Journal of Nuclear Fuel Cycle and Waste Technology

In order to understand the long-term behavior of radionuclides in granite environments, geochemical behavior characteristics of uranium in granitic host rock of KURT (KAERI Underground Research Tunnel) were investigated by dissolution experiment with different reaction time and solutions. In the dissolution experiment, significantly increased dissolution levels of uranium from granite powder samples were identified during the reaction time of 0~10 days for reaction solutions (UD-CO3 and UD-Bg) containing a large amount of CO3 2-. On the other hand, significantly increased dissolution levels of uranium were also identified for reaction solutions containing Na and Ca after 60 days. Dissolution of uranium continuously increased in reaction solutions of UD-CO3 (44.61 μg·L-1), UD-Bg (41.01 μg·L-1), UD-Na (26.87μg·L-1), UD-Ca (20.26 μg·L-1), UD-CaSi (17.03 μg·L-1), and UD-Si (10.47 μg·L-1) in the experimental period of ~270 days. However, after day 270, dissolution of uranium showed a decreasing tendency. This is thought to have occurred because existing uranium in granite samples reached the limit of dissolution by interaction with reaction solutions. Concentrations of dissolved uranium and points of maximum concentration value were found to differ depending on the CO3 2- presence in the mixed reaction solution and on the geochemical type of the water. It is estimated that differences in the reaction rate between the granite sample and the reaction solution are due to the influence of dissolved ions in the reaction solution.

Keywords

High-level radioactive waste,KURT,Granite,Uranium,Dissolution,Uranyl-carbonate complex