The critical flaw size is computed for a cracked nozzle in a reactor pressure vessel using a ductile tearing instability assessment and is compared to the Failure Assessment Diagram method. A material resistance J-R curve and elastic-plastic finite element analyses are used to evaluate the crack stability. The expectation is that the critical crack size will be larger from the tearing instability assessment compared to the FAD assessment, since the rising J-R curve gives higher toughness as stable tearing occurs. A reactor pressure vessel nozzle geometry with a postulated surface crack is used as an example to examine the analysis details and common difficulties encountered when creating the crack model, obtaining the necessary elastic-plastic FEA convergence to compute the J-integral values, and determining the tearing stability point.
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