Developing an RIPB design framework for external hazards

Some background: RP3C is a special committee created by the ANS Standards Board to provide guidance to ANS standards committees on the use of risk-informed, performance-based (RIPB) methods. The CoP is part of RP3C’s charter, which includes training and knowledge-sharing of RIPB principles to exchange ideas outside of the normal management and project process. CoPs are used frequently by organizations to help break down barriers that impede the flow of information.

The speaker: RP3C chair N. Prasad Kadambi opened the CoP with brief introductory remarks about the committee before he welcomed this month’s presenter: Fred F. Grant, a principal at Simpson Gumpertz & Heger (SGH) with 20 years of experience in external hazards risks in nuclear power plant structures and chair of the ANS/ASME Joint Committee for Nuclear Risk Management Seismic Working Group. Grant shared the results of SGH-led research on RIPB design methods for external hazards in advanced reactors that culminated in a report, “Implementation of Licensing Modernization Project Risk-Informed Performance-Based Design Framework for External Hazards: Assessment of Challenges, Gaps, and Research Needs,” published in September 2024.

The research: Through a variety of methods, including a literature review and stakeholder input via surveys and workshops, this research sought to evaluate current, ongoing activities in the AR industry related to RIPB design for external hazards following the Nuclear Energy Institute 18-04 framework and the implementation of the licensing modernization project.

Both NEI 18-04 and the licensing modernization project were developed primarily with internal hazards in mind. This has caused complications in implementing their guidance to external hazard design. The ultimate goal of this research was to find exactly what those complications and gaps in guidance are and what future best practices and needed areas of research might be.

With these complications better understood, the researchers hope that their work will “support and accelerate the adoption of RIPB design” in order to establish “clear, industry-wide methodology and detailed implementation guidance,” which would foster “consistency across AR licensing applications,” according to the report abstract. It goes on to say that consistency in the AR industry “would benefit both applicants and regulatory staff in the licensing process.”

In addition to engaging with stakeholders and conducting a literature review, the research team constructed a demonstration example implementing RIPB design into the development of probabilistic risk assessment (PRA) for external hazards in a nuclear facility. Broken into nine steps, the PRA demonstration was designed to give practical, concrete experience in this process with a specific example while also finding key takeaways (the aforementioned complications, gaps in guidance, and best practices) that remain broadly applicable to the diversity of technology within the advanced reactor design space.

The findings: From these three areas of research, Grant shared some conclusions broken down into three categories: challenges, benefits, and follow-up research.

The first highlighted challenge was the lack of site- and plant-specific data and design information for new ARs, which makes the initial PRA needed for an RIPB more vulnerable to uncertainty and inaccuracy. The second challenge was the interdisciplinarity of RIPB implementation, requiring teams that don’t normally work together to become familiar with each other’s department-specific terminology, concepts, and workflow.

While the primary benefits of this research were also highlighted in the report’s abstract, Grant also touched on RIPB external hazards design’s potential to increase cost effectiveness and inform the code and standard selection process. Areas of future research include the criteria for risk-informed codes and standards and the treatment of seismic events in RIPB design.

Go deeper: A recording of April’s CoP presentation can be viewed on YouTube. The report that this work culminated in was published by EPRI and is available for EPRI members to read in full.

Slides and recordings from previous presentations are available on the RP3C page on ANS’s website. Individuals interested in becoming a member of RP3C or joining one of the monthly CoP presentations are encouraged to contact standards@ans.org.