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Nakayama, Masashi; Ishii, Eiichi; Aoyagi, Kazuhei; Hayano, Akira; Murakami, Hiroaki; Ono, Hirokazu; Takeda, Masaki; Fukatsu, Yuta; Mochizuki, Akihito; Ozaki, Yusuke; et al.
JAEA-Review 2025-042, 136 Pages, 2025/12
JAEA-Review-2025-042.pdf:12.95MB
The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant technologies for geological disposal of high-level radioactive waste through investigating the deep geological environment within the host sedimentary rocks at Horonobe-cho in Hokkaido, north Japan. In the fiscal year 2024, we continued R&D on "Study on near-field system performance in geological environment", "Demonstration of repository design options", and "Understanding of buffering behaviour of sedimentary rock to natural perturbations". These are identified as key R&D on challenges to be tackled in the Horonobe underground research plan for the fiscal year 2020 onwards. Specifically, "full-scale engineered barrier system (EBS) performance experiment" and "solute transport experiment with model testing" were carried out as part of "Study on near-field system performance in geological environment". "Demonstration of engineering feasibility of repository technology" and "evaluation of EBS behaviour over 100
C" were addressed for "Demonstration of repository design options". The validation of a method for assessing permeability using the Ductility Index and a method for estimating the state of in-situ ground pressure from hydraulic perturbation tests were investigated as part of the study "Understanding of buffering behaviour of sedimentary rock to natural perturbations". In FY2024, we continued construction of the East Access Shaft and the Ventilation Shaft, and construction of these shafts were completed to a depth of 500 m. After the completion of the East Access Shaft, excavation of the West Access Shaft and 500 m gallery has began. As of the end of FY2024, excavation progress is as follows, the East Access Shaft and the Ventilation Shaft were 500 m depth, the West Access Shaft was 472 m depth, 500 m gallery was 112.9 m, respectively. In the Horonobe International Project (HIP), Management Board and Joint Task Meeting was held at the Horonobe URL in June 2024 to review the progress of construction of galleries and preparations of experiments. Task Meetings to review the implementation plan for in-situ testing and analysis were also held. HIP will be implemented in two phases: Phase 1 (from FY2022 to FY2024) and Phase 2 (from FY2025 to FY2028), the research results of Phase 1 were compiled in FY2024.
Ozaki, Yusuke; Ogata, Sho*; Nakaoka, Kenichi*; Shimizu, Hiroyuki*; Yasuhara, Hideaki*; Akaki, Toshifumi*; Aoyagi, Kazuhei; Fukuda, Daisuke*
Dai-51-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu(Internet), p.125 - 130, 2025/12
The Subcommittee on Research of Coupled Phenomena in Rock, under the Japan Society of Civil Engineers, conducts coupled numerical simulations using various approaches by participating members. The evaluation of the excavation damaged zone (EDZ) in the Horonobe Underground Research Laboratory using hydro-mechanical coupled simulation is one of the tasks of the subcommittee. In this presentation, the problem statement, modeling approaches, and current results from participating organizations are summarized.
Kawata, Kento*; Ogata, Sho*; Aoyagi, Kazuhei; Ozaki, Yusuke; Iwai, Hiromasa*; Yasuhara, Hideaki*
Dai-51-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu(Internet), p.113 - 118, 2025/12
In the deep geological disposal of High-Level Waste, it is essential to understand the fracturing behavior of the rock mass surrounding the disposal tunnel due to excavation for assessing the safety of the repository. In this study, 2D tunnel excavation analysis models based on damage theory were developed and were applied to an in-situ tunnel excavation conducted at Horonobe Underground Research Laboratory. The results of the analysis were then compared with in-situ data available on the purpose of validation. As a result, 18 different analysis models were constructed by changing model parameters, and two models that exhibited the best agreement with the measured data were proposed.
