10 CFR Part 53 is a proposed NRC regulatory framework mandated by the Nuclear Energy Innovation and Modernization Act (NEIMA) of 2019, designed to provide a technology-inclusive, risk-informed, and performance-based licensing pathway for advanced nuclear reactors. Unlike Parts 50 and 52, which were developed primarily around light-water reactor technology and prescriptive design requirements, Part 53 aims to establish safety criteria based on radiological risk outcomes rather than technology-specific design features. This approach is intended to accommodate the full spectrum of advanced reactor technologies, including molten salt reactors, sodium-cooled fast reactors, lead-cooled fast reactors, high-temperature gas reactors, and microreactors, without forcing non-light-water designs into a regulatory framework built for fundamentally different technologies.
The NRC published a proposed Part 53 rule in October 2024, with the public comment period closing in February 2025. A draft final rule is expected to be presented to the Commission in 2025, with the final rule targeted for publication by the end of 2027. The NRC estimates that Part 53 will save applicants between $53.6 million and $68.2 million compared to licensing under Part 50 or Part 52, primarily by reducing the scope of analysis required for designs with inherent and passive safety features. For example, a reactor with TRISO fuel that retains fission products at temperatures well above any credible accident scenario should not be required to demonstrate the same containment performance as a reactor with conventional oxide fuel, and Part 53's risk-informed approach would recognize this distinction.
The advanced reactor industry has been eagerly anticipating Part 53, as many developers, including Kairos Power, TerraPower, Oklo, X-energy, Radiant Industries, and Nano Nuclear Energy, are designing reactors that do not fit neatly into the existing light-water-centric regulatory frameworks. However, Part 53 is not yet available for licensing applications, which is why current advanced reactor projects are proceeding under Part 50 and Part 52. The framework's eventual availability is expected to accelerate the licensing of second-generation advanced reactor projects in the late 2020s and 2030s. Industry stakeholders have emphasized that Part 53's success will depend on the NRC developing sufficient technical expertise in diverse reactor technologies and staffing review teams capable of evaluating novel safety cases within reasonable timelines.