The role of Al₂O₃ in the long-term corrosion stability of nuclear waste glasses

The corrosion stability of borosilicate waste glasses has been investigated, as a function of the AlO_1.5 (in balance with SiO₂) content. The AlO_1.5 content ranged from 6.7 to 18.2 mol%. Surface area to solution volume (SA/V) values of 100, 500, 2500 and 10000 m^-1, and temperatures of 90 and 150°C were considered. High SA/V and T were especially used to accelerate the corrosion. The leaching medium was distilled water, total durations up to 600 days, and the tests were interpreted in terms of solution composition either without or after ultrafiltration. The data reveal that long term dissolution of the soluble elements B, Na and Li is diffusion-controlled for all glasses. SA/V appears to be a meaningful corrosion accelerating parameter. The glass composition determines the sequence and kind of the dissolution processes, but final solution data for the soluble elements are not that different. The "final" experimental data for B range between 700 and 1050 mgl^-1 at 90°C (105 days at 10000 m^-1), and between 19000 and 56000 mgl^-1 at 150°C (400 days at 10000 m^-1).