A scoping study is presented in order to investigate the potential of bentonite extrusion on radionuclide transport in a water-saturated planar fracture. A coupled mathematical model for an abstracted case describing the mass conservation of radionuclides and bentonite extrusion into the fracture is established to observe the mass transport phenomena due to bentonite extrusion in the fracture domain. Results of numerical simulations are then analyzed in order to interpret the potential importance of extrusion in the near-field rock on the overall performance of the engineered barrier system (EBS). The mathematical model developed in this study for radionuclide migration incorporates spatial and temporal changes in porosity due to movement of bentonite particles. Finite element solutions have been derived for the porosity and for the radionuclide concentration.

With a sufficiently strong sorption, the radionuclide is observed to be contained within the region of bentonite extrusion, indicating that radionuclides would be retained within the extrusion region even if the waste canister fails early while bentonite is extruding in fractures. Such results imply the potential of the extrusion region to enhance performance in the EBS and warrant more rigorous modeling studies of this domain.