Long Mott Xe-100: NRC Targets November Safety Evaluation, 320 MWe Dow Plant

The US Nuclear Regulatory Commission (NRC) targets November 2026 for its final safety evaluation of the Long Mott Generating Station, Dow's four-module, 320 MWe Xe-100 plant at Seadrift, Texas, after a mandatory hearing the NRC scheduled for Sept. 22, 2026.

The plant would be the first Xe-100 deployment and, Dow said in May, expected to be the first grid-scale advanced reactor in North America built to serve an industrial site. Dow subsidiary Long Mott Energy LLC filed the construction permit application on March 31, 2025. The NRC's project page, last updated Sept. 14, lists the hearing and the permit decision itself as "TBD". A final safety evaluation is a staff finding, not a permit: the Commission still has to decide.

For readers tracking firm power for AI campuses, the stake is the design rather than the site. Long Mott supplies a chemical plant, not a data center, but it is the licensing test case for the reactor Amazon backs elsewhere. Energy Northwest's proposed Cascade plant in Washington would start with four Xe-100 modules expected to make 320 MW, with no construction permit application described as filed. The same design is in the 960 MW Indiana study Voltgrid profiled on Oct. 25. How long the NRC takes on Long Mott is the best evidence those later projects will have.

How the Xe-100 Helium-Cooled Reactor Works

The Xe-100 is a small modular high-temperature gas-cooled reactor: helium cools the core instead of water, and the fuel is TRISO particles, uranium kernels sealed in ceramic and carbon layers, according to Nuclear Engineering International. Running hot is the point. Each module is rated at 80 MWe of electricity or about 200 MWt of thermal output, the NRC says, and the four-module plant is listed at 800 MWt and 320 MWe in total; these are design figures for a plant not yet permitted. Dow wants both products: electricity and high-temperature steam for its UCC Seadrift Operations, which the company says turn out more than 4 billion pounds of materials a year.

DOE Cost Share and Project Funding

Long Mott sits in the Department of Energy's Advanced Reactor Demonstration Program (ARDP), selected in 2020. Nuclear Engineering International describes it as a 50/50 cost share covering up to $2.4 billion in total estimated costs; the sources Voltgrid read do not break out a dollar amount for Long Mott alone. Dow and X-energy set up a $50 million initial fund for site-specific engineering under a 2023 joint development agreement, and X-energy signed an engineering, procurement and construction contract with Fluor in April 2026, the same outlet reported. No source read for this file states a final investment decision by Dow, and no construction start or first-power date has been published by the NRC.

Long Mott NRC Licensing Timeline

The NRC docketed the application on May 12, 2025, and set its review schedule on June 10, 2025. Staff produced a draft safety evaluation in February 2026, issued an environmental assessment with a finding of no significant impact on May 18, 2026, and completed an advanced safety evaluation for its reactor safeguards committee in August 2026. The NRC scheduled the uncontested, or mandatory, hearing for Sept. 22 in Port Lavaca, Texas, and set Oct. 6 as the deadline for written comments; the project page still lists the hearing as TBD.

A contested track ran alongside. San Antonio Bay Estuarine Waterkeeper petitioned to intervene on Aug. 11, 2025. The Atomic Safety and Licensing Board admitted two narrow financial-qualification claims in January 2026 and rejected the rest, then dismissed those claims as moot after Long Mott Energy supplemented its application and terminated the proceeding on June 25, 2026, according to the company's filing on the NRC docket, which Voltgrid could not re-read on this run; the NRC's Aug. 18 Federal Register notice still described the contested proceeding as ongoing. Waterkeeper asked the Commission to review those rulings on July 20; Long Mott Energy filed its opposition on Aug. 14. Voltgrid found no Commission ruling on that petition in the documents it reviewed.

What Long Mott Means for Data Center Power

A construction permit lets the holder build but not operate; an operating licence is a later step. Long Mott, then, settles how the NRC handles an Xe-100 application, not when any Xe-100 makes power. If the November target holds and the Commission follows, later Xe-100 projects, including Amazon-backed ones, would apply against a reviewed design and financial claims dismissed as moot with a petition for Commission review still pending, which suggests an Energy Northwest or AEP filing would have a precedent to point to. A slip on Long Mott would push back that reference point.

What to Watch After the Final Safety Evaluation

The NRC's final safety evaluation, targeted for November 2026, is next. After it come the Commission's decision on the permit, still listed as TBD, and its answer to Waterkeeper's petition for review. Beyond the NRC, the dates to watch are Dow's decision to build and the start of construction, neither of which has been announced.