Associating Physical and Chemical Properties to Evaluate Buffer Materials by Th and U Sorption

Résumé du livre

The physical and chemical properties of buffer materials to be used for a radwaste disposal repository should be evaluated prior to use. In a conventional approach, independent studies of physical and/or chemical characteristics are conducted. This study investigated the relationship between the plastic index (PI) and distribution ratio (Rd) of buffer materials composed of varying ratios of quartz sand and bentonite. Thorium (Th) and Uranium (U) were the nuclides of interest, and both synthetic groundwater and seawater were used as the liquid phases to simulate conditions representative of deep geological disposal within an island. Atterberg tests were used to determine PI values, and batch sorption experiments were employed to measure Rd values. The results show that Th reached maximum sorption behavior when the bentonite content exceeded 30 % of the mixture. Contrariwise, the sorption of U increased linearly with bentonite content, up to bentonite contents of 100%, and this correlation was present regardless of the liquid phase used. A further result is that U has a better additivity with respect to Rd than Th in both synthetic groundwater and synthetic seawater. These results will allow a determination of more effective buffer material composition, and improved estimates of the overall Rd of the buffer material mixture from the Rd of each mineral component.