THE EFFECTS OF MATRIX DIFFUSION ON RADIONUCLIDE MIGRATION IN ROCK COLUMN EXPERIMENTS

Rock column experiments were performed to examine the effects of matri x diffusion and hydrodynamic dispersion on the migration of radionucli des at the laboratory scale. Tritiated water and chloride transportati on was studied in intact mica gneiss and in altered more porous tonali te columns with narrow flow channels. The column diffusion properties were estimated prior to water flow experiments using the gas diffusion method with helium as the tracer gas. The numerical compartment model for advection and dispersion, with and without matrix diffusion, was used to interpret the tracer transport in the columns. Matrix diffusio n behavior was also distinguished from dominating hydrodynamic dispers ion in rock column experiments at the slowest water flow rates.