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Journal Articles

Analysis of the distribution of microfractures and micropores within granitic rock using simultaneous polarization-fluorescence microscopy

Yuguchi, Takashi*; Usami, Akane*; Ishibashi, Masayuki

Heliyon (Internet), 6(8), p.e04815_1 - e04815_6, 2020/08

The analysis of the distribution of microfractures and micropores is important to accurately characterise mass transfer within a rock body. In this paper, a new "simultaneous polarization-fluorescence microscopy" method is presented, which can be used to analyse the distribution of microscopic voids, including microfractures and micropores, in granitic rock. In this method, thin sections prepared with fluorescent dye are analysed under a polarizing microscope equipped with a fluorescent reflected light source. Using both the transmitted and the fluorescent light sources, both the distribution of microfractures and micropores, and petrographic characteristics (mineral occurrences) can be determined efficiently and simultaneously. The distribution of microfractures and micropores observed in images of granites obtained using simultaneous polarization-fluorescence microscopy is consistent with the distribution observed in backscattered electron images.

Journal Articles

Characterizing the permeability of drillhole core samples of Toki granite, central Japan to identify factors influencing rock-matrix permeability

Kubo, Taiki*; Matsuda, Norihiro*; Kashiwaya, Koki*; Koike, Katsuaki*; Ishibashi, Masayuki; Tsuruta, Tadahiko; Matsuoka, Toshiyuki; Sasao, Eiji; Lanyon, G. W.*

Engineering Geology, 259, p.105163_1 - 105163_15, 2019/09

 Times Cited Count:2 Percentile:46.54(Engineering, Geological)

Rock matrix permeability is mainly controlled by microcracks. This study aims to identify the factors influencing the permeability of the Toki granite, central Japan. Permeability of core samples, measured by a gas permeameter, largely increases in the fault and fracture zones. Although a significant correlation is identified between permeability and P-wave velocity, this correlation is enhanced by classifying the samples into two groups by the Mn/Fe concentration ratio. Thus, lithofacies is another control factor for permeability due to the difference in mineral composition. Moreover, permeability shows significant negative and positive correlations with Si and Ca concentrations, respectively. These concentrations are probably affected by dissolution of silicate minerals and calcite generation in the hydrothermal alteration process. Therefore, a combination of hydrothermal alteration and strong faulting are the predominant processes for controlling permeability.

Journal Articles

Role of micropores, mass transfer, and reaction rate in the hydrothermal alteration process of plagioclase in a granitic pluton

Yuguchi, Takashi*; Shobuzawa, Kaho*; Ogita, Yasuhiro*; Yagi, Koshi*; Ishibashi, Masayuki; Sasao, Eiji; Nishiyama, Tadao*

American Mineralogist, 104(4), p.536 - 556, 2019/04

 Times Cited Count:3 Percentile:34.7(Geochemistry & Geophysics)

This study describes the plagioclase alteration process with a focus on the role of micropores, mass transfer and reaction rate in the Toki granitic pluton, central Japan. The plagioclase alteration process involves albitization, K-feldspathization, and the formation of illite, calcite, fluorite and epidote. Such secondary minerals of hydrothermal origin in plagioclase within granitic rocks record the chemical characteristics of the hydrothermal fluid. Our results highlight (1) the nature of micropores such as distribution and volume in plagioclase, (2) the reaction nature of plagioclase alteration inferred by petrography and chemistry, (3) the physical conditions including alteration age and temperature, (4) the sequential variations of the fluid chemistry and (5) the mass transfer rate and reaction rate in the plagioclase alteration.

JAEA Reports

DECOVALEX-2019 Task C; GREET Intermediate report

Iwatsuki, Teruki; Onoe, Hironori; Ishibashi, Masayuki; Ozaki, Yusuke; Wang, Y.*; Hadgu, T.*; Jove-Colon C. F.*; Kalinina, E.*; Hokr, M.*; Balv$'i$n, A.*; et al.

JAEA-Research 2018-018, 140 Pages, 2019/03

JAEA-Research-2018-018.pdf:40.68MB

DECOVALEX-2019 Task C aims to develop modelling and prediction methods using numerical simulation based on the water-filling experiment to examine the post drift-closure environment recovery processes. In this intermediate report, the results of Step 1 (Modelling and prediction of environmental disturbance by CTD excavation) are summarized from each of the research teams (JAEA, Sandia National Laboratories, Technical University of Liberec). Groundwater inflow rates to the tunnel during the excavation, hydraulic drawdown, and variation of chlorine concentration at monitoring boreholes in the vicinity of the tunnel were chosen as comparison metrics for Step1 by mutual agreement amongst the research teams. It is likely to be possible to foresee the scales of inflow rate and hydraulic drawdown based on a data from the pilot borehole by current simulation techniques.

