X-energy has announced that its advanced modular reactor, the Xe-100, has been formally accepted into the UK’s Generic Design Assessment (GDA) process. The acceptance officially initiates the regulatory review of the design by British authorities — a mandatory step before any site-specific operating licence can be issued.
The GDA is the UK’s established regulatory pathway for new nuclear technologies. It assesses safety, physical security, safeguards, and environmental impact independently of any particular site. The review will be conducted by the Office for Nuclear Regulation (ONR), the Environment Agency, and Natural Resources Wales, with a conclusion expected by the end of 2029. After three years of in-depth technical work, the ONR will issue a Design Acceptance Confirmation and the Environment Agency a Statement of Design Acceptability.
The Xe-100 is a fourth-generation high-temperature gas-cooled reactor (HTGR) rated at 80 MWe per unit. It can be deployed in configurations of four to twelve modules, delivering a total output ranging from 320 to 960 MWe. The reactor produces both electricity and high-temperature heat and steam for industrial applications. Its fuel is TRISO-X — uranium particles coated in ceramic and carbonaceous layers capable of withstanding extremely high temperatures without melting, a feature that significantly enhances the reactor’s passive safety profile.
Behind this application lies a broader agreement. In September 2025, Centrica and X-energy signed a Joint Development Agreement to build the UK’s first advanced nuclear fleet, with the stated goal of deploying up to 6 GW of new nuclear capacity nationwide. The preferred site for the first plant is Hartlepool, where a twelve-unit configuration delivering a total of 960 MWe is planned. Between the signing of that agreement and today, both companies completed their early engagement with regulators and submitted the formal GDA entry application — which has now been accepted.
The process will also benefit from collaboration between the ONR and the US Nuclear Regulatory Commission (NRC), which allows for the direct transfer of design documentation and safety analyses already developed in the United States. X-energy has been engaged in the American licensing process for some time, and that body of work can now be leveraged in the UK review, reducing duplication and improving overall process efficiency. The company estimates the total economic value of the fleet over its lifetime at a minimum of £40 billion, with around £12 billion generated by the first project alone.
The UK has long-standing familiarity with gas-cooled reactors: eight Advanced Gas-Cooled Reactors remain in operation across the country, a technology that shares fundamental principles with X-energy’s HTGR. This technical and regulatory heritage could facilitate productive dialogue between the company and the authorities. If the GDA concludes on schedule, by 2029 the Xe-100 could have all the regulatory groundwork in place to move into the site-specific authorisation phase — with Hartlepool set to be the first real proving ground for Britain’s new generation of modular reactors.
