Study on confirmation of borehole closure for intermediate disposal of radioactive waste

Sawaguchi, Takuma ; Murakami, Hiroaki  ; Takeuchi, Ryuji  ; Takai, Shizuka ; Sasagawa, Tsuyoshi  ; Takeda, Seiji 

In the intermediate depth disposal of radioactive waste, the monitoring boreholes are backfilled and sealed at the end of the monitoring period to prevent potential migration pathways for radioactive materials. However, the method to confirm whether the borehole is properly sealed has not been established, and there is a lack of scientific knowledge to determine the validity of borehole sealing. The aim of this study is to develop the confirmation method. Therefore, based on previous studies, experimental and analytical considerations were performed to identify the confirmation points of borehole sealing. In the former, laboratory experiments were performed to understand the swelling behavior and permeability of bentonite block in the borehole. These results indicated that the initial water content of the bentonite block could affect the internal structure after swelling. In the latter, groundwater flow analyses were performed for the hydrogeological structures with backfilled boreholes to understand the effect of backfill conditions on the borehole sealing. It was shown that the backfill conditions to prevent the formation of water pathways in the borehole were the grouting BDZ (Borehole Disturbed Zone), etc.