IN Brief:
- The US NRC has approved a construction permit for four proposed Xe-100 high-temperature gas-cooled reactors at Dow’s Seadrift site.
- Each proposed module has a nominal 80MWe electrical rating and 200MWt thermal rating, with helium cooling and TRISO coated-particle fuel.
- Dow expects to consider preliminary investment in 2027; a final build decision and separate operating licence are still required.
The US Nuclear Regulatory Commission has granted a construction permit for Long Mott Generating Station, the proposed four-unit X-energy Xe-100 reactor project at Dow’s Seadrift chemical manufacturing complex in Texas. Announced on 9 November, the decision follows completion of the regulator’s safety and environmental reviews and represents a further licensing stage beyond the earlier safety-review milestone. Dow has not made a final decision to build the installation, and the construction permit does not authorise reactor operation.
Long Mott is being developed to supply both electricity and high-temperature industrial steam. The design comprises four helium-cooled, graphite-moderated reactors, each with nominal ratings of 80MWe and 200MWt. Four modules would therefore represent 320MWe of electrical nameplate capacity and 800MWt of reactor thermal capacity. Electrical and thermal ratings measure different outputs, and they should not be added together or interpreted as an assurance that both maximum deliveries can be sustained simultaneously under any given operating arrangement.
Dow’s wholly owned subsidiary Long Mott Energy submitted its construction permit application in March 2025. The NRC has now authorised construction within the permit’s approved design and safety requirements, after completing the assessments prescribed for this stage of the licensing process. Before fuel loading and start-up, the plant would need a separate operating licence. Engineering completion and commercial authorisation are consequently still substantial requirements even after the construction permit decision.
The proposed reactors would replace ageing on-site energy and steam facilities serving Dow’s UCC Seadrift operation, rather than being developed solely as an independent generator for the public electricity market. Chemical production requires dependable electrical power and heat delivered at pressures and temperatures suited to industrial processes. Designing a reactor installation for both services brings the steam-generation interface, site utilities and continuity of supply into the project scope alongside the nuclear island and electrical systems.
In the Xe-100 design, helium carries heat from a graphite-moderated reactor core to equipment that produces steam. Its TRISO coated-particle fuel incorporates multiple layers intended to retain fission products and withstand high operating temperatures. X-energy has highlighted these fuel properties and the thermal behaviour of the reactor in its safety case. The NRC’s finding applies to Long Mott’s submitted application and site-specific conditions; it is not a general operating approval for future Xe-100 developments.
Integrating the plant into an operating industrial complex will require electrical protection, steam distribution, control systems and interfaces with existing manufacturing processes to be engineered together. Equipment installation must also account for maintenance, testing and continuity of essential site services. X-energy and Dow say work will continue on design finalisation, long-lead components and supply-chain readiness before major construction is considered. The permit does not settle the procurement cost, contractor allocation or the details of the final plant configuration.
According to X-energy, this is the first US construction permit for a high-temperature gas-cooled reactor in nearly 60 years and the first granted for a pebble-bed high-temperature design. Long Mott forms part of the US Department of Energy’s Advanced Reactor Demonstration Program. That programme context and the NRC decision establish a regulatory milestone for one proposed industrial application, while subsequent sites would still require their own approvals and technical submissions.
Edward Stones, business vice president for Energy & Climate at Dow, said the company would continue assessing “competitiveness, execution readiness, and capital affordability before any decision regarding construction is made.” Dow expects to consider a preliminary investment decision in 2027, and full-scale work would follow a further final decision. The company’s stated criteria underline the distinction between permission to construct the facility and a commitment to spend the capital needed to do so.
If approved for construction, the project is targeting initial operation early in the next decade. The companies describe a potential 60-year operating life, which is a design expectation rather than an established record. Reaching operation would still involve detailed engineering, nuclear-grade component manufacture, quality assurance, site construction, inspections and licensing. A fixed first-power date has not been established by the regulator’s permit, and the remaining programme depends partly on the investment decisions that Dow has yet to take.
The NRC’s environmental review reached its finding of no significant impact in May 2026, and its final safety assessment was completed before the November construction permit. The regulator has thus advanced the proposal through a defined sequence of approvals without removing the later operating-licence requirement. For Dow and X-energy, the next steps concern design and procurement readiness, the commercial decision to proceed and the operating licence application. Those decisions will determine whether the permitted four-reactor scheme becomes a construction project supplying power and process steam at Seadrift.
