Evaluation of sealing performance of bentonite materials in excavated damaged zone for sedimentary rocks at the Horonobe Underground Research Laboratory

木村 駿  ; 武田 匡樹 ; 本島 貴之*

Kimura, Shun; Takeda, Masaki; Motoshima, Takayuki*

Excavated damaged zone (EDZ) with changes in flow and transport properties induced by modification of hydraulic and mechanical properties could become short-circuit flow paths between a repository and the ground surface in the geological disposal of high-level radioactive waste. Hence, a sealing plug with slots that exceed the width of EDZ and filling the slots with clay material that has low hydraulic permeability is proposed as a countermeaure to prevent the flow of radionuclides through the tunnels and EDZ. Therefore, a small-scale experiment has been conducted to validate the performance in EDZ developing sedimentary rocks at the Horonobe Underground Research Laboratory. A circumference shape slot around a long borehole from the floor of the tunnel. Then, water-tight wall was constructed by filling with bentonite pellets. Results of hydraulic test in the long borehole show that the slot filling with bentonite pellet is effective to decrease hydraulic connectivity in EDZ for sedimentary rocks.