APPLICATION OF 1ST AND 2ND-ORDER RELIABILITY METHODS IN THE SAFETY ASSESSMENT OF CRACKED STEAM-GENERATOR TUBING

The First- and Second Order Reliability Methods (FORM and SORM) have b een applied in the safety assessment of steam generator tubes with thr ough-wall axial stress corrosion cracks. The underlying probabilistic fracture mechanics model takes into account the scatter in tube geomet ry, material properties and stable crack propagation. Also, the effect of the maintenance strategy has been considered. A realistic numerica l example has been given to compare the failure probabilities calculat ed by FORM and SORM to those obtained by different versions of Monte C arlo simulations. The relative errors of the numerical methods employe d have been analysed, which has shown that FORM performs in an accepta ble and SORM in an excellent manner. Some changes in failure surface p roperties, caused by different maintenance strategies, are indicated a nd a sensitivity analysis of influencing parameters is made. The resul ts obtained demonstrate the applicability of FORM and SORM in the safe ty assessment of stress corrosion cracked steam generator tubing.