Regulatory Considerations for the Adoption of Probabilistic Assessment Methodologies for Pressure Boundary Component Aging Evaluations

Abstract of the technical presentation presented at:
1st International Conference of Materials, Chemistry and Fitness-For-Service Solutions for Nuclear Systems
May 15-17, 2019

Prepared by:
Blair Carroll, M. Eng., P. Eng.
Canadian Nuclear Safety Commission

Abstract

Traditionally, deterministic methods have been used to evaluate the effects of aging to establish the remaining useful life of pressure boundary components for Canadian CANDU™ nuclear power plants (NPPs). The deterministic methods have been effective in maintaining the safe operation of NPPs, and they incorporate safety factors and bounding values for input parameters to address uncertainties associated with the actual operation of components. Considerable effort is underway within the CANDU™ industry to gain regulatory acceptance of probabilistic methodologies to evaluate the effects of aging on NPP pressure boundary components. Probabilistic methodologies, such as probabilistic fracture mechanics (PFM), use research and operational experience to better characterize the in-service performance of pressure boundary components and more accurately predict remaining useful life.

Canadian Nuclear Safety Commission (CNSC) staff recognizes that there are potential benefits to using probabilistic methodologies; however, their adoption is often not a simple process. The pressure boundary codes, standards and assessment methodologies that currently form the licensing basis for NPPs are based primarily on deterministic approaches. When considering the acceptability of probabilistic assessment methodologies, CNSC staff must ensure that acceptable design and safety margins are maintained.

This technical presentation provides an overview of the considerations of CNSC technical staff tasked with reviewing the application of probabilistic aging evaluations to pressure boundary components.

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