The Office for Nuclear Regulation (ONR) has played a key role in the development of an international toolkit designed to support collaboration between nuclear regulators reviewing advanced reactor technologies.
The International Atomic Energy Agency (IAEA) has published the Nuclear Harmonisation and Standardisation Initiative (NHSI) Regulatory Cooperation Toolkit, a major output from NHSI Phase II (2025–2026).
Developed jointly by regulators participating in the NHSI Regulatory Track and the SMR Regulators' Forum, the toolkit provides practical guidance, templates and methodologies to help regulators collaborate, leverage existing reviews and address differences between national regulatory frameworks.
It comprises two complementary resources: Approaches for Addressing Areas of Regulatory Difference and Resources for Leveraging Regulatory Reviews.
UK good practices recognised
ONR experts contributed to the toolkit drawing on experience from new UK regulatory policy development, SMR design assessments, international cooperation agreements and multinational reactor reviews. Several UK good practices have been recognised within the published IAEA materials, including how ONR documents leveraged regulatory information in Generic Design Assessments , approaches to internationalising assessment work , transparency about the UK's regulatory footprint on assessed designs , and the use of early engagement to advise on regulatory differences ahead of formal assessment.
Building on practical experience
The publication reflects several years of work under the NHSI Regulatory Track and complements ONR's ongoing collaboration with international partners including the US Nuclear Regulatory Commission and the Canadian Nuclear Safety Commission.
Looking ahead: Global Framework for Advanced Reactor Reviews (GFARR)
Publication of the toolkit marks the completion of a major phase of NHSI activity and creates the foundation for the Global Framework for Advanced Reactor Reviews (GFARR) - a harmonised, technology-inclusive framework for advanced reactor reviews.
ONR has been actively involved in developing the first GFARR Technical Aspects document alongside international regulatory and industry experts.
Building on IAEA Safety Standards, this document covers areas such as defence in depth, safety classification, design basis analysis and engineered safety systems, helping to support future collaborative reviews through greater clarity and consistency in applying internationally recognised safety requirements.
Diego Fernandez Lisbona, ONR’s Head of Regulation for Advanced Nuclear Technologies and TerraPower Natrium GDA, who represents the UK in the NHSI Regulatory Track, said:
"The publication of the NHSI Regulatory Cooperation Toolkit is an important milestone for international cooperation. It demonstrates how regulators can work together to share experience, build trust and improve the efficiency of regulatory reviews without compromising independence or safety standards.
"The IAEA recognising several UK regulatory practices within the toolkit, reflects the valuable contributions made by ONR colleagues and our international partners over several years of collaboration.
"The toolkit is not an end point. It provides the practical foundation for the Global Framework for Advanced Reactor Reviews, where we are working with international experts to develop common approaches to the review of advanced reactor technologies. As advanced reactors move towards deployment around the world, our commitment towards NHSI includes making GFARR compatible regulatory judgements so that future design internationalisation plans by vendors benefit from forward-looking regulatory harmonisation efforts in the UK, and internationally."