Synthesis report on the R&D for the Horonobe Underground Research Laboratory Project carried out between fiscal years 2020-2024

Nakayama, Masashi; Ishii, Eiichi; Aoyagi, Kazuhei; Hayano, Akira; Ono, Hirokazu; Ozaki, Yusuke; Mochizuki, Akihito; Takeda, Masaki; Kimura, Shun

JAEA-Research 2025-016, 141 Pages, 2026/03

JAEA-Research-2025-016.pdf:13.37MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA). The main aim of the project is to enhance the reliability of relevant technologies for the geological disposal of high-level radioactive waste by investigating the deep geological environment within the host sedimentary rocks at Horonobe in Hokkaido, northern Japan. These investigations have been conducted in three phases: "Phase 1: Surface-based investigation", "Phase 2: Construction" (investigation during tunnel excavation) and "Phase 3: Operation" (investigation in subsurface facilities). Since the fiscal year 2020, we have been conducting R&D based on the Horonobe Underground Research Plan for the Fiscal Year 2020 Onwards, which was approved by Hokkaido Prefecture and Horonobe Town. In particular, we are working on the following key tasks with the aim of completing JAEA's 3rd and 4th Mid- and Long-Term Plans: "Study on near-field system performance in geological environments", "Demonstration of repository design options" and "Understanding of buffering behaviour of sedimentary rocks to natural perturbations". This report summarizes the R&D activities on the three above-mentioned key tasks, the goals of which were achieved between fiscal years 2020 and 2024. The results obtained from these tasks will be systematically organized as part of the "Systematic integration of technologies towards EBS emplacement" which has been in progress since fiscal year 2024. This task includes concepts related to the layout of galleries and pits, installation methods for engineered barrier materials, and methods for evaluating their containment performance.

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.

Numerical simulation of coupled THM behaviour of full-scale EBS in backfilled experimental gallery in the Horonobe URL

Sugita, Yutaka; Ono, Hirokazu; Beese, S.*; Pan, P.*; Kim, M.*; Lee, C.*; Jove-Colon, C.*; Lopez, C. M.*; Liang, S.-Y.*

Geomechanics for Energy and the Environment, 42, p.100668_1 - 100668_21, 2025/06

https://doi.org/10.1016/j.gete.2025.100668

The international cooperative project DECOVALEX 2023 focused on the Horonobe EBS experiment in the Task D, which was undertaken to study, using numerical analyses, the thermo-hydro-mechanical (or thermo-hydro) interactions in bentonite based engineered barriers. One full-scale in-situ experiment and four laboratory experiments, largely complementary, were selected for modelling. The Horonobe EBS experiment is a temperature-controlled non-isothermal experiment combined with artificial groundwater injection. The Horonobe EBS experiment consists of the heating and cooling phases. Six research teams performed the THM or TH (depended on research team approach) numerical analyses using a variety of computer codes, formulations and constitutive laws.

Modeling of coupled processes in full-scale engineered barrier system performance experiment at Horonobe Underground Research Laboratory, Japan

Ono, Hirokazu; Takayama, Yusuke*

Geomechanics for Energy and the Environment, 41, p.100636_1 - 100636_14, 2025/03

https://doi.org/10.1016/j.gete.2025.100636

Horonobe Underground Research Laboratory Project; Investigation program for the fiscal year 2024

Nakayama, Masashi

JAEA-Review 2024-033, 64 Pages, 2024/09

JAEA-Review-2024-033.pdf:5.15MB

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 2024, we continue R&D on "Study on near-field system performance in geological environment", "Demonstration of repository design options", and "Understanding of buffering behaviour of sedimentary rocks to natural perturbations". 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. We summarise the solute transport experiments for the excavation damaged zone and the effects of organic matter, micro-organisms and colloids, and develop the assessment methodology. We summarise the evaluation methodology using the deep Wakkanai Formation as a case study for block-scale solute transport experiments. As for "Demonstration of repository design options", we summarise the results of investigations and experiments on changes in the geological environment after tunnel excavation and closure, and summarise the applicability and technical challenges of the closure technology for boreholes excavated from tunnels. The systematic integration of technologies towards EBS emplacement, including the organisation of investigation and evaluation methods and analysis, will be promoted. Experiments to confirm the performance of the engineered barrier system under critical conditions, such as high temperatures (100C), continue the in-situ tests started in 2023.

Horonobe Underground Research Laboratory Project Investigation Report for the 2022 Fiscal Year

Nakayama, Masashi

JAEA-Review 2023-032, 159 Pages, 2024/02

JAEA-Review-2023-032.pdf:19.37MB

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 Town in Hokkaido, north Japan. In the fiscal year 2022, 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 100C" were addressed for "Demonstration of repository design options". A study on "Understanding of buffering behaviour of sedimentary rock to natural perturbations" was also implemented in two areas, "evaluation of intrinsic buffering against endogenic and exogenic processes" and "development of techniques for evaluating excavation damaged zone (EDZ) self-sealing behaviour after backfilling". The Horonobe International Project (HIP) was initiated in February 2023 to promote research and development in collaboration with national and international organizations.

