Towards a Single-Solvent Process for U/TRU Recovery and Minor Actinide/Lanthanide Separations: Speciation and Partitioning of Tetravalent (Th, Pu) and Hexavalent (U) Actinides with HEH[EHP] and T2EHDGA

Understanding actinide speciation in lipophilic organic systems is a critical factor for developing novel liquid-liquid extraction processes for advanced nuclear fuel reprocessing and lanthanide and actinide recovery from ore containing naturally occurring radioactive materials (NORM). A simplified process is desirable to reduce costs, secondary waste generation, and increase safety. Several advanced solvent extraction processes for the recovery of uranium, transuranics, and minor actinides (U/TRU/MA) have been developed worldwide: Euro-GANEX, ExAm, CHALMEX, NEXT, etc. A US-based process for separating minor actinides (MA) from lanthanides (Ln) in spent nuclear fuel has been previously developed, called the Actinide Lanthanide Separation Process (ALSEP). This process has proven effective in separating Am and Cm from Ln in spent fuel mixtures feasible by the combination of the organophosphorus acidic extractant 2- ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP], P507) and a neutral diglycolamide (DGA) extractant, N,N,N,N-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) in n-dodecane. If processes such as ALSEP could be applied to also separate the other actinides (An) this could result in a more sustainable fuel cycle that would be an indispensable aid in combating the issues of pollution and greener energy. We report here proof-of-principle experimental results and the speciation studies of An in organic media. In contrast to the EU approach, the proposed process does not separate Pu from U, thus creating a suitable stream for advanced fuel fabrication, while keeping the proliferation risks at minimum. Experimental data on Pu and Th partitioning with HEH[EHP] and EXAFS analysis of uranyl in the T2EHDGA organic phase are shown in Fig 1 and 2. (authors)