Abstract
AbstractThe durability of high level nuclear waste glasses must be predicted on geological time scales. Waste glass surfaces form hydrogels when in contact with water for varying test durations. As the glass hydrogels age, some exhibit an undesirable resumption of dissolution at long times while others exhibit near steady‐state dissolution, that is, nonresumption of dissolution. Resumption of dissolution is associated with the formation of zeolitic phases while nonresumption of dissolution is associated with the formation of clay minerals. Hydrogels with a stoichiometry close to that of imogolite, (Al2O3·Si(OH)4), with ferrihydrite (Fe2O3·0.5H2O), have been shown to be associated with waste glasses that resume dissolution. Aluminosilicate hydrogels with a stoichiometry of allophane‐hisingerite ((Al,Fe)2O3·1.3‐2Si(OH)4) have been shown to be associated with waste glasses that exhibit near steady‐state dissolution at long times. These phases are all amorphous and poorly crystalline and are also found on natural weathered basalt glasses. Interaction of these hydrogels with excess alkali and OH− (strong base) in the leachates, causes the Al2O3·nSiO2 (where n=1‐2) hydrogels to mineralize to zeolites. Excess alkali in the leachate is generated by alkali in the glass. Preliminary rate‐determining leach layer forming exchange reactions are hypothesized based on these findings.
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