The NRC completed its safety review of X-energy's Xe-100 high-temperature gas-cooled reactor, issuing a Final Safety Evaluation Report for the proposed Long Mott Generating Station, X-energy said on October 30. The report documents NRC staff's conclusion that the plant and site provide the safety basis to begin construction under 10 CFR Part 50.

The review covered the plant's principal design criteria, preliminary design, safety analyses, probabilistic risk assessment and research and development programs. The Advisory Committee on Reactor Safeguards, which advises the Commission, separately reviewed the staff evaluation and supports issuance of the construction permit.

"Licensing a new reactor is earned through the quality of the application and the rigor of the regulator's review," said Dragan Popovic, X-energy's chief global operating officer.

The Xe-100's safety case relies on the passive physics of its TRISO-X coated particle fuel and pebble-bed core, alongside defense-in-depth systems. The design supports a 400-meter emergency planning zone, against 10 miles for conventional light-water reactors.

The NRC finished its environmental review in May 2026 with an Environmental Assessment and Finding of No Significant Impact. With both reviews complete, the construction permit application moves to the final stages of NRC review.

The Xe-100 is the first HTGR construction permit application to use the NRC's technology-inclusive, risk-informed and performance-based licensing framework. X-energy's pre-application engagement with the NRC dates to 2018. The project is developed with Dow under the Department of Energy's Advanced Reactor Demonstration Program. In the U.K., the Xe-100 was accepted into Generic Design Assessment.