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

Using probabilistic fracture mechanics (PFM), we performed qualitative eval uations on effectiveness of various maintenance strategies for steam genera tor (SG) tubes used in pressurized water reactors (PWRs). Here inspection a ccuracy, inspection interval, sampling inspection and SCC allowance operati on were selected as parameters for sensitivity analyses. Although the analy ses were mainly conducted for SG tubes made of Inconel 600 mill anneal (MA) material, additional analyses were performed for assumed materials whose r esistance to PWSCC was improved. The results demonstrated that failure probabilities were influenced signifi cantly by the crack propagation law in 1600 material. In both 1600 and the assumed materials, the improvement of inspection accuracy would dramaticall y 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 effectiv e maintenance strategies with being taken account of various maintenance me thods.