The Effect of Inspection Uncertainties in Predicting the Probability of Leak of Steam Generator Tubing Due to Pitting Available to Purchase

Pitting corrosion is a serious form of degradation in steam generator (SG) tubing of some nuclear generating stations. The nature and extent of the pitting process is assessed through inspection programs, typically using eddy current probes. Although the data can be used in a probabilistic framework to predict the probability of a tube leak in future time intervals, the consideration of uncertainties associated with inspection tools is extremely important. The paper shows that the defect size data collected through inspections are significantly contaminated by probability of detection and measurement error such that the data present an incomplete picture of the defect population. The use of inspection data without accounting for inspection uncertainties in the analysis results in highly biased estimates of the leak probability. The paper presents a statistically correct likelihood method to account for inspection uncertainties and demonstrates its effectiveness through examples.