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Aoyagi, Kazuhei; Ishii, Eiichi
Environmental Earth Sciences, 83(3), p.98_1 - 98_15, 2024/02
Times Cited Count：0 Percentile：0.04(Environmental Sciences)The long-term geological disposal of high-level radioactive waste relies on predictions of future changes in a disposal facility's hydro-mechanical characteristics to assess potential leakage through fractures in the excavation damaged zone (EDZ) after backfilling the facility. This study evaluated the transmissivity of EDZ fractures using in situ hydraulic tests around the area of a full-scale, experimental, engineered barrier system in the Horonobe Underground Research Laboratory, Hokkaido, Japan. After their installation, the buffer blocks swelled, altering the stresses within the EDZ fractures. The effects of these changing stresses on the fractures' transmissivity were assessed over a period of 4 years. The transmissivity continuously decreased in this period to about 41% of its value measured prior to the swelling. Using the Barton-Bandis normal-stress-dependent fracture-closure model, the decrease in transmissivity is quantitatively attributed to closure of the EDZ fractures, which was caused by the swelling pressure increasing up to 0.88 MPa. Evidence of fracture closure came from seismic tomography surveying, which revealed a slight increase in seismic velocity in the study area with increasing swelling pressure. The results show that EDZ fractures were closed by swelling of the full-scale buffer material. They also demonstrate the applicability of the Barton-Bandis model to preliminary estimation of the long-term transmissivity of EDZ fractures in facilities for the geological disposal of radioactive waste.
Takayama, Yusuke; Sato, Daisuke*; Kikuchi, Hirohito*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(2), p.101 - 111, 2022/12
Swelling pressure tests have been conducted to understand the swelling properties of bentonite which is planned to be used as a buffer material in repositories for the geological disposal of radioactive waste. It has been reported that the swelling pressure obtained by swelling pressure test increases monotonically or temporarily decreases after increasing with the passage of the time depending on the initial water content. In this study, swelling pressure tests were conducted under several different initial water content conditions, and the change in wet density distribution inside the specimen during the swelling pressure tests was observed by X-ray CT measurement. It was confirmed that the presence or absence of collapse behavior and its magnitude affect the shape of the change in swelling pressure. When the collapse deformation was large, the amount of temporary decrease in swelling pressure was large. On the other hand, swelling pressure increased monotonically when there was no deformation due to collapse.
Takayama, Yusuke; Kikuchi, Hirohito*
Doboku Gakkai Rombunshu, C (Chiken Kogaku) (Internet), 77(3), p.302 - 313, 2021/09
Numerous swelling pressure tests have been conducted to understand the swelling properties of bentonite which is planned to be used as a buffer material in repositories for the geological disposal of radioactive waste. In this study, in order to clarify the cause of the decrease in swelling pressure during the swell-in pressure test period, the change in wet density distribution inside the specimen during the swelling pressure test was observed by X-ray CT measurement. It was supposed that this phenomenon was caused by the collapse inside the specimen. Furthermore, in order to confirm that collapse is generated by water absorption, the swelling deformation test was carried out under various load conditions. As a result, it was confirmed that collapse occurs even under the load conditions that are equal to or slightly smaller than the swelling pressure. These test data are expected to be used for validation of coupled analysis codes for evaluating the mechanical behavior of disposal facilities during re-saturation period.
Chijimatsu, Masakazu*; Fujita, Tomoo; Sugita, Yutaka; Taniguchi, Wataru
JNC TN8400 2000-008, 339 Pages, 2000/01
JNC-TN8400-2000-008.pdf:30.96MB
Geological disposal of high-level radioactive waste (HLW) in Japan is based on a multibarrier system composed of engineered and natural barriers. The engineered barriers are composed of vitrified waste confined within a canister, overpack and buffer material. Highly compacted bentonite clay is considered one of the most promising candidate buffer material mainly because of its low hydraulic conductivity and high adsorption capacity of radionuclides. In a repository for HLW, complex thermal, hydraulic and mechanical (T-H-M) phenomena will take place, involving the interactive processes between radioactive decay heat from the vitrified waste, infiltration of ground water and stress generation due to the earth pressure, the thermal loading and the swelling pressure of the buffer material. In order to evaluate the performance of the buffer material, the coupled T-H-M behaviors within the compacted bentonite have to be modelled. Before establishing a fully coupled T-H-M model, the mechanism of each single Phenomenon or partially coupled phenomena should be identified. Furthermore, in order to evaluate the coupled T-H-M phenomena, the analysis model was developed physically and numerically and the adequacy and the applicability was tested though the engineered scale laboratory test and in-situ test. In this report, the investigative results for the development of coupled T-H-M model were described. This report consists of eight chapters. In Chapter l, the necessity of coupled T-H-M model in the geological disposal project of the high-level radioactive waste was described. In Chapter 2, the laboratory test results of the rock sample and the buffer material for the coupled T-H-M analysis were shown. The rock samples were obtained from the in-situ experimental site at Kamaishi mine. As the buffer material, bentonite clay (Kunigel V1 and Kunigel OT-9607) and bentonite-sand mixture were used. In Chapter 3, in-situ tests to obtain the rock property were shown. As ...
Fukazawa, E.*; Tanaka, M.*; Yamamoto, H.*; Taira, K.*; Yamamoto, M.*; Okutsu, Kazuo*; Hane, Koji*; Aoyagi, Takayoshi*; Morikawa, Seiji*; Furuichi, Mitsuaki*
PNC TJ1100 98-007, 60 Pages, 1998/02
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Fukazawa, E.*; Tanaka, M.*; Yamamoto, H.*; Taira, K.*; Yamamoto, M.*; Okutsu, Kazuo*; Hane, Koji*; Aoyagi, Takayoshi*; Morikawa, Seiji*; Furuichi, Mitsuaki*
PNC TJ1100 98-006, 434 Pages, 1998/02
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Hibiya, Keisuke*; *; Shiogama, Yukihiro*; Masumoto, Kazuhiko*; Fukazawa, E.*; Taira, K.*; Tanaka, Toshiyuki*; Kondo, Y.*; Yamamoto, M.*; Okutsu, Kazuo*; et al.
PNC TJ1100 97-003, 130 Pages, 1997/02
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Niimi, Ken; Osawa, Hideaki; Yanagizawa, Koichi; ; Yoshida, Hidekazu; Seo, Toshihiro;
PNC TN7410 94-022, 190 Pages, 1994/03
None
Takayama, Yusuke; Kikuchi, Hirohito*; Yamamoto, Yoichi*; Goto, Takahiro*
no journal, ,
In this report, permeability, swelling characteristics, and consolidation characteristics of kaolinite were examined and these characteristics of kaolinite were are compared with kunigel V1.
