Crack arrest in thick section steel plate

Crack arrest in thick section steel plate is considered in relation to the conditions for crack arrest in a nuclear reactor pressure vessel, when this is subjected to thermal stresses resulting from a hypothetical loss of coolant accident. The results of a theoretical analysis, based primarily on recent developments in quasi-static crack propagation theory, provide further support for the view that the arrest toughness Ksub(Ia) is essentially a material property. However, since the theoretical results also suggest that Ksub(Ia) is reduced by neutron irradiation, and because there is, as yet, no conclusive experimental data on the effect of neutron irradiation on Ksub(Ia), it is proposed that with highly irradiated steel, instead of using a Ksub(Ia) crack arrest criterion, it is better to use a more conservative criterion, based on the concept that arrest occurs within the vessel at a position where the temperature exceeds that temperature above which the cleavage fracture mode is unable to oeprate. (orig.)