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Ono, Hirokazu
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.140 - 143, 2024/12
In the geological disposal of high-level radioactive waste, after emplacement of an EBS, the near-field environment is affected by processes such as heat release from the waste, groundwater infiltration into the EBS, swelling and deformation of the buffer material, and chemical reactions between groundwater and minerals. It is crucial to develop simulation codes to evaluate such coupled thermal-hydraulic-stress-chemical (THMC) processes for safety assessment of geological disposal. The full-scale vertical-emplacement EBS experiment (Horonobe EBS experiment) has been undertaken in the 350 m gallery of the Horonobe Underground Research Laboratory (URL) with the Horonobe geological environment. In the Horonobe EBS experiment, various sensors were installed in the buffer and backfill material to obtain the data required to evaluate coupled THMC processes in near-field. In Task C of the Horonobe International Project (HIP), the dismantling experiment of the Horonobe EBS experiment will be carried out and the data obtained from this experiment will be used to understand the coupled processes and to evaluate the simulation code.
Nakayama, Masashi
JAEA-Review 2024-042, 111 Pages, 2024/11
JAEA-Review-2024-042.pdf:7.83MB
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 2023, 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 FY2023, we resumed construction of the subsurface facilities, 3 new tunnels in the 350 m gallery and resumed excavation of the East Access Shaft and the Ventilation Shaft. By the end of FY2023, the 350 m gallery extension (tunnel extension 66 m) had been completed, and the depths of the East Access Shaft and Ventilation Shaft were GL-424 m and GL-393 m respectively.
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.
