High level waste, separation actinides from

Bond, W.D., and R.E. Leuze, 1980, Removal of americium and curium from high-level wastes, in Actinide Separations, ACS Symposium Series, Vol. 117, eds J.D. Navratil and W.W. Schulz (American Chemical Society, Washington, DC) p. 441. 

After the separation of the actinides from the high-level waste, it is desirable to remove certain other fission products from the nuclear wastes. Some Cs and Sr are low-charged cations that react well with macro-cyclic ligands (e.g., crown ethers, calixarenes). Research to synthesize and investigate the properties of macrocyclic ligands for application in nuclear waste treatment has been an active effort internationally. Some of the results obtained are discussed in section 12.7. 

In tlie PUREX process, the spent fuel and blanket materials are dissolved in nitric acid to form nitrates of plutonium and uranium. These are separated chemically from the other fission products, including the highly radioactive actinides, and then the two nitrates are separated into tv/o streams of partially purified plutonium and uranium. Additional processing will yield whatever purity of the two elements is desired. The process yields purified plutonium, purified uranium, and high-level wastes. See also Radioactive Wastes in the entry1 on Nuclear Power Technology. Because of the yield of purified plutonium, the PUREX process is most undesirable from a nuclear weapons proliferation standpoint,... 

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. 

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. 

Figure 7. Flowsheet of actinide separation from Fur ex high-level waste with...

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. 

Manohar, S., Sharma, J.N., Shah, B.V., Wattal, P.K. 2007. Process development for bulk separation of trivalent actinides and lanthanides from radioactive high-level liquid waste. Nuclear Science and Engineering 156 96-102. 

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. 

Hirano, H., Koma, K., Koyama, T. 2002. Waste minimization in actinides(IH)/ lanthanides(III) separation process from high-level liquid waste. 7th Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation, October, Jeju, Republic of Korea. 

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. 

The CTH actinide separation process was developed as a possible means to reduce the expected long term dose to man from a geologic repository containing solidified radioactive waste from the reprocessing of spent nuclear fuel The distribution data for the elements present in significant amounts in the high level liquid waste (HLLW) from a Purex plant, the general principles and the flowsheet have been described in detail elsewhere A... 

The thrust of the experimental program at ICPP was to find a separation procedure that would separate plutonium, americium, and curium from high-level first-cycle raffinate (see Table I) and leave behind the cladding elements, salting agents, and the bulk of the fission products. Fission-product lanthanides, because of their similar valence and ionic size, would be expected to follow americium in nearly any simple separation scheme. Americium and curium are present in ICPP waste as trivalent ions while plutonium is most likely present as both Pu(IV) and Pu(VI). Any separation scheme must be applicable to all these ionic actinide species. 

The major problem to be solved is the separation of the minor actinides (MA), mainly americium and curium, without producing large quantities of secondary waste. At present, most of the extractants are applied in a two-step process MA are first coextracted with the rare earths from the high-level liquid waste and then MA are separated from the rare earths. One difficulty of this... 

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