Migration behavior of cesium released from fully radioactive waste glass in compacted sodium bentonite

Migration experiment with compacted sodium-type bentonite saturated with distilled water was carried out at room temperature in order to investigate the coupled processes of Cs release from fully radioactive waste glass and its transport in compacted bentonite. Under these conditions, leaching of Cs from the waste glass and diffusion and sorption of Cs in compacted bentonite occur simultaneously. Cesium migration behavior was analyzed by geochemical and transport modelling. The input data for this analysis were derived from the following individual measurements and models: (a) The leaching behavior of Cs from the waste glass was analyzed by congruent dissolution with silica before its saturation and subsequently with boron. (b) The diffusion coefficient of Cs in bentonite porewater was estimated from an electrochemical interaction model with the bentonite surface. (c) The distribution coefficient of Cs was estimated from a cation exchange model. The individual models were applied to compacted bentonite with consideration of the porewater chemistry, microstructure and surface characteristics of the bentonite and the solid/liquid ratio. The modelling results show a good agreement with the experimental observations. (author)