The UK Department for Energy Security & Net Zero (DESNZ) has asked the Office for Nuclear Regulation (ONR), along with the Environment Agency (EA) and Natural Resources Wales (NRW) to begin a three-step Generic Design Assessment (GDA) for X-energy UK Holdings Ltd’s Xe-100 high-temperature gas-cooled reactor design.
The Xe-100 is an 80 MWe helium-cooled HTGR that can be deployed in modular 4-unit or 12-unit configurations. The design simultaneously generates grid electricity and high-temperature heat/steam. This makes it ideal for heavy industrial decarbonisation. It uses X-energy’s TRISO-X Tri-structural Isotropic particle fuel pebbles.
DESNZ made the request to the regulators following its readiness review of X-energy’s application, which determined that the Xe-100 design meets the rigorous prerequisites necessary to enter the UK’s regulatory assessment pipeline
The decision coincides with the one-year anniversary of the partnership between Centrica and X-energy through which they intend to deploy up to 6 GWe of new nuclear capacity across the UK requiring 10-20 Xe-100 power stations. The companies have identified the Hartlepool site in north-east England as their preferred initial deployment location. The currently operating AGR plant at Hartlepool is scheduled to close in the coming years.
The companies have engaged a range of specialist firms to commence site studies and planning and consenting activities and have collaborated with local bodies in Hartlepool to support workforce development and training, including the launch of a new Nuclear and Electrical Trades Academy.
X‑energy’s long‑standing investment in the UK market builds on a deep national heritage in gas‑cooled reactor technology, a field in which the UK played a pioneering role over decades of research and deployment.
The GDA process is expected to take approximately three years. It will evaluate the safety, safeguards, security, and environmental impacts of the reactor. Successful completion will culminate in a Design Acceptance Confirmation. To streamline the three-step GDA, UK regulators plan to collaborate with the US Nuclear Regulatory Commission (NRC). This allows the direct transfer of design documentation and safety analyses already processed during the Xe-100’s US licensing progress.
Separate from the formal GDA start, X-energy is also currently engaged with UK regulators in a Tier 3 Preliminary Design Review (PDR) to evaluate selected high-priority topic areas of the design. The PDR serves as a crucial early-engagement mechanism alongside the main GDA pipeline. According to the ONR Early Engagement Guidance, the PDR framework allows regulators to review up to six targeted submissions from the applicant. The main objective is to identify potentially significant gaps against UK regulatory expectations before entering the GDA.
By focusing on select, high-priority topic areas of the Xe-100 design, X-energy receives early regulatory advice and guidance on how to resolve technical gaps. This helps the company better understand project risks and build a credible plan for the standard licensing pathway.
At the conclusion of this parallel review, regulators will issue a summary report evaluating the targeted submissions. This report will explicitly state the regulators’ level of confidence that their criteria can be met moving forward. This proactive engagement runs concurrently with the formal multi-year GDA process, optimising X-energy’s timeline as they transition toward site-specific permitting.
‘‘This is an important milestone in our plans to bring advanced nuclear power to Britain, and it shows the tremendous progress our partnership with X-energy has made in just 12 months,” said Centrica CEO. Chris O’Shea. “Without energy security, we don’t have true national security. Nuclear has a critical role to play in this. Deploying advanced nuclear technology at scale, with up to 6GW of new capacity across the UK, will not only strengthen our energy security, but it will create tens of billions of economic value and thousands of highly skilled jobs.”
J Clay Sell, CEO of X‑energy said: “Together with Centrica, we are advancing the development work required to move from a first project at Hartlepool to a fleet of Xe‑100 plants across the country. The UK has the industrial capability, nuclear expertise and policy ambition to lead the deployment of advanced nuclear technology, and we are committed to building the partnerships and supply chain needed to deliver that opportunity.”
In the US, X-energy is partnering with Dow to build a four-unit Xe-100 facility at Dow’s UCC Seadrift Operations under the Department of Energy’s Advanced Reactor Demonstration Program (ARDP). In May 2026, the Nuclear Regulatory Commission (NRC) completed its Environmental Assessment (EA) for the project’s Construction Permit Application ahead of schedule, issuing a Finding of No Significant Impact (FONSI). This marked the first time a commercial nuclear reactor in the US qualified for the streamlined EA pathway rather than being subjected to a standard, multi-year Environmental Impact Statement (EIS). The review took less than a year.
