Risk-Informed Approach to Structure Integrity Prediction and Optimization of In-Service Inspection of Heat Exchange Equipment with High Defect Statistics

A physically and statistically based approach to steam generator heat exchange tube integrity assessment is proposed in the paper. The method is based on stochastic laws of crack dimensions distribution taking into account their growth, limit load model of cracked tube and SG plugging statistics. Based on the history of plugging tubes of specific SG, three statistical parameters have to be found: initial number of defects, initial defect size and defect growth rate. The developed method was used to predict HET failure for all Ukrainian SGs and to justify pressure reduction of hydrostatic test (HT) for primary side of NPPs with VVER. It is shown that pressure reduction does not practically increase the fracture probability during operation.