Nanostructure evolution under irradiation of Fe(C)MnNi model alloys for reactor pressure vessel steels

Radiation-induced embrittlement of bainitic steels is one of the most important lifetime limiting factors of nuclear light water reactor (LWR) pressure vessels. The primary mechanism of embrittlement is the obstruction of dislocation motion produced by nanometric defect structures that develop in the bulk of the material due to irradiation. The chemical elements that are thought to influence most the response under irradiation of low-Cu steels, especially at high fluence, are Ni and Mn, hence there is an interest in modelling the nanostructure evolution in irradiated FeMnNi alloys. As a first step in this direction, we developed sets of parameters for object kinetic Monte Carlo (OKMC) simulations under simplifying assumptions, using a ‘‘grey alloy’’ approach that extends the already existing OKMC model for neutron irradiated Fe–C binary alloys. Our model proved to be able to describe the trend in the buildup of irradiation defect populations at the operational temperature of LWR, in terms of both density and size distribution of the defect cluster populations. In particular, the reduction of the mobility of point-defect clusters as a consequence of the presence of solutes proves to be key to explain the experimentally observed disappearance of detectable point-defect clusters with increasing solute content.