A multi-scale approach for prediction of irradiation effect on RPV steel toughness

Nuclear reactor pressure vessel steels are subjected to an irradiation-induced embrittlement in service and this may lead to a shift of the ductile-to-brittle transition temperature. The prediction of irradiation effect on toughness requires an accurate description of the elasto-visco-plastic behavior of irradiated steels. Recent progresses have been done to describe microstructural evolutions induced by irradiation. Ab-initio computations, molecular dynamics and discrete dislocations dynamics can predict the defects. formation and the hardening induced by the dislocations - defects interactions. At this level, the irradiation effect is essentially reported as an increase of the critical resolved shear stress on the crystallographic slip systems. A numerical homogenization method is proposed to predict stress-strain curves of irradiated steels from the computed critical resolved shear stress evolution. Computations of realistic 3D aggregates and classical homogenization are performed with a Finite Element code [1]. Each grain is described as a single crystal with a crystal plasticity law, which naturally introduces the irradiation effect on the slip systems activity. The resulting average response over the whole aggregate corresponds to classical stress-strain curves. A Beremin type local approach is then applied to compute the fracture toughness of irradiated CT specimens. Assuming that the local approach parameters do not depend on the irradiation level, this methodology is able to take benefits of MD and DDD results to predict the irradiation effect on RPV steels toughness.