Development of a leach model for a commercial nuclear waste glass

A leach model is presented for a commonly studied commercial nuclear waste glass, PNL 76-68. Boron release is taken to be a monitor of the reaction rate of the glass, while the actual releases of many other glass constituents into solution during static tests are evidently controlled by solubilities. The reaction rate determined in this way passes from linear to parabolic kinetics over the duration of the experiments analyzed, and boron concentrations in solution are found to be a function of the product of time and surface areato-solution volume ratio. This behavior is found to be explained well by assuming the reaction is impeded by resorption of reaction products onto the reacting surface. Two model parameters are found as functions of temperature by fitting the model to published data. It is concluded that the accumulation of silica near the glass surface in a waste package in a repository could limit the rate of reaction of the glass, but not that the reaction would cease as silica reaches its solubility limit in solution