Current status of geological disposal by "all-Japan" activities, 2; Site characterization technology for geological disposal

Saegusa, Hiromitsu*; Matsuoka, Toshiyuki*; Niwa, Masakazu; Sasao, Eiji; Hayano, Akira

Nihon Genshiryoku Gakkai-Shi ATOMO, 64(1), p.46 - 50, 2022/01

https://doi.org/10.3327/jaesjb.64.1_46

This paper is a review article to introduce the concept of the site selection for geological disposal in geological environment of Japanese Islands, and the current status of related research and development.

Deposition of radiocesium on the river flood plains around Fukushima

Saegusa, Hiromitsu; Oyama, Takuya; Iijima, Kazuki; Onoe, Hironori; Takeuchi, Ryuji; Hagiwara, Hiroki

Journal of Environmental Radioactivity, 164, p.36 - 46, 2016/11

https://doi.org/10.1016/j.jenvrad.2016.04.020

The environments of Fukushima have been contaminated due to the Fukushima Daiichi Nuclear Power Plant accidents caused by the Great East Japan Earthquake on March 11, 2011. Released radio-cesium mainly affects radiation dose in the environment of Fukushima. It is concerned that redistribution of the radiation dose due to water discharge will be occurred due to the transportation of radio-cesium. Especially, deposition of the transferred soil particle with radio-cesium at flood plain with downstream area is possible cause of increasing radiation dose. Therefore, it is important to understand the influence of deposition behavior of radio-cesium on radiation dose. The paper discusses the deposition behaviors of radio-cesium at river based on the data obtained from the river investigations.

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.

Influence on groundwater flow conditions by groundwater pressure change induced by earthquakes; Case study of Tono Area

Takeuchi, Ryuji; Tsuyuguchi, Koji*; Onoe, Hironori; Saegusa, Hiromitsu*; Beppu, Shinji

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 22(2), p.37 - 52, 2015/12

https://doi.org/10.3327/jnuce.22.2_37

Assessment of the geological environment for the long term safety of geological disposal systems for high-level radioactive waste requires consideration for any phenomenon resulting in cumulative change to the geological environment at the regional scale. Groundwater pressure changes induced by earthquakes, for example, are one of the phenomena to be considered. Groundwater pressure changes induced by earthquakes have been observed during long-term monitoring carried out by Japan Atomic Energy Agency in the Tono Area, Gifu. In this paper, the observations of groundwater pressure change induced by earthquakes are summarized. In addition, an impact on groundwater flow conditions induced by earthquakes is discussed. In order to evaluate the long-term stability of groundwater flow condition, it is important to focus not only the change of groundwater pressure by earthquakes but also the change of the hydraulic gradient and hydraulic permeability.

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.

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.

Study of hydrogeology in the Mizunami Underground Research Laboratory Project; Hydrogeological modeling at site scale in Phase II

Onoe, Hironori; Kosaka, Hiroshi*; Takeuchi, Ryuji; Saegusa, Hiromitsu

JAEA-Research 2015-008, 146 Pages, 2015/08

JAEA-Research-2015-008.pdf:76.46MB

Mizunami Underground Research Laboratory (MIU) Project is being carried out by Japan Atomic Energy Agency (JAEA) in the Cretaceous Toki granite in the Tono area, central Japan. The MIU Project has three overlapping phases: Surface-based Investigation (Phase I), Construction (Phase II) and Operation (Phase III). In this study, calibration of hydrogeological model and groundwater flow simulation using the data obtained by the Phase I and Phase II were carried out in order to develop the methodology for construction and update of hydrogeological model on Site Scale. As a result, hydrogeological model on Site Scale, which is able to simulate comprehensively the obtained data regarding groundwater pressure distribution before excavation of the MIU facilities, hydraulic responses and inflow volume during excavation of the MIU facilities, was constructed.

Groundwater flow modeling focused on the Fukushima Daiichi Nuclear Power Plant site

Saegusa, Hiromitsu; Onoe, Hironori; Kohashi, Akio; Watanabe, Masahisa

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 7 Pages, 2015/05

Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Company is facing contaminated water issues. The amount of contaminated water is continuously increasing due to groundwater leakage into the underground part of reactor and turbine buildings. Therefore, it is important to understand the groundwater flow conditions at the site and to predict the impact of countermeasures taken for isolating groundwater from the source of the contamination, i.e. the reactor buildings. Installations, such as of land-side and sea-side impermeable walls have been planned as countermeasures. In this study, groundwater flow modeling has been performed to estimate the response of groundwater flow conditions to the countermeasures. From the modeling, groundwater conditions and changes in response to implementation of the countermeasures could be reasonably estimated. The results indicate that the countermeasures will decrease the volume of inflow into underground part of the buildings. This means that the countermeasures will be effective in reducing the discharge volume of contaminated groundwater to ocean.

Groundwater recovery experiment in Mizunami Underground Research Laboratory; Numerical simulation of H-M coupled behavior of rock and backfill materials to evaluate the influence on the surrounding rock

Takayama, Yusuke; Sato, Toshinori; Onoe, Hironori; Iwatsuki, Teruki; Saegusa, Hiromitsu; Onuki, Kenji

Dai-43-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.313 - 318, 2015/01

In the Mizunami Underground Research Laboratory, groundwater recovery experiment is being conducted to construct the method to understand the transition of geological environment due to groundwater recovery at the -500m access and research gallery-north. As a part of this experiment, backfill test is planned using drilling pits filled with artificial materials (clay and concrete) to evaluate the influence on the surrounding rock mass due to the interaction of rock and artificial materials. In this study, numerical simulation of the backfill test has been carried out to predict the qualitative hydro-mechanical behavior.

Mizunami Underground Research Laboratory Project, Plan for fiscal year 2014

Hama, Katsuhiro; Mikake, Shinichiro; Nishio, Kazuhisa; Sasao, Eiji; Saegusa, Hiromitsu; Iwatsuki, Teruki; Ikeda, Koki; Sato, Toshinori; Osawa, Hideaki; Koide, Kaoru

JAEA-Review 2014-035, 34 Pages, 2014/10

JAEA-Review-2014-035.pdf:44.83MB

The Mizunami Underground Research Laboratory (MIU) project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies through investigations of the deep geological environment within the host crystalline rock at Mizunami City in Gifu, central Japan. The project proceeds in three overlapping phases, "Phase I: Surface-based investigation Phase", "Phase II: Construction Phase" and "Phase III: Operation Phase". 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. The present report summarizes the research and development activities planned for fiscal year 2014 based on the MIU Master Plan updated in 2010.