Research activities related to KRSKO steam generator maintenance

In the paper three main topics aimed to support Krsko NPP steam generator maintenance are presented: (1) Data based analysis introduced by short overview of tube degradation processes and recent status of steam generator tubes. Special attention is given to stress corrosion cracking in tube roll transition zone as degradation mechanism commonly observed in many steam generators with tubes made from Inconel 600, and to tube defects at the tube support plates since they recently became the most sever problem. All performed analyses base on non-destructive examination records. (2) mechanistic modelling of stress corrosion crack propagation in residual stress field based on linear-elastic fracture mechanics and estimating residual and operating stresses by non-linear finite element analysis. (3) probabilistic fracture mechanics based analysis of tube failure probability based on applied First and Second Order Reliability Methods (FORM and SORM) in the safety assessment of steam generator tubes with axial through wall stress corrosion cracks. (Author) 15 refs