The Design Of An Out-Diffusion Experiment And The Use Of Geochemical Analyses For The Purpose Of Matrix Pore Fluid Extraction And Characterization: A Case Study For Radioactive Waste Disposal

Abstract

Deep crystalline rock formations of low permeability have been identified as a possible geological medium for high-level radioactive waste disposal. In order for the safe disposal of radioactive waste, a site characterization must be performed. A comparison of site characterization methods found out-diffusion methods to be the most viable technique for pore fluid extraction. Crush and leach, chemical and isotopic analyses such as, Cl-, 37Cl, 18O, 2H and 87Sr were valuable in characterizing the signature/origin of the pore fluids. Variations in the signatures of the pore fluids were observed and attributed to small differences in heterogeneity within the host rock and water to rock interactions. Estimates of the rate of effective diffusivity (De) were evaluated experimentally and with an analytical solution. Modelled De values were much greater than those determined experimentally, suggesting that the analytical solution provides a more conservative estimate of De for assessing radionuclide migration.