Actinides extraction from high-level

Synthesis of agents for lanthanide and actinide extraction from high-level activity nuclear waste is the only one not related to the medical field where the 1,4-dioxane derivative of cobalt bis-(dicarbollide) was successfully applied. Moreover, the first described reaction of oxonium ringopening in polyhedral boron hydrides was performed specifically in this field [77]. During the last 10 years, numerous cobalt bis(dicarbollide)-based extraction agents were synthesized, including... 

Ansari, S.A., Pathak, P.N., Manchanda, V.K., Husain, M., Prasad, A.K., Parmar, V.S. 2005. A,A,A ,A -tetraoctyl diglycolamide (TODGA) a promising extractant for actinide-partitioning from high-level waste (HLW). Solvent Extr. Ion Exch. 23 463-479. 

The study of these polyanionic platforms in liquid-liquid extraction of various trivalent lanthanide and actinide cations from high-level radioactive acidic waste solutions was tested." It is interesting to emphasize that these novel ionic ligands have shown a dramatic enhanced extraction ability for trivalent actinides and lanthanides, particularly for Am + a thorough extraction (>99%) has been achieved in a single extraction step." " " ... 

The above information was used to develop conceptual flowsheets for the extraction of all of the actinides (U, Np, Pu, Am, and Cm) from high-level liquid waste from PUREX processing using 0.4 M 0fuel using 0.8 M DHDECMP in DEB. In both flowsheets, no oxidation state of Pu is necessary since the III, IV, and VI state extract into the organic phase. 

Conceptual flowsheet for the extraction of actinides from high-level liquid waste using 0.4 M 0<)>D[IB]CMP0 in DEB. 

Chitnis, R.R., Wattal, P.K., Ramanujam, A. et al. 1999. Recovery of actinides extracted by TRUEX solvent from high-level waste using complexing agents II. Counter-current studies. J. Radioanal. Nucl. Chem. 240 (3) 727-730. 

Dhami, P.S., Chitnis, R.R., Gopalakrishnan, V. et al. 2001. Studies on the partitioning of actinides from high level waste using a mixture of HDEHP and CMPO as extractant. 

Naik, P.W. Dhami, P.S. Misra, S.K. Jambunathan, U. Mathur, J.N. Use of organo-phosphorus extractants impregnated on silica gel for the extraction chromatographic separation of minor actinides from high level waste solutions, J. Radioanal. Nucl. Chem. 257 (2003) 327-332. 

Separation of Actinides from High-level Waste (HLW). From the point of view of seeking a possible approach to the ultimate disposal of the HLW from the reprocessing of spent nuclear fuels, processes of solvent extraction and ion-exchange techniques have been studied to recover both americium and lanthanides from the HLW and to separate those subsequently. 

Siddall investigated the ability of these compounds to extract Am(III), Ce(III), Pm(III), and HN03 from 0.1 to 12M HN03 solutions. His favorable results led him to suggest such bidentate extractants could be used to remove trivalent actinides from high-level TBP extraction process waste. This idea was later patented (5). Schulz demonstrated in 1973 that DHDECMP was an effective extractant for americium and plutonium from radioactive Hanford generated wastes (6). 

In addition, Na2C03 scrub waste will be generated in the clean-up of the dihexyl-N,N-diethyl carbamoylmethylene phosphonate (DHDECMP) extractant which is to be used to extract all of the actinides from high-level liquid waste (HLLW) in the proposed waste treatment facility described by Tedder, Finney, and Blomeke (3). 

Ansari, S.A., Mohapatra, P.K., Raut, D.R., Seshagiri, T.K., Rajeswari, B., and Manchanda, V.K. 2009. Performance of actinide partitioning extractants in hollow fiber supported liquid membrane for the transport of actinides and lanthanides from high level nuclear waste. J. Membr. Sci. 337 304-309. 

They reported the distribution ratios (Dm) of lanthanide and actinide ions and compared the Dm values with that of Am " in the extraction system of 1 M HNO3 and 0.1 M TODGA/ M-dodecane as shown in Table 18.11. The order of extractability of actinide ions from 1 M HNO3 is An, An > An02 > An02. The TODGA has an ability of co-extraction of trivalent actinide ions and lanthanide ions from high-level liquid radioactive waste. 

Mathur, J.N. Murali, M.S. Iyer, R.H. Ramanujam, A. Dhami, P.S. Gopalkrishnan, V. Rao, M.K. Badheka, L.P. Baneiji, A. Extraction chromatographic separation of minor actinides from purex high-level wastes using CMPO, Nucl. Technol. 109 (1995) 216-225. 

Morita, Y., Sasaki, Y., Tachimori, S. 2001. Development of TODGA extraction process for high level liquid waste. Preliminary evaluation of actinide separation by calculation. Global 2001 Back-end of the Fuel Cycle From Research to Solutions, September, Paris, France. 

The third fact is that spent nuclear fuel is not waste. Spent nuclear fuel contains 2% to 3% waste, but is about 97% recoverable uranium and plutonium. Each bundle has the potential electric energy equivalent of more than 10 million barrels of oil. High-level nuclear wastes consist of fission products and actinides that are extracted from spent fuel, but not saved for commercial use or research. Spent fuel may be temporarily stored until it is reprocessed to separate the waste from the valuable plutonium and uranium. The remaining glassified waste will then be permanently entombed. 

There are many examples of the studies on SLM for nuclear applications in the literature. SLMs were tested for high-level radioactive waste treatment combined with removal of actinides and other fission products from the effluents from nuclear fuel reprocessing plants. The recovery of the species, such as uranium, plutonium, thorium, americium, cerium, europium, strontium, and cesium, was investigated in vari-ons extracting-stripping systems. Selective permeation... 

Experimental work on new partitioning techniques is performed in the fiiamework of two projects. The first one has the objective to develop processes for the separation of minor actinides from very acidic aqueous solutions containing high level waste without the generation of secondary solid waste. In the second one, extractants selective to strontium, actinides -I- lanthanides, and actinides only such as calixarene and crown ether derivatives will be synthesised. The extracting properties of these compounds will be determined experimentally and modelled with molecular mechanics and molecular dynamics simulations. 

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). 

Over the past 10 years, modifications to the PUREX process have made it possible to more effectively separate neptunium. To effect the efficient separation of Np within the conventional PUREX process, Np is oxidized to VI state by nitrous add and is extracted in the first cycle along with U and Pu into the organic phase. The extracted Np( VI) follows the uranium stream and is later separated during the second purification cycle of uranium. In the RFC, the neptunium is sent to vitrification and disposed of as HLW but in an AFC option, the neptunium can be blended with MOX fuel or fabricated into special targets for later transmutation. The other minor actinides, ameridum and curium cannot be separated by reasonable modifications to the PUREX process. These elements will require the addition of special processing steps to separate them from the PUREX high-level waste stream. 

The SNF (after a cooling period to allow for decay of short-lived radionuclides) is chopped up and dissolved in nitric acid. The gasses emitted in the process are treated to avoid their release to the environment. The solution is filtered to separate the insoluble residues and sent to the solvent extraction stage in which the uranium and plutonium are extracted into the organic phase (usually TBP in a hydrocarbon solvent) and the fission products and minor actinides remain in the aqueous phase. The radioactive fission products may then be treated as high-level-waste while the uranium and plutonium are then separated from each other by selective back-extraction. 

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