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The deep geological repository (DGR) system has been selected by most of the world's nuclear waste management organizations for the long-term disposal of radioactive wastes. The DGR mainly consists of a multi-barrier system—comprising the natural host rock and an engineered barrier system—to contain and isolate high-level radioactive waste, including used fuel containers (UFCs), to protect humans and the environment. Bentonite materials and host rock are the main components of the DGR's engineered and natural barrier system, respectively. It is crucial to understand the coupled behavior of bentonite and rock materials under various in situ conditions over long-term durations, as it supports safety assessments and enhances the overall safety level of DGR systems. This study presents a methodology for the numerical modeling of a hypothetical DGR using developed coupled models. The developed model was used to investigate the hydromechanical (HM) and thermomechanical (TM) response within the near-field (the area within a radius of 50 m near the UFC and multiple-barrier system) of a simplified hypothetical DGR, based on the proposed design concept of the Nuclear Waste Management Organization (NWMO) of Canada. The analysis results included the evolution of temperature, thermal stresses, saturation, and swelling pressure at different stages of the DGR system's lifetime. The results indicated that it could take up to 10,000 years to fully saturate the bentonite materials with a corresponding swelling pressure of 2.7 MPa associated with a decrease in the rock's strength/stress ratio near the placement room; however, the ratio did not indicate a significant system failure. Sensitivity analysis was also conducted to assess the impact of various parameters on the saturation time and the strength/stress ratio in a DGR. The results highlighted that saturation time was highly influenced by the permeability of both the rock formation and the bentonite, resulting in saturation times ranging from 500 to 20,000 years. Moreover, the strength/stress ratio was found to be sensitive to the model's parameters, particularly the maximum swelling pressure. The results of the TM analysis show that temperature development around the placement of rooms in a DGR is highly influenced by room spacing, with a lower factor of safety (FOS) as time and temperature progressed due to elevated temperature, while the rock remained stable over the 150-year analysis period. The inclusion of temperature-dependent mechanical properties produced negligible changes to the overall stability of the rock around the placement rooms of the DGR. [ABSTRACT FROM AUTHOR]

A typical deep geological repository (DGR) design consists of a multi-barrier system, including the natural host rock and the engineered barrier system. Understanding the swelling behavior of bentonite-based sealing materials (BBSM), as a candidate material for the engineered barrier system, is crucial for DGR's long-term safety. In this study, a hydromechanical (HM) column-type test was designed to model the hydration of BBSM from the underground water and determine the resulting swelling pressure in vertical and radial directions. Five hydration tests were carried out on identical compacted samples of 70% bentonite and 30% sand (70-30 bentonite-sand) mixtures with a dry density of 1.65 g/cm3 for varied durations of hydration, between 1 day and 120 days. The experiments were performed parallel to the compaction direction. Following each HM column-type test, the advancement of the wetting front was determined for each test. After 120 days, 56,339 mm3 of water infiltrated the sample and the wetting front reached over 50% of the sample height. The evolution of axial swelling pressure revealed an initial increase in swelling pressure with time in all tests, followed by a reduction in the rate at later times. After early stages of swelling, radial sensors showed an increase in swelling pressure. After 120 days, the radial pressure sensor closest to the hydration front showed 52% more radial pressure than the axial swelling pressure. [ABSTRACT FROM AUTHOR]