Experimental investigation of the migration of radionuclides of the elements Sr, Cs, Rb, I and C in the covering rock of the final store at Gorleben

The absorption behaviour of the radionuclides was examined in batch and pillar experiments. The objects of the experiments were about 30 non-binding sediments from geological strata between 8 m and 200 m together with natural groundwater or groundwater produced from analytical data with very different salt contents. The dispersivities are in the region of millimetres. In flow pillar experiments, the retardation and re-occurrence rates were determined at filter speeds of about 2x10-4 cm/sec. The experiments gave a reduction in retardation factors and an increase in re-occurrence rates for cations with an increasing salt content of the groundwater. No specific effects could be found for anions. The adsorption equilibrium coefficients of the binding sediments were higher by about two orders of magnitude, where the absorption process on the binding sediments seemed to be more reversible than those on the non-binding sediments. Parameter variations depend greatly on the equilibrium coefficient of the carrier content of the radionuclide. Selective effects on the absorption values can be caused by organic materials present in the groundwater, e.g. tensides. One can expect only a small effect on the absorption coefficient due to a changed ambient temperature. The results show that the spread of the radionuclides examined depends mainly on the sediment sample examined and the salt content of the associated groundwater. With 26 tabs., 8 figs