IAEA publication assesses applicability of current safety standards to innovative technologies

16 January 2024

The International Atomic Energy Agency (IAEA) has completed a project to assess how well existing IAEA safety standards apply to new technologies such as small modular reactors. The results are presented in the IAEA Safety Report No 123 Applicability of Safety Standards to Non-Water-Cooled Reactors and Small Modular Reactors. The 292-page report identifies gaps and areas for additional consideration covering over 90 safety standards related to the entire life cycle of nuclear power plants.

“These types of reactor may use innovative safety technologies, including passive and inherent safety features, various types of fuel and coolant, and various approaches to practically all aspects of a reactor lifetime, such as construction, operation, waste management, decommissioning and transportation, the report says in its Foreword. “Therefore, non-water cooled reactors and small modular reactors present important areas of novelty compared with the current fleet of large, land based water cooled reactors. As with the current fleet of reactors, non-water cooled reactors and small modular reactors must meet the objective of protecting people and the environment and minimising the possibility of accidents. A key element of meeting this objective is demonstrating compliance with the IAEA safety standards.”

IAEA notes that, because many evolutionary and innovative designs (EIDs) are still under development, “designs are often not complete, meaning that their potential vendors may have made claims for their EIDs that have yet to be substantiated”. It adds: “In the absence of more detailed information, the experts that contributed to this study have made statements such as ‘may be less stringent’, ‘may not be needed’, may be acceptable’, and ‘may not require a safety class 1’. Readers should be aware that such statements, much less the publication as a whole, must not be construed as endorsing these claims.”

The review “confirmed that the safety standards are applicable to EIDs with some exceptions…. The existing safety framework described in the safety standards contains the tools to assess and regulate the safety of an EID, but some modifications or additions may be necessary to supplement the IAEA Safety Standards Series publications to address in an equitable way the full range of reactor technologies being considered.”

Key findings in the different technical areas included: siting; design & construction; commissioning & operation; leadership & management for safety; safety of nuclear fuel cycle facilities; safety assessment; radiation protection & safety; management of radioactive waste & spent fuel; decommissioning; emergency preparedness & response; legal & regulatory framework for safety; and interface between safety, security & safeguards.

While in most cases safety standards were deemed to be applicable, generally applicable or “sufficiently general to apply”, some gaps were identified in design and construction. IAEA noted: “Some of the areas of the safety standards focus on conventional WCRs [water-cooled reactors] and therefore do not cover some of the design of EIDs. For example, EIDs can use novel fuels, new coolants and can have different confinement provisions. EIDs tend to rely extensively on passive systems and inherent safety features and modularity. EIDs can include multiple modules and related HSI [human–system interface] design features. Some EIDs may be designed to enable alternative operating models such as factory construction, commissioning and refuelling, as well as remote operation.”

The report added: “In some cases, there is a lack of experience on how the safety standards apply to EIDs and therefore there is a lack of consensus on adequate interpretations for these designs. For example, on the concepts of ‘severe accident’ and ‘design extension conditions’ and the implementation of DiD [defence in depth] level 4 and level 5, interpretations of these terms, design provisions and safety features can be different from those used for conventional WCRs. There is also a scarcity of experience on what PIEs are to be considered in the design and a lack of knowledge about the response of some EIDs to these PIEs [postulated initiating events].

An important finding of the review for all EID technologies “is that there is a lack of regulatory and operating experience and a need to consider how this can be addressed, particularly when considering first of a kind technologies and designs”. EIDs “may introduce phenomena, failure modes and hazards that are not relevant to WCRs and that are not considered in the current safety standards”.

Finally, “The standards also do not cover specific issues for the design of TNPPs [transportable NPPs] related to the transport of the plant throughout its lifetime. Furthermore, there are some gaps related to construction. For example, the safety standards do not consider novel or advanced manufacturing techniques, factory-based manufacturing, common servicing and refuelling facilities or the potential increase in complexity in the supply chain.”

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