The ion exchange phase in corrosion of nuclear waste glasses

The diffusion-controlled ion exchange phase in the corrosion of nuclear waste borosilicate glasses has been examined using the Doremus’ model accounting for interdiffusion and exchange of the cations in the glass with protons from the water. Ion exchange is the principal radionuclide release mechanism for conditions when glass network hydrolysis is suppressed, such as in silica-saturated solutions when ion exchange may persist over geological time scales. In dilute aqueous solutions ion exchange controls the initial cation release and can dominate for tens and many hundreds of years if temperatures are low at low and neutral pH. Ion exchange rates are shown to have inverse square root time dependences, an Arrhenius-controlled temperature relationship and a 10−0.5pH dependence with the pH of the contacting water. Due to radioactive decay the radionuclide releases from nuclear waste glasses are limited to certain upper values, which can be calculated based on available experimental data.