Modeling of colloid-associated radionuclide transport in porous groundwater aquifers at the Gorleben site, Germany.

Abstract

Results are presented which have been obtained in prediction studies on the colloid-associated transport of radionuclides through porous groundwater aquifers overlying as geochemical barrier the planned nuclear repository site at Gorleben, Germany. The studies incorporate three-phase retardation factors for 227 Ac, 228 Th, 232 U and 210 Pb in site-specific groundwater aquifers containing humic colloids and efficiencies for Brownian deposition of colloidal carriers onto immobile sedimentary grains. It is shown that colloidbound radionuclide migration can be approximately modeled by using the basic advection-dispersion transport equation modified with three-phase retardation coefficients and colloid-chemical attachment factors due to the presence of multiple phases, i.e., fluid, colloid and immobile solid. Moreover, results of sitespecific assessment studies indicate that the transport of colloid-associated radionuclides in porous groundwater aquifers overlying the Gorleben salt dome may not occur over long distances, provided that the nuclides are transported by porous flow only.