Fluorinated Diluents - New Possibilities For Radiochemical Technology
- RPA 'V.G.Khlopin Radium Institute', 194021, Saint-Petersburg, 28, 2nd Murinsky av. (Russian Federation)
A variety of extraction mixtures for recovery of one or several hazardous radionuclides has been proposed to treat high-level radioactive wastes (HLW) generated in PUREX-process. Extraction methods for spent fuel reprocessing and waste treatment are considered in many reviews. Such compounds as di-phosphine dioxides, carbamoyl-methylene-phosphine oxides, crown-ethers, chlorinated cobalt dicarbollide, diamides of malonic acid, diamides of di-glycolic acid, different calixarenes, zirconium salts of organophosphorus acids are offered as extractants. The majority of these extractants are polar compounds, since they are poorly dissolved in saturated hydrocarbons, in particular their complexes with metals. Despite this fact, it is mainly proposed to use them in hydrocarbon diluents. For some extractants like diamides of malonic or di-glycolic acids it has been possible to find some compounds containing rather long alkyl radicals which are readily dissolved in saturated hydrocarbons. The drawback of such approach is concerned with hazardous occurrence of high-molecular decomposition products which are not removed from organic phase. Besides, this approach does not permit to attain high solubility of such extractant classes as dicarbollides, carbamoyl-phosphine oxides, di-phosphine dioxides etc. To provide the solubility of carbamoyl-phosphine oxides or crown-ethers in saturated hydrocarbons, one can use some modifiers, i.e. polar compounds like tributyl phosphate; to afford the solubility of malonamides or diamides of di-glycolic acid, monoamides of carboxylic acids are used; in the case of crown-ethers octanol is applied. To provide the higher solubility of calix[4]arene-bis-(tertoctylbenzo- crown-6) - BOBCalixC6 in hydrocarbon diluent Isopar L, 0.750 M of fluorinated modifier Cs-7SB were added at cesium extraction from alkaline solutions (CSSX-process), as well as at combined extraction of Cs and Sr by FPEX-process (Fission Product Extraction). Adding a modifier increases solubility of metal solvates, but, as a rule, the hazard of forming the third phase or precipitate remains even on complete saturation. Introduction of modifier into the system results in additional formation of new plausible radiolysis products, the effect of which on extraction and especially on stripping process calls for further investigation. An alternative approach to improving the solubility of extractants consists in the use of well-solvating polar solvents. Diluents modify the extraction ability of extractant over a wide range. The polar diluents enhance the extraction process of metals and the solubility of complexes in many cases, especially as applied to polydentate compounds. The use of fluorinated polar diluents for many extractants allows to offer much more effective extraction flowsheets of radionuclide recovery. The operating experience on meta-nitro-benzo-trifluoride (MNBTF, F-3, fluoro-pole-732) has shown that it is more readily regenerated than saturated hydrocarbons. Its radiolysis products are washed-out into aqueous phase and are not accumulated in organic phase. Some doubts on high corrosion hazard are overestimated, as is obvious from practical implementation. Based upon the principle of optimizing not an individual operation, but the process as a whole the fluorinated diluents may be considerably more efficient than the traditional hydrocarbon ones. Unfortunately, up till now there has been no way to determine the effect of diluent structure on the extraction properties of system. Nevertheless, the empirical regularities generalizing the large volume of experimental data have made it possible to define several classes of compounds showing promise as potential commercial diluents. (author)
- Research Organization:
- American Nuclear Society, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
- OSTI ID:
- 20979677
- Resource Relation:
- Conference: Advanced nuclear fuel cycles and systems (GLOBAL 2007), Boise - Idaho (United States), 9-13 Sep 2007; Other Information: Country of input: France; 89 refs; Related Information: In: Proceedings of GLOBAL 2007 conference on advanced nuclear fuel cycles and systems, 1873 pages.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Diamide derivatives of di-picolinic acid as actinide and lanthanide extractants in a variation of the UNEX process
Joint Recovery of f-Elements Using Solvent Based on Carbamoyl-phosphine Oxides Heading Toward ORGA-Process