Long-term changes in the chemical, microstructural, and transport properties of a low-pH cement shotcrete during operation of the Horonobe Underground Research Laboratory, Japan

Mochizuki, Akihito; Matsui, Hiroya; Nakayama, Masashi; Sakamoto, Ryo*; Shibata, Masahito*; Motoshima, Takayuki*; Jo, Mayumi*

Case Studies in Construction Materials, 22, p.e04648_1 - e04648_20, 2025/07

https://doi.org/10.1016/j.cscm.2025.e04648

The properties of low-pH cement used in the geological disposal of radioactive waste may change through atmospheric carbonation and degradation caused by groundwater during the long-term operation of a repository. In this study, we investigated the effects of atmospheric carbonation and groundwater contact on the chemical, microstructural, and transport properties of shotcrete made from low-pH, high-fly-ash silica-fume cement (HFSC) over a period of 16 years in an underground research laboratory. In both carbonated and degraded zones of the HFSC shotcrete, capillary porosity increased for pores of 300 nm in diameter, and the total porosity was higher than in undegraded zones. These changes in porosity may be associated with the decalcification of calcium-silicate-hydrate and decomposition of ettringite. Such changes were minor in altered zones of OPC shotcrete, indicating that HFSC shotcrete is less resistant to atmospheric carbonation and groundwater leaching under the studied conditions. However, the hydraulic conductivity in HFSC was low enough to fulfill the specific functional requirements of low-pH cements for geological disposal.

DECOVALEX-2023: An International collaboration for advancing the understanding and modeling of coupled thermo-hydro-mechanical-chemical (THMC) processes in geological systems

Birkholzer, J. T.*; Graupner, B. J.*; Harrington, J.*; Jayne, R.*; Kolditz, O.*; Kuhlman, K. L.*; LaForce, T.*; Leone, R. C.*; Mariner, P. E.*; McDermott, C.*; et al.

Geomechanics for Energy and the Environment, 42, p.100685_1 - 100685_17, 2025/06

https://doi.org/10.1016/j.gete.2025.100685

Current status and future prospects of the Horonobe International Project

Aoyagi, Kazuhei; Ozaki, Yusuke; Hayano, Akira; Ono, Hirokazu; Tachi, Yukio

Nihon Genshiryoku Gakkai-Shi ATOMO, 67(6), p.354 - 358, 2025/06

https://doi.org/10.3327/jaesjb.67.6_354

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.

Comparative analysis of primary variables selection in modeling non-isothermal two-phase flow; Insights from EBS experiment at Horonobe URL

Kim, M.*; Lee, C.*; Sugita, Yutaka; Kim, J.-S.*; Jeon, M.-K.*

Geomechanics for Energy and the Environment, 41, p.100628_1 - 100628_9, 2025/03

https://doi.org/10.1016/j.gete.2024.100628

This study investigates the impact of primary variables selection on the modeling of non-isothermal two-phase flow, by using the numerical work on the full-scale Engineered Barrier System (EBS) experiment conducted at Horonobe URL as part of the DECOVALEX-2023 project. A validated numerical model is employed to simulate the coupled thermo-hydrological behavior of heterogeneous porous media within the EBS. Two different primary variable schemes are compared in discretizing the governing equations, revealing significant difference in results.

Results of environmental impact investigations as part of environmental monitoring investigation in backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (FY2023)

Takeuchi, Ryuji; Kokubu, Yoko; Nishio, Kazuhisa*

JAEA-Data/Code 2024-015, 68 Pages, 2025/02

JAEA-Data-Code-2024-015.pdf:4.25MB

The Tono Geoscience Center of Japan Atomic Energy Agency (JAEA) has been conducting the environmental monitoring investigation to confirm the environmental impacts associated with the backfilling of shafts and tunnels at the Mizunami Underground Research Laboratory (MIU). This report summarizes the results of the environmental impact investigations conducted as part of the environmental monitoring investigation around the MIU Site in FY2023, which include groundwater level measurement in wells, river flow rate measurement, water analysis of Hazama river, noise and vibration surveys, and soil survey.

Excavation damaged zone around a simulated disposal pit for high level radioactive waste disposal excavated in soft sedimentary rock

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.

Results of groundwater pressure and hydrochemical monitoring as part of environmental monitoring investigation in backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (FY2023)

Takeuchi, Ryuji; Kokubu, Yoko; Nishio, Kazuhisa*

JAEA-Data/Code 2024-011, 120 Pages, 2024/12

JAEA-Data-Code-2024-011.pdf:4.68MB
JAEA-Data-Code-2024-011-appendix(CD-ROM).zip:261.39MB

The Tono Geoscience Center of Japan Atomic Energy Agency (JAEA) has been conducting the groundwater pressure and hydrochemical monitoring to confirm the restoration process of the surrounding geological environment associated with the backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (MIU). This report summarizes the data of the groundwater pressure and hydrochemical monitoring from boreholes and so forth at and around the MIU conducted in FY2023.

Current status and future prospects of the Horonobe International Project (HIP), 2; Task A: Solute transport experiment with model testing

Ozaki, Yusuke

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.128 - 133, 2024/12

https://nuce.aesj.or.jp/jnuce/vol31/jnuce-vol31-2-p128-133.pdf

Task A of the Horonobe International Project (HIP) aims to investigate the characteristics of solute transport of the Koetoi Formation at 250 m stage of the Horonobe underground research laboratory (URL). The objective of this task is to develop a modeling approach of solute transport considering actual phenomena occurring in the rock based on in-situ tracer experiments along with the discussion on transferability of data and modeling approach from different geological environment. Phase 1 of task A is divided into four subtasks of planning of in situ experiments, laboratory experiments, field experiments, and modeling. These subtasks are tackled by participating organizations as collaborative research, and I present the current situation of each subtask and our cooperation.

Current status and future prospects of the Horonobe International Project; Importance of the international joint project in Horonobe Underground Research Project

Aoyagi, Kazuhei; Tachi, Yukio

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.124 - 127, 2024/12

https://nuce.aesj.or.jp/jnuce/vol31/jnuce-vol31-2-p124-127.pdf

Japan Atomic Energy Agency launched "Horonobe International Project (HIP)" utilizing the Horonobe Underground Research Laboratory. Currently, 11 organizations from 8 countries/regions are joining this project. The main objective of this project is 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. The research tasks consist of 1) Solute transport experiment with model testing, 2) Systematic integration of repository technology options, and 3) Full-scale EBS dismantling experiment. In these tasks, experimental galleries will be excavated and in situ experiments will be performed at these galleries, then the analysis and investigation methods will be validated. This is a unique and original aspect of the HIP and three research tasks described above are challenging from an international perspective. Thus, HIP can be a good practice of international collaboration utilizing the underground facility.

Relationship between fault transmissivity, flow dimensions and effective hydraulic conductivity in siliceous mudstone of the Wakkanai Formation around the Horonobe Underground Research Laboratory in Japan

Ozaki, Yusuke; Ishii, Eiichi

Geoenergy (Internet), 2(1), p.geoenergy2023-056_1 - geoenergy2023-056_11, 2024/12

https://doi.org/10.1144/geoenergy2023-056

This study estimated the effective hydraulic conductivity around the Horonobe URL from the monitoring data of inflow into shaft and change in hydraulic pressure measured in HDB-6 for over ten years. The effective hydraulic conductivity was related to the fault transmissivities and flow dimension using Landau-Lifshitz-Matheron's formula. From the comparison of the estimated effective hydraulic conductivity with the calculated fault transmissivities, the effective hydraulic conductivity was compatible with the transmissivities considering the dependency on ductility index and flow dimension.