Monte Carlo simulation of the corrosion of irradiated simplified nuclear waste glasses

Abstract

Ballistic effects due to recoil nuclei will be the predominant mode of long-term radiation damage of nuclear waste glass in disposal facilities. While these ballistic effects are known to modify the glass structure in ways that have been quantified using molecular dynamics (MD) simulations, the effect of irradiation-induced structural changes on glass corrosion is not understood. Monte Carlo (MC) simulations were therefore performed to quantify the effects of structural changes determined from MD simulations on the corrosion of simplified nuclear waste glasses, namely sodium borosilicate and sodium alumino-borosilicate glasses. MC simulations were first performed to determine separately the effects of irradiation-induced changes in boron coordination, the number and nature of Qn species, and the angular distribution of SiOSi linkages, that is, changes to the short-range order of the glass. Generally, the MC simulations showed the resulting effects on the kinetics (B release rate) and extent (B leached thickness) of corrosion were correlated to the extent of depolymerization of the glass network introduced by these local structural changes. The combined effects of these structural changes, as parameterized using the results of MD simulations, were then determined using a glass composition for which relevant experimental data were available for comparison. Here, the combined effect of local changes was lower than the increase in alteration depth observed upon irradiation. This insight from the MC simulations highlighted the need to consider changes in the medium-range order to completely account for experimental observations.