ON THE RISK-BASED STEAM-GENERATOR LIFETIME OPTIMIZATION

A probabilistic fracture mechanics model is employed to estimate the f ailure probability of axially cracked steam generator tubes. The model estimates the failure probability from the random changes of the infl uencing parameters such as tube and crack geometry, material propertie s and non-destructive examination results, reliability and sizing accu racy and stable crack propagation. The performance of the model is ill ustrated by a numerical example. A steam generator tubing severely aff ected by the stress corrosion cracking is studied during most unfavour able accidental conditions. Two different plugging approaches are anal yzed and the quality is compared, showing: the superior performance of crack length oriented approach over tube wall thickness reduction bot h in terms of SC failure probability and extent of plugging. Thus, apa rt from setting the acceptable SG failure probability, all elements fo r the risk-based SG lifetime optimisation are provided on the example of stress corrosion cracking in the tube expansion transition zone.