The Impact of Probabilistic Modeling in Life-Cycle Management of Nuclear Piping Systems.

Flow accelerated corrosion (FAG) is a serious form of degradation in primary heat transport piping system (PHTS) of the nuclear reactor~ Pipes transporting hot coolant from the reactor to steam generators are particularly vulnerable to FAG degradation, such as tight radius pipe bends with high flow velocity. FAG is a life limiting factor, as excessive degradation can result in the loss of structural integrity of the pipe. To prevent this, engineering codes and regulations have specified minimum wall thickness require- ments to ensure fitness for service of the piping system. Nuclear utilities have imple- mented periodic wall thickness inspection programs and carried out replacement of pipes prior to reaching an unsafe state. To optimize the life-cycle management of PHTS, accu- rate prediction of time of replacement or ~`end of life" of pipe sections is important. Since FAG is a time-dependent process of uncertain nature, this paper presents two probabilis- tic models for predicting the end of life. This paper illustrates that the modeling assump- tions have a significant impact on the predicted number of replacements and life-cycle management of the nuclear piping system. A practical case study is presented using wall thickness inspection data collected from Canadian nuclear plants. [DOl: 1O.1115/1.4000897J [ABSTRACT FROM AUTHOR]