Actinide Lanthanide Separation Process—ALSEP

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Abstract

Separation of the minor actinides (Am, Cm) from the lanthanides at an industrial scale remains a significant technical challenge for closing the nuclear fuel cycle. To increase the safety of used nuclear fuel (UNF) reprocessing, as well as reduce associated costs, a novel solvent extraction process has been developed. The process allows for partitioning minor actinides, lanthanides, and fission products following uranium/plutonium/neptunium removal, minimizing the number of separation steps, flowsheets, chemical consumption, and waste. This new process, actinide lanthanide separation (ALSEP), uses an organic solvent consisting of a neutral diglycolamide extractant, either N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) or N,N,N′,N′-tetraoctyldiglycolamide (TODGA), and an acidic extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]), dissolved in an aliphatic diluent (e.g., n-dodecane). The An/Ln coextraction is conducted from moderate-to-strong nitric acid, while the selective stripping of the minor actinides from the lanthanides is carried out using a polyaminocarboxylic acid/citrate buffered solution at pH anywhere between 3 and 4.5. The extraction and separation of the actinides from the fission products is very effective in a wide range of HNO3 concentrations, and the minimum separation factors for lanthanide/Am exceed 30 for Nd/Am, reaching >60 for Eu/Am under some conditions. The experimental results presented here demonstrate the great potential for a combined system, consisting of a neutral extractant such as T2EHDGA or TODGA, and an acidic extractant such as HEH[EHP], for separating the minor actinides from the lanthanides.

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