X-energy submits Xe-100 reactor for UK regulatory review

X-energy put its Xe-100 into the United Kingdom’s Generic Design Assessment on June 2, 2026, turning a long-running export pitch into a formal regulatory milestone. The GDA is the UK’s voluntary design review for new nuclear plants before construction, and this one now sits in the hands of the Office for Nuclear Regulation, the Environment Agency, Natural Resources Wales and the Department for Energy Security and Net Zero. If the submission is accepted, current guidance points to a review running to the end of 2029.

That matters because GDA is the point where an advanced reactor stops being just a plan on paper and starts earning a place in the UK’s build queue. The regulators use it to scrutinise safety, security, environmental protection and waste management before a project moves toward site-specific work. The UK’s newer framework also includes a Leveraging International Regulators’ Judgements Policy, aimed at making design assessment more efficient without cutting corners, which is exactly the kind of gate a vendor like X-energy wants to clear early.

The submission also locks into X-energy’s partnership with Centrica, announced on September 15, 2025, for a potential UK fleet of up to 6 GW. Centrica identified Hartlepool as the preferred first site for a 12-unit Xe-100 plant, adjacent to the existing Hartlepool Power Station, and said that deployment could power up to 1.5 million homes. Centrica also put the broader partnership’s economic value at at least £40 billion, with more than £12 billion tied to the first project alone, and said full-scale activities could begin in 2026 if approvals keep moving.

The reactor itself is the reason this file has legs. X-energy describes the Xe-100 as an 80 MWe high-temperature gas-cooled reactor that can be deployed in four-unit or twelve-unit plants. It uses TRISO-X fuel, helium coolant, a graphite core, online refuelling and load-following capability. That is not just a grid machine. X-energy is pitching it as a source of electricity, high-temperature heat and steam for industrial users, with manufacturing, refining and hydrogen production all in scope. For Britain, that process-heat angle is the real prize.

X-energy said it has been in active dialogue with UK regulators since 2024, and ONR records show early engagement started in March 2025. The company has already gone through Canadian pre-licensing milestones under the Canadian Nuclear Safety Commission’s Vendor Design Review, and it says it can benefit from document transfer and safety-analysis sharing with the U.S. Nuclear Regulatory Commission. The pattern is clear: the company is stacking regulatory receipts in multiple jurisdictions before anyone talks seriously about steel in the ground.

For the UK, the immediate question is no longer whether the Xe-100 can be described convincingly on a slide deck. It is whether the GDA filing gets accepted, the review stays on schedule, and Hartlepool starts to look less like a promise and more like the first concrete step toward a build.