Constraint effects on behaviour of surface cracks in cladded reactor pressure vessels subjected to PTS transients

Crack tip fields of some surface crack configurations through the cladding were investigated in two types of reactor pressure vessel subjected to severe pressurized/thermal transients. The crack driving force expressed by J and the crack tip constraint expressed by h and Q were evaluated along the crack fronts. The magnitude and distributions of the cladding residual stresses and their contributions to the crack driving force were investigated. Some issues on employing the R6-method in fracture assessment of such cracks were also discussed. It was observed that while the different crack tip constraint parameters were effectively identical for uniaxial loading, large deviations would be observed for multiaxial loading. The crack tip constraint expressed by the parameter h during the studied transients significantly exceeded the value at the SSY conditions. This may question the use of plane-strain fracture toughness data in performing integrity assessments of reactor pressure vessels under PTS transients.

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