Mechanisms for hydrothermal leaching of glass and glass-ceramic nuclear waste forms

The very different chemical constituents contained in the waste glass lead to a specific leaching behavior under hydrothermal conditions. The results are still difficult to interpret in detail but the mechanism in deionized water resembles the one where a protective layer is formed by some of the glass constituents which determine the further release of material from the sample surface. Magnesium, Al, Zn, and Ti were found to contribute considerably to the layer formation in addition to waste constituents such as rare earths and U, Zr. The former elements have already been used for glass frit formulations in order to better digest the waste oxides. They might also be helpful, if used at appropriate concentration levels, to increase the leach resistance of the waste form