Untersuchung der Uebertragbarkeit von Labordaten auf natuerliche Verhaeltnisse am Beispiel von Gorleben Aquifersystemen Abschlussbericht

The aquifer system at the Gorleben site was chosen as the case for verifying the applicability of laboratory data describing the solubility and sorption of radionuclides to the conditions at the real site. For this purpose, the data derived from geochemical models, predicting the distribution of the chemical species in the ground water, were compared with the experimental data obtained by spectroscopic speciation on site. This procedure allows to perform a validation of the geochemical model and of the data underlying the model. The study reported encompasses work for establishing or supplementing the thermodynamic database, an analysis of site-specific data, as e.g. on the formation of colloids, as well as the comparative analyses for ascertainment of applicability. Upon compilation and critical review of data found in the literature, the thermodynamic regime of geochemically relevant reactions of selected actinide ions was examined, leading to data describing the thermodynamics of the hydrolysis of (Cm (III), Pu (IV), Np (V) and Pu (VI)), or the complexation with carbonate (Am (III), Cm (III) and Np (V)). The data are obtained by pH-dependent solubility measurements, or derived by spectroscopic speciation. In addition, a thermodynamic model was established which gives a quantitative description of the geochemically relevant complexation with humic substances (Am (III), Cm (III), and Np (V)). It was found that the increase of the redox potiental, induced in strongly salty solutions by #alpha#-radiolysis, was worth to be studied for its effect on the stabilisation of Pu (VI). Solubility measurements detected the formation of hypochlorito-complexes and of metastable, polynuclear Pu (VI)-species, which was verified by spectroscopy. (orig.)Available from TIB Hannover: RO 9945(00792) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman