Seismic vibrations of the underground cavern type disposal facility during construction and operation phase were evaluated by considering the influence of ground motion on engineered barriers such as concrete pit, low diffusion layer and buffer. Two-dimensional FEM seismic response analyses with three different earthquake ground motions were carried out. The results indicated the cementitious materials (i.e., concrete pit and low diffusion layer) could withstand large earthquake motions, while the soil-based buffer would have some shear failure with small residual displacement after the earthquake. Even such failure, its influence on the permeability of the buffer was negligible because the increase of the permeability coefficient of the buffer was estimated to be small.
Among the underground cavern type disposal facility (hereafter referred to as "underground cavern facility"), relatively large disposal cavern excavated in ground deeper than 70 m below the ground surface is planned for intermediate-level disposal. Fig.1 shows an example of the concept of the underground cavern facility in which engineered barriers composed of cement-based and soil-based materials are used to isolate the wastes. The concrete pit is made of steel-reinforced concrete for ensuring mechanical stability, radiation shielding, and migration resistance with nuclide sorption capability. Low diffusion layer is made of mortar for shielding, migration resistance with low diffusivity and high sorption, and bentonite buffer is also used for suppression of groundwater intrusion and migration resistance. These properties are required for the performance of the facility.
Underground structures are known to be relatively stable against earthquake, in general, and many studies have been conducted so far to evaluate the stability of rock mass and rock support for disposal tunnels in underground cavern facilities. Even though, the influence of earthquake loading on the stability of underground cavern facility that include engineered barriers is less examined. In this paper, we evaluate the influence of earthquake loading on the underground cavern facility during construction and operation phase with presumed ground motions, and the resulting deformation behaviors of the main components of the engineered barriers such as concrete pit, low diffusion layer, and buffer are reported.
