Americium Recovery from Highly Active PUREX Raffinate by Solvent Extraction: The EXAm Process. A Review of 10 Years of R&D

In the framework of the R&D program conducted in France on partitioning and transmutation of minor actinides, a solvent extraction process was developed for separating americium from a PUREX raffinate arising from the dissolution of spent nuclear fuels in nitric acid. The so-called EXAm process uses a mixture of a malonamide (DMDOHEMA, N,N’-dimethyl-N,N’-dioctyl-hexyloxyethyl-malonamide) and HDEHP (di-2-ethylhexylphosphoric acid) in organic phase in combination with a water-soluble complexing agent TEDGA (N,N,N’,N’-tetraethyldiglycolamide) in aqueous phase to enhance Am/Cm separation. Am/Ln separation is then obtained by selective Am stripping with polyaminocarboxylic acids (HEDTA or DTPA) buffered by citric or malonic acid at low acidity. Started in 2008, an important R&D program was conducted at CEA to optimize and model the process. The feasibility of the direct recovery of Am from a genuine PUREX raffinate by solvent extraction was demonstrated in 2010 and reported, for the first time in the literature. R&D was then conducted to adapt the process for a future scale-up and for application from concentrated PUREX raffinates. The results of the final EXAm process performed on a highly active PUREX concentrate are presented after a summary of 10 years of R&D on this process development.