A multi-barrier can be applied for the deep geological disposal of high-level radioactive waste. The multi-barrier comprises an engineered barrier and the natural barrier of the host rock. In the engineered barrier, the bentonite buffer is the key component for the disposal container, and the bentonite buffer thickness is given important consideration when designing the engineered barrier. This study reviewed the safety functions of bentonite buffers. Subsequently, the requirements and factors necessary to determine the thickness of the bentonite buffer, including criteria for radiological safety and the thermal stability of the disposal system, were identified. Additionally, the bentonite buffer thicknesses required for the top, bottom, and side of the disposal container were calculated. A double-layered emplacement method is also proposed for the bentonite buffer to improve disposal efficiency in terms of thermal management. Based on radiological safety and thermal stability analyses, an optimal thickness of 0.36 m was found to be appropriate for the bentonite buffer surrounding the disposal container. The thickness of the bentonite buffer above the disposal container can be determined based on the excavation damaged zone depth. The study findings can be used as a reference when designing deep geological disposal systems.

In Korea, two types of spent nuclear fuels (SNFs) are generated, pressurized light water reactor type (PWR) and pressurized heavy water reactor type (PHWR; CANDU), that differ greatly in size, decay heat, and radioactive characteristics. Technology development for the disposal of SNFs has mainly focused on PWR SNFs that are large in size and have extremely high decay heat and radioactivity. However, CANDU SNFs should be considered differently from PWR SNFs in deep geological disposal systems because their characteristics significantly differ from those of PWR SNFs in terms of their dimensions, number of SNF bundles, and handling systems in nuclear power plant sites. In this paper, after reviewing the status of the CANDU SNF disposal concept by Canada and Korea, concepts related to the direct geological disposal of CANDU SNFs were described, and two concepts were proposed based on the results of the development. The engineered barrier systems developed using these two concepts were comparatively analyzed in terms of disposal safety, disposal efficiency, and technical maturity. Based on the results of the comparative analyses, a vertical-type emplacement disposal concept was determined as a reference concept for the deep geological disposal of CANDU SNFs.

Disposal cover as an engineered barrier of a near-surface disposal facility for low and very low-level radioactive waste is composed of a multi-layer to isolate radioactive waste from environmental influences for the long term. To acquire a realistic forecast for the post-closure period of the disposal facility, it is essential to carry out long-term experimental research in a similar condition to the actual disposal environment. Hence, a performance test facility of the disposal cover was constructed in Gyeongju low and intermediate level radioactive waste disposal center in 2022. The constructed performance test facility has differences from the material properties presented in the design. These differences are factors that affect the prevent rainfall infiltration, which is one of the important roles of the disposal cover. Therefore, in this study, a numerical simulation of rainfall infiltration into the performance test facility was performed for the designed case and the actual constructed case. To simulate the behavior of water infiltration, the FEFLOW software based on the finite element method is used. Through the analysis of numerical simulation results, it is confirmed that the hydraulic conductivity of the material constituting the multi-layer of the disposal cover greatly influences the amount of water infiltration.