The effects of alpha-radiolysis on UO2 dissolution determined from batch experiments with 238Pu-doped UO2

The effects of alpha dose-rate on UO2 dissolution were investigated by performing dissolution experiments with 238Pu-doped UO2 materials containing nominal alpha-activity levels of ∼1–100 Ci/kg UO2 (actual levels 0.4–80 Ci/kg UO2), in 0.1 M NaClO4 and in 0.1 M NaClO4 + 0.1 M carbonate. Dissolution rates increased less than 10-fold for an almost 100-fold increase in doping level and fall within the range of predictions of the Mixed Potential Model (a detailed mechanistic model for used fuel dissolution). Dissolution rates were lower in carbonate-free solutions and enrichment of 238Pu on the UO2 surface was suggested in carbonate solutions. Effective G values, defined as the ratio of the total amount of U dissolved divided by the maximum possible amount of U dissolved by radiolytically produced H2O2, increased with decreasing doping levels. This suggests that the dissolution reaction at high dose rates is limited by the reaction rate between UO2 and H2O2, but becomes increasingly limited by the rate of production of H2O2 at lower dose rates.