Abstract:
A coupled thermos-hydro-mechanical-chemical (THMC) numerical model is presented to predict the long-term change in permeability of the porous rocks that are composed purely of quartz. Especially, the chemo-mechanical process of the pressure dissolution is explicitly taken into account in the model. By simulating the burial of high-level radioactive wastes in the deep subsurface (i.e., by applying the simulated confining pressure and temperature conditions), the long-term evolution of the rock permeability was predicted using the model. The predictions obtained a significant influence of the pressure dissolution on the change in permeability with time. The predicted permeability of the rocks close to the wastes decreased by roughly one order of magnitude in 104 years when considering the pressure dissolution, while the permeability changed little during the same period when the pressure dissolution was not considered. The reduction should delay the transportation of the radioactive materials.
Introduction
It is important to address the coupled thermo-hydro-mechanical-chemical processes when projecting a long-term underground isolation of the high-level radioactive wastes. The rocks that work as natural barriers to the migration of radionuclides should be influenced by the coupled phenomena, including the transfer of heat from the wastes, the groundwater flow, the variation in induced stresses, and the geochemical reactions, such as mineral dissolution and precipitation [1], [2]. Therefore, in order to predict the long-term evolution of the hydraulic property, a numerical model that can account for the coupled thermo-hydro-mechanical-chemical (THMC) processes is required.
In this study, a coupled THMC numerical model that includes the important process of the pressure dissolution, as well as the free-face dissolution and precipitation, is presented [3]. Then, the long-term evolution of the permeability in porous rock was predicted under the expected stress and temperature conditions where high-level radioactive wastes are disposed. In particular, the influence of the pressure dissolution on the change in the rock permeability was examined intensively.
