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 d ispersal in the presence of colloids, extending the cases previously c alculated for the geosphere in the absence of colloids. The analysis i s based on theoretical considerations, presenting a unified approach t o dispersal from the scale of individual colloids up to that of geosph ere breakthrough problems. A feature is the bridging of the gap betwee n the standard continuum models of macroscopic transport and the consi derations of colloid science, where colloids and complexes are subject to microscopic experimental analysis. In the radionuclide-colloid ana lysis 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 breakthroug h, although since there is also exclusion of the colloid-bound radionu clides from the surrounding saturated rock matrix it is important to c onsider the reduction of the matrix retardation applicable to the solu te.