A long-term underground isolation of radioactive wastes from our living areas should be safely conducted. Under high pressure, temperature, and pH conditions, chemical reactions such as mineral dissolution/precipitation should be active, resulting in the change of mechanical and hydraulic properties of the host rocks. Thus, an intensive investigation on dissolution/precipitation kinetics of rocks of interest should be conducted.

In this study, flow-through experiments using granite samples with a single fracture, which is recovered from Mizunami, Japan, have been conducted under high pH conditions so as to understand the evolution of permeability induced by the high pH permeant. Throughout the experiments, the confining pressures and temperatures are well-controlled. Effluent concentrations are also measured for the ten elements of Si, Al, K, Fe, Ca, Na, Mg, Ti, S, and Cl that are included mainly in the targeted rocks. At 20 °C, the fracture permeability little change throughout the experiment, whereas at 90 °C, the permeability decreased by two orders of magnitude within 600 hrs. This completely contrasting results are enigmatic. Therefore, further experiments should be conducted.

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