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X-energy’s Long Mott Reactor Clears a Major Texas Safety Review

A reactor’s safety buffer can now shrink to a few hundred meters instead of ten miles, at least on paper. Here’s what Texas regulators have actually confirmed, and what the…

Industrial power plant under a blue sky, representing the Long Mott reactor safety review in Texas

A conventional nuclear reactor needs an emergency zone reaching ten miles in every direction. The reactor design now closest to a construction permit in Texas is licensed around one that stops at roughly a quarter mile. That claim sits at the center of X-energy’s Xe-100 project at Dow’s Long Mott Generating Station in Calhoun County, and on October 30, trade outlets report, the Nuclear Regulatory Commission finished the Long Mott safety review, the last major technical step before a construction permit decision. The NRC’s own public project tracker, last updated in September, had been aiming for that exact milestone in November. If the October date holds, X-energy and Dow are running on schedule, maybe a little ahead of it. Nothing is built yet, and the agency still hasn’t said when, or whether, a permit follows.

What the NRC’s Long Mott Safety Review Actually Covers

Long Mott Energy, a Dow subsidiary, filed for the construction permit back in March 2025. The NRC docketed the application that May and spent more than a year working through it. Two milestones matter most. In May 2026, the agency issued an Environmental Assessment and a Finding of No Significant Impact, closing out the environmental half of the review. The remaining piece, the Final Safety Evaluation Report, is the one World Nuclear News and Construction Review Online say landed on October 30.

The project itself is four Xe-100 reactors: a high-temperature, gas-cooled design that moves heat with helium instead of water and runs on TRISO fuel enriched to HALEU levels. Together the four units would produce 320 megawatts of electricity, or 800 megawatts of heat. Two reactors would power Dow’s adjacent Seadrift chemical operations directly, a third would supply steam heat to the same plant, and the fourth would export power to the Texas grid, according to reporting on the project. None of that is locked in. The NRC’s own project page still lists the construction permit decision as “to be determined,” and the agency told followers on social media only to “stay tuned.”

A Reactor Built Around a Much Smaller Safety Buffer

The emergency planning zone is the real technical story here, not the megawatt count. A typical large reactor needs an evacuation zone stretching 10 miles from the plant. X-energy’s licensing filings put the Xe-100’s zone at about 1,300 feet, roughly 400 meters, small enough to fit inside Dow’s own property line. That shrinkage isn’t a marketing line. It follows from the reactor’s physics. TRISO fuel particles are individually wrapped in layers of carbon and ceramic meant to contain radioactive material even if the reactor loses cooling, and a helium-cooled core has no water to flash into steam or hydrogen if something goes wrong.

Smaller potential consequences, under the NRC’s newer risk-informed licensing framework, can justify a smaller emergency zone. If regulators accept that reasoning for Long Mott, trade press coverage suggests it would be one of the first U.S. construction permit applications to win approval mainly on reactor physics, rather than on thicker containment and backup water systems the way older designs do.

The Long Mott Project, at a Glance

Detail Figure
Applicant Long Mott Energy, LLC, a Dow Chemical subsidiary
Location Calhoun County, Texas, next to Dow’s Seadrift Operations
Reactor design Four X-energy Xe-100 high-temperature, gas-cooled reactors
Total output 320 MWe / 800 MWth combined
Fuel TRISO particles, HALEU-enriched (5-20% U-235)
Emergency planning zone About 1,300 feet (400 m), versus 10 miles at a conventional plant
Application filed March 31, 2025
Environmental clearance Assessment and Finding of No Significant Impact issued May 18, 2026
Final Safety Evaluation Report Reported Oct. 30, 2026 by trade press; NRC’s own tracker listed November 2026 as the target
Next step Construction permit decision; no date announced

Source: U.S. NRC’s Long Mott project page (accessed Nov. 6, 2026), World Nuclear News (Nov. 2, 2026) and Construction Review Online (Nov. 3, 2026).

How Long Mott Compares to Other SMR Permits

Long Mott wouldn’t be the first U.S. construction permit for an advanced reactor. TerraPower’s Natrium design got one in March 2026, and the NRC approved TVA’s BWRX-300 at Clinch River, Tennessee that September. Both are different reactor families. Natrium is sodium-cooled, and the BWRX-300 is a water-cooled boiling water reactor scaled down from a conventional design. Long Mott would be the first high-temperature, gas-cooled design to reach this stage, and the first Xe-100 unit anywhere close to construction.

That matters beyond Texas. The same reactor, and the same company, also underpins a planned 960-megawatt plant on a retired coal site in Indiana, and its TRISO fuel depends on the same HALEU supply chain we’ve tracked all year. If Long Mott’s permit clears, it becomes the reference project every other Xe-100 customer, including the Indiana developers, can point to.

What’s Still Unconfirmed

  • The exact FSER date: trade press says Oct. 30, but the NRC’s own project page, last updated in September, still listed the Final Safety Evaluation as a November target rather than a completed step.
  • No construction permit date. The NRC’s social media account says only that an announcement is coming “soon.”
  • A widely repeated $2.4 billion figure traces to a Department of Energy cost-share ceiling for development expenses under the Advanced Reactor Demonstration Program, not a confirmed total construction cost for the plant.
  • Dow has not announced a final investment decision to actually build Long Mott.
  • No date exists for when construction, if the permit is granted, would start or finish.

Who Benefits and How

This is an industrial energy story, not a consumer product, so most people feel it indirectly, if at all.

  • Dow’s Seadrift complex, which already turns out billions of pounds of plastics and other materials a year, would get power and steam that don’t require burning natural gas, a detail that matters for a company that has publicly committed to cutting emissions at its biggest sites.
  • Calhoun County, where the NRC held a public hearing on the project on September 22 in Port Lavaca, stands to gain construction and operating jobs if the plant moves forward, though neither Dow nor X-energy has published a jobs estimate specific to Long Mott the way AEP and Amazon did for their Indiana project.
  • The wider test is whether a reactor built around a much smaller safety buffer can also permit faster and cheaper than a conventional plant. If that holds up here, it is a template other industrial energy users, the ones paying for process heat today, could eventually follow.

None of that is available yet. It depends on a construction permit the NRC hasn’t issued, and a final investment decision Dow hasn’t made.

So here’s the question worth watching: does the NRC’s “soon” mean weeks, or does Long Mott sit in permit limbo the way other advanced-reactor applications have? The agency beat its own schedule by four months on the Clinch River review, so it clearly can move fast when it wants to. Whether it does that again for a reactor type it has never fully licensed before is what actually decides if Calhoun County gets a working reactor, or just another status update.

Sources

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