Probabilistic failure assessment of PWR nuclear power plant piping components against erosion-corrosion

Erosion-corrosion (EC) is one of the important and complex degradation mechanisms in the nuclear power plant piping systems. Depending on the nature of piping material, piping geometry and operating conditions, different components of piping system are susceptible to EC to different degrees. Due to variations in operating conditions and inherent uncertainty associated with the prediction models, EC is to be treated as a random phenomenon. The effect of randomness should be considered in the design of piping components. In this paper, an attempt is made to apply system reliability concept to determine the reliability of an elbow against EC at different times. The application of system reliability concept helps in taking into account: there are a number of sections within a given piping component that are vulnerable to undergo EC - reflecting the complexity of EC mechanism, and, the safety margins of these sections within a component, connected in series, are positively correlated. The usefulness of the model developed in estimation of reliability of elbows at different times is demonstrated through two example problems. A flowchart that can be used for reliability-based design of piping components against EC (in conjunction with ASME design procedure) is also presented. (author)