NRC issues Long Mott construction permit for four Xe-100 reactors

The Nuclear Regulatory Commission has issued a construction permit for Long Mott Generating Station, four X-energy Xe-100 high-temperature gas-cooled reactors that Dow subsidiary Long Mott Energy proposes to build at Dow's Seadrift Operations site in Calhoun County, Texas, the agency announced on November 9, 2026. The NRC calls it the first construction permit for a high-temperature gas-cooled reactor in nearly 60 years and the third advanced reactor construction permit it has issued this year. The four reactors total 800 MWt, or 320 MWe, per the NRC staff's final safety evaluation, and would mainly make high-temperature steam for industrial use at the Dow site, with excess electricity exported to the grid.

The permit is permission to build, and Dow has not made a final decision to build. The NRC notes that the company still needs a separate operating license before loading fuel or operating the reactors. "Receipt of the construction permit does not represent a final decision by Dow to proceed with construction of the proposed facility," Dow said the same day, naming continued engineering and design finalization and review by its board of directors among the milestones that remain. If approved, Dow says, construction could begin later this decade, with startup early next decade.

What the NRC approved

The design is new territory for the regulator, which lists four firsts in the permit: its first approval of a multimodule advanced reactor facility, its first approval of a reactor with a pebble-bed core, its first approval of a design featuring online refueling, and its first review of a high-temperature gas-cooled reactor under its risk-informed, technology-inclusive Licensing Modernization Project framework. In the Xe-100's pebble-bed design, heat comes from fission inside thousands of spherical, coated TRISO fuel particles, the Commission's order describes; our SMR explainer covers the fuel and the licensing path.

The schedule was met or beaten, depending on who is talking. "We delivered on the 18-month schedule," NRC Chairman Ho K. Nieh said, "proving we can do rigorous safety reviews on predictable timelines that move advanced nuclear technology from design to construction." X-energy chief executive J. Clay Sell said the companies got the permit earlier than expected. Long Mott Energy applied on March 31, 2025, and the NRC accepted the application for docketing on May 12, 2025, per the safety evaluation. The NRC says its staff finished that evaluation in October, one month ahead of schedule; it was dated October 30, as we reported at the time.

The permit came three days after the Commission turned down San Antonio Bay Estuarine Waterkeeper. On November 6 the Commission denied the group's petition for review of the licensing board decisions that had rejected or dismissed all of its contentions and ended the contested proceeding, finding no reversible error by the board and no substantial question warranting review. Long Mott's permit follows the BWRX-300 permit for TVA's Clinch River site dated September 28; the Advanced reactors in the US: SMRs and microreactors page tracks the rest of the field.

Who pays

The NRC judged Long Mott's finances by a different test from the one Part 50 sets for reactor construction permits. Long Mott Energy asked for an exemption from the Part 50 financial qualification requirements, and the staff, finding the exemption warranted, applied instead the Part 70 standard normally used for licensing the possession and use of special nuclear material: whether the applicant "appears to be" financially qualified, per the safety evaluation. The rulebook is moving the same way: the Commission's November 6 order notes that the agency has written the "appears to be financially qualified" standard into Part 53, its framework for advanced reactors, and has proposed a rule that, if finalized, would bring it into Parts 50 and 52. Waterkeeper had challenged the exemption in one of the contentions the board turned away.

Dow carried the test. The staff relied on a February 23, 2026 financial support agreement under which Dow Chemical, Long Mott Energy's parent, will fund construction costs up to a specified dollar amount (unless Dow substitutes a loan facility or letter of credit with the NRC's written consent), a sum the staff says is more than 50 percent of the projected construction cost estimate. The agreement also lets Long Mott Energy incur project costs before federal reimbursement through the Department of Energy's Advanced Reactor Demonstration Program. On that basis the staff found the company "appears to be financially qualified" to construct the plant. Neither the public safety evaluation nor the NRC, Dow or X-energy releases put a dollar figure on the construction cost.

Dow, in other words, has signed an agreement to fund more than half of the projected construction cost of a plant it has not made a final decision to build. "As we move forward, we will continue to evaluate the project through the lens of competitiveness, execution readiness, and capital affordability before any decision regarding construction is made," said Edward Stones, Dow's business vice president for energy and climate.

X-energy's release sketches the order of events. The companies plan to finalize and standardize the Xe-100 design, mature the supply chain for long-lead components and develop an operating license application, so that design, equipment and materials are in place before Dow allocates major capital to full-scale construction. Dow "is expected to consider a preliminary investment decision in 2027," the release says, and full-scale nuclear construction would begin after Dow's final investment decision. X-energy puts first delivery in the early 2030s. The application itself expects construction to be completed no later than 2033, the safety evaluation notes.

Some of that supply chain is already moving: X-energy announced the first steam generator tubing order for the Texas plant on November 4, as our roundup noted. The application also names who would run the plant: Long Mott Energy has selected a subsidiary of NextEra Energy Resources as operator, the safety evaluation says, citing the preliminary safety analysis report.