Non-steady-state conditions and incascade clustering in radiation damage modeling

Abstract

The results of molecular dynamics simulations of displacement cascades indicate that a large fraction of the point defects that survive after intracascade annealing may be found in clusters, rather than as individual point defects. In addition, the mobility of these small point defect clusters may be relatively high. The impact of these clusters is discussed in the framework of a radiation damage model for austenitic stainless steel using the chemical reaction rate theory. Although this theory has been broadly applied in models simulating such radiation-induced phenomena as void swelling, irradiation creep, and embrittlement, such models have generally not fully accounted for incascade clustering. Many of these models have also focused on the assumed steady state behavior and tended to neglect the explicit dose and temperature dependence of the sink structure. A previously-developed model has been modified to permit a more extensive investigation of the time (dose) dependence of the point defect and extended defect concentrations and of the impact of incascade clustering. A preliminary evaluation of the so-called production bias was also carried out with this model. The results indicate that defect behavior is complex and that the limiting behavior predicted by simple analytical solutions is frequently not achieved. The comparison of the production bias and the conventional dislocation/interstitial bias found that two were comparable if examined separately at 500°C, but that the production bias effect was minimized in the presence of a reasonable dislocation/interstitial bias.