Solute migration through unsaturated fractured chalk under variations in saturation degree, flow rate and aperture

Spent fuel (SF) produced in the nuclear industry, requires long term disposal solutions for 10⁵-10⁶ years, to allow its decay in an isolated setting as means to reduce the environmental threat of radioactive contamination. The feasibility of locating SF repository within a fractured carbonate formation as the host rock in the unsaturated zone, requires better understating of radionuclide transport patterns under these specific conditions. An innovative system was developed to simulate conditions of unsaturated flow and transport in fractured chalk. The system consists of an artificially fractured chalk core, situated in a flow cell, which lays on top of a ceramic membrane. The membrane separates it from a lower sealed cell where constant negative pressure is forced. Subsequently, a pressure gradient along the rock core is being developed. The system is placed on a scale in order to monitor the degree of saturation in the core throughout the experiment. Uranine fluorescent dye is used as a conservative tracer to investigate the impact of: (1) the initial degree of saturation; (2) fracture aperture; and (3) flow rate, on the transport and recovery of conservative contaminants. Preliminary results show that a conservative tracer migrates faster through the fracture when the matrix is initially nearly saturated (s=99%) than when the matrix is undersaturated (s=75%). These results will be used for comparison with radionuclide and radionuclide-simulants transport in current studies.