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Fukatsu, Yuta; Hu, Q.*; Tachi, Yukio
Journal of Contaminant Hydrology, 276, p.104789_1 - 104789_12, 2026/01
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 nearfield 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.
Koike, Ayaka*; Ueno, Fuga*; Ishidera, Takamitsu; Iwata, Hajime; Fukatsu, Yuta; Taneichi, Yayoi; Nonaka, Mai
NUMO-TR-25-03, p.124 - 126, 2025/10
no abstracts in English
, I
and HDO onto pre-Neogene sedimentary rocksHou, L.*; Fukatsu, Yuta; Okamoto, Shunichi*; Toda, Kanako*; Nakata, Kotaro*; Nohara, Shintaro*; Ishidera, Takamitsu; Saito, Takumi*
Journal of Nuclear Science and Technology, 14 Pages, 2025/00
Times Cited Count：1 Percentile：76.46(Nuclear Science & Technology)Hamamoto, Takafumi*; Koike, Ayaka*; Ishidera, Takamitsu; Iwata, Hajime; Fukatsu, Yuta; Taneichi, Yayoi
NUMO-TR-24-03, p.85 - 86, 2024/10
no abstracts in English
Hamamoto, Takafumi*; Fukatsu, Yuta
NUMO-TR-24-01, p.95 - 97, 2024/05
no abstracts in English
Soler, J. M.*; Jurado, D.*; Saaltink, M. W.*; Mart
nez, L.*; Hidalgo, J. J.*; Lanyon, G. W.*; Heule, M.*; Fukatsu, Yuta; Siitari-Kauppi, M.*; Havlov
, V.*; et al.
Applied Geochemistry, 162, p.105927_1 - 105927_12, 2024/02
Times Cited Count：0 Percentile：22.89(Geochemistry & Geophysics)Hu, Q.*; Wang, Q. M.*; Zhang, T.*; Zhao, C.*; Iltaf, K. H.*; Liu, S. Q.*; Fukatsu, Yuta
Energy Reports (Internet), 9, p.3661 - 3682, 2023/12
Times Cited Count：11 Percentile：66.56(Energy & Fuels)Soler, J. M.*; Kek
linen, P.*; Pulkkanen, V.-M.*; Moreno, L.*; Iraola, A.*; Trinchero, P.*; Hokr, M.*; 
ha, J.*; Havlov, V.*; Trpko
ov, D.*; et al.
Nuclear Technology, 209(11), p.1765 - 1784, 2023/11
Times Cited Count：5 Percentile：70.39(Nuclear Science & Technology)Yuan, X.*; Hu, Q.*; Lin, X.*; Zhao, C.*; Wang, Q.*; Tachi, Yukio; Fukatsu, Yuta; Hamamoto, Shoichiro*; Siitari-Kauppi, M.*; Li, X.*
Journal of Hydrology, 618, p.129172_1 - 129172_15, 2023/03
Times Cited Count：6 Percentile：60.39(Engineering, Civil)
Cs NMR chemical shift of clay minerals via machine learning and DFT-GIPAW calculationsOkubo, Takahiro*; Takei, Akihiro*; Tachi, Yukio; Fukatsu, Yuta; Deguchi, Kenzo*; Oki, Shinobu*; Shimizu, Tadashi*
Journal of Physical Chemistry A, 127(4), p.973 - 986, 2023/02
Times Cited Count：7 Percentile：65.17(Chemistry, Physical)The identification of adsorption sites of Cs on clay minerals has been studied in the fields of environmental chemistry. The nuclear magnetic resonance (NMR) experiments allow direct observations of the local structures of adsorbed Cs. The NMR parameters of Cs, derived from solid-state NMR experiments, are sensitive to the local neighboring structures of adsorbed Cs. However, determining the Cs positions from NMR data alone is difficult. This paper describes an approach for identifying the expected atomic positions of Cs adsorbed on clay minerals by combining machine learning (ML) with experimentally observed chemical shifts. A linear ridge regression model for ML is constructed from the smooth overlap of atomic positions descriptor and gauge-including projector augmented wave (GIPAW) ab initio data. The Cs chemical shifts can be instantaneously calculated from the Cs positions on any clay layers using ML. The inverse analysis from the ML model can derive the atomic positions from experimentally observed chemical shifts.
