Modeling of dislocation loop formation and radiation induced grain boundary segregation in stainless steels under light water reactor conditions

Modeling of dislocation loop formation and radiation-induced segregation at grain boundaries using rate theory approach was carried out for stainless steels under neutron irradiation at the conditions relevant to core structures of light water reactors. In the model of dislocation loop formation, a cluster of four interstitials treated as nucleus of a Frank loop. The growth of the loops was described using 25 groups for loop sizes. Radiation-induced segregation was modeled as a Fe-CrNi-Si-Mo system, in which both interstitialand vacancy-mechanisms were considered for solute migration. Based on sensitivity analyses of physical parameters such as diffusion coefficients, a set of physical parameters was decided to fit measured data in cold-worked SUS316 stainless steels irradiated to 73 dpa in a PWR. The model calculations reveal that irradiation temperature and damage rate affect dislocation loop formation and grain boundary segregation whereas the initial dislocation density has little effect.