Inhaltszusammenfassung

In the context of the long-term safety assessment of a future disposal for high-level nuclear waste the actinides uranium, neptunium, plutonium and americium are of particular importance since they all exhibit very long-lived isotopes. As part of spend nuclear fuels, for example the isotopes U-238 (t1/2 = 4.47*10^9 a), Np-237 (t1/2 = 2.14*10^6 a) and Pu-239 (t1/2 = 2.41*10^4 a) must be named. Because it is planned to safely embed the radioactive waste up to 1 million years in deep geological ...In the context of the long-term safety assessment of a future disposal for high-level nuclear waste the actinides uranium, neptunium, plutonium and americium are of particular importance since they all exhibit very long-lived isotopes. As part of spend nuclear fuels, for example the isotopes U-238 (t1/2 = 4.47*10^9 a), Np-237 (t1/2 = 2.14*10^6 a) and Pu-239 (t1/2 = 2.41*10^4 a) must be named. Because it is planned to safely embed the radioactive waste up to 1 million years in deep geological formations with argillaceous rocks, crystalline rocks or salt as host rock it is of great importance to have a deep knowledge of the actinide behavior in these conditions. In order to investigate these systems, in the present work the coupling of a capillary electrophoresis (CE) to an inductively coupled plasma mass spectrometer (ICP-MS) was employed. Here, the combination of the high separation capability of the CE with the possibility of multi element detection with very low detection limits of the ICP-MS was utilized. This analytical method provides very good results, especially in the case of very low concentration ranges of the actinides in environmentally relevant systems. First, in the frame of this work, investigations on the redox speciation of actinides in 1 M acetic acid as the background electrolyte (BGE) were conducted. The electrophoretic mobilities μi of the redox stable actinides Am(III), Th(IV), Np(V) and U(VI) could be determined and based on that the μi of all Pu species with the oxidation states +III - +VI. The trend in the μi turned out to be An(III) > An(VI) > An(V) > An(IV) for all actinides. Additionally, an approach for the estimation of the μi of non-stable oxidation states of actinides, e.g. Np(III) or U(V), was developed. By comparing the so determined μi with experimentally determined values, the applicability of this proceeding could be validated. Furthermore, the stability constants of the actinides Am(III), Th(IV), Np(V) and U(VI) with the ligands acetate, propionate, gluconate and citrate at an ionic strength of I = 0.3 M were examined. For each system a complete set of stability constants could be obtained, the results were extrapolated to zero ionic strength by means of the Davies equation. The basics for the determination of kinetic parameters of redox reactions by CE-ICP-MS were investigated for the reduction of Np(V) by hydroxylamine hydrochloride. In doing so, the rate constants of the reaction at different temperatures and based on that the Arrhenius parameters could be determined. In addition, the rate constants at different temperatures and the Arrhenius parameters were obtained for the reduction of Pu(VI) by Fe(II). It could be shown clearly by the results presented in this work, that the coupling of CE to ICPMS is a powerful analytical method for the investigation of actinides in low concentration ranges. The resulting electrophoretic mobilites can deal as the basis for the interpretation of CE expriments. The determined stability constants are of great importance in the long-termsafety assessment of a future nuclear waste disposal for high-level nuclear waste. With a prove-of-principle study the applicability of CE-ICP-MS for the determination of kinetic parameters of redox reactions could be shown.» weiterlesen» einklappen

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DDC Sachgruppe:
Chemie