Abstract
Water migration is an important issue in sealability of underground radioactive waste disposal (URWD) and is significantly controlled by permeability of rock. Whereas, the permeability of rocks varies with various factors such as stress and temperature. In and around an underground radioactive waste disposal site, the rock stress changes by excavation of caverns for URWD and rock temperature changes by decay heat where the temperature change induces thermal stress. Therefore, water migration should be evaluated considering the effect of stress and temperature. In this regard, a series of triaxial compression tests was carried out under confining pressure between 1 and 14 MPa at 295 K and 353 K, and the permeability under residual strength state was measured. Shikotsu welded tuff, Kimachi sandstone and Inada granite were considered for the experiment to cover wide range of physical properties. The equations for the stress and temperature dependent permeability of fractured rocks were proposed. Fluid inflow was calculated with a 2-D elastic FEM for a simple URWD cavern with or without considering the stress and temperature dependency as an example to show the effect on water inflow. The results showed that water inflow became smaller considering the dependency. This could contribute for optimum design of underground caverns. Several new indices were also correlated with the post-compression permeability to show how well it could be predicted. The effects of temperature became slightly smaller by considering the permeability of fractured rock with the indices than that of average effective stress (AES). Further consideration is needed because the effects of temperature could be seen in the indices-permeability plots and the new indices were almost not effective to improve the approximation for granite.
Water migration is an important factor in sealability of underground radioactive waste disposal (URWD) from the environmental point of view and is significantly controlled by permeability of rock. The permeability of rocks varies with various factors including stress and temperature (Alam et al., 2014 and 2015). The rock stress changes by excavation of caverns for URWD and rock temperature changes by decay heat and the temperature change induces thermal stress. Water migration around URWD should be therefore evaluated considering the effect of stress and temperature. In underground the rock masses are fractured and the state of stress is compressive. In this regard, a series of triaxial compression tests was carried out under confining pressure between 1 and 14 MPa at 295 K and 353 K, and the permeability under residual strength state was measured. The three types of rock (Shikotsu welded tuff, Kimachi sandstone and Inada granite) are considered for the experiment to cover wide range of physical properties of rock. The equations which represent the post-compression permeability by average effective stress and temperature were proposed (Alam et al., 2015).
