Our model considers the contaminants as dissolved in the aqueous phase and sorbed to the sediment or sorbed to mobile and immobile colloids. All sorption processes are assumed to be reversible and are modeled as a kinetic-Langmuir reaction.
The Europium Migration ExperimentThe column experiments with •52Eu(II!) in a humic-rich groundwater were performed by Klotz and Lazik [1996]. Batch experiments with the same groundwater sediment system were conducted to determine the s0rption .distribution coefficient Rs More than 98% of europium in the injected solution is bound to colloidal humic particles, and the predominant humic colloid size is in the range from 1 to 100 nm.
The release and transport of radionuclides from underground repositories into the biosphere is controlled by geological and technical barriers. As part of this barrier system geological formations play a decisive role with respect to the long-term safety of repositories. Various geochemical processes can cause a significant reduction of the contaminant concentration on its way through the geological formations in the far-field of a repository. This paper gives an overview of recent work concerning the modelling of nonlinear sorption processes and colloid facilitated contaminant transport and shows the influence of these geochemical processes in the performance assessment.The models and data applied in performance assessments are usually derived from laboratory experiments. For technical reasons these experiments can only be performed over limited time periods. However, the times which have to be considered for the contaminant transport through the geosphere are in the order of a million years. Thus the effects of geochemical processes have to be assessed for correspondingly long times. For this purpose the investigations of suitable geological analogues may help to better understand the complex interrelations between transport and retention of radionuclides under natural conditions and may indicate whether the results of laboratory experiments are transferable and applicable to real systems.
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