Horonobe Underground Research Laboratory Project; Investigation program for the 2022 fiscal year

Nakayama, Masashi

JAEA-Review 2022-026, 66 Pages, 2022/11

JAEA-Review-2022-026.pdf:12.31MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies for geological disposal of High-level Radioactive Waste through investigations of the deep geological environment within the host sedimentary rock at Horonobe Town in Hokkaido, north Japan. In fiscal year 2022, we continue to conduct research on "Study on near-field system performance in geological environment", "Demonstration of repository design options", and "Understanding of buffering behaviour of sedimentary rocks to natural perturbations", which are the important issues shown in the Horonobe underground research plan from fiscal year 2020. The main studies to be conducted in fiscal year 2022 are as follows. As "Study on near-field system performance in geological environment", we will continue to the test under the simulated condition in which the heat generation by the high-level radioactive waste has subsides in the full-scale engineered barrier system (EBS) performance experiment. We will also conduct solute transport experiment with model testing that take into account the effects of organic matter, microbes, and colloids, and initiate borehole investigation to evaluate solute transport experiments on fractures distribute in Koetoi formation. As "Demonstration of repository design concept", we will continue experiment and analysis of concrete deterioration in the underground environment as a demonstration of remote technique for emplacement and retrievable. As a demonstration of the closure techniques, laboratory tests will be continued to investigate the mechanism of bentonite runoff behaviour, which could be a factor in changing the performance of backfill material, and to expand data on swelling and deformation behaviour. In addition, in-situ borehole closure tests will be conducted to evaluate the applicability of the closure method. As "Understanding of buffering behaviour of

Horonobe Underground Research Laboratory Project; Investigation report for the 2020 fiscal year

Nakayama, Masashi

JAEA-Review 2021-053, 133 Pages, 2022/02

JAEA-Review-2021-053.pdf:14.45MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA). The main aim of this project is to enhance the reliability of relevant disposal technologies for geological disposal of high-level radioactive waste through a comprehensive research and development (R&D) program in the deep geological environment within the host sedimentary rock at Horonobe in Hokkaido, north Japan. In fiscal year 2020, JAEA continued R&D on three important issues specified in the "Horonobe Underground Research Plan from Fiscal Year 2020", which involve "Study on nearfield system performance in geological environment", "Demonstration of repository design options", and "Understanding of buffering behavior of sedimentary rock to natural perturbations". Specifically, 'full scale engineered barrier system (EBS) experiment' and 'solute transport experiment' were carried out as part of "Study on near-field system performance in geological environment". 'Development and testing of EBS emplacement / retrieval and tunnel closure technologies' and 'evaluation of EBS behavior over 100C' were addressed for "Demonstration of repository design options". A study on "Understanding of buffering behavior of sedimentary rock to natural perturbations" was also implemented in two areas, 'evaluation of hydromechanical responses of faults to water pressure changes' and 'development of techniques for evaluating self-sealing behavior of an excavation damaged zone after backfilling'. The results of the R&D, along with those obtained in other departments of JAEA, will reinforce the technical basis for both repository implementation and safety regulation. For the sake of this, JAEA will steadily proceed with this project in collaboration with relevant organizations and universities both domestically and internationally and also widely publish the plans and results of the R&D to ensure their transparency and technical reliability.

Horonobe Underground Research Laboratory Project; Investigation program for the 2021 fiscal year

Nakayama, Masashi

JAEA-Review 2021-009, 54 Pages, 2021/07

JAEA-Review-2021-009.pdf:5.02MB

The Horonobe URL Project is being pursued by the JAEA to enhance the reliability of relevant disposal technologies for geological disposal of High-level Radioactive Waste through investigations of the deep geological environment within the host sedimentary rock at Horonobe Town in Hokkaido, north Japan. In 2021 fiscal year (2021/2022), JAEA continue to conduct research on "Demonstration of EBS in geological environment", "Demonstration of disposal concept", and "Validation of buffer capacity of the sedimentary rock to tectonism", which are the important issues shown in the Horonobe underground research plan after 2020 fiscal year. The main studies to be conducted in 2021 fiscal year are as follows. As "Demonstration of EBS in geological environment", we will shift to the test under the condition that the influence of heating is eliminated in the full scale EBS experiment. As "Demonstration of disposal concept", as a demonstration of the closure techniques, it details the conditions under which long-term transitions in the tunnel and surrounding bedrock have a significant impact on safety assessments. And we will continue engineering scale experiment to confirm the workability and performance of plugs and laboratory tests to examine the interaction between backfilling materials and buffer materials. As "Validation of buffer capacity of the sedimentary rock to tectonism", we will analyze the results of the hydraulic disturbance test and continue to study the hydraulic disconnection of faults/fissures in the Wakkanai Formation. As an advancement of technology for investigating and evaluating areas where the flow of groundwater is extremely slow, a boring exploration will be conducted to confirm the three-dimensional distribution of the fossil seawater area.

Backfill material characteristics using the bentonite/excavated rock mixture in the Horonobe Underground Research Laboratory Project (Contract research)

Sugita, Yutaka; Kikuchi, Hirohito*; Hoshino, Emiko*

JAEA-Data/Code 2020-017, 39 Pages, 2021/01

JAEA-Data-Code-2020-017.pdf:2.96MB

In Japan, high-level radioactive waste (HLW) will be buried in a purpose built repository in deep underground. In the vertical disposal concept of HLW, nuclear waste canisters will be emplaced in excavated vertical disposal holes, surrounded by bentonite/sand mixture. And the galleries will be backfilled with bentonite/excavated rock mixture, which will be isolated with a concrete plug. Japan Atomic Energy Agency has performed swelling test, permeability test, thermal property measurement, uniaxial compression test, water potential measurement and infiltration tests to identify coupled thermal-hydraulic-mechanical-chemical behavior that will operate in the backfill material using excavated rock in the Horonobe Underground Research Laboratory (URL). The obtained data will be used to support an ongoing full scale, in-situ experiment being conducted in the Horonobe URL.