Aoyagi, Kazuhei; Tamura, Tomonori; Ozaki, Yusuke; Ishii, Eiichi; Motoshima, Takayuki*; Sugawara, Kentaro*
Dai-51-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu(Internet), p.119 - 124, 2025/12
In a high-level radioactive waste disposal, it is important to understand the extent of the Excavation Damaged Zone (EDZ) because it can be one of the factors to determine whether disposal galleries or pits can be excavated or not in the design or construction phases. In this study, we performed a hydro-mechanical coupling analysis to simulate the three-dimensional excavation of the twin galleries which were excavated at a depth of 500 m in the Horonobe Underground Research Laboratory. The analysis revealed that the EDZ was developed 1.5-2.0 m from the gallery wall. The stress acting on the shotcrete was within the ultimate limit state. Based on these results, we estimated that the stability of the twin galleries will be maintained, despite the relatively large extent of the EDZ.
Tachi, Yukio; Aoyagi, Kazuhei; Ozaki, Yusuke; Hayano, Akira; Ono, Hirokazu; Takeda, Masaki; Mochizuki, Akihito; Dei, Shuntaro; Minaka, Jumpei; Murakami, Hiroaki; et al.
NEA/NE(2025)20 (Internet), 118 Pages, 2025/11
Nakayama, Masashi; Ishii, Eiichi; Hayano, Akira; Aoyagi, Kazuhei; Murakami, Hiroaki; Ono, Hirokazu; Takeda, Masaki; Mochizuki, Akihito; Ozaki, Yusuke; Kimura, Shun; et al.
JAEA-Review 2025-027, 80 Pages, 2025/09
JAEA-Review-2025-027.pdf:6.22MB
The Horonobe Underground Research Laboratory Project is being pursued by the Japan Atomic Energy Agency to enhance the reliability of relevant technologies for geological disposal of high-level radioactive waste through investigating the deep geological environment within the host sedimentary rocks at Horonobe Town in Hokkaido, north Japan. In the fiscal year 2025, we continue R&D on "Study on near-field system performance in geological environment" and "Demonstration of repository design options". These are identified as key R&D challenges to be tackled in the Horonobe underground research plan for the fiscal year 2020 onwards. In the "Study on near-field system performance in geological environment", we continue to obtain data from the full-scale engineered barrier system performance experiment, and work on the specifics of the full-scale engineered barrier system dismantling experiment. As for "Demonstration of repository design options", the investigation, design, and evaluation techniques are to be systemized at various scales, from the tunnel to the pit, by means of an organized set of evaluation methodologies for confinement performance at these respective scales. Preliminary borehole investigations will be conducted within a 500 m gallery, with the objectives of obtaining rock strength and rock permeability data, as well as surveying the extent of the excavation damaged zone surrounding the test tunnel via tomographic analysis. A planning study for the in-situ construction test will be conducted to investigate the construction of backfill material and watertight plugs. The volume of water inflow associated with the excavation of the 500 m gallery will be observed, and its magnitude will be compared with the range of water inflow predicted in the analysis. The test plan to determine the extent of the excavation damaged zone around the pit, which is planned to be constructed in the 500 m gallery, will be studied to determine the in-situ excavation damaged zone. In addition, the investigation and evaluation methods for the amount of water inflow from fractures and the extent of the excavation damaged zone around the pit will be organized. Concerning the construction and maintenance of the subsurface facilities, excavation of the West Access Shaft and the 500 m gallery will continue. It is anticipated that the construction of the facilities will be completed by the end of the fiscal year 2025. In addition, we continue R&D on the following three tasks in the Horonobe International Project; Task A: Solute transport experiment with model testing, Task B: Systematic integration of repository technology options, and Task C: Full-scale engineered barrier system dismantling experiment.
Aoyagi, Kazuhei; Tamura, Tomonori; Murakami, Hiroaki; Hayano, Akira; Ozaki, Yusuke; Ono, Hirokazu; Ishii, Eiichi
Shigen, Sozai Koenshu (Internet), 12(2), 7 Pages, 2025/09
no abstracts in English
Aoyagi, Kazuhei; Ozaki, Yusuke; Hayano, Akira; Ono, Hirokazu; Tachi, Yukio
Nihon Genshiryoku Gakkai-Shi ATOMO
, 67(6), p.354 - 358, 2025/06
Japan Atomic Energy Agency launched the Horonobe International Project (HIP) utilizing the Horonobe Underground Research Laboratory. The main objectives of this project are to develop and demonstrate advanced technologies to be used in repository design, operation and closure and a realistic safety assessment in deep geological disposal, and to encourage and train the next generation of engineers and researchers. In this review, an overview of the HIP is presented.
