The UK Office for Nuclear Regulation (ONR) has published its first report on international regulatory collaboration for small modular reactors (SMRs) and advanced modular reactors (AMRs). The 21-page report outlines ONR’s work with international counterparts to create more efficient, harmonised approaches to reactor design assessment, benefiting both industry and global nuclear safety. It highlights significant progress in facilitating global deployment of standard designs.

Key achievements described in the report include:

  • Signing a trilateral memorandum of cooperation with the US Nuclear Regulatory Commission (NRC) and Canadian Nuclear Safety Commission (CNSC) in March 2024, establishing a framework for streamlined regulation while maintaining each nation’s independent regulatory authority.
  • Leading international harmonisation efforts through the ONR’s vice-chair role in the IAEA’s SMR Regulators’ Forum and chairmanship of the OECD Nuclear Energy Agency’s Working Group on New Technologies.
  • Progressing three significant Generic Design Assessments (GDA) for Rolls-Royce SMR (now in Step 3), GE-Hitachi BWRX-300, and Holtec SMR-300 (both in Step 2 of two Step GDAs), with potential additional assessments and ongoing regulatory engagement for a number of other projects.
  • Pioneering international regulatory observation by inviting five European nuclear regulators to observe the Rolls-Royce SMR assessment process—the first time in GDA history.

The report details numerous collaborative activities undertaken by ONR between October 2024 and March 2025 to advance regulatory harmonisation, including regular high-level meetings with international regulators and industry representatives, holding technical workshops on a range of key design elements and attending international forums.

The coming months will see joint workshops and reports with CNSC and NRC on advanced construction techniques, discussions with international partners on emerging reactor designs and supporting UK government trade delegations and bilateral forums with Hungary.

Tim Parkes, ONR’s Head of Regulation – GDA said: “Our international collaboration is delivering tangible efficiency improvements to our assessment of new reactor designs and to harmonising regulatory approaches to SMRs and AMRs. This collaboration will support the global deployment of standard designs and help to ensure the highest safety standards are maintained.”

 Potential future projects include:

  • The Westinghouse AP300: In August 2024, ONR received a request … to undertake a two-step GDA on US Westinghouse Electric Company’s AP300 design. “At the time of writing this report we are engaging with Westinghouse to establish cost recovery arrangements and agree a project schedule, although we anticipate the GDA will start later this year. The delay arises from a request from Westinghouse to pause the commencement of the project.” Since May 2023, Westinghouse has been engaged in pre-application activities with NRC ahead of an expected application for design certification of the AP300. Westinghouse has indicated that it intends to provide GDA submissions to UK regulators in parallel with submissions to NRC; this is expected to yield significant opportunities for collaboration and result in efficiencies for regulators and Westinghouse.
  • Last Energy: Since May 2024, US Last Energy has been participating in ONR’s early engagement framework to inform its plans to develop and deploy PWR-20 microreactors in the UK. In January 2025 Last Energy entered the nuclear site licensing process pre application phase as it intends to obtain a nuclear site licence to construct and operate four PWR-20 units at the Llynfi site in South Wales. “The PWR-20 has not been through the GDA process and so we will undertake assessment of the design in parallel with licensing of the corporate body.”
  • Newcleo: In September 2024 ONR began early engagement with France-based Newcleo on its proposals to build and operate its LFR-AS-200 lead-cooled fast reactor technology in the UK. Subsequently it applied to enter GDA in 2025. ONR is awaiting a decision from the Department for Energy Security & Net Zero (DESNZ) on the outcome of Newcleo’s application. In June 2024 Newcleo completed the ‘preparatory phase’ of the licensing process with France’s Autorité de Sûreté Nucléaire (ASN – Nuclear Safety Authority) regarding its plans to construct a 30 MWe demonstration facility in France, which it hopes will be operational by 2030. “Should Newcleo’s GDA application be successful we will engage with ASN to identify opportunities for information exchange and collaboration on Newcleo’s reactor design.”
  • TerraPower: In November 2024 ONR began early engagement with US TerraPower on proposals to deploy its Natrium sodium-cooled fast reactor technology in the UK. TerraPower has signalled an intention to apply for a GDA on the Natrium design. In March 2024 TerraPower applied to NRC for a construction permit for a single Natrium reactor at the Kemmerer Power Station in Wyoming. “Should TerraPower be successful in any future GDA application we will engage with NRC to collaborate on the assessment of the Natrium design.”
  • X-Energy: In March 2025 ONR began early engagement with US X-Energy on proposals to deploy its Xe-100 high temperature gas reactor in the UK. X-Energy has signalled its intention to apply for a GDA on the Xe-100 design.       X-Energy has been engaged in pre-application activities with NRC since September 2018, and in January 2024 the Xe-100 completed phases 1 and 2 of CNSC’s vendor design review process. “Should any future GDA application be successful we will engage with NRC and CNSC to exchange information relating to the Xe-100 and explore opportunities for collaborative assessment of the design.”