A probabilistic failure assessment based on the fracture and fatigue modules of European FITNET procedure is presented in this work. Analysis of the leak probability of a complex nozzle structure with postulated flaw defect under thermal mechanical loading is performed. Crack growth is calculated using FITNET fatigue module, in which the crack driving force ΔKeq considering mixed-mode load is applied. For the structural safety evaluation, the failure assessment diagram (FAD) within the frame of FITNET fracture module is utilized with the parameter Keff combing KI and KII. The fracture mechanical parameters are calculated using finite element (FE) method because of the complex geometry and load conditions. To meet the needs of probabilistic analyses, formulas calculating crack driving force are developed specific for this nozzle structure through nonlinear regression based on the FE results. With an initial crack depth of 5 mm, the nozzle failure probability in form of leak comes to 1.84×10−4 in next fifty years. The good agreement of the results of Monte Carlo simulation and stratified sampling technique confirms that the crack growth parameter C and the initial crack shape ratio c/a have considerable effect on the structural failure probability.

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