A constraint-equivalent approach for assessing fracture toughness of RPV steels under neutron irradiation

Neutron irradiation damages reactor pressure vessel (RPV) steels. As a result of material degradation, the mechanical properties of the material are changed and the crack tip stress and deformation fields are altered. The reduction of fracture toughness due to neutron irradiation is shown to be equivalent to a “constraint shift” exhibited by the ductile–brittle transition curve. Using the J–A2 two-parameter fracture theory to quantify the crack tip stress field and a critical crack opening stress as the fracture criterion, the fracture toughness of an irradiated RPV steel can be predicted from its nonirradiated value. The procedure and examples are given in the paper.

► We show the crack tip stress is changed as the RPV steel undergoes irradiation.
► This change reduces the fracture toughness.
► The reduction of fracture toughness is equivalent to a materials “constraint shift”.
► Method for predicting the shift is developed.