Lanthanides Purex process

The SETFICS process (Solvent Extraction for Trivalent /-elements Intragroup Separation in CMPO-Complexant System) was initially proposed by research teams of the former Japan Nuclear Cycle Development Institute (JNC, today JAEA) to separate An(III) from PUREX raffinates. It uses a TRUEX solvent (composed of CMPO and TBP, respectively dissolved at 0.2 and 1.2 M in -dodecane) to coextract trivalent actinides and lanthanides, and a sodium nitrate concentrated solution (4 M NaN03) containing DTPA (0.05 M) to selectively strip the TPEs at pH 2 and keep the Ln(III) extracted by the TRUEX solvent (239). However, the DFs for heavy Ln(III) are rather poor. An optimized version of the SETFICS process has recently been proposed as an alternative process to extraction chromatography for the recovery of Am(III) and Cm(III) in the New Extraction System for TRU Recovery (NEXT) process. NEXT basically consists of a front-end crystallization of uranium, a simplified PUREX process using TBP for the recovery of U, Np, and Pu, and a back-end Am(III) + Cm(III) recovery step (240, 241). 

The flowsheet of the UREX process, developed in the United States, includes the following extraction cycles (1) separation of uranium and technetium, (2) separation of plutonium, (3) separation of cesium and strontium, (4) separation of MAs and Rare Earth Elements (REE), and (5) group separation of MA from REE metals.9,10 Flowsheet development in Europe11 includes a modified PUREX process and, after that, the DIAMEX process for separation of MAs and lanthanides, the SANEX process for separation of MAs from lanthanides, and a special cycle for Am/Cm separation. Cesium and strontium will be in the raffinate of the DIAMEX process, and this raffinate will be vitrified, or cesium can be preliminarily extracted.12... 

SANEX [Selective ActiNide Extraction] A process for removing lanthanide elements from actinides in the Purex process. Not yet fully developed. The name is used also for a range of toiletries. 

As shown in Figure 6, diisodecylphosphoric acid (DIDPA) gives higher distribution ratios compared with those of DEHPA, being more suitable for using as extractant at higher acid concentrations. One M DIDPA diluted with normal paraffins can be used to recover americium and lanthanides from the HLW of PUREX process. 

Already for some years (1991-93) studies have been made for procedures to separate the long-lived actinides from the fission products in the high-level wastes of the PUREX process. The aim of friis work was to develop a flowsheet for a solvent extraction process and the main finding of the last years was that all extractants containing only sulphur are not suitable for the separation of transplutonides (III) from lanthanides (ill). 

The P/T process will be coupled after an improved PUREX process that puts all technetimn, iodine, and neptunium into the waste fraction or into special fractions. Thus, the waste will contain fission products and minor actinides (americium and curium). The process will probably be a solvent extraction process although molten salt systems are also studied as an alternative. The main issue will be to obtain pure Am and Cm fractions for subsequent destruction, i.e., fractions that do not contain any lanthanides. Some of the lanthanides, which are chemically very similar to trivalent actinides, have very high neutron cross sections. Therefore, they must be removed to make actinide burning possible. In some cases, it may also be desirable to transmute some long-lived fission products, e.g., Tc and l, to more shortlived nuclides. 

In the AREVA version of the PUREX process, plutonium is removed from the uranium after the original extraction, converted to oxide and used in MOX fuel fabrication. Neptunium, americium, curium, and other remaining FPs (including lanthanides) are vitrified and incorporated in the HEW form (Richter et al., 2006). 

Modolo, G., Asp, H., Vijgen, H. et al. 2007. Demonstration of a TODGA/TBP process for recovery of trivalent actinides and lanthanides from a PUREX raffinate. GLOBAL 2007, Boise, ID, September 9-13, pp. 1111-1116. 

A new concept integrating both the PUREX and the TRPO processes is proposed by the INET researchers. This simplified PUREX-TRPO process uses a binary mixture of TBP (20%) and TRPO (20%) in kerosene to extract all actinides including TPEs, which can be back-extracted together with the trivalent lanthanides in a 5.5 M HN03 solution as in the TRPO process (94). 

The ZEALEX Process Researchers from KRI have shown that the zirconium salt of dibutyl phosphoric acid (ZS-HDBP) was soluble in Isopar-L in the presence of 30% TBP. This super PUREX solvent, known as ZEALEX, extracts actinides (Np-Am) together with lanthanides and other fission products, such as Ba, Cs, Fe, Mo, and Sr from nitric acid solutions. The extraction yields depend on both the molar ratio between Zr and HDBP in the 30% TBP/Isopar-L mixture and the concentration of HN03 (232). Trivalent transplutonium and lanthanide elements can be stripped together from the loaded ZEALEX solvent by a complexing solution, mixing ammonium carbonate, (NH4)2C03, and ethylenediamine-N.N.N. N -tetraacetic acid (EDTA). An optimized version of the process should allow the separation of... 

Di(2-ethylhexyl) phosphoric acid (HDEHP) is an extractant molecule used for An(III)/Ln(III) separation. Used in TALSPEAK-type processes in a mixture with TBP, or in the DIAMEX-SANEX process in a mixture with a malonamide (154-157), it has also been proposed, in a mixture with TBP, to remove strontium from PUREX acid waste solution in the Hanford B plant (158). Therefore, numerous studies have focussed on the radiolytic degradation of HDEHP and its effects on the extraction of Sr(II), lanthanides(III), and actinides(III) (10, 158-163). 

The recovery of actinides from such solutions by acidification with HNO3 followed by solvent extraction is hampered by the accumulation of H2MBP and HDBP in the solvent. This problem may be overcome by extracting the H2MBP and HDBP from the acidified carbonate solutions with 2-ethylhexanol, EHOH, prior to acidification. Laboratory trials indicated that such a process was potentially applicable to Purex waste streams. Problems identified were the formation of precipitates of H MBP or HDBP complexes on neutralization of the carbonate solutions and the transfer of some EHOH through the process into the actinide extractant used. The extraction of oxidation state (IV) and (VI) actinides could be accomplished using TBP while DHDECMP could be used to extract oxidation state (III) actinides and lanthanides also. 

The Selective ActiNide Extraction (SANEX) process has been developed by Madic and Hill (Hill et al., 2002, 17-21 Madic et al., 2002). As part of the management of minor actinides, it has been proposed that the lanthanides and trivalent minor actinides (Am and Cm) should be removed from the PUREX raffinate by a process such as DIAMEX in France or TRUEX in the USA. To allow the actinides such as americium to be reused in industrial sources or used as fuel, the lanthanides must be removed. The lanthanides have large neutron cross sections and hence they would poison a neutron-driven nuclear reaction. 

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