Simulation of excavation and long-term permeability test at 350 m gallery in Horonobe Underground Research Laboratory based on large-scale three-dimensional coupled analysis

Suetake, Koya*; Ogata, Sho*; Yasuhara, Hideaki*; Aoyagi, Kazuhei; Inui, Toru*; Kishida, Kiyoshi*

Dai-16-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), p.304 - 309, 2025/01

It is very important to predict the extent of EDZ (excavation disturbed zone) and the behavior of hydraulic conductivity after excavation of shafts and tunnels for geological disposal of radioactive waste. In this study, we attempted to reproduce the in-situ tunnel excavation test and the subsequent permeability test at the Horonobe Underground Research Laboratory (URL) using a three-dimensional tunnel excavation simulator. As a result, similar results to the in-situ tests were obtained for the extent of EDZ propagation by excavation and the results of permeability tests. The simulator is effective in predicting the mechanical effects of excavation, coupled phenomena such as deformation and seepage, and hydraulic conductivity in deep mudstones in Japan.

Effect of grain refinement on transgranular stress corrosion cracking in SUS304L under boiling water reactor conditions

Hirota, Noriaki; Nakano, Hiroko; Takeda, Ryoma; Ide, Hiroshi; Tsuchiya, Kunihiko; Kobayashi, Yoshinao*

Zairyo No Kagaku To Kogaku, 61(6), p.248 - 252, 2024/12

A comparative analysis of the 0.2 % yield stress in SUS304L stainless steel revealed that lower strain rates and higher temperatures significantly reduce yield stress. Grain refinement from 68.6 m to 0.59 m minimally impacted the rate of yield stress reduction at slower strain rates. However, finer grains showed a decrease in yield stress at reactor operating temperature compared to room temperature. In slow strain rate tests under conditions promoting intragranular stress corrosion cracking (SCC), SUS304L with grain sizes of 28.4 m or smaller exhibited similar fracture strains comparable to those at reactor operating temperatures, whereas coarse-grained SUS304L showed reduced fracture strain. Microstructural analysis showed that in smaller grains, over 87 % of the fracture surface was ductile. In particular, SUS304L with 0.59 m grains exhibited a higher presence of {111} / 3 boundaries, which decreased with grain growth. These results indicate that grain refinement will suppress intragranular SCC by slowing corrosion progression through increased {111} / 3 boundaries.

Uncertainty analysis of model selection based on information criterion; A Case study of a probability estimation model for fuel cladding tube fracture during LOCA

Narukawa, Takafumi; Udagawa, Yutaka

Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03

Behavior of FeCrAl-ODS cladding tube under loss-of-coolant accident conditions

Narukawa, Takafumi; Kondo, Keietsu; Fujimura, Yuki; Kakiuchi, Kazuo; Udagawa, Yutaka; Nemoto, Yoshiyuki

Journal of Nuclear Materials, 582, p.154467_1 - 154467_12, 2023/08

https://doi.org/10.1016/j.jnucmat.2023.154467

Modelling heterogeneous hydration behaviour of bentonite by a FracMan-Thames coupling method for the Bentonite Rock Interaction Experiment (BRIE) at sp HRL

Sawada, Atsushi; Sakamoto, Kazuhiko*; Watahiki, Takanori*; Imai, Hisashi*

SKB P-17-06, 154 Pages, 2023/08

Recent improvements of probabilistic fracture mechanics analysis code PASCAL for reactor pressure vessels

Lu, K.; Takamizawa, Hisashi; Katsuyama, Jinya; Li, Y.

International Journal of Pressure Vessels and Piping, 199, p.104706_1 - 104706_13, 2022/10

https://doi.org/10.1016/j.ijpvp.2022.104706

Development plan of failure mitigation technologies for improving resilience of nuclear structures

Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*

Transactions of the 26th International Conference on Structural Mechanics in Reactor Technology (SMiRT-26) (Internet), 8 Pages, 2022/07

Utilizing fracture control, we are developing a technology to suppress the expansion of damage caused by an event that exceeds the design assumption. We made a plan to develop three issues; (1) Technology for mitigating failure consequence at extremely high temperatures, (2) Technology for mitigating failure consequence against excessive earthquakes, and (3) Methodology for improving reactor structure resilience.

Long-term density-dependent groundwater flow analysis and its effect on nuclide migration for safety assessment of high-level radioactive waste disposal with consideration of interaction between fractures and matrix of rock formation in coastal crystalline groundwater systems

Park, Y.-J.*; Sawada, Atsushi; Ozutsumi, Takenori*; Tanaka, Tatsuya*; Hashimoto, Shuji*; Morita, Yutaka*

Proceedings of 3rd International Conference on Discrete Fracture Network Engineering (DFNE 2022) (Internet), 8 Pages, 2022/00

Safety analysis for underground disposal facilities for high-level radioactive waste requires thorough understanding of long-term groundwater flow and nuclide migration processes in geologic media. In the coastal subsurface systems, groundwater flow is defined by the complex interactions between freshwater of meteoric origin and denser saline water from the sea. In addition, sea levels are expected to fluctuate significantly due to a transgression and regression of the sea over the millions of years for safety analysis. This study presents long-term evolution of groundwater environment such as salinity concentration and flow velocity with focus of the interaction between fractures and matrix blocks in regional and near-field scale analysis framework for groundwater flow and nuclide migration for underground disposal facilities in hypothetical fractured crystalline coastal systems.

A Scaling approach for retention properties of crystalline rock; Case study of the in-situ long-term sorption and diffusion experiment (LTDE-SD) at the sp Hard Rock Laboratory in Sweden

Tachi, Yukio; Ito, Tsuyoshi*; Gylling, B.*

Water Resources Research, 57(11), p.e2020WR029335_1 - e2020WR029335_20, 2021/11

https://doi.org/10.1029/2020WR029335

This paper focuses on the scaling approach for sorption and diffusion parameters from laboratory to in-situ conditions using the dataset of LTDE-SD experiment performed at the sp HRL. The near-surface heterogeneities at both fracture surface and rock matrix could be evaluated by conceptual model with high porosity and diffusivity, and sorption capacity, and their gradual change at the near-surface zones. The modelling results for non-sorbing Cl-36 and weak-sorbing Na-22 could validate the model concept and the parameter estimation of porosity and diffusivity, by considering the disturbed zone of 5 mm thickness with gradual parameter changes. The De values of these cationic and anionic tracers showed typical cation excess and anion exclusion effects. The modelling results for high sorbing tracers (Cs-137, Ra-226, Ni-63 and Np-237) with different sorption mechanism could confirm the validity of the scaling approaches of Kd values as a function of particle size and their relation to the near-surface disturbances.

Application of probabilistic fracture mechanics to reactor pressure vessel using PASCAL4 code

Lu, K.; Katsuyama, Jinya; Li, Y.; Yoshimura, Shinobu*

Journal of Pressure Vessel Technology, 143(2), p.021505_1 - 021505_8, 2021/04

https://doi.org/10.1115/1.4048103