Soler, J. M.*; Keklinen, P.*; Pulkkanen, V.-M.*; Moreno, L.*; Iraola, A.*; Trinchero, P.*; Hokr, M.*; ha, J.*; Havlov, V.*; Trpkoov, D.*; et al.
SKB TR-21-09, 204 Pages, 2021/11
Cs, and 
I in compacted Ca-montmorillonite; Experimental and modeling approachesFukatsu, Yuta; Yotsuji, Kenji*; Okubo, Takahiro*; Tachi, Yukio
Applied Clay Science, 211, p.106176_1 - 106176_10, 2021/09
Times Cited Count：23 Percentile：86.69(Chemistry, Physical)Okubo, Takahiro*; Yamazaki, Akio*; Fukatsu, Yuta; Tachi, Yukio
Microporous and Mesoporous Materials, 313, p.110841_1 - 110841_11, 2021/01
Times Cited Count：12 Percentile：47.81(Chemistry, Applied)Pore distributions in water-saturated Ca-montmorillonite were investigated using 
H NMR measurements under various dry densities (0.8 - 1.6 g/cm
) and porewater salinity conditions (deionized water, 0.1 and 1 M CaCl
), at the temperature range of 233 - 303 K. The volume fractions of the interlayer pore including two and three hydrated layers and the non-interlayer pore in compacted Ca-montmorillonite were quantified by NMR relaxometry including 
and 
distribution analysis, and were compared with NMR cryoporometry and X-ray diffractometry. These analysis provided consistent pictures on the pore distributions in compacted Ca-montmorillonite, in contrast to Na-montmorillonite. The main factor affecting the pore distribution in compacted Ca- and Na-montmorillonite is the density, whereas the effect of porewater salinity is relatively smaller. The effect of interlayer cations is also relatively smaller at higher density, although the differences in the pore structures are significant at low density.
Hu, Q.*; Wang, Q.*; Zhao, C.*; Zhang, T.*; Tachi, Yukio; Fukatsu, Yuta
no journal, ,
Fukatsu, Yuta; Ishidera, Takamitsu; Tachi, Yukio
no journal, ,
no abstracts in English
Hu, Q.*; Wang, Q.*; Zhao, C.*; Tachi, Yukio; Fukatsu, Yuta
no journal, ,
A low aqueous-phase diffusion in low-permeable clay barrier materials has been accepted as a critical process in the long-term performance evaluation of nuclear waste repository. Low-permeable clay materials whose pores are poorly interconnected are known to have anomalous diffusion properties that strongly impact long-term net diffusion. Related research works with mudrocks of Wakkanai formation of Horonobe URL in Japan, Opalinus clay of Mt. Terri URL in Switzerland, as well as various shale and clay mineral, utilizes a complementary suite of pore structure characterization approaches (e.g., mercury intrusion porosimetry, small angle neutron scattering) and tracer experiments followed with micro-scale mapping with laser ablation-ICP-MS. These results presents the relationship between pore connectivity and anomalous diffusion in clay materials. Pore size is not the major contributor to slow fluid flow and radionuclide transport, the anomalous behavior appears to be caused by low pore connectivity.
Tachi, Yukio; Yotsuji, Kenji*; Fukatsu, Yuta; Sugiura, Yuki; Okubo, Takahiro*
no journal, ,
Understanding the radionuclide migration in clay minerals contained in the buffer material bentonite and rocks is important for the safety assessment of geological disposal of radioactive waste. The pore structures and the electrostatic interactions at the surface, formed by the clay mineral with a layered structure, are key components for developing the radionuclide migration model in clay minerals. In this study, in order to evaluate the influence of alteration from Na- to Ca-montmorillonite on radionuclide migration, the diffusion and sorption model was developed by considering the effects of both pore structures and electrostatic interactions in the compacted montmorillonite.
Hu, Q.*; Wang, Q.*; Oware, P.*; Tachi, Yukio; Fukatsu, Yuta; Ilavsky, J.*; Almer, J.*
no journal, ,
Tachi, Yukio; Ito, Tsuyoshi*; Fukatsu, Yuta; Akagi, Yosuke*; Sato, Hisao*; Martin, A. J.*
no journal, ,
