Abstract
This study dealt with the sorption and the diffusion mechanisms of Sr and Cs in Portland Type-I cement and local host rocks, including granite from Kinmen, basalt from Penghu, and andesite from Orchid Island. The attention of this study was paid on sorption and diffusion experiments in both natural and engineered barriers as the multi-barrier concept has been considered to be the most feasible way to construct a radwaste repository, where whole rocks and crushed rocks were taken as natural barriers, and cement as an engineered barrier herein. The experimental results show that the sorption capacities of the tested cement and host rocks are lower than those of clay minerals, where the sorption capacity is dominated by the content of Mg- and Fe-rich minerals in rocks. The diffusion of Sr and Cs depends on the microporous structure of tested media, such as decreases of constrictivity and increases of tortuosity. Hydration is the major factor affecting the sorption and diffusion of cement. Hopefully, the results from this study can be taken as a reference for radwaste repository site assessment and for further studies in natural barriers.