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Murakami, Hiroaki; Nishiyama, Nariaki; Takeuchi, Ryuji; Iwatsuki, Teruki
Oyo Chishitsu, 64(2), p.60 - 69, 2023/06
In order to confirm the quality control items for borehole closure in radioactive waste disposal projects, in-situ borehole sealing tests using bentonite material were conducted. As a result, the closure performance was successfully demonstrated by comparing the data of water injection tests conducted before and after the installation of the closure material. However, the breakthrough was observed after closing, probably due to high differential pressure applied to the seal section. Thus, it is important to ascertain throughout the entire operation that the borehole is adequately closed. The placement and specifications of the closure material should be determined according to the hydrogeological structure in the borehole. The confirmation items to use bentonite for sealing material are identified to be: to consider swelling and density loss in the borehole; to place the planned depth using appropriate emplacement technique; to be placed without damage to seals when use some backfilling materials, considering effect of permeability on adjacent seals.
Murakami, Hiroaki; Iwatsuki, Teruki; Takeuchi, Ryuji; Nishiyama, Nariaki*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(1), p.22 - 33, 2020/06
Geological disposal of radioactive waste requires the large amounts of fundamental technical knowledge throughout the project. Monitoring is carried out to collect site-relevant information for the creation of an environmental database, to assist in the decision-making process, etc. We summarized the current technical level and problems of the groundwater monitoring in the world. Through the research and technology development so far, the technologies have been developed for drilling borehole in the geological environment survey prior to monitoring and the selection of the monitoring site. However, the following technical developments are remaining issues: long-term operation method of monitoring equipment, retrieving method of monitoring equipment after long-term operation, transport method of backfill material for borehole sealing, technical basis for the sealing performance when the borehole-protective casing and strainer tube are left.
; ; *
JNC TY7430 2000-001, 57 Pages, 2000/03
JNC-TY7430-2000-001.pdf:2.17MB
no abstracts in English
Chijimatsu, Masakazu*; Sugita, Yutaka; Fujita, Tomoo; Amemiya, Kiyoshi*
JNC TN8400 99-034, 177 Pages, 1999/07
It is an important part of the near field perfformance assessment of nuclear waste disposal to evaluate coupled thermo-hydro-mechanical (T-H-M) phenomena, e.g., thermal effects on groundwater flow through rock matrix and water seepage into the buffer material, the generation of swelling pressure of the buffer material, and thermal stresses potentially affecting porosity and fracture apertures of the rock. An in-situ T-H-M experiment named 'Engineered Barrier Experiment' has been conducted at the Kamaishi Mine, of which host rock is granodiorite, in order to establish conceptual models of the coupled T-H-M processes and to build confidence in mathematical models and computer codes. In 1995, fourteen boreholes were excavated in order to install the various sensors. After the hydraulic tests, mechanical tests were carried out to obtain the rock properties. After that, a test pit, 1.7m in diameter and 5.0m in depth, was excavated. During the excavation, the change of pore pressure, displacement and temperature of rock mass were measured. In 1996, the buffer material and heater were set up in the test pit, and then coupled thermo-hydro-mechanical test was started. The duration of heating phase was 250 days and that of cooling phase was 180 days. The heater surface was controlled to be 100
C during heating phase. Measurment, was carried out by a number pf sensors installed in both buffer and rock mass during the test. The field experiment leads to a better understanding of the behavior of the coupled thermo-hydro-mechanical phenomena in the near field.
; *; Araki, Kunio
JAERI-M 82-163, 47 Pages, 1982/11
no abstracts in English
Murakami, Hiroaki; Iwatsuki, Teruki; Takeuchi, Ryuji; Maeda, Toshikatsu
no journal, ,
no abstracts in English
Murakami, Hiroaki; Nishiyama, Nariaki*; Iwatsuki, Teruki; Takeuchi, Ryuji
no journal, ,
no abstracts in English
Murakami, Hiroaki; Nishiyama, Nariaki*; Iwatsuki, Teruki; Takeuchi, Ryuji
no journal, ,
no abstracts in English
Nishiyama, Nariaki*; Takeuchi, Ryuji; Iwatsuki, Teruki; Murakami, Hiroaki
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.
