Exponential Responses with Double Exponential Measurement Error: A Model for Steam Generator Inspection

摘要

Steam generators in pressurized water reactors contain thousands of tubes through which water from the reactor core flows to generate steam. In use, a tube can be degraded, or thinned, until its integrity under normal or accident conditions is suspect or until a leak occurs. To combat these problems, periodic inservice inspections are made at which a sample of tubes is selected and measured and decisions made as to which tubes should be plugged and whether additional actions are required. To study the performance of candidate inspection plans, a probability model has been developed. Under this model, the variation of actual tube degradation across a steam generator follows an exponential distribution and measurement error follows a double exponential distribution, independent of actual degradation. The distribution of measured degradation can then be derived and used to investigate the operating characteristics of sampling plans and plugging criteria. Available data from operating reactors provide the opportunity to assess the goodness of fit of this model and to estimate the parameters. An example is given and some problems in estimation are pointed out. (ERA citation 04:013248)