Numerical modeling of bentonite extrusion and radionuclide migration in a saturated planar fracture

摘要

A case study of limited scope is presented in order to assess the potential of the performance of the engineered barrier in terms of the effects of bentonite extrusion on radionuclide transport in a water-saturated planar fracture. Under saturated conditions, bulk bentonite in the engineered barrier system will swell when contacted by groundwater. Due to this swelling, the bentonite will extrude into the intersecting fracture. A coupled mathematical model that describes the mass conservation of radionuclides in the fracture and the extrusion of bentonite into the fracture is established. The model for radionuclide migration incorporates spatial and temporal change in fluid porosity in the extrusion region due to movement of solid particles in the intersecting fracture. Finite element solutions have been derived for the fluid porosity in the bentonite extrusion region and the radionuclide concentration in the fracture. Numerical simulations of this model produced spatial distributions for radionuclide concentration. Results indicate that with sufficiently strong sorption, the radionuclide is observed to be confined within the region of bentonite extrusion. These results imply that the performance of the engineered barrier to limit radionuclide release is potentially enhanced and warrant more rigorous modeling studies of this phenomenon.