Ishii, Eiichi; Ozaki, Yusuke; Aoyagi, Kazuhei; Sugawara, Kentaro*
Hydrogeology Journal, 33(1), p.63 - 85, 2025/02
Times Cited Count：0 Percentile：61.45(Geosciences, Multidisciplinary)This study performed virtual packer tests on modeled single fractures on computer and derived the relationship between flow dimension and mappable indicator, DI, which is defined by the mean stress, groundwater pressure, and rock tensile strength. The greater DI results in the smaller flow area in faults or fractures, subject to fracture-normal closure. Comparing the derived relationship with results from in situ hydraulic tests on natural faults in rock with few fracture-mineral-fillings revealed that flow-path connectivity is high (flow dimension 
1.5) when DI was 
2.0 while was low (flow dimension 
1.5) when DI was 2.0. This relationship was valid even when DI was varied, or faults were sheared, during injection tests on faults, and even in rock with abundant fracture-mineral-fillings. However, flow-path connectivity in minor fractures far from faults could be also low even when DI was 2.0 probably due to poor connection to the main fault network or sealing effects of fracture-mineral-fillings. When the permeability of intact rock is high, flow-path connectivity in fractures was high even when DI was 2.0. These findings can be helpful to map the spatial distribution of flow-path connectivity in faults or fractures from limited borehole data.
Aoyagi, Kazuhei; Ozaki, Yusuke; Ono, Hirokazu; Ishii, Eiichi
Dai-16-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), p.269 - 274, 2025/01
We investigated the development of the excavation damaged zone (EDZ) induced by the excavation of modeled disposal pit which was excavated as a part of the full-scale engineering barrier experiment at 350 m depth. Seismic and electric tomography surveys, observation of rock core samples, borehole televiewer surveys and three-dimensional excavation analysis were performed to evaluate the extent of the EDZ around the pit. It was clarified that the EDZ was developed 0.8 to 1.6 m from the wall of the pit at a relatively shallower depth caused by the effect of the EDZ induced around the floor of the gallery. The extent of the EDZ was gradually reduced along the depth, and the maximum extension was 0.3 m from the wall of the pit at the deeper section.
Nagasawa, Makoto*; Shimizu, Yusuke*; Yamaguchi, Akiko; Tokunaga, Kohei; Mukai, Hiroki*; Aoyagi, Noboru; Mei, H.; Takahashi, Yoshio*
Chemical Geology, 670, p.122431_1 - 122431_25, 2024/12
Times Cited Count：5 Percentile：82.67(Geochemistry & Geophysics)Ozaki, Yusuke; Aoyagi, Kazuhei; Ono, Hirokazu; Kimura, Shun
Proceedings of 4th International Conference on Coupled Processes in Fractured Geological Media; Observation, Modeling, and Application (CouFrac2024) (Internet), 10 Pages, 2024/11
Electrical resistivity tomography was repeatedly carried out to investigate the changes of the electrical resistivity distribution around 350m Niche No. 2 and No. 4 in the Horonobe Underground Research Laboratory. The electrical resistivity around Niche No. 2 did not change so much after the high resistive zone appeared around the tunnel by the excavation under opened condition during the studied period. Around Niche No. 4, the electrical resistivity was investigated under closed condition by engineered barrier system (EBS) where the EBS and surrounding rocks were disturbed artificially by water injection and heating. Our results could capture the change in the distribution of electrical resistivity due to the artificial disturbances in and around of Niche No. 4. These results would help us to understand the time lapse behavior of excavation damaged zone and re-saturation process in and around the EBS from the construction to the closure.
Aoyagi, Kazuhei; Ozaki, Yusuke; Tamura, Tomonori; Ishii, Eiichi
Proceedings of 4th International Conference on Coupled Processes in Fractured Geological Media; Observation, Modeling, and Application (CouFrac2024) (Internet), 10 Pages, 2024/11
In high-level radioactive waste disposal, it is crucial to estimate the transmissivity of gallery excavation-induced fractures, i.e., excavation damaged zone (EDZ) fractures, because EDZ fractures can be a radionuclide migration pathway after the backfilling of the facility is completed. From previous research, the transmissivity of the fracture can be estimated through the empirical equation using the parameter ductility index (DI), which corresponds to the effective mean stress normalized to the tensile strength of the rock. In this research, we performed a hydromechanical coupling analysis of a gallery excavation at the Horonobe Underground Research Laboratory to estimate the transmissivity of the EDZ fracture before the excavation. At first, we simulated the gallery excavation at 350 m and showed that the measured transmissivity was within the range of the estimated transmissivity using the DI. After that, we also predicted the excavation of a gallery at 500 m by setting the hydromechanical parameters acquired from the laboratory tests before the excavation. The estimated transmissivity at 500 m was one order of magnitude less than that at 350 m. This result might be related to the closure of the fracture under high-stress conditions and low rock strength.
