Effects of gluco-isosaccharinate on Cs, Ni, Pm and Th sorption onto, and diffusion into cement

Journal article, 1998

The conditions in the Swedish design for a repository of intermediate to low level radioactive waste include a high alkalinity buffer from the concrete construction in combination with cellulose materials in the waste. Experiments have been undertaken in order to quantify the effects of cellulose degradation products on the radionuclide retention capability of the concrete enclosure. Studies of the sorption of Cs, Ni, Pm and Th onto crushed cement and the diffusion of Cs, Ni and Pm in cement and concrete discs of 2 cm thickness were made in a nitrogen-flushed glovebox facility, using different cellulose degradation product additives to the alkaline pore-water. Samples of the liquid phases were taken during a period of 12 months and the sorption and diffusion behaviour was evaluated by radioanalytical methods. In the experiments of alkaline degradation of cellulose the major constituent was found to be D-gluco-isosaccharinate, a potential metal complexing agent, which was synthesized as its Ca salt and used as a 5mM additive in sorption and diffusion experiments. The other additives were leachates of 5 kg/m3 and 100 kg/m3 cellulose in alkaline water. The results show that the additives caused a significant, but transient reduction of the sorption of Pm and Th. The sorption of Cs and Ni were not influenced. The diffusion of D-gluco-isosaccharinate itself was also studied and this indicates that its apparent diffusivity in cement is low, probably due to its strong sorption on cement. This would explain the transient reduction of the radionuclide sorption.