This paper presents probabilistic fracture mechanics analyses of nuclear piping with an embedded crack. If the same crack depth and the same aspect ratio are supposed to both the surface and the embedded cracks, break and leak probabilities of the embedded crack case are much smaller than those of the surface crack case. This is because both of length and area of the embedded crack are one half of those of the surface crack, and when the center position of the embedded crack is close to the pipe surface, the crack comes out to the outside of the pipe partially. Consequently, an effective crack size is smaller than that given by probabilistic density function. Even when both of the area and aspect ratio of the embedded crack are the same as those of the surface crack, this tendency does not change. Although the embedded crack grows in the two directions of an inner and an outer surface of the pipe and the crack growth rate is higher than that of the surface crack, this effect does not appear in the failure probability clearly. The surface crack is effective for conservative evaluation, but it is not proper for a rational evaluation. Employing the realistic embedded crack model can lead to rational failure probability.
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