Colloid migration in groundwaters: Geochemical interactions of radionuclides with natural colloids. Final report

摘要

In this joint research program, the significance of groundwater colloids in far field radionuclide migration has been studied. The characterization, quantification, and theoretical interpretation of colloid-borne transport phenomena for radionuclides were the main objectives of this research program. Groundwaters, colloids and sediments were sampled from aquifer system overlying a saltdome in the Gorleben area in northern Germany and were characterized by various analytical methods (ICP-MS, ICP-AES, neutron activation analysis (NAA), DOC-Analyser, HPIC, potentiometric titration). Different natural isotopes (H-2, H-3, C-13, C-14, O-18, S-34, and U/Th decay series) were determined and their ratios were compared with one another in the order to ascertain the provenance of the groundwater colloids. The investigated groundwaters contain substantial amounts of colloids mainly composed of humic and fulvic acids loaded with various metal ions. The chemical interaction of radionuclide ions of various oxidation states (Am, Eu, for M(III), Th, Pu for M(IV), Np for M(V), and U for M(VI)) with groundwater colloids was investigated in order to determine the colloid facilitated migration behavior of actinides in a given aquifer system. A modeling program was developed to predict chemical transport of radionuclides in the presence of humic colloids using a modified version of the CHEMTARD code. (orig.)