Investigation of physical mechanisms behind full-scale engineered barrier systems through coupled thermal-hydraulic-mechanical (THM) simulations

This work presents simulation results of the FEBEX experiment, performed using the 2019 rendition of the coupled thermal-hydraulic-mechanical-chemical simulator, HYDROGEOCHEM 5.3 (HGC 5.3 Taiwan Power Company version). These simulations were carried out as part of the DECOVALEX-2019 project. The simulations consider the variably saturated flow, thermal transport, and linear geomechanics, including the effects of bentonite swelling. This study systematically investigates the hydro-thermal-mechanical processes in bentonite, which services as the sealing material in a near-field full-scale engineering barrier system. It explores important issues such as how the engineering barrier in the disposal site undergoes resaturation processes, thermal transport processes, and the resulting stress behavior. The simulation results are compared with experiments to understand the underlying physical mechanisms. We can qualitatively and quantitatively predict most of the experimental results, including the evolution and radial distribution of relative humidity, the evolution of heating power, the evolution as well as axial and radial distribution of temperature, the evolution of total stress, and the distribution of degree of saturation and moisture content for the first and final dismantling.

Through this study, we aim to better understand the dominant physical mechanisms behind the evolution of material properties of engineering barriers. This understanding will enable us to evaluate the functions of near-field engineering barriers and improve the numerical technical capabilities for the safety assessment and analysis of nuclear waste disposal. The insights gained from this research can be applied to address important environmental issues involving these fundamental processes, particularly the safety of nuclear waste disposal repositories that use bentonite as a buffer or backfill material.