Sorption behavior is one of the most important characteristics of material considered to be used in engineered barrier on the sites for radioactive wastes repositories. One such site in Russia is located near Krasnoyarsk on the Yeniseyskiy site, in the Nizhnekansky rock massive. It is designed for intermediate and high level radioactive wastes, including self-heating radioactive wastes containing actinides . Consequentially, during the loading period and the initial timeframe of operation local areas of elevated temperature could exist .
We studied sorption behavior of clays of different mineralogical content from sites located in the vicinity of the repository site both at room temperature and at 90°С to simulate the processes that could be important in the near repository zone. The sorption behavior of the clays was estimated within the following scheme: sorption kinetics study, distribution coefficients (Kd) calculation, and speciation of sorbed radionuclides according to the Tessiers technique.
All sorption experiments were done with dried, crushed and sieved clay samples of different content (natural bentonites, Na-bentonite, kaolin clay) and with model groundwater containing actinides and some fission products. It was shown that increasing the temperature of contact caused increasing Kd and sorption rates. A higher temperature of contact shifts the speciation of sorbed radionuclides to more strongly bounded species. Increasing the contact time also causes stronger bonding of radionuclides to clay.
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