Journal Articles

Position-by-position cooling paths within the Toki granite, central Japan; Constraints and the relation with fracture population in a pluton

Yuguchi, Takashi*; Sueoka, Shigeru; Iwano, Hideki*; Izumino, Yuya*; Ishibashi, Masayuki; Danhara, Toru*; Sasao, Eiji; Hirata, Takafumi*; Nishiyama, Tadao*

Journal of Asian Earth Sciences, 169, p.47 - 66, 2019/01

 Times Cited Count:3 Percentile:35.43(Geosciences, Multidisciplinary)

This study presents position-by-position $$t-T$$ paths within a granitic pluton based on thermochronological data, and describes their constraints and their relationship with fracture frequency, as an example from the Toki granite, central Japan. The cooling paths have position-specific characteristics; a single $$t-T$$ path does not represent the cooling behavior of the entire pluton. Such position-specific $$t-T$$ paths enable us to evaluate three-dimensional thermal evolution within the granitic pluton, and thus can clarify the detailed formation history of the entire pluton after the incipient intrusion of the granitic magma into the shallow crust. This study reveals the relationship between position-specific $$t-T$$ paths and fracture frequency, and thus provides a criterion for evaluating the fracture population in terms of thermal stress.

Journal Articles

Hydro-Mechanical-Chemical (HMC) simulation of Groundwater REcoverry Experiment in Tunnel (GREET)

Ozaki, Yusuke; Ishibashi, Masayuki; Onoe, Hironori; Iwatsuki, Teruki

Proceedings of 10th Asian Rock Mechanics Symposium & The ISRM International Symposium for 2018 (ARMS 2018) (USB Flash Drive), 11 Pages, 2018/11

Understanding of a post-closure geological environment around a large underground facility is important for the safety assessment of geological disposal of high-level radioactive waste. Japan Atomic Energy Agency (JAEA) has performed the GREET (Groundwater REcovery Experiment in Tunnel) at the Mizunami Underground Research Laboratory (MIU) to evaluate the environmental recovery process after closure. For understanding of coupled behavior of subsurface environment after closure of drift, we perform a Hydro-Mechanical-Chemical coupled simulation of GREET. This study presents the simulation results of excavation stage of test drift for closure test. Our simulation results show that the inflow rate into test drift after excavation is relatively predictable variavle comparing to the hydraulic pressure or chlorite concentration observed in borehole.

Journal Articles

Transition of near surface resistivity of tunnel wall during drift closure test

Ozaki, Yusuke; Ishibashi, Masayuki; Matsushita, Tomoaki*; Masumoto, Kazuhiko*; Imasato, Takehiko*

Proceedings of 13th SEGJ International Symposium (USB Flash Drive), 4 Pages, 2018/11

In the Mizunami Underground Research Laboratory, Groundwater REcoverty Experiment in Tunnel (GREET) is performed to understanding the recovery process of geological environment after the closure of drift. In this experiment, we performed 2D electrical resistivity surveys three times. First survey was performed before the closure of test drift. Second and third surveys were performed after the closure test. The first survey detected two layers conformation that consists of conductive and resistive zones at shallower and deeper part from the drift surface, respectively. These layers correspond to the shotcrete and host rock, respectively. Second and third measurements show that the conductive zone expanded to deeper resistive part while the shallower conductive part did not change. We concluded that we captured the saturation process of dried fractures near the drift wall by closure of drift as an electrical resistivity response.

JAEA Reports

Mizunami Underground Research Laboratory Project, Annual report for fiscal year 2016

Ishibashi, Masayuki; Hama, Katsuhiro; Iwatsuki, Teruki; Matsui, Hiroya; Takeuchi, Ryuji; Nohara, Tsuyoshi; Onoe, Hironori; Ikeda, Koki; Mikake, Shinichiro; Iyatomi, Yosuke; et al.

