The potential release of radionuclides into the geosphere is an important problem in the disposal of nuclear waste. The speed that radionuclides travel can be accelerated due to their adsorption onto colloidal backfill materials like clay that move with groundwater. The transport of these radionuclide-carrying colloids is complicated by inherent coupling of physical and chemical heterogeneities (e.g. pore space geometry, grain size, charge, wetting) in natural porous media. These heterogeneities can exist at length scales of a few grains up to several kilometers. In addition, the colloids themselves are often heterogeneous in their surface properties. Both physical and chemical heterogeneities influence transport and retention of radionuclides under various groundwater conditions. However, the precise mechanisms of how these coupled heterogeneities influence colloidal transport are large elusive.

The objective of this project is to identify the dominant transport mechanisms of radionuclide-carrying colloids in saturated porous media. The approach relies on a series of complementary experiments and numerical simulations at both microscopic and macroscopic scales. In collaboration with Ning Wu  we developed a pore-scale microfluidic sediment analog with tunable physical and chemical heterogeneities. Within these analogs we measure breakthrough times, effective retention and colloid distribution. This data in compared to Lattice Boltzmann simulation performed in Xiaolong Yin’s  roup at Colorado School of Mines. In collaboration with Jaehun Chun and Wooyong Um at Pacific Northwest National Laboratory (PNNL) column-scale experiments were performed to assess the impacts of heterogeneities at the centimeter scale.

This project is supported by the United States Department of Energy.