Development of Safety Factors for the UT Data Analysis Method in Plant Piping

Abstract

There are several thousand piping components in a nuclear power plant. These components are affected by degradation mechanisms such as FAC (Flow-Accelerated Corrosion), cavitation, flashing, and LDI (Liquid Droplet Impingement). Therefore, nuclear p ower plants implement inspection programs to detect and control damages caused by such mecha nisms. UT (Ultrasonic Test), one of the non-destructive tests, is the most commonly used method for inspecting the in tegrity of piping components. According to the management plan, several hundred components, being composed of as many as 100 to 300 inspection data points, are inspected during every RFO (Re-Fueling Outage). To acquire UT data of components, a large amount of expense is incurred. It is, however, difficult to find a proper method capable of verify ing the reliability of UT data prior to the wear rate evaluation. This study describes the review of UT evaluation process and the influence of UT measurement error. It is explored that SAM (Square Average Method), which was suggested as a method for reliability analysis in the previous study, is found to be suitable for the determination whether the meas ured thickness is acceptable or not. And, safety factors are proposed herein through the statistical analysis taking into account the components’ type.