Chemistry of Diglycolamides: Promising Extractants for Actinide Partitioning

The removal of the most long-lived radiotoxic elements from used nuclear fuel, minor actinides, is foreseen as an essential step toward increasing the public acceptance of nuclear energy as a key component of a low-carbon energy future. Once removed from the remaining used fuel, these elements can be used as fuel in their own right in fast reactors or converted into shorter-lived or stable elements by transmutation prior to geological disposal. The SANEX process is proposed to carry out this selective separation by solvent extraction. Recent efforts to develop reagents capable of separating the radioactive minor actinides from lanthanides as part of a future strategy for the management and reprocessing of used nuclear fuel are reviewed. The current strategies for the reprocessing of PUREX raffinate are summarized, and some guiding principles for the design of actinide-selective reagents are defined. The development and testing of different classes of solvent extraction reagent are then summarized, coverin...

Use of soft heterocyclic N-donor ligands to separate actinides and lanthanides.

Actinide partitioning is a proposed strategy for effective mitigation of the long-term hazards associated with high-level waste (HLW). Octyl-(phenyl)–N,N-diisobutyl carbamoyl methyl phosphine oxide (CMPO) and diphenyl–N,N-diisobutyl carbamoyl methyl phosphine oxide (DφCMPO) are amongst the promising extractants extensively studied since the 1980s for actinide partitioning from wastes of different origin. During the last two decades, substituted malonamide extractants such as N,N'-dimethyl-N,N'-dibutyl tetradecyl malonamide (DMDBTDMA) and N,N'-dimethyl-N,N'-dioctyl hexylethoxy malonamide (DMDOHEMA) have emerged as viable green alternatives to phosphine oxides. During the last decade, diglycolamide-based extractants such as N,N,N′,N′-tetraoctyl diglycolamide (TODGA) and N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (TEHDGA) have received considerable attention due to overwhelmingly favourable extraction and stripping efficiencies of minor actinides from different types of transuranium (TRU) wastes. The focus o...

Aqueous Partitioning of Minor Actinides by Different Processes

The extractant, N,N,N′,N′‐tetraoctyl diglycolamide (TODGA) has been evaluated for the separation of actinides(III) and lanthanides(III) from a high active raffinate (HAR). The effect of oxalic acid and HEDTA complexant on the extraction of actinides(III), lanthanides(III), and important fission products (e.g. Mo, Pd, Sr, Zr, Ru etc.) from synthetic HAR has been studied with 0.2 mol/L TODGA in TPH. With an extractant mixture of TODGA and tributyl phosphate (TBP) the amount of oxalic acid can be reduced to less than 0.3 mol/L for the effective complexation of zirconium, whereas the distribution ratios of actinides(III) and lanthanides(III) are still high for the separation from HAR. Furthermore the maximum loading of lanthanides (e.g. Nd) can be significantly increased by adding TBP to the extractant. However, the extraction of oxalic acid and nitric acid also increased by the addition of TBP, which can lead to problems during back extraction of the loaded extractant. Extraction studies after radio...

Development of a TODGA based Process for Partitioning of Actinides from a PUREX Raffinate Part I: Batch Extraction Optimization Studies and Stability Tests

Efficient recovery of minor actinides (MA) from genuine PUREX raffinate has been successfully demonstrated by the TODGA + TBP extractant mixture dissolved in an industrial aliphatic solvent TPH The process was carried out in centrifugal contactors using an optimized flow-sheet involving a total of 32 stages, divided into 4 stages for extraction, 12 stages for scrubbing and 16 stages for back-extraction Very high feed decontamination factors were obtained (Am, Cm 40 000) and the recovery of these elements was higher than 9999% Of the non-lanthanide fission products only Y and a small part of Ru were co-separated into the product fraction together with the lanthanides and the MA

Demonstration of a TODGA based Extraction Process for the Partitioning of Minor Actinides from a PUREX Raffinate

The efficiency of the partitioning of trivalent actinides from a PUREX raffinate is demonstrated with a TODGA+TBP extractant mixture dissolved in an industrial aliphatic solvent TPH. Based on the results of cold and hot batch extraction studies and with the aid of computer code calculations, a continuous counter‐current process is developed and two flowsheets are tested using miniature centrifugal contactors. The feed solution used is a synthetic PUREX raffinate, spiked with 241Am, 244Cm, 252Cf, 152Eu, and 134Cs. More than 99.9% of the trivalent actinides and lanthanides are extracted and back‐extracted and very high decontamination factors are obtained for most fission products. The co‐extraction of zirconium, molybdenum, and palladium is prevented using oxalic acid and HEDTA. However, 10% of ruthenium is extracted and only 3% is back‐extracted using diluted nitric acid. The experimental steady‐state concentration profiles of important solutes are determined and compared with model calculations ...

Demonstration of a TODGA‐Based Continuous Counter‐Current Extraction Process for the Partitioning of Actinides from a Simulated PUREX Raffinate, Part II: Centrifugal Contactor Runs

A 30% (w/w) N,N,N',N'-tetraoctyldiglycol-amide (TODGA) and 10% (w/w) tributyl-phosphate (TBP)-containing resin was prepared and the batch uptake of several actinides [U(VI), Th(IV), Am(III), Cm(III), Cf(III)] and selected fission products from nitric acid solutions was investigated. Two chromatographic column tests were carried out with a synthetic PUREX raffinate containing nominal amounts of fission products and trace amounts of Am(III), Cm(III) and Cf(III). The results of the separation experiments revealed that actinides and lanthanides could be separated from the bulk of other fission products by extraction chromatography using TODGA and TBP as the stationary phases.

Recovery of actinides and lanthanides from high-level liquid waste by extraction chromatography using TODGA+TBP impregnated resins

The efficiency of the partitioning of trivalent actinides from a PUREX raffinate has been demonstrated with a TODGA + TBP extractant mixture dissolved in an industrial aliphatic solvent TPH. Based on the results coming from cold and hot batch extraction studies and with the aid of computer code calculations a continuous counter current process have been developed and two flowsheets were tested using miniature centrifugal contactors. The feed solutions was a synthetic PUREX raffinate, spiked with {sup 241}Am, {sup 244}Cm, {sup 252}Cf, {sup 152}Eu and {sup 134}Cs. More than 99.9 % of the trivalent actinides and lanthanides were extracted and back-extracted and very high decontamination factors to most fission products were obtained. Co-extraction of zirconium, molybdenum and palladium was prevented using oxalic acid and HEDTA. However 10% of ruthenium was extracted and only 3 % could be back extracted using diluted nitric acid. (authors)

Hanna Asp

Papers

Development of a TODGA based Process for Partitioning of Actinides from a PUREX Raffinate Part I: Batch Extraction Optimization Studies and Stability Tests

Demonstration of a TODGA‐Based Continuous Counter‐Current Extraction Process for the Partitioning of Actinides from a Simulated PUREX Raffinate, Part II: Centrifugal Contactor Runs

Recovery of actinides and lanthanides from high-level liquid waste by extraction chromatography using TODGA+TBP impregnated resins

Demonstration of a TODGA/TBP process for recovery of trivalent actinides and lanthanides from a PUREX raffinate