Hydraulic properties of bentonite buffer material beyond 100 °C

Area of Science:

• Geotechnical Engineering
• Nuclear Engineering
• Materials Science

Background:

• Bentonite is vital for engineered barrier systems in high-level radioactive waste disposal.
• Current design temperatures (<100°C) limit disposal efficiency; higher temperatures require evaluating thermal-hydraulic-mechanical properties.
• Increasing buffer material temperature can reduce the necessary disposal area.

Purpose of the Study:

• To evaluate the hydraulic properties of Gyeongju (KJ) bentonite buffer material at elevated temperatures (>100°C).
• To investigate the impact of temperature on soil-water characteristic curve (SWCC) and hydraulic conductivity.
• To assess the applicability of the Van-Genuchten SWCC model at high temperatures.

Main Methods:

• Manufactured an experimental system to measure suction and saturated hydraulic conductivity above 100°C.
• Measured relative humidity of KJ bentonite at 25-149°C with varying initial water content (0, 0.06, 0.12).
• Derived Van-Genuchten SWCC fitting parameters using experimental data from 25°C-149°C.

Main Results:

• Suction decreased with increasing temperature (10%-25% reduction from 99°C-149°C).
• The modified Van-Genuchten SWCC model showed applicability in the tested temperature range.
• Hydraulic conductivity increased nonlinearly with temperature above 100°C due to molecular motion and structural changes.

Conclusions:

• Elevated temperatures significantly impact bentonite's hydraulic properties, reducing suction and increasing hydraulic conductivity.
• Findings support increasing the target temperature for bentonite buffer materials in radioactive waste disposal.
• The study validates the modified Van-Genuchten model for predicting SWCC at high temperatures.