On Safety Assessment of Structures Containing Cracks: Deterministic Analysis

In this paper, safety assessment of structures of nuclear power facilities, containing cracks or crack-like defects, is addressed. A so-called deterministic procedure recommended by Swedish Radiation Safety Agency is reviewed and discussed. The procedure provides a possibility for evaluation of crack growth due to courses of fatigue and stress corrosion, and for prediction of safety reservation margin due to fracture and plastic failure. The review and discussion focus on various assumptions and limitations behind this procedure, and cares that must be taken of when using this procedure for safety assessment. Applications recently conducted for a defect tolerance analysis of aging BWR components are used as examples to address the reliability and accuracy of the assessment and its relevance to rules given by ASME BPV code. It is concluded that for some cases the reliability of such an assessment need to be carefully questioned and there is a great need for alternative procedures for fully achieving a reliable, accurate and effective assessment.