Seismic response of canisters embedded in a repository analyzed through centrifuge modeling

Abstract

High-level waste (HLW), one of the most poisonous materials known to science, includes spent fuel from nuclear power plants. Therefore, nuclear engineers seek to isolate HLW from the Earth's biosphere by using multibarrier systems, including engineered and natural barriers deep below the surface of the earth. Typically, disposal holes are drilled into intact rocks. Canisters and buffer materials are then placed in the drilled holes. These highly stable canisters should not be easily affected by the natural environment, human activities, and tectonic movement. However, Taiwan is located in the Ring of Fire of the Pacific Ocean; thus, earthquakes threaten Taiwan frequently. Consequently, scholarly investigations must expand knowledge regarding the effects of earthquake-induced vibration on the canisters and buffer materials placed in the drilled holes and on the disposal system. This study assumes that the relevant disposal holes are created in granite deposit layers and have no deformations and cracks. The methods and geometry of the KBS-3 V system were examined; in this study a physical apparatus one-tenth the size of the KBS-3 V system was designed. The one-tenth-scale physical apparatus was subjected to an artificial acceleration field of 10 g as a simulation of the in-situ stress between the canisters and buffer material. The physical model was positioned on a shaking table and subjected to simulated seismic events. During shaking, sensors measured the acceleration, pore water pressure, and total pressure values to determine the interactive behavior between canisters and buffer materials during seismic activity. Six models were developed with different initial water content and hydration conditions; these models simulated the state of the buffer material after construction, after underground water invasion of the disposal hole, and after saturation of the buffer material. After centrifuge modeling had been conducted, the container was disassembled to check for crack development in the surrounding buffer material. The results can be used to distinguish the difference between each stage of buffer blocks and to determine the behavior of canisters during shaking; thus, these results can be employed to design HLW repositories in seismically active zones.