AbstractA probabilistic model for the assessment of non-destructively determined flaws in welds is presented. Fracture mechanics is used to define acceptance and failure criteria. The model serves as a theoretical background for investigations of non-destructive evaluation (NDE) uncertainties and their impact on component and systems reliability of welded structures. A probabilistic treatment of NDE uncertainties includes advanced Monte Carlo methods and approximative first-order reliability calculations. Results are given of a numerical example relating to design activities on blanket concepts for a DEMO-reactor.