Corrosion mechanisms of vitrified high-level waste

The corrosion mechanisms of a number of reference high-level waste glasses have been studied, to enable to conclude about their long term dissolution behaviour in repository conditions. Using various values for surface area to solution volume (SA/V) and temperatures (T), the concept of a 'final' glass dissolution rate has been clearly demonstrated for three reference disposal media: granitic groundwater, salt brines, and clay/claywater mixtures. This rate is much smaller than the initial corrosion rate. The SiO₂ saturation, and associated hydrolysis reaction constant, is a major factor in the dissolution process. The 'final' dissolution rate in salt brines is different in NaCl or MgCl₂ based brines. This rate is different also depending on the kind and amount of clay interacting with the glass. The presence of gamma irradiation does not influence the glass dissolution. In-situ experiments in the Boom clay for two years at 90°C yield similar results as the laboratory tests. Short term experiments suggest that no measurable difference exists between fully active and inactive simulate waste glasses, in terms of leaching.