The barrier effect of calcium silicate hydrate (C - S - H), which is secondarily formed around a repository owing to the utilization of cementitious materials, was explored. Eu was employed as a chemical analog of Am (a key radionuclide in high-level radioactive wastes), and its interaction with C - S - H was analyzed via synthesis experiments. For the experiments, calcium oxide, fumed silica, and a Eu solution were mixed to interact Eu with C - S - H that had not undergone drying. Fluorescence Raman spectroscopies were performed to analyze the coexistence of Eu with C - S - H. The results indicated that Eu was mostly undissolved in the liquid phase and that it was incorporated into the C - S - H structure rather than precipitated as its hydroxide species even at the pH conditions for Eu hydrolysis. Additionally, the C - S - H formation at 50 degrees C, as well as its incorporation of Eu, were accelerated compared to 25 degrees C. The findings indicated the possibility of immobilizing Eu and Am by C - S - H formed in the underground environment even under groundwater conditions in which Eu and Am form mobile colloids via the hydrolysis.
