Journal of Nuclear Fuel Cycle and Waste Technology

This study examines the thermal relaxation and pressure attenuation behavior of Bentonil-WRK, a Ca-type bentonite, under a constant temperature of 130°C. A one-month pressure-measurement experiment was conducted using a stainless-steel cell equipped with a high-temperature load cell and a pressure–volume controller, applying hydration and thermal loading simultaneously. The specimen was compacted to a dry density of 1.60 g·cm^-3. Following initial heating and hydration, the measured total pressure reached approximately 3,700 kPa, after which it exhibited gradual, non-linear attenuation throughout the 30-day period. Five empirical attenuation models were evaluated, and the logarithmic model provided the best fit (R² = 0.996; RMSE = 6.82 kPa), capturing both the early attenuation and slow long-tail behavior. Using this model, the pressure trend was extrapolated to 1,000 years under a conservative assumption that thermal relaxation continues without convergence at 130°C. Because this study was limited to single-temperature, dry density, and hydration condition, the extrapolated results should be interpreted as a methodological demonstration rather than a prediction of repository performance. Nevertheless, the findings provide useful insights into the empirical characterization of thermal relaxation in Ca bentonites under elevated temperatures.

Keywords

Swelling pressure, Calcium bentonite, High temperature, Thermal relaxation, Pressure attenuation, Deep geological disposal