Role of risk in plant life management - an overview

Most of the tools and methods used to determine fitness for service of CANDU structural components are deterministic in nature, usually derived from relevant engineering codes and standards. Such design codes act as surrogates for managing risk by applying conservative models and safety factors that effectively ensure that the likelihood of failure of plant structural components is very low. A problem arises when aging-related degradation mechanisms make it difficult or impossible to demonstrate compliance with traditional methods. The approach being adopted in many countries is to manage the incremental risks directly. This requires the availability of models and data to estimate the likelihood of failure of the components of interest, a means to translate changes in component failure probabilities into risk increments and a means to address the associated uncertainties. Recent work involving the application of risk-based approaches to feeder degradation is used to illustrate some of the important issues. (author)