JAEA-Review 2017-026, 72 Pages, 2018/01

JAEA-Review-2017-026.pdf:18.23MB

The Mizunami Underground Research Laboratory (MIU) project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of geological disposal technologies through investigations of the deep geological environment in the crystalline host rock (granite) at Mizunami, Gifu Prefecture, central Japan. On the occasion of the research program and management system revision of the entire JAEA organization in 2014, JAEA identified three important issues on the geoscientific research program: "Development of countermeasure technologies for reducing groundwater inflow", "Development of modeling technologies for mass transport" and "Development of drift backfilling technologies", based on the latest results of the synthesizing research and development (R&D). The R&D on three important issues have been carrying out on the MIU project. In this report, the current status of R&D activities and construction in 2016 is summarized.

Journal Articles

Spatial distribution of the apatite fission-track ages in the Toki granite, central Japan; Exhumation rate of a Cretaceous pluton emplaced in the East Asian continental margin

Yuguchi, Takashi*; Sueoka, Shigeru; Iwano, Hideki*; Danhara, Toru*; Ishibashi, Masayuki; Sasao, Eiji; Nishiyama, Tadao*

Island Arc, 26(6), p.e12219_1 - e12219_15, 2017/11

 Times Cited Count:7 Percentile:46.4(Geosciences, Multidisciplinary)

The spatial distribution of AFT age in the granitic body is a favorable key to reveal a cooling behavior of the whole pluton. The cooling behavior is attributable to the regional exhumation of the Toki granite related to the regional denudation of the Tono district. Combination of the AERs and AFT inverse model applying to the granite is a powerful procedure for evaluating the cooling and exhumation history of the granitic pluton and thus denudation history of the tectonic region that surrounded the rock body.

JAEA Reports

Mizunami Underground Research Laboratory Project, Plan for fiscal year 2017

Ishibashi, Masayuki; Hama, Katsuhiro; Iwatsuki, Teruki; Matsui, Hiroya; Takeuchi, Ryuji; Ikeda, Koki; Mikake, Shinichiro; Iyatomi, Yosuke; Sasao, Eiji; Koide, Kaoru

JAEA-Review 2017-019, 29 Pages, 2017/10

JAEA-Review-2017-019.pdf:3.21MB

The Mizunami Underground Research Laboratory (MIU) project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of geological disposal technologies through investigations of the deep geological environment in the crystalline host rock (granite) at Mizunami City in Gifu Prefecture, central Japan. On the occasion of the reform of the entire JAEA organization in 2014, JAEA identified three important issues on the geoscientific research program: "Development of countermeasure technologies for reducing groundwater inflow", "Development of modelling technologies for mass transport" and "Development of drift backfilling technology", based on the latest results of the synthesizing research and development (R&D). These R&D on three remaining important issues have been carrying out on the MIU project. This report summarizes the R&D activities planned for fiscal year 2017 based on the MIU Master Plan updated in 2015 and so on.

Journal Articles

Development of new method for evaluating the mineral distribution and mode; Quantitative image analysis using the elemental maps obtained by the scanning X-ray analytical microscope

Ishibashi, Masayuki; Yuguchi, Takashi*

Oyo Chishitsu, 58(2), p.80 - 93, 2017/06

Mode of granitic rocks is important information for evaluating their formation process, characterizing fracture distribution and understanding mass transfer in the rock matrix. However, previous methods to evaluate the mode of granitic rocks have several issues. Thus, this study provides the new image analysis method (MJPD method) using scanning X-ray analytical microscope for evaluation of mineral distribution and mode including the secondary minerals. The MJPD method can deal with the heterogeneity of elemental distribution in each mineral. For evaluating the applicability of MJPD method, the method was applied to elemental maps of thin sections. As a result, it was found out that the mineral distribution and mode are easily evaluated by MJPD method using the elemental maps measured in approximately 10,000 seconds. In addition, the MJPD method can be potentially applied to the elemental maps obtained by other analytical instrumentation such as EPMA and SEM-EDS.

JAEA Reports

Mizunami Underground Research Laboratory Project, Annual report for fiscal year 2015

Hama, Katsuhiro; Iwatsuki, Teruki; Matsui, Hiroya; Mikake, Shinichiro; Ishibashi, Masayuki; Onoe, Hironori; Takeuchi, Ryuji; Nohara, Tsuyoshi; Sasao, Eiji; Ikeda, Koki; et al.

