Treatment of Uncertainties in Risk-Informed Decision Making within the Canadian Regulatory Framework

Abstract of the technical paper/presentation presented at:
International Workshop on Treatment of Uncertainties for Novel Aspects of Risk Analyses
31 March - 2 April 2025

Prepared by:
Katherine Gromek, Abderrazzaq Bounagui, Michael Xu
Canadian Nuclear Safety Commission (CNSC)

Abstract:

Identification and evaluation of different types of uncertainties from various sources is a fundamental part of any risk management and risk-informed decision-making (RIDM) process (IAEA INSAG-25, CSA N290.19:18). Industry accepted methods and tools for uncertainty classification, representation and assessment are well established and widely incorporated into the Probabilistic Safety Assessment (PSA) framework for the existing nuclear reactors (US NRC RG 1.174, ASME/ANS RA-S-1.1, US NRC NUREG-1855, EPRI 1016737, CSA N290.17:23). Upon rapidly developing new reactor technologies in the recent years, the industry is investigating provisions to reduce uncertainty and compensate for incomplete knowledge of accident initiation and progression for advanced reactor designs given the limited experience with these technologies. Several initial reviews and studies on treatment of uncertainties for new nuclear reactor designs have been published (NEI 18-04, ASME/ANS RA-S-1.4, IAEA-TECDOC-2010, EPRI 3002026495) and have further evolved during the development and licensing of new reactors around the world.

Given a growing interest in deployment of the next generation of nuclear power plants, regulators worldwide have adapted their regulatory frameworks which have been comprehensively reviewed over the past several years regarding their application to SMR and advanced reactor new build projects. The Canadian Nuclear Safety Commission (CNSC) has established a flexible regulatory framework, as outlined in the CNSC regulatory document REGDOC-3.5.3, which allows the licensees to apply graded approach or to propose alternative means of achieving compliance and involves use of RIDM to evaluate acceptability of the proposed solutions without compromising safety. REGDOC-3.5.3 also calls for systematic and comprehensive uncertainty analysis and explains approaches to the plant design and operation features associated with greater uncertainty.

This paper describes the methods and tools employed by CNSC staff for treatment of uncertainties in PSA within the RIDM framework for generally established and novel aspects of the new reactor designs. It also provides examples of the best practices by CNSC staff in review of the novel designs and identifies topics for international collaboration to address specific focus areas of compliance to regulatory requirements.