The Effect of Phase Formation on Glass Leaching

Abstract

The leaching of nuclear waste glasses in aqueous solution is still considered to be the most important process when discussing a potential release of radionuclides. However, in the last few years it has become clear that the release mechanism under static leaching conditions is very complex involving several processes [1]. The kinetics gave no evidence for pure leaching (i.e. the alkali-ion exchange) which should result in a square root time law, or for pure corrosion (i.e. congruent dissolution of the glass) which should result in a linear time law. Moreover, fits using a combination of these two processes gave unsatisfactory results. This is certainly due to additional processes which are not considered by ion exchange and congruent dissolution. Some explanations may be the build up of alteration layers, saturation effects of some elements with phase formation due to solubility limits and disappearance of metastable phases. To describe such a complicated system thermodynamic data are needed and measurements of mass losses as well as analyses of leachates and surfaces layers have to be performed.