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Miyakawa, Kazuya; Aoyagi, Kazuhei; Akaki, Toshifumi*; Yamamoto, Hajime*
JAEA-Data/Code 2021-002, 26 Pages, 2021/05
JAEA-Data-Code-2021-002.pdf:2.14MB
JAEA-Data-Code-2021-002-appendix(CD-ROM).zip:40.99MB
Investigations employing numerical simulation have been conducted to study the mechanisms of desaturation and oxygen infusion into sedimentary formations. By mimicking the conditions of the Horonobe underground research laboratory, numerical simulations aided geoscientific investigation of the effects of dissolved gas content and rock permeability on the desaturation (Miyakawa et al., 2019) and mechanisms of oxygen intrusion into the host rock (Miyakawa et al., 2021). These simulations calculated multi-phase flow, including flows of groundwater and exsolved gas, and conducted sensitivity analysis changing the dissolved gas content, rock permeability, and humidity at the gallery wall. Only the most important results from these simulations have been reported previously, because of publishers' space limitations. Hence, in order to provide basic data for understanding the mechanisms of desaturation and oxygen infusion into rock, all data for 27 output parameters (e.g., advective fluxes of heat, gas, and water, diffusive fluxes of water, CH
, CO
, O, and N, saturation degree, water pressure, and mass fraction of each component) over a modeling period of 100 years are presented here.
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 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 infusion into the rock were almost identical. Decreasing humidity with relatively low permeability leads to extensive accumulation of O into the EDZ even though with a relatively large amount of dissolved gas. In the HURL, the shotcrete attenuates O concentration and keeps 100% humidity at the boundary of the gallery wall, which inhibits O infusion. Without the shotcrete, humidity at the gallery wall decreases according to seasonal changes and ventilation, which promotes O intrusion into the EDZ but the chemical reaction related to O buffering such as pyrite oxidation consumes O.
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 
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.