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Murakami, Hiroaki; Nishiyama, Nariaki*; Iwatsuki, Teruki; Takeuchi, Ryuji
no journal, ,
no abstracts in English
Sawaguchi, Takuma; Abe, Takeyasu; Sasagawa, Tsuyoshi; Murakami, Hiroaki; Takeuchi, Ryuji; Iida, Yoshihisa; Takeda, Seiji
no journal, ,
no abstracts in English
Sawaguchi, Takuma; Murakami, Hiroaki; Takeuchi, Ryuji; Takai, Shizuka; Sasagawa, Tsuyoshi; Takeda, Seiji
no journal, ,
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.
Sawaguchi, Takuma
no journal, ,
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.
Sawaguchi, Takuma; Takai, Shizuka; Uchikoshi, Emiko*; Takeda, Seiji
no journal, ,
In the intermediate depth disposal of radioactive waste, it is necessary to confirm that the monitoring boreholes are properly backfilled to prevent potential migration pathways for radioactive materials. In this study, groundwater flow analysis was performed to understand the effects of backfilled boreholes on radionuclide migration by varying conditions related to the boreholes and their surrounding hydrogeologic structure. The results showed that in the case of a single borehole in an aquifer isolated by clay layer, when the borehole was backfilled with highly permeable sand, groundwater flowing several tens of meters around the borehole changed the flow direction along the borehole and the average flow velocity was approximately three times greater than that in the case of no borehole. On the other hand, when the borehole was backfilled with low permeability bentonite, the flow direction and velocity were no different. In addition, assuming the presence of two boreholes backfilled with sand and spaced 20 m apart, the flow velocities through two boreholes and in the geological medium between their boreholes were increased. Furthermore, the effects of different hydrogeologic structures on flow direction and velocity associated with the borehole presence were evaluated.