Quantitative evaluation of maintenance strategies for steam generator tubes using probabilistic fracture mechanics

Using probabilistic fracture mechanics (PFM), we performed qualitative evaluations on effectiveness of various maintenance strategies for steam generator (SG) tubes used in pressurized water reactors (PWRs). Here inspection accuracy, inspection interval, sampling inspection and SCC allowance operation were selected as parameters for sensitivity analyses. Although the analyses were mainly conducted for SG tubes made of Inconel 600 mill anneal (MA) material, additional analyses were performed for assumed materials whose resistance to PWSCC was improved. The results demonstrated that failure probabilities were influenced significantly by the crack propagation law in 1600 material. In both 1600 and the assumed materials, the improvement of inspection accuracy would dramatically reduce the failure probabilities. With respect to SCC allowance operation crack, the results showed that it is preferable to improve the inspection accuracy. The probabilistic approach conducted in this study enables to make effective maintenance strategies with being taken account of various maintenance methods.