Long-Term Performance Assessment of Nuclear Waste and Natural Glasses in the Geological Repository: a Geochemical Modelling

Nuclear waste loaded and natural (analogue) glasses were studied to understand neo-formed mineral species, formed in equilibrium with the physico-chemical conditions existing in the geological repository. To predict alteration-phases, dissolution equations for average vitrification system (AVS), barium borosilicate (BBS) and obsidian glass were calculated, considering glass composition, pressure, temperature and pH conditions. Progress of reaction plotted against saturation index, indicates saturation with solid phases - chamosite, chalcedony and Ca-beidellite in obsidian; greenalite and fayalite in AVS; and coffinite BBS glass. Activities and molalities of aqueous species together with the number of moles of each mineral species produced and degenerated during the progress of the reaction (as a function of time) are discussed in this communication.