The selective separation of Am(III) from highly radioactive PUREX raffinate

The long-term heat load and radiotoxicity of spent nuclear fuel depicts a major challenge for its disposal as the size and cost of a deep geological repository is governed by the heat generation of the waste. A major reduction of the long-term heat load of radioactive waste is currently achieved by the separation and recycling of uranium and plutonium using the PUREX (plutonium and uranium reduction extraction) process. The remaining trivalent minor actinides americium and curium dominate the heat load after decay of the fission products. However, due to the short half-life of curium and its high neutron emission, any handling involving curium requires extensive neutron shielding. Therefore, the selective separation of americium from curium and the fission products is considered an advantageous option to further reduce cost and size of a final repository, although the separation of americium from curium is one of the most challenging tasks in separation chemistry. A novel process for the separation of trivalent actinides from PUREX raffinate, the innovative selective actinide extraction process (i-SANEX), was developed previously and is taken as the basis of this work. The counter current laboratory-scale demonstration of the i-SANEX process in centrifugal contactors was carried out in context of this work. In this process, the co-extraction of trivalent actinides and lanthanides is carried out using a diglycolamide solvent followed by the selective back-extraction of trivalent actinides using a highly selective hydrophilic complexant. Several combinations of lipophilic extractants and hydrophilic complexants were tested for their selectivity for americium over curium with the aim to increase the selectivity for americium in solvent extraction processes. Two hydrophilic complexants were found to provide promising selectivity towards americium in combination with a diglycolamide based lipophilic extractant. Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) investigations of selected actinide and lanthanide complexes with the hydrophilic complexing agents were carried out to better understand the fundamental mechanisms of complexation of the metal ions with these complexants. Conditional complex stability constants were derived for different media to analyze the influence of acidity and nitrate anions. Additionally, biphasic TRLFS-experiments were carried out to analyze the interaction between lipophilic and hydrophilic complexants. The data generated from solvent extraction and fluorescence-spectroscopic investigations enable for the development of a process for the selective separation of americium from PUREX-raffinate