Numerical Analysis of Coupled Thermo-Hydro-Mechanical (THM) Behavior of In-situ Demonstration of Engineered Barrier System (In-DEBS) in Early Stage of Operation

Coupled thermo-hydraulic (TH) behavior is expected owing to a decay heat from high-level radioactive waste and water intake from rockmass in high-level radioactive waste disposal system. And coupled thermo-hydro-mechanical (THM) behavior is expected in high-level radioactive waste disposal system owing to thermal stress and swelling pressure generated by changes in temperature and saturation. Since 2016, an in-situ demonstration of an engineered barrier system (In-DEBS) at the KAERI Underground Research Tunnel (KURT) has been performed to investigate the coupled THM behavior in the high-level radioactive waste disposal system and nearby rockmass. In this study, a numerical simulation using TOUGH-MP/FLAC3D and an axisymmetric model was carried out to analyze the in-situ experimental data and estimate the coupled THM behavior. In addition, input parameters and THM models used in this study are evaluated and the practical applicability of TOUGH2-MP/FLAC3D to THM simulations is examined by comparison of in-situ data with calculation results. Temperature and relative humidity evolutions are well captured in the numerical simulation. In addition, even though the calculated displacement is relatively small, its evolution trend shows agreement with the in-situ data. The axisymmetric model was useful for analyzing coupled THM behavior in the In-DEBS experiment however, a 3D analysis including a consideration of the effect of KURT geometry is necessary to thoroughly investigate coupled THM behavior in the rockmass. The input parameters and the THM models in this study can be applied to predict the long-term behavior in the In-DEBS experiment and to carry out a performance assessment of the coupled THM behavior in a high-level radioactive waste disposal system.