Hydraulic properties of bentonite buffer material beyond 100 °C

Bentonite buffer materials are important components of engineered barrier systems for the disposal of high-level radioactive waste produced during nuclear power generation. The design temperature of the buffer material is < 100 °C, and increasing the design temperature can reduce the required disposal area. This characteristic necessitates the evaluation of the thermal–hydraulic–mechanical properties of the buffer at temperatures above 100 °C to increase its target temperature. Therefore, the hydraulic properties of Gyeongju (KJ) bentonite buffer material were evaluated in this study, including the soil–water characteristic curve (SWCC) and hydraulic conductivity. An experimental system was manufactured to measure the suction and saturated hydraulic conductivity of KJ bentonite buffer material above 100 °C; the relative humidity of KJ bentonite buffer material was measured at 25–149 °C with an initial water content of 0, 0.06, and 0.12 under constant saturation conditions. The suction decreased as the temperature increased (10%–25% reduction at 99 °C-149 °C). The Van-Genuchten SWCC fitting parameters were also derived at 25 °C-149 °C using previously reported and newly generated experimental results, and the applicability of the modified Van-Genuchten SWCC model in this temperature range was verified. The hydraulic conductivity was proportional to temperature up to 100 °C, in agreement with the theoretical model results. Between 100 °C and 150 °C, the hydraulic conductivity increased nonlinearly because of molecular motion and structural changes inside the sample.