The risk-informed approach has been increasingly utilized by the nuclear industry and the regulators in Canada and around the world. This involves the assessment of plant risk and the considerations for defence-in-depth, safety margin and other nuclear safety principles. The estimates of reliability metric have been commonly obtained using probabilistic methods that involve distributed inputs. While the engineering focus has typically been on finding a solution for a specific problem, the scientific community and the regulators are concerned with generic principles, foundation of probabilistic approaches and definition of reliability metric used in the assessment. In this paper, the concept of a time-dependent reliability framework is discussed to facilitate selecting the appropriate approach to meet, in principle, the assessment intent. In the end, any probabilistic assessment should be fundamentally meaningful, consistent and transparent to inspire confidence in the public and the regulators.

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