Characterization of high activity waste glasses and a comparison with simulated and natural glasses

The study compares a highly radioactive glass with a simulated inactive product in terms of devitrification and leaching behaviour in order to map possible differences. Highly active waste glass were prepared in Marcoule, France. The results of comparison showed that the crystallization and corrosion of the highly active glass is much the same as that of the inactive simulated glass. The chemical corrosion of borosilicate glasses in concentrated salt solutions is accompanied by the formation of reaction layers. The corrosion rate is indirectly influenced by the layer in that the precipitating phases control the silicon concentration in solution. It is pointed out that there are various difficulties in the interpretation of glass corrosion in solutions with high ion strengths, when activity coefficients are not known. Natural basalt glasses were used as analogues for predicting the long-term behaviour of waste borosilicate glass. The experimentally studied corrosion products of basalt glasses, their natural long-term corrosion products and those of borosilicate glasses were compared. Data on naturally altered basalt glasses (e.g. time dependence of corrosion, role of layer formation in release of elements and identification of stable phase in the precipitates) can be used in presently available release codes (QTERM). (author). 29 refs, 11 figs, 4 tabs