X-Energy on Nov. 30 announced the completion of the U.S. Nuclear Regulatory Commission’s safety review for the initial deployment of X-energy’s Xe-100 high-temperature gas-cooled reactor.
The proposed Long Mott Generating Station would be the first grid-scale advanced nuclear reactor at an industrial facility in U.S. history, advancing in partnership with Dow under the U.S. Department of Energy’s Advanced Reactor Demonstration Program.
The NRC’s Final Safety Evaluation Report follows a comprehensive review of the Xe-100 plant’s principal design criteria, preliminary design, safety analyses, probabilistic risk assessment, and research and development programs, documenting the NRC staff’s conclusion that the proposed plant and site provide the safety basis to begin construction under 10 CFR Part 50.
The Advisory Committee on Reactor Safeguards, an independent body that advises the Commission, separately reviewed the NRC staff’s evaluation and supports issuance of the construction permit.
The Xe-100’s safety case leverages the passive physics of its TRISO-X coated particle fuel and pebble-bed core design, as well as traditional defense-in-depth systems to enable a new, broader range of applications for nuclear technology, the company said.
The design’s safety profile enables applicants to pursue a compact site footprint with a 400-meter emergency planning zone compared to 10 miles for conventional light-water reactors. This allows new generation to be sited closer to the point of need, including inside the perimeter of a large industrial facility, or closer to populated areas.
While future applications will be reviewed individually, the NRC’s review establishes regulatory precedents for every Xe-100 project that follows, creating replicable pathways for increased efficiency in commercial nuclear licensing.
Commercial licensing for X-energy’s technology is supported by both extensive pre-application engagement with the NRC dating to 2018, as well as decades of U.S. Department of Energy research on HTGR technology.
The Xe-100 is the first HTGR construction permit application to use the NRC’s technology-inclusive, risk-informed, and performance-based licensing framework, building on licensing modernization proposals first developed for the DOE’s Next Generation Nuclear Plant program in 2008. TRISO-X fuel is based on TRISO fuel designs pioneered by the DOE through the Advanced Gas Reactor Program, providing both irradiation data and production specifications over 20 years of testing that are central to the fuel’s design today.
In May 2026, the NRC completed its environmental review with an Environmental Assessment and Finding of No Significant Impact.
With both primary reviews complete, the project moves to the final stages of the NRC’s construction permit review.
