Thermo-Hydro-Mechanical Coupled Modeling of In-Situ Behavior of the Full-Scale Heating Test in the Callovo-Oxfordian Claystone

Within the context for deep geological disposal (DGD) of high-level radioactive waste(HLW), thermo-hydro-mechanical (THM) coupled numerical modeling has become significantly important for studying the safe disposal of HLW. In this work, a 3D mechanical module is incorporatedinto the thermal-hydraulic (TH) coupled code TOUGH2, thus forming an integrated THM coupledsimulator referred to as TOUGH2Biot. The Galerkin finite element method is used to discretizethe space for rock mechanical calculation. The mechanical process is sequentially coupled with thefluid and heat flow processes, which further gives feedback to the flow through stress-dependenthydraulic properties (e.g., porosity and permeability). Based on the available geological data atthe Meuse/Haute-Marne Underground Research Laboratory (MHM URL) in France, the improvedsimulator is used to analyze the coupled THM behaviors of the Callovo-Oxfordian claystone (COx)induced by thermal loading. The anisotropy of material parameters (e.g., permeability and thermalconductivity) caused by the bedding and of in-situ stresses are well considered in our model. The numerical simulation can reasonably reproduce the field observations, including changes in temperatureand pore pressure at monitoring boreholes during the ALC1604 experiment. The modeling resultsindicate that the anisotropic effects are remarkable, and temperature, pore pressure, and effectivestress along the bedding increase more rapidly than in the vertical direction. Insight into numericalresults through the visual model is beneficial for helping us to interpret the field observations andto understand the complex THM problem in the COx claystone formation. The numerical methodand the modeling results presented in this work can be effectively used in support of performanceassessment studies of HLW disposal sites to build confidence in the safety of future applications ofnuclear energy systems.