Comparison of nuclear safety regulatory requirements for advanced modular reactors in the UK and US

Advanced Nuclear Technologies (ANTs), which includes Small Modular Reactors (SMRs) and Advanced Modular Reactors (AMRs), have the potential to support countries in transitioning away from fossil fuels and achieving greater energy security . Their deployment, however, requires regulatory regimes that can accommodate novel designs and passive safety features. This paper uses a comparison of the regulatory regimes in the United Kingdom (UK) and the United States (US), two countries with mature but distinct approaches to nuclear regulation, to discuss the implications for regulatory harmonisation. Focusing on four key aspects of the regulations, category of Licensing Basis Events (LBEs), classification of Structure, System and Component (SSC), Defence-in-Depth (DiD) philosophy and probabilistic safety assessments, the paper highlights both where there are convergences and divergences. Both the UK and US regulatory frameworks share core safety principles and emphasize robust safety assessments for licensing ANTs. While this offers potential for harmonising AMR licensing, differences in regulatory approaches, such as SSC classification and the use of probabilistic safety assessments, mean that additional justifications or methodological adjustments may be needed for cross-border deployment. Leveraging the collaboration between regulators is expected to allow for further harmonisation and minimise additional justifications or methodological adjustments.