SOLUTE TRANSPORT IN FRACTURED MEDIA - THE IMPORTANT MECHANISMS FOR PERFORMANCE ASSESSMENT

The most important mechanisms that control the release of contaminants from a repository for nuclear or chemical waste have been studied. Fo r the time scale of interest for the disposal of nuclear and even chem ical waste, diffusion into the rock matrix is an important factor whic h retards and dilutes the contaminants. It is found that the water flo w-rate distribution and the now-wetted surface are the entities that p rimarily determine the solute transport. If the diffusion into the roc k matrix is negligible, the solute transport is determined by the wate r flow rate and the flow porosity. This is shown using analytical solu tions obtained for simple geometries, such as the flow in a fracture w ith constant aperture or a channel. Similar results are obtained for m ore complex systems, such as flow in a fracture with variable aperture and through a network of channels. It is also found that the use of a retardation factor relating the travel times of interacting and nonin teracting solutes is inappropriate and may be misleading. (C) 1997 Els evier Science B.V.