THE IMPACT OF COLLOIDS ON THE MIGRATION AND DISPERSAL OF RADIONUCLIDES WITHIN FRACTURED ROCK

The objective of this paper is to make calculations for radionuclide dispersal in the presence of colloids, extending the cases previously calculated for the geosphere in the absence of colloids. The analysis is based on theoretical considerations, presenting a unified approach to dispersal from the scale of individual colloids up to that of geosphere breakthrough problems. A feature is the bridging of the gap between the standard continuum models of macroscopic transport and the considerations of colloid science, where colloids and complexes are subject to microscopic experimental analysis. In the radionuclide-colloid analysis it is shown that breakthrough curves could be both enhanced and retarded by the presence of colloids, according to the levels assumed for sorption to free and immobile colloid material. Within a fracture, such enhancement is limited above by a 30% faster average breakthrough, although since there is also exclusion of the colloid-bound radionuclides from the surrounding saturated rock matrix it is important to consider the reduction of the matrix retardation applicable to the solute.