This contribution highlights recent studies at KIT-INE on actinide chemistry at elevated temperatures performed within the German ThermAc project. ThermAc project is extending the chemical understanding and available thermodynamic database for actinides, long-lived fission products and relevant matrix elements in aquatic systems at elevated temperatures. To this end, a systematic use of estimation methods, new experimental investigations and quantum-chemistry based information is used. Work is developed with the aim of improving the scientific basis for assessing nuclear waste disposal scenarios at elevated temperature conditions.<br/>The focus of KIT-INE within ThermAc is presently on long-lived actinides in oxidation states III, V and V. The temperature range from ~20°C up to ~90°C is studied, with a focus on systems at low or intermediate ionic strength. Chemical analogs for the actinide elements are used, especially in order to gain information on solid phase transformation processes. As examples from the studies of KIT-INE at elevated temperature conditions four examples will be shown, addressing (i) solubility and speciation of U(VI) in NaCl solution, (ii) effect of T on the Ca-U(VI)-CO<sub>3</sub> system, (iii) Np(V) solid phase transformation processes, and (iv) hydrolysis and solubility of trivalent actinides.

Studies on actinide chemistry at elevated temperatures at KIT-INE within the German collaborative ThermAc project

256th National Meeting (2018)

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