[en] Due to their similar size and chemical state, separation of trivalent lanthanide and actinide ions has always been a challenging topic of research. Of late, the growing concern for the radioactive waste management in the back end of the nuclear fuel cycle has led to the possibility of transmuting the long-lived transuranides in high flux reactors. This necessitates the development of processes for the separation of lanthanides and actinides in acidic/low pH media. In view of the high absorption cross section of few lanthanides, their presence in relatively large proportion (10-100 times) impedes the transmutation process. Processes such as the TRAMEX and TALSPEAK have been used for the separation of lanthanides from trivalent actinides. Of late soft donor ligands containing S and N donor atoms have been used for the selective extraction of trivalent actinide ions. The commercially available S-donor compound, CYANEX 301 (bis(2,4,4-trimethylpentyl) dithiophosphinic acid) has been used to yield separation factor (S.F.) values in the excess of 6000. Synergistic extraction with N-donor ligands such as 2,2'-bipyridyl and 1,10-phenanthroline have yielded S.F. values close to 40,000. N-donor ligands such as BTP (bis-triazinylpyridine), BTBP (bis-triazinylbipyridyl) and BTPhen (bis-triazinyl-phenanthroline) have been particularly effective from relatively acidic feed conditions. The present lecture will give a brief outline of the separation processes and experimental results of studies carried out using various S and N donor ligands. Use of room temperature ionic liquids for more favorable separations will be highlighted. Liquid membrane separation results for application to back end nuclear fuel cycle will also be discussed. (author)

[en] Californium-252 is produced in the High Flux Isotope Reactor (HFIR) and separated in the Transuranium Processing Plant (TRU) at Oak Ridge National Laboratory. The facilities themselves and the nuclear and chemical processes involved in ²⁵²Cf production are described. (Auth.)

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[en] After ether extraction was scaled up to plant status, solvent extraction grew rapidly, intensively, and extensively. This paper recounts developments at the ORNL in three fields: Fuel Reprocessing, Uranium Production, and Transplutonium Element Recovery. Fuel Reprocessing: In the late 1940's, soon after TBP was discovered to be an extractant, the Purex process was developed to recover, decontaminate, and separate Pu and U (from nitric acid solutions of spent reactor fuels) without the need of added salting agents. Uranium Production: Around 1950, the ORNL Raw Materials Section launched an intensive search for reagents that could extract uranium from sulfuric acid leach liquors. This was accomplished with di(2-ethylhexyl)phosphoric acid (HDEHP) and a suite of high-molecular-weight alkylamines. The resulting Dapex and Amex processes eventually dominated domestic uranium production, spread world-wide, and provided bases for innovative processes in other fields. Transplutonium Element Recovery: Tramex and Talspeak processes accomplish separation of the trivalent actinides from the similar lanthanides. Tramex (1961; amine extraction from concentrated lithium chloride) has been used in the ORNL Transuranium processing Plant (TRU) since 1966. Talspeak (1964; HDEHP extraction from carboxylic acid + aminopolyacetate complexer) has wider potential because it is less corrosive, and it is being extensively studied for separating americium and curium from fuel reprocessing wastes

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[en] A single-stage reprocessing of the irradiated target on the basis of curium heavy isotopes is described. The target was irradiated in the SM-2 reactor with an integral flux of 3.5x10²² neutr/cm². The extraction and separation of transplutonium elements (TRE) were made in the lithium chloride-trioctyalammonium chloride system in an extraction-chromatographic mode. Extraction in the chloride medium was performed in the following order: Cm< Bk approximately Es< Cf, the separation factor for curium and californium being 7.5. No considerable separation of berkelium and einsteinium was observed, the curium yield in the process being 94.7% and californium yield 93%. By successively using several eluents with a varying concentration of lithium chloride the separation of structural materials( Tramex process), intergroup separation of actinoid and fission elements and also intragroup separation of TPE were made

[en] Since 1966, TRU has been the main center of production for transcurium elements in the US, producing 460 mg ²⁴⁹Bk, 4 g ²⁵²Cf, 18 mg ²⁵³Es, and 10 pg ²⁵⁷Fm. During the 14 years operation, 39 chemical processing campaigns were conducted to process 265 HFIR targets and 195 SRP production reactor targets

[en] The Trivalent Actinide-Lanthanide Separation by Phosphorus Extractants and Aqueous Complexants (TALSPEAK) process was developed in the late 1960's at Oak Ridge National Laboratory as a potential replacement for the TRAMEX process. Conventional TALSPEAK combines bis-(2- ethylhexyl)phosphoric acid (HDEHP) with an aqueous medium composed of the water-soluble polyamino-poly-carboxylic acid complexing agent diethylenetriamine-N,N,N'-N-,N-pentaacetic acid (DTPA) in a concentrated lactic acid buffer medium. While TRAMEX derives its effectiveness from the greater strength of An(III) interactions with Cl^-, selective retention of actinides in the TALSPEAK aqueous phase derives primarily from the stronger interaction of An(III) with DTPA. As research and development on closing of the nuclear fuel cycle via the suite of UREX processes (under development in the U.S.) progresses, TALSPEAK has been selected as the currently-favored system for partition of trivalent actinides away from fission product lanthanides. A recent review of the TALSPEAK process summarized previous research characterizing the performance of this system. Attempts were made in that report to develop correlations between the previous separations data and the thermodynamic data that describes interactions among the components of the separation system. However, the diversity of observations and the breadth of conditions employed in the many studies from the literature make comparisons between TALSPEAK system performance and existing thermodynamic data challenging. To better test the adequacy of the available thermodynamic database for modeling this system, an internally consistent set of observations of lanthanide extraction under TALSPEAK conditions has been completed. The extraction of the lanthanides from La through Lu (excluding Pm) plus Y, and that of Am³⁺ from buffered lactic acid solutions containing DTPA into organic solutions of HDEHP solutions in 1,4-diisopropylbenzene or n-dodecane has been investigated as a function of temperature, pH and ionic strength. Extraction of both lanthanides and Am³⁺ decreases with increasing pH and with temperature. At the same time, separation factors remain approximately constant. Calculations based on an internally consistent thermodynamic data set confirm the prior conclusion that the existing thermodynamic data do not predict the observed decline in partitioning with increased pH, though the data do support constancy of separation factors. There are also indications that the heavy lanthanides are very slow to reach biphasic equilibrium. In this presentation, the thermodynamic and kinetic features of the TALSPEAK process will be discussed. The emphasis will be on identifying the contributions of reactions occurring in both the aqueous and organic phases on the net separation efficiency. Work supported by the University - Nuclear Energy Research Initiative (U-NERI) program of the U.S. Department of Energy Office of Nuclear Energy and Technology at Washington State University, project number DE-FC07-05ID14643. (authors)

[en] Separation of trivalent actinide (An) and lanthanide (Ln) elements is one of the burning topics in the back end of the nuclear fuel cycle due to the similarity in their chemical behaviour. A significant amount of research is being carried out worldwide to develop suitable ligands for the separation of the trivalent actinides and lanthanides. Some of the research groups are engaged in continuous improvement of the di-ethylene-triamine-penta acetic acid (DTPA) based Ln/An separation method, whereas extensive research is going on for the development of the lipophilic and hydrophilic 'N' donor heteropolycyclic ligands as the actinide selective ligand. A number of 'S' donor ligands are also explored for the Ln/An separation. In the present review, we made an attempt to highlight various separation processes based on soft donor ligands developed for Ln/An separations. Beside the conventional solvent extraction processes, separation possibilities membrane based and solid phase extraction techniques are evaluated for the Ln/An separation and are compiled in the present review.