first permit for any advanced reactor: POWER magazine notes that TerraPower’s Kemmerer Unit 1 received its construction permit on March 4, after a full environmental impact statement.
Review timeline from application to permit
Dow and X-energy announced on March 31, 2025 that they had submitted the application, and an American Nuclear Society report quoted the companies as saying construction could begin later this decade only if Dow confirms it can deliver the project while meeting its financial return targets. The NRC accepted the application for review on May 12, 2025, and opened a window in June 2025 for parties to request a hearing, as the society also reported.
The environmental assessment and Finding of No Significant Impact came in May, and the NRC says its safety evaluation finished in October, one month ahead of schedule. POWER magazine reported that X-energy described the project as the first commercial advanced reactor effort in a Part 50 construction permit proceeding to complete environmental review through an assessment rather than a full impact statement. NRC Executive Director for Operations Mike King said that approach reflected the project’s relatively low potential for environmental impacts.
Dragan Popovic, X-energy’s chief global operating officer, offered a measured line at the time: there are no shortcuts in nuclear safety.
X-energy’s path to this permit was long. Nuclear Engineering International traces formal engagement with the NRC to 2016, selection for the Advanced Reactor Demonstration Program in 2020, Dow signing on as the first major commercial offtaker in 2022, and a joint development agreement with a $50 million initial fund in 2023. In April 2026 X-energy signed an engineering, procurement and construction contract with Fluor. POWER magazine adds that the NRC licensed TRISO-X, an X-energy subsidiary, in February to fabricate TRISO fuel particles at Oak Ridge, Tennessee, the first Category II fuel fabrication facility licensed in the country. The NRC’s 18-month clock traces to Executive Order 14300, according to that account.
Construction-only authority and the operating license still ahead
The permit authorizes construction only. Long Mott Energy must obtain a separate NRC operating license before it can load fuel or run the reactors, and the Dow decision on financial return targets still stands between the permit and groundbreaking. How long the operating-license review takes, and whether Dow confirms the project, are the next unanswered dates. The NRC release does not state a schedule for the operating-license application, and POWER magazine’s account likewise says only that a separate license is needed before fuel loading and commercial operation, so the timeline from construction permit to first steam is still open.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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