Recent work conducted using the Advanced Finite Element Analysis (AFEA) method to simulate the ‘natural’ crack growth of a circumferential PWSCC demonstrated that a subcritical surface crack can transition to a through-wall crack with significant differences between the inner diameter and outer diameter crack lengths. In the current version of the xLPR (Extremely Low Probability of Rupture) code, once the surface crack penetrates the wall thickness, an idealized through-wall crack (which has an equivalent area as the final surface crack) is formed. This type of crack transition was selected since no general stress intensity factor (K) solutions were available for crack shapes that would form during the transitioning stages, i.e., non-idealized or slanted through-wall cracks. However, during the pilot study of the xLPR code, it has been identified that this crack transition method may provide non-conservative results in terms of leak-rate calculations. In this paper, in order to compare the ‘natural’ versus ‘idealized’ crack transition behavior, limited example cases were considered where both crack transitions were simulated using 3D finite element analyses. In addition, leak-rate calculations were performed to study how the two different crack transition methods can affect the leak-rates. The results of the present study demonstrate that the ‘idealized’ transition from surface to through-wall crack can significantly affect the leak-rate calculations.

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