Kinetic Monte Carlo simulations of initial process of solute atom cluster formations based on ab initio data base

An accurate prediction of embrittlement of neutron-irradiated reactor pressure vessel steel is very important for the long term operation of light water reactors. Although solute atom clusters formed in the steel have been observed by using three dimensional atom probe technique, understanding of the elementary mechanisms of the formation of the clusters have not been established. We have carried out ab initio calculations to determine the interactions among solvent, solute atoms and vacancies, and migration barriers in Fe based dilute alloys and built a database used to parameterize pair energies for kinetic lattice Monte Carlo simulations. The result of calculation shows surplus vacancies act as nucleus of small Cu clusters and are trapped by the clusters, and the number of clusters depends on the number of vacancies in the system. This indicates the importance of vacancy concentrations in the alloys caused by irradiations for the initial process of the solute atom cluster formation. (author)