Flaws encountered in nuclear pressure tubes must be evaluated to ensure that a delayed hydride cracking (DHC) mechanism is not initiated where the stress concentration at a flaw tip causes diffusion of hydrogen and precipitation of zirconium hydride at the flaw tip. A fracture initiation model for DHC involves a process zone description for the interaction of hydride precipitation with the flaw tip stress distribution. Analytical techniques for this model are practical and accurate for two-dimensional geometry, but cannot be easily applied to the three-dimensional features of finite length surface flaws. Recently, a numerical rendition of the model has been incorporated into a finite element program so that arbitrary geometry and material properties can be managed. The three-dimensional finite length model is applied to specific flaw geometries used in an experimental program. Comparison with corresponding two-dimensional tests demonstrates that the finite length flaw has a significantly higher threshold load than that predicted on the basis of a two-dimensional model.

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