LBB analyses typically involve a two-step process. The first step is a determination of the crack length that can be detected at normal operating conditions. A safety factor is applied to the leakage detectable flaw and then the stability of the flaw at transient loads (i.e., seismic) is calculated. Probabilistic LBB analyses have shown that the leakage flaw size is more important to the failure probability than the fracture mechanics analysis at the seismic loads. The crack morphology is an important parameter in the calculation of the leakage flaw size. This paper will contrast results from using different crack morphology assumptions used in leak-rate calculations. The results show that using a statistical analysis of surface roughness and numbers of turns from cracks removed from service can result in crack sizes that are greatly different for different cracking mechanisms. Using improper morphology parameters can lead to large errors in leakage crack size and can produce nonconservative margins on the LBB critical crack size.
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