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Journal Articles

Numerical simulation of oxygen infusion into desaturation resulting from artificial openings in sedimentary formations

Miyakawa, Kazuya; Aoyagi, Kazuhei; Akaki, Toshifumi*; Yamamoto, Hajime*

Dai-15-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), p.609 - 614, 2021/01

Desaturation is expected due to excavation of an underground repository, especially in the newly created fractures zone (EDZ). During the construction and operation of facilities, the air in the gallery infuses into the rock around the gallery though the excavation affected area and causes oxidation of host rock and groundwater, which increase nuclide mobilities. In the Horonobe underground research laboratory (HURL), which is excavated in the Neogene sedimentary formations, no pyrite dissolution or precipitation of calcium sulfates was found from the cores drilled in the rock around the gallery. The reason for no oxidation is estimated that the release of dissolved gases from groundwater due to pressure decrease flows against the air infusion. In this research, the mechanism of O$$_{2}$$ intrusion into the rock was investigated by numerical multiphase flow simulation considering advection and diffusion of groundwater and gases. In the simulation, only Darcy's and Henry's laws were considered, that is, chemical reaction related to oxidation was not handled. The effects of dissolved gas and rock permeability on O$$_{2}$$ infusion into the rock were almost identical. Decreasing humidity with relatively low permeability leads to extensive accumulation of O$$_{2}$$ into the EDZ even though with a relatively large amount of dissolved gas. In the HURL, the shotcrete attenuates O$$_{2}$$ concentration and keeps 100% humidity at the boundary of the gallery wall, which inhibits O$$_{2}$$ infusion. Without the shotcrete, humidity at the gallery wall decreases according to seasonal changes and ventilation, which promotes O$$_{2}$$ intrusion into the EDZ but the chemical reaction related to O$$_{2}$$ buffering such as pyrite oxidation consumes O$$_{2}$$.

Journal Articles

The Effect of dissolved gas on rock desaturation in artificial openings in geological formations

Miyakawa, Kazuya; Aoyagi, Kazuhei; Sasamoto, Hiroshi; Akaki, Toshifumi*; Yamamoto, Hajime*

Proceedings of 5th ISRM Young Scholars' Symposium on Rock Mechanics and International Symposium on Rock Engineering for Innovative Future (YSRM 2019 and REIF 2019) (USB Flash Drive), 6 Pages, 2019/12

The construction and operation of geological repositories require excavation and ventilation of galleries, with significant groundwater drainage. Desaturation of rock around galleries is unavoidable and may affect hydraulic properties and redox conditions. This study used numerical modeling to assess the influence of dissolved gas on the degree of saturation of rock surrounding excavated galleries, focusing on siliceous mudstone rock in the 140 m, 250 m, and 350-m-deep galleries of the Horonobe Underground Research Laboratory, Japan. Based on previous ${it in situ}$ electrical survey, the degree of saturation in the 250 m gallery was higher than that in the 140 m and 350 m galleries. In the Horonobe area, deep groundwater contains high concentrations of dissolved methane, and exsolution of this methane from pore water can affect desaturation. Simple numerical modeling, including simulation of multiphase flows, was undertaken for each gallery to confirm the effect of dissolved gas and rock permeability on desaturation. A sensitivity analysis was performed by varying dissolved gas contents and permeability. Results indicate that the dissolved gas content affects both the degree of saturation and its spatial extent, whereas rock permeability affects only the latter. Higher dissolved gas concentrations result in lower degrees of saturation with a greater spatial extent of desaturation, and higher permeability leads to greater extents of desaturation. It is therefore likely that gas content, rather than rock permeability, caused the observed variations in the saturation degree.

Journal Articles

Evaluating test conditions for in situ tracer migration test in fractured siliceous mudstone involving groundwater with dissolved gas

Takeda, Masaki; Ishii, Eiichi; Ono, Hirokazu; Kawate, Satoshi*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 25(1), p.3 - 14, 2018/06

Fault zones and excavation damaged zones have the potential to act as flow paths, and the characterization of solute transport in such zones in mudstones is important for the safe geological disposal of radioactive waste. However, few in situ tracer migration tests have been conducted on fractures in mudstones. The Japan Atomic Energy Agency has conducted in situ tracer migration experiments using uranine, for fractures in siliceous mudstone of the Wakkanai Formation. 18 experiments were conducted under various conditions An injection flow rate that is slightly higher than the pumping flow rate is ideal for tracer migration experiments involving injection and pumping, as conducted in this study. In situ tracer migration experiments involving injection and pumping conducted in a groundwater environment with dissolved gases allow empirical evaluation of the relationship of the tracer recovery ratio and the groundwater degassing with the injection and pumping flow rate ratio. This evaluation is effective for the design of experimental conditions that account for degassing and ensure high levels of tracer recovery.

JAEA Reports

Improvement and development of geochemical monitoring system for groundwater installed in the 350 m gallery of the Horonobe Underground Research Laboratory

Mezawa, Tetsuya; Miyakawa, Kazuya; Sasamoto, Hiroshi; Soga, Koichi*

JAEA-Technology 2016-003, 25 Pages, 2016/05


Development of the monitoring technique for hydro-geochemical conditions of groundwater in low permeable sedimentary rocks with high content of dissolved gases in the underground facility is one of key issues in the Underground Research Laboratory (URL) project in order to obtain the reliable geochemical data. Development of the monitoring system for the groundwater geochemistry was conducted previously at the 140m gallery in the Horonobe URL. Thereafter, improvement and development of the monitoring system have been performed at the 350m gallery as the course of development technology to monitor the hydro-geochemical conditions during the URL construction. In this report, the results including the improvement and development of the monitoring system for the groundwater geochemistry at the 350m gallery and the several examples of data acquisition are presented.

Journal Articles

Compressed air energy storage system two-phase flow experiment

Kumamaru, Hiroshige; ; Murata, Hideo; Kukita, Yutaka; Akiyama, Mamoru*; *; *; *; *; *; et al.

Proc. of ASME$$cdot$$JSME 4th Int. Conf. on Nuclear Engineering 1996 (ICONE-4), 1(PART B), p.669 - 674, 1996/00

no abstracts in English

Oral presentation

Evaluation of pH changes associated with long-term geological processes; An Effect of degassing

Miyakawa, Kazuya; Sasamoto, Hiroshi; Murakami, Hiroaki

no journal, , 

no abstracts in English

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