Results of the pilot borehole investigations conducted from bottom of shafts at the Mizunami Underground Research Laboratory

Tsuruta, Tadahiko  ; Takeuchi, Shinji; Takeuchi, Ryuji  ; Mizuno, Takashi   ; Oyama, Takuya 

The excavation and pumping of water from the shafts of Mizunami Underground Research Laboratory (MIU) project were halted on October 2005 due to fluoride and boron concentrations in the discharge water that exceeded the Japanese Environmental Standards for discharge into rivers. The numerical simulations indicate that predicted volume of inflow water into the shafts would be considerably greater as the shaft sinking advances. Consequently, JAEA decided to carry out pilot borehole investigations from the bottom of the two shafts to acquire information for increasing the capacity of the water treatment facility, planning for the grouting and reconsideration of the facility design by obtaining information on the geological environment. Based on the pilot borehole investigations, information on the geological environment to a depth of around 500 mbGL was obtained and synthesized.