JAEA-Review 2016-023, 65 Pages, 2016/12

JAEA-Review-2016-023.pdf:47.32MB

The Mizunami Underground Research Laboratory (MIU) project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of geological disposal technologies through investigations of the deep geological environment in the crystalline host rock (granite) at Mizunami City in Gifu Prefecture, central Japan. On the occasion of the reform of the entire JAEA organization in 2014, JAEA identified three important issues on the geoscientific research program: "Development of countermeasure technologies for reducing groundwater inflow", "Development of modelling technologies for mass transport" and "Development of drift backfilling technologies", based on the latest results of the synthesizing research and development (R&D). These R&D on three important issues have been carrying out on the MIU project. In this report, the current status of R&D activities and construction in 2015 is summarized.

Journal Articles

Characteristics of micro transfer paths and diffusion phenomena in the matrix of deep crystalline rock

Ishibashi, Masayuki; Sasao, Eiji; Hama, Katsuhiro

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 23(2), p.121 - 130, 2016/12

Matrix diffusion is one of the important phenomena for safety assessment of radioactive waste disposal because it has an effect of retarding the mass transport in crystalline rocks. Although there is not enough knowledge on the matrix diffusion in unaltered (intact) rocks around fractures. Intact granitic rocks around fractures are affected by primary alteration related to hydrothermal fluid resulting from crystallization of granitic magma. Therefore, detailed observations were carried out to clarify the effects of primary alteration focused on the intact granite around fractures sampled from the MIU, central Japan. The results of observation provide that the micropores are formed in plagioclases affected by primary alteration and have the potential of acting as matrix diffusion paths. This is indicating the possibility that intact granitic rock around fractures in an orogenic belt such as Japan have also the retardation functions due to matrix diffusion.

JAEA Reports

Data on fractures based on the borehole investigations in underground facility

Ishibashi, Masayuki; Sasao, Eiji

JAEA-Data/Code 2016-009, 10 Pages, 2016/08

JAEA-Data-Code-2016-009.pdf:3.65MB
JAEA-Data-Code-2016-009-appendix(CD-ROM).zip:0.64MB

Japan Atomic Energy Agency (JAEA) Tono Geoscience Center (TGC) is pursuing a geoscientific research in crystalline rock environment in order to construct scientific and technological basis for the geological disposal of High-level Radioactive Waste. This report compiles the information of the fractures in the Toki Granite, central Japan, obtained by Borehole TV observations of borehole investigations, drilled in underground facility.

JAEA Reports

Development of geological models in the Mizunami Underground Research Laboratory Project; Updating from "Shaft500 Geological Model" to "Stage500 Geological Model" in Phase II

Sakai, Toshihiro; Nohara, Tsuyoshi; Ishibashi, Masayuki

JAEA-Research 2016-009, 27 Pages, 2016/07

JAEA-Research-2016-009.pdf:4.05MB

In the Phase II, the geophysical and geological surveys, and the borehole investigation of the research galleries were carried out and the results obtained were used to validate and update the geological model. Through these surveys and analysis work, we confirmed the geological properties and the distribution of model components and evaluated the accuracy of these research methods. This report presents the geological model updated based on the information of the distributions of lithofacies and geological structures at a depth 500m research galleries, and besides, the validity of the geological model of the site scale developed in the Phase I is confirmed by comparing with the updated model.

Journal Articles

Long term behavior of hydrogeological structures associated with faulting; An Example from the deep crystalline rock in the Mizunami URL, Central Japan

Ishibashi, Masayuki; Yoshida, Hidekazu*; Sasao, Eiji; Yuguchi, Takashi*

Engineering Geology, 208, p.114 - 127, 2016/06

 Times Cited Count:14 Percentile:21.26(Engineering, Geological)

Damage zone (DS) formed by faulting in crystalline rocks can act as significant transport pathway. Therefore, this paper describes the features of WCFs and their long-term behavior associated with faulting based on the results of investigations at the GL -300m and -500m in the MIU. The results of detailed investigations in and around DZ indicate that there are three stages in the development of hydrogeological structures: 1st stage) the formation of background fractures; 2nd stage) the formation of a DZ and corresponding increase in the hydraulic permeability as a result of formation of small fractures; and 3rd stage) the formation of fracture fillings and the hydraulic permeability of the DZ decrease. In the late 3rd stage, unconsolidated clayey fillings formed associated with faulting resulting in decreased permeability of fractures in the DZ. These results underline the importance of understanding the development stages for evaluating the effect of faulting in orogenic belt plutons.

Journal Articles

Zircon growth in a granitic pluton with specific mechanisms, crystallization temperatures and U-Pb ages; Implication to the "spatiotemporal" formation process of the Toki granite, central Japan

Yuguchi, Takashi*; Iwano, Hideki*; Kato, Takenori*; Sakata, Shuhei*; Hattori, Kentaro*; Hirata, Takafumi*; Sueoka, Shigeru; Danhara, Toru*; Ishibashi, Masayuki; Sasao, Eiji; et al.

