The effect of adsorbed lead on the chemical durability of nuclear waste glasses

The chemical durability of two types of nuclear waste glasses was measured by the MCC-1 method, with and without the presence of lead in the leachant. This presence has a significant effect on the chemical durability of the sample with the initially bad durability (T-60) and a minor effect on the other glass (C-411), initially more durable. Surface analysis using X-ray Photoelectron Spectroscopy (XPS) was performed on both samples. The O 1s spectra yield a correlation between the number of non-bridging oxygens (NBOs) on the surface and the chemical durability, the latter decreasing with increasing the numbers of NBOs. These NBOs are created in the rate limiting step of the silica-water reaction by breaking the structural Si-O bonds. A lead ion can react with an NBO and inhibit the reaction that destroys the structural component in the glass. This effect is dominant in the less durable T-60 but is only minor for C-411, where most of the surface is composed of Al₂O₃ which is non soluble, giving the glass its initial good durability.