Separation and transmutation <i>via</i> fissioning is one option being considered for managing the minor actinide elements (americium and curium) in the commercial nuclear fuel cycle. This approach would reduce the heat load on a geologic repository, allowing for higher density packing of the used fuel for disposal, and would substantially reduce the radiotoxicity of the used fuel after a decay period of only a few hundred years (rather than tens-of-thousands of years). The neutron-absorbing lanthanide elements must be separated from the minor actinide elements to achieve the most efficient use of neutrons in transmuting the minor actinides to short-lived or stable isotopes. We have been investigating two solvent extraction systems for separating the actinides (An) from the lanthanides (Ln) that utilize 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) as the extractant. Both techniques rely on the complexation of the trivalent Ln ions in the organic phase by the HEH[EHP] extractant, and the selective binding of the An ions in the aqueous phase by an polyaminocarboxalate ligand. Under these conditions, the Ln can be separated from the An by separating the two phases from one another, with the organic phase containing the Ln and the aqueous phase containing the An. In this paper, we will summarize the status of the development of these HEH[EHP]-base Ln/An separation systems. The focus will be on recent efforts to overcome relatively slow transfer of certain f-block element ions across the phase boundary. Solutions to these issues have been sought by changing of the process chemistry, and by changes in the process equipment (shifting from centrifugal contactors to mixer-settlers).

Use of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester as an extractant for minor actinide separations

251st National Meeting (2016)

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