Generic Design Assessment (GDA) is a process carried out by the Office for Nuclear Regulation (ONR), the Environment Agency and Natural Resources Wales to assess the safety, security, and environmental protection aspects of a nuclear power plant design that is intended to be deployed in Great Britain (Great Britain is England, Scotland and Wales). The GDA process is a voluntary, non-mandatory process. Successful completion of the three-step GDA culminates in the issue of a Design Acceptance Confirmation from the ONR and a Statement of Design Acceptability from the Environment Agency. In May 2021, the UK’s Department for Business, Energy and Industrial Strategy opened the GDA process to advanced nuclear technologies, including small modular reactor (SMRs).
“Subject to acceptance, submission marks a significant milestone in X-energy and Centrica’s efforts to deploy up to 6 GW of new nuclear in the United Kingdom, initiating a critical step in the UK licensing process,” X-energy said. It expects the GDA assessment of the Xe-100 to conclude by the end of 2029.
X-energy noted it has been in active dialogue with UK regulatory authorities since 2024 through the Early Engagement process. The company’s latest submission builds on its US licensing progress and is expected to further benefit from expanded collaboration between ONR and the US Nuclear Regulatory Commission that allows for direct transfer of design documentation and safety analyses. This streamlined approach allows applicants to leverage NRC-approved technical documents throughout the assessment, creating opportunities for enhanced efficiency in the UK’s licensing process.
“Advanced modular reactors like the Xe-100 are the cornerstone of Britain’s future energy security, and would bring clean, reliable power as well as renewed opportunities for British industry,” said Alistair Black, Vice President and UK Market Lead at X-energy. “We welcome the regulators’ recent steps towards a more efficient GDA process, and look forward to working collaboratively to support an efficient, thorough review. GDA submission marks an important milestone in bringing our technology to the UK on a fleet-scale, with the potential to create thousands of high-quality jobs where needs are greatest.”
The Xe-100 is a Generation IV advanced reactor design which X-energy says is based on decades of high-temperature gas-cooled reactor operation, research, and development. It is designed to operate as a standard 320 MWe four-pack power plant or scaled in units of 80 MWe. At 200 MWt of 565°C steam, the Xe-100 is also suitable for other power applications, including mining and heavy industry. The Xe-100 uses tri-structural isotropic (TRISO) particle fuel, which has additional safety benefits because it can withstand very high temperatures without melting.
In September 2025, British multinational energy and services company Centrica and X-energy Reactor – a subsidiary of X-energy LLC of the USA – announced the signing of a Joint Development Agreement to deploy X-energy’s Xe-100 reactors in the UK. The companies have identified EDF and Centrica’s Hartlepool site as the preferred first site for a planned UK fleet of up to 6 GWe. Under their plan, a plant comprising up to 12 Xe-100 units, generating up to 960 MWe, would be developed at a site adjacent to Hartlepool’s existing nuclear power station, which is currently scheduled to cease generating electricity in 2028. In addition to generating electricity, the new plant would also supply high-temperature heat to support Teesside’s heavy industries. Subject to regulatory approval, the first electricity generation would be expected in the mid-2030s. Centrica and X-energy said they are already in discussions with additional potential equity partners, as well as leading global engineering and construction companies, with the goal of establishing a UK-based development company to develop this first and subsequent projects.
In 2024, X-energy was selected for the UK Department for Energy Security and Net Zero’s Future Nuclear Enabling Fund to develop UK-specific deployment plans including assessment of domestic manufacturing opportunities, supply chain development, constructability, modularisation studies, and fuel management. This culminated in multiple technical and commercial studies estimating a minimum of GBP40 billion (USD54 billion) in lifetime economic value, with GBP12 billion arising from the first project alone.
In Texas, X-energy and Dow are advancing a proposed four-unit plant under the US Department of Energy’s Advanced Reactor Demonstration Program. This is expected to be followed by Energy Northwest’s Cascade Advanced Energy Facility – the first of several projects to deploy at least 5 GW with Amazon by 2039.