Nara, Yoshitaka*; Kashiwaya, Koki*; Oketani, Kazuki*; Fujii, Hirokazu*; Zhao, Y.*; Kato, Masaji*; Aoyagi, Kazuhei; Ozaki, Yusuke; Matsui, Hiroya; Kono, Masanori*
Zairyo, 73(3), p.220 - 225, 2024/03
The fractures in the rock are the main pass of groundwater flow and solute transport. The filling of fine-grained particle, such as clay minerals, was confirmed to decrease the permeability of rock by laboratory experiment. This research aimed to verify the occurrence of the phenomena in the field. The water containing the clay minerals was injected into the rock at the 200m stage of the Mizunami Underground research laboratory. The hydraulic conductivity decreased two order before and after the injection. This result suggested that the decrease of hydraulic conductivity by the filling of fine-grained particle in the fractures occurred in the real field.
Pt-labeled platinum complex and evaluation of its biodistribution in healthy miceOmokawa, Marina*; Kimura, Hiroyuki*; Hatsukawa, Yuichi*; Kawashima, Hidekazu*; Tsukada, Kazuaki; Yagi, Yusuke*; Naito, Yuki*; Yasui, Hiroyuki*
Bioorganic & Medicinal Chemistry, 97, p.117557_1 - 117557_6, 2024/01
Times Cited Count：1 Percentile：11.80(Biochemistry & Molecular Biology)Ozaki, Yusuke; Ono, Hirokazu; Aoyagi, Kazuhei
Shigen, Sozai Koenshu (Internet), 6 Pages, 2023/09
In the Horonobe Underground Research Laboratory, the in-situ experiment for performance confirmation of engineered barrier system was performed at the 350 m stage to develop the technology for geological disposal. Several measurements have been conducted in and around the test drift to investigate the time dependent impact of the experiment on the rock and backfilled tunnel. Some measurement results are introduced in this presentation.
Zhan, Y.*; Kuwata, Yusuke*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi
Experimental Thermal and Fluid Science, 120, p.110249_1 - 110249_12, 2021/01
Times Cited Count：14 Percentile：71.16(Thermodynamics)Zhan, Y.*; Kuwata, Yusuke*; Maruyama, Kiyotaka*; Okawa, Tomio*; Enoki, Koji*; Aoyagi, Mitsuhiro; Takata, Takashi
Experimental Thermal and Fluid Science, 112, p.109953_1 - 109953_8, 2020/04
Times Cited Count：19 Percentile：76.79(Thermodynamics)Kuwata, Yusuke*; Zhan, Y.*; Enoki, Koji*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi
Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 10 Pages, 2018/10
This study aims improvement of safety analysis for sodium fire accidents in sodium-cooled fast reactors. In the experiment, effect of viscosity on liquid jet impact on solid surface was studied.
Kuwabara, Kazumichi*; Aoyagi, Yoshiaki; Ozaki, Yusuke; Matsui, Hiroya
JAEA-Research 2017-002, 39 Pages, 2017/03
JAEA-Research-2017-002.pdf:3.58MB
Authors developed a displacement meter using optical fiber sensor. The displacement meter can be set at any locations in a borehole and guarantee the measurement accuracy up to 5MPa. Total twelve displacement meters were installed in three boreholes to measure the rock mass displacement during groundwater recovery test. The measurement of the rock mass displacement was stated on March, 27, FY 2014. During the first and second groundwater recovery experiments, compressive displacements were observed close to the closure test drift wall. Magnitude of the measured displacements, except vicinity of test drift wall, was smaller than that of calculated under the assumption of it is an isotropic elastic material.
