Multiscale simulation of ion diffusion in unsaturated nanoscale porous media

The transport of ions in unsaturated porous media is an important fundamental process in many natural and technical settings. A realistic description of transport processes in unsaturated porous media in Reactive Transport Modelling (RTM) across scales is still an unresolved scientific challenge. The main scientific aim of this activity is to extend our previously developed multiscale model, which combines the pore-scale modeling with the molecular-scale simulation, to simulate ion diffusion in unsaturated nanoscale porous media. The other aim of this visit is to contribute to the realization of the joint (PSI-FZJ) research activity within DONUT, which included the development of upscaling approaches. During this two-week visit, we organized two formal meetings to discuss the cross-scale simulation of ion diffusion in unsaturated nanoscale porous media, relevant to the deep geological disposal of nuclear waste. The general framework of this simulation is to first build the liquid-gas distributions in microstructures by the Shen-Chen Lattice Boltzmann Method (LBM) and then to simulate the species diffusion in the liquid phase by LBM. After the simulations, the relationships of effective diffusivities with respect to the water content in clays will be presented. Several preliminary simulations showed that the water film on the clay surface controls solute diffusion at low water contents. The pore-scale simulation at the micrometer scale needs to be modified to consider the thin water films. We combined, in particular, the scientific expertise available at PSI with respect to pore-scale and continuum-scale reactive transport modeling with the advanced high-performance computing (HPC) resources provided by the Jülich Supercomputing Centre (JSC) to solve computationally demanding simulations. The intensive exchange with leading scientists from PSI also enhanced my knowledge and skills about the development of reactive transport models relevant within the context of radioactive waste management and deep geological disposal of radioactive waste.