Abstract
For the last 50 years, inservice inspection (ISI) of passive components, i.e., vessels, piping, etc., has played a pivotal role in maintaining the safety of the current nuclear fleet. The original inspection programs were designed on a sampling strategy, where a sampling of similar components is scheduled to provide a measure of assurance that all components are safe. Over the last several years, the U.S. Nuclear Regulatory Commission has approved plant-specific extensions to in-service inspection frequencies with a basis that includes operational experience and risk-informed arguments. In addition, risk assessment has been used to allow classification of components into risk categories with low-risk categories being exempt for certain inservice inspection requirements. From a risk-perspective, the impact of passive component failure on overall plant safety is typically small. However, these calculations are based on current state of knowledge and many times lack the ability to foresee potential degradation issues. The operational experience suggests that even though the discovery of new degradation mechanics has slowed over the years, continuing degradation and its impact on risk-insights should be considered when evaluating the need for periodic inspection of passive components. This paper presents some thoughts on the impacts of eliminating in-service inspection requirements for passive components and how monitoring performance is essential to plant safety.