Journal of Mineralogical and Petrological Sciences, 111(1), p.9 - 34, 2016/02

 Times Cited Count:6 Percentile:61.58(Mineralogy)

Zircon growth collected from a granitic pluton shows four (1st - 4th) events with specific mechanisms, crystallization temperatures and U-Pb ages, revealing the sequential formation process from intrusion through emplacement to crystallization / solidification. The events are recognized by: (1) internal structure of zircon based on the cathodoluminescence observation, (2) crystallization temperatures by the Ti-in-zircon thermometer in the internal structure and (3) U-Pb ages in the internal structure.

JAEA Reports

Information collection regarding geoscientific monitoring techniques during closure of underground facility in crystalline rock

Hosoya, Shinichi*; Yamashita, Tadashi*; Iwatsuki, Teruki; Saegusa, Hiromitsu; Onoe, Hironori; Ishibashi, Masayuki

JAEA-Technology 2015-027, 128 Pages, 2016/01

JAEA-Technology-2015-027.pdf:33.66MB

The study for development of drift backfilling technologies is one of the critical issues in the Mizunami Underground Research Laboratory (MIU) project, and its purposes are to develop closure methodology and technology, and long-term monitoring technology, and to evaluate resilience of geological environment. To achieve the purposes, previous information from the case example of underground facility constructed in crystalline rock in Europe has been collected. In particular, the boundary conditions for the closure, geological characteristics, technical specifications, and method of monitoring have been focused. The information on the international project regarding drift closure test and development of monitoring technologies has also been collected. In addition, interviews were conducted to specialists who have experiences involving planning, construction management, monitoring, and safety assessment for the closure. Based on the collected information, concept and point of attention, which are regarding drift closure testing, and planning, execution management and monitoring on the closure of MIU, have been specified.

JAEA Reports

Mizunami Underground Research Laboratory Project, Annual report for fiscal year 2014

Hama, Katsuhiro; Mikake, Shinichiro; Ishibashi, Masayuki; Sasao, Eiji; Kuwabara, Kazumichi; Ueno, Tetsuro; Onuki, Kenji*; Beppu, Shinji; Onoe, Hironori; Takeuchi, Ryuji; et al.

JAEA-Review 2015-024, 122 Pages, 2015/11

JAEA-Review-2015-024.pdf:80.64MB

Japan Atomic Energy Agency (JAEA) at Tono Geoscience Center (TGC) is pursuing a geoscientific research and development project namely the Mizunami Underground Research Laboratory (MIU) Project in crystalline rock environment in order to construct scientific and technical basis for geological disposal of High-level Radioactive Waste (HLW). The MIU Project has three overlapping phases: Surface-based Investigation phase (Phase I), Construction phase (Phase II), and Operation phase (Phase III). The MIU Project has been ongoing the Phase III, as the Phase II was concluded for a moment with the completion of the excavation of horizontal tunnels at GL-500m level in February 2014. This report presents the results of the investigations, construction and collaboration studies in fiscal year 2014.

JAEA Reports

Study for development of the methodology for multi-scale hydrogeological modeling taking into account hydraulic heterogeneity caused by fracture network

Saegusa, Hiromitsu; Onoe, Hironori; Ishibashi, Masayuki; Tanaka, Tatsuya*; Abumi, Kensho*; Hashimoto, Shuji*; Bruines, P.*

JAEA-Research 2015-011, 59 Pages, 2015/10

JAEA-Research-2015-011.pdf:49.44MB

It is important to evaluate groundwater flow characteristics on several spatial scales for assessment of long-term safety on geological disposal of high-level radioactive wastes. An estimation of hydraulic heterogeneity caused by fracture network is significant for evaluation of the groundwater flow characteristics in the region of tens of meters square. Heterogeneity of equivalent hydraulic properties is needed to estimate for evaluation of the groundwater flow characteristics in the region of several km square. In order to develop the methodology for multi-scale hydrogeological modeling taking into account the hydraulic heterogeneity, spatial distribution of fractures and their hydraulic properties have been modeled using discrete fracture network (DFN) model. Then, hydrogeological continuum model taking into account the hydraulic heterogeneity has been estimated based on the DFN model. Through this study, the methodology for multi-scale hydrogeological modeling according to type of investigation data has been proposed.

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