Horonobe Underground Research Laboratory Project; Investigation program for the fiscal year 2026

Nakayama, Masashi; Ishii, Eiichi; Aoyagi, Kazuhei; Hayano, Akira; Murakami, Hiroaki; Ono, Hirokazu; Ozaki, Yusuke; Mochizuki, Akihito; Iwai, Ryo; Kato, Yoshinari; et al.

JAEA-Review 2026-023, 64 Pages, 2026/08

JAEA-Review-2026-023.pdf:6.33MB

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 2026, 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", dismantling experiment will be conducted on the full-scale engineered barrier system performance experiment in the 350 m depth gallery. Regarding the "Demonstration of repository design options", tracer tests will be conducted in fractures surrounding the 250 m depth gallery and within the excavation damaged zone (EDZ) of the 500 m depth gallery in order to evaluate containment performance at both tunnel and pit scales. Vertical boreholes will be drilled from the floor of the 500 m depth gallery to assess the extent of the EDZ and the volume of water flow, which will inform the selection of the test pit location. A monitoring and assessment plan will then be established to evaluate the EDZ during pit excavation, including analytical approaches for EDZ characterization and their application to tunnel support design. Based on the outcomes of hydraulic disturbance tests performed in the 350 m depth gallery, an assessment will be conducted to evaluate the resistance of pre-existing fractures and faults to displacement. In addition, while continuing to collect the data required to address the issues outlined above, operational monitoring and maintenance inspections of the underground facility equipment will be conducted. Furthermore, 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.

Horonobe Underground Research Laboratory Project; Investigation program for the fiscal year 2025

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.

Decommissioning report for Wastewater Treatment Facility (Part 2); Chapter on contamination inspection section

Yamamoto, Keisuke; Nakagawa, Takuya; Shimojo, Hiroto; Kijima, Jun; Miura, Daiya; Onose, Yoshihiko*; Namba, Koji*; Uchida, Hiroaki*; Sakamoto, Kazuhiko*; Ono, Chika*; et al.

JAEA-Technology 2024-019, 211 Pages, 2025/02

JAEA-Technology-2024-019.pdf:35.35MB

The uranium enrichment facilities at the Nuclear Fuel Cycle Engineering Laboratories of Japan Atomic Energy Agency (JAEA) were constructed sequentially to develop uranium enrichment technology with centrifugal separation method. The developed technologies were transferred to Japan Nuclear Fuel Limited until 2001. And the original purpose has been achieved. Wastewater Treatment Facility, one of the uranium enrichment facilities, was constructed in 1976 to treat radioactive liquid waste generated at the facilities, and it finished the role in 2008. In accordance with the Medium/Long-Term Management Plan of JAEA Facilities, interior equipment installed in this facility had been dismantled and removed since November 2021 to August 2023. This report summarizes the findings obtained through the work related to the contamination inspection methods cancellation the controlled area of Wastewater Treatment Facility from September 2023 to March 2024.

A Terrestrial SER Estimation Methodology Based on Simulation Coupled With One-Time Neutron Irradiation Testing

Abe, Shinichiro; Hashimoto, Masanori*; Liao, W.*; Kato, Takashi*; Asai, Hiroaki*; Shimbo, Kenichi*; Matsuyama, Hideya*; Sato, Tatsuhiko; Kobayashi, Kazutoshi*; Watanabe, Yukinobu*

IEEE Transactions on Nuclear Science, 70(8, Part 1), p.1652 - 1657, 2023/08

https://doi.org/10.1109/TNS.2023.3280190

Single event upsets (SEUs) caused by neutrons is a reliability problem for microelectronic devices in the terrestrial environment. Acceleration tests using white neutron beam provide realistic soft error rates (SERs), but only a few facilities can provide white neutron beam in the world. If single-source irradiation applicable to diverse neutron source can be utilized for the evaluation of the SER in the terrestrial environment, it contributes to solve the shortage of beam time. In this study, we investigated the feasibility of the SER estimation in the terrestrial environment by any one of these measured data with the SEU cross sections obtained by PHITS simulation. It was found that the SERs estimated by our proposed method are within a factor of 2.7 of that estimated by the Weibull function. We also investigated the effect of simplification which reduce the computational cost in simulation to the SER estimation.

Impacts of freeze-thaw processes and subsequent runoff on Cs washoff from bare land in Fukushima

Igarashi, Yasunori*; Onda, Yuichi*; Wakiyama, Yoshifumi*; Yoshimura, Kazuya; Kato, Hiroaki*; Kozuka, Shohei*; Manome, Ryo*

Science of the Total Environment, 769, p.144706_1 - 144706_9, 2021/05

https://doi.org/10.1016/j.scitotenv.2020.144706

Irradiation damages of structural materials under different irradiation environments

Wakai, Eiichi; Takaya, Shigeru; Matsui, Yoshinori; Nagae, Yuji; Kato, Shoichi; Suzudo, Tomoaki; Yamaguchi, Masatake; Aoto, Kazumi; Nogami, Shuhei*; Hasegawa, Akira*; et al.

Journal of Nuclear Materials, 543, p.152503_1 - 152503_16, 2021/01

https://doi.org/10.1016/j.jnucmat.2020.152503

Author correction; Radionuclides from the Fukushima Daiichi Nuclear Power Plant in terrestrial systems

Onda, Yuichi*; Taniguchi, Keisuke*; Yoshimura, Kazuya; Kato, Hiroaki*; Takahashi, Junko*; Wakiyama, Yoshifumi*; Coppin, F.*; Smith, H.*

Nature Reviews Earth & Environment (Internet), 1(12), P. 694_1, 2020/12

https://doi.org/10.1038/s43017-020-00119-7

Reconstruction of a Fukushima accident-derived radiocesium fallout map for environmental transfer studies

Kato, Hiroaki*; Onda, Yuichi*; Gao, X.*; Sanada, Yukihisa; Saito, Kimiaki

Journal of Environmental Radioactivity, 210, p.105996_1 - 105996_12, 2019/12

https://doi.org/10.1016/j.jenvrad.2019.105996

Evaluation of hydrogeochemical processes provoked by tunnel excavation and closure based on simulated experiment in a mock-up test drift

Hayashida, Kazuki; Kato, Toshihiro*; Kubota, Mitsuru*; Murakami, Hiroaki; Amano, Yuki; Iwatsuki, Teruki

Chikyu Kagaku, 52(1), p.55 - 71, 2018/03

https://doi.org/10.14934/chikyukagaku.52.55

In this study, the simulated experimental drift was constructed in the granite of 500 m depth at Mizunami Underground Research Laboratory, and the hydrochemical process after the drift closure was observed. The groundwater chemistry around the drift changed with the change of the groundwater flow in the fractures when the gallery was constructed. The redox potential increased due to the infiltration of oxygen from the drift into the rock. After closing the drift, the redox potential of the groundwater plunged due to microbial activity, while the groundwater became alkalized conditon due to the influence of cement material such as shotcrete. The amount of cement material consumed for this alkalization was small, and it was considered that its influence would last long in accordance with the amount of cement used.

Evaluation of radiocaesium wash-off by soil erosion from various land uses using USLE plots

Yoshimura, Kazuya; Onda, Yuichi*; Kato, Hiroaki*

Journal of Environmental Radioactivity, 139, p.362 - 369, 2015/01

https://doi.org/10.1016/j.jenvrad.2014.07.019