Insights from the risk-informed inservice inspection and the break exclusion region programs in the USA

A 'risk-informed' approach to plant regulation, design and operational decision-making represents a philosophy whereby risk insights from a plant's Probabilistic Safety Analysis (PSA) are considered together with deterministic factors and operational experience to establish requirements that focus attention on design and operational issues commensurate with their importance to public health and safety. To date, one of the most successful risk-informed applications in the US is Risk-Informed In-Service Inspection (RI-ISI). This application has provided a basis to enhance the existing ASME in-service inspection programs by focusing inspections on the most important weld elements and by improving efficiency in inspection techniques. Typical RI-ISI applications have resulted in a very small change in plant risk, often a risk improvement, while significantly reducing radiation exposure and cost. This article will provide an overview of the RI-ISI methodology and will summarize typical results and benefits gained from the RI-ISI application. (author)