Applicability of laboratory experimental data (solubilities and sorption coefficients) to natural aquifer systems, for example, the Gorleben aquifer system. Final report

The main objective of the research project is to elucidate the migration behaviour of long-lived radionuclides, especially actinides and technetium, in natural aquifer systems. Particular emphasis is directed to answer the question whether or not the experimental data obtained in laboratory can be applied without restriction to natural aquifer systems. For this purpose, the Gorleben aquifer system is taken as an example. As the subject encompasses a wide variety of geochemical reactions of long-lived radionuclides of diverse elements, experiments have been confined to notable examples selected with regard to chemical nature of each element. Common reactions of geochemical importance, which are not well or poorly understood in the literature, are given priority in the present investigation. Laboratory experiments have been conducted on hydrolysis, carbonate complexation, humate complexation, redox reaction and colloid generation. Column experiments were performed for the elucidation of the migration behaviour of colloid-borne actinides. The applicability of laboratory data has been examined by comparison of thermodynamic speciation with direct spectroscopic speciation for given actinides in natural aquatic solution. Whenever the colloid generation is involved, either formation of 'real' or 'pseudo' colloids, the application of thermodynamic speciation becomes failed. In this case a new approach to appraisal of the actinide migration behaviour appears indispensable. This fact has inspired us to develop a novel method for the quantification of aquatic colloids of nanosize (10-100 nm) in very dilute concentrations (ppt range). (orig.)