Study on Practical Application of Risk Informed In-Service Inspection (Case Study on Class 1 Piping of a Boiling Water Reactor)

Abstract

This paper describes pilot study relevant to the application of Risk Informed In-Service Inspection (RI-ISI) in a BWR plant. This study conducted for typical BWR5 plant of Tokyo Electric Power Company, and partial application of RI-ISI limited in class 1 piping was carried out. A series of studies related to RI-ISI-segments division process, assessment of degradation possibility in segments, failure probability assessment of segments, risk assessment, risk significant assessment and ISI planning-was performed. The inspected portion and its frequency at the time of applying RI-ISI was decided so as to not exceed core damage probability (CDF) at the time of applying the conventional inspection method. As a result, volumetric examination in ISI will not required in 70% of segments (47 segments in 68 segments), and it suggests that the application of RI-ISI is much effective for reduction of radioactive exposure of inspectors without increase of risk by introducing RI-ISI.