US nuclear regulator permits four reactors at Long Mott

The US Nuclear Regulatory Commission announced on 9 November 2026, that it had issued Long Mott Energy a permit to build four X-energy Xe-100 reactors at Long Mott Generating Station in Calhoun County, Texas. The permit does not allow the company to load fuel or run the reactors; those steps require a separate operating license.

The regulator said it was its first construction permit for a high-temperature gas-cooled reactor in nearly 60 years, but its third advanced-reactor construction permit this year. Dow and reactor developer X-energy are developing the proposed station for Dow’s Seadrift Operations complex on the Gulf Coast between Houston and Corpus Christi.

Steam and electricity for Seadrift

Each reactor would have 80 megawatts of generating capacity, for a combined 320 megawatts. The NRC said the station would primarily produce high-temperature steam for industrial use at Seadrift, with excess electricity exported to the grid. Natural-gas turbines at the site currently supply electricity and process heat.

The US Department of Energy’s Advanced Reactor Demonstration Program selected X-energy for support in 2020 to build four Xe-100 units and a TRISO fuel fabrication facility. Dow and X-energy chose Seadrift in May 2023, and Dow subsidiary Long Mott Energy applied for the construction permit on 31 March 2025. The NRC issued an environmental assessment finding no significant impact in May 2026 and completed its safety evaluation in October, one month ahead of schedule.

A different design and safety concerns

Unlike conventional reactors that use water for cooling and fuel rods, the Xe-100 uses helium gas and a moving bed of fuel pebbles containing TRISO fuel, developed over decades in Energy Department laboratories. The design relies on what is called functional containment: the fuel pebbles' properties and movement help prevent runaway heating. NRC advanced-reactor official Mehdi Reisi Fard said the approach relies less on pumps or human intervention to address problems than current control systems.

X-energy CEO J. Clay Sell has described the reactor as physically impossible to melt down, while the Energy Department says TRISO particles cannot melt in a commercial high-temperature reactor. Edwin Lyman, nuclear power safety director at the Union of Concerned Scientists, disputes claims that the fuel is indestructible or meltdown-proof and says it has vulnerabilities. He also said developers use safety arguments to justify dispensing with physical containment, which he identified as a way to reduce containment costs.

Diane Wilson, a retired fourth-generation shrimper from nearby Seadrift and director of the local environmental group San Antonio Bay Waterkeeper, has raised concerns about spent fuel remaining on-site indefinitely because the US lacks a permanent national disposal site. Her group challenged the permit application over safety concerns in 2025; the NRC dismissed the challenges, Inside Climate News said.

The decisions ahead

Dow said it still must make a final decision on whether to proceed. If it does, construction could begin before 2030. Long Mott Energy would then need a separate NRC operating license before loading fuel or operating the reactors.

According to the project timeline, Dow expects a preliminary investment decision in 2027 and says it may not make a final funding decision until 2028, after submitting an operating-license application. The station is expected to come online in the early 2030s.