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 power plants implement inspection programs to detect and control damages caused by such mechanisms. UT (Ultrasonic Test), one of the non-destructive tests, is the most commonly used method for inspecting the integrity 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 verifying 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 measured thickness is acceptable or not. And, safety factors are proposed herein through the statistical analysis taking into account the components’ type.
Highlights
Korea is operating 23 nuclear power plants at present, and seven more units either operational, under construction and/or in preparation stage within 10 years
This study describes the review of UT evaluation process and the influence of UT measurement error
This paper explores UT evaluation process used in nuclear power plants
Summary
Korea is operating 23 nuclear power plants at present, and seven more units either operational, under construction and/or in preparation stage within 10 years. A nuclear power plant is composed of numerous devices and equipment connected each other by piping components. The piping installed at the secondary system in nuclear power plants is made of carbon steel. The carbon steel components experience wall thinning as the plant operates over the years due to variety of degradation mechanisms. Under the severe water-chemical conditions of high temperature and high pressure, the components are susceptible to FAC (Flow-Accelerated Corrosion). FAC is the major cause of the inside metal loss of piping components. There is a need to continuously monitor the wall thickness of the FAC susceptible ones [1]
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