Experimental studies on unsaturated zone surrounding rock using Characterizing Laboratory test on Unsaturated zonE(CLUE)

Kikuchi, Hirohito*; Sugita, Yutaka ; Chijimatsu, Masakazu*; Suzuki, Hideaki*; Komatsu, Mitsuru*; Nishigaki, Makoto*

In geological disposal of high-level radioactive waste (HLW), unsaturated zone will be developed around the disposal tunnel due to the construction of the tunnel. The development of the unsaturated zone would lead to the intrusion of the air into the surrounding rock and then oxygen would dissolve into ground water. Dissolved air affects the redox potential of the ground water and also oxidizes minerals existed in surrounding rock and changes their sorption capacity. These influences would change the geochemical conditions of the repository and affect the corrosion behavior of the overpack. Therefore, Characterizing Laboratory test on Unsaturated zonE (CLUE) was designed and assembled to understand the development process of the unsaturated zone. The CLUE is designed from the viewpoint of the hydraulic characteristics. CLUE has two test tanks. The test tank A uses glass beads to simulate rock mass, the test tank B uses rock block sample. Fundamental hydraulic data of the glass beads on saturation/unsaturation conditions for numerical analysis was obtained. Tests using the test tank A used the piezometer and frequency domain reflectometry (FDR) to measure the unsaturation behavior. From the results of the test tank A, the unsaturated zone was developed around the tunnel. The piezometer and FDR measured the distribution and the time history of the unsaturated zone well. In stable condition, measurement data was in good agreement with the analytical results.