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

Abstract

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-hexyloxyethylmalonamide) 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.

Engineering lanmodulin's selectivity for actinides over lanthanides by controlling solvent coordination and second-sphere interactions

“…11 Some of the most studied metal chelators are those for the extraction and purication of rare earth elements, [5][6][7] and for actinide/ lanthanide partition in the frame of nuclear spent fuel reprocessing. [12][13][14][15][16][17] However, f-element separations are among the most difficult due to the chemical similarities among trivalent actinide (An 3+ ) and lanthanide (Ln 3+ ) ions, both within and between the 4f and 5f series. 18,19 For instance, separation of lanthanide ssion products from heavy actinides (i.e., Am 3+ and Cm 3+ ) present in nuclear spent fuel is a critical challenge to overcome for closing the nuclear fuel cycle, but processes able to separate the 4f and 5f series are notoriously arduous to develop and implement 11 equivalent to the separation of individual lanthanides but with additional radiation-related constraints.…”

Pyridine-di-phosphonates as chelators for trivalent f-elements: kinetics, thermodynamic and interfacial study of Am(iii)/Eu(iii) solvent extraction

“…7 One of the technological schemes for the reprocessing of the PUREX raffinate is the ExAm-process. 8,9 However, this complex system shows low separation factor for Am and light lanthanides and requires the use of additional separation stages.…”

Way to Enforce Selectivity via Steric Hindrance: Improvement of Am(III)/Eu(III) Solvent Extraction by Loaded Diphosphonic Acid Esters

“…Organophosphorus extractants are among the first classes used in the processing of SNF and in other radiochemical technologies . They are the main compounds investigated to solve such practical tasks as the group extraction of An elements (tri- n -butylphosphate in the PUREX process), the group extraction of An­(III) and Ln­(III) (CMPO, SETFICS process), the extraction of Am­(III) and Cm­(III) (HEHEHP, ALSEP process , ), and the selective extraction of Am (HDEHP, ExAm process). The disadvantages of the above-mentioned compounds are a lack of selectivity toward americium in the presence of Ln elements and the need to use water-soluble ligands for selective scrubbing and back-extraction of Am­(III) from the organic phase.…”