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Journal of Radioanalytical and Nuclear Chemistry
Authors: S. Ravi, S. Ravi, A. K. Deepa, A. K. Deepa, S. Susheela, S. Susheela, P. V. Achuthan, P. V. Achuthan, S. Anil Kumar, and U. Jambunathan

Summary  

A method has been developed for the estimation of 90Sr in reprocessed uranium oxide samples obtained from the Purex processing of natural uranium spent fuel discharged from the research reactor. The method employs a combination of precipitation and solvent extraction procedure to eliminate other beta-impurities prior to resorting to the estimation of 90Sr by beta-counting. 106Ru was eliminated by volatalizing with perchloric acid, uranium was removed by carrier precipitation with strontium as sulphate. The sulphate precipitate was converted to carbonate and dissolved in nitric acid. 234Th and 234Pa were eliminated by synergistic solvent extraction using tri-n-butyl phosphate and thenoyl trifluoroacetone extractant mixture in xylene. An iron scavenging step was included to remove any residual impurities. Finally, strontium is precipitated as SrC2O4 . H2O. The separated 90Sr activity was followed to check the equilibrium growth of 90Y.

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Abstract  

The identification of isotopic composition of depleted uranium obtained after the reprocessing of spent fuel is very much important as far as their further applications are concerned. The concentration of 235U in the reprocessed uranium will be lower and their depletion depends mainly on the type of the reactor and burn up. The depleted uranium has a variety of applications in nuclear fuel cycle operations and industries warranting quick assessment of its isotopic composition. This paper describes the methodology developed and used for the estimation of 235U concentration in reprocessed uranium in the form of uranyl nitrate solution. A non destructive technique by high resolution gamma-ray spectrometry with HPGe detector has been used for the analysis. The activity ratio of 238U/235U, obtained from the absolute activity measurement on the 185 keV gamma-line of 235U and 1001 keV gamma-line of 234mPa, has been used for the estimation of 235U isotopic content in the sample using a mathematical formula. This method offers rapid and reliable estimate of the 235U concentration in samples comparable with that of mass spectrometry measurements. The results show that 235U concentration in the sample can be determined within 5% error for 10000 seconds counting.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: S. Ravi, A. Deepa, B. Surekha, S. Susheela, P. Achuthan, S. Anil Kumar, K. Vijayan, U. Jambunathan, S. Munshi, and P. Dey

Abstract  

90Sr estimation in reprocessed uranium was carried out by a series of solvent extraction and carrier precipitation techniques using strontium and lanthanum carriers. Fuming with HClO4 was used to remove 106Ru as RuO4. Three step solvent extraction with 50% tri-n-butyl phosphate in xylene in presence of small amounts of dibutyl phosphate and thenoyl trifluoro acetone was carried out to eliminate uranium, plutonium, thorium and protactinium impurities. Lanthanum oxalate precipitation in acid medium was employed to scavenge the remaining multivalent ions. Strontium was precipitated as strontium oxalate in alkaline pH and 137 Cs was removed by washing the precipitate with water. A strontium recovery well above 70% was obtained. Final estimation was carried out by radiometry using end window GM counter after drying the precipitate under an infra red lamp. The same procedure was extended to the estimation of 90Sr in a diluted sample of the actual spent fuel solution. An additional lanthanum oxalate precipitation step was required to remove the entire 144Ce impurity from this sample. This modified procedure was employed in the determination of 90Sr in a number of reprocessed uranium samples and the over all precision of the method was found to be well within ±10%. An additional barium chromate precipitation step was necessary for the analysis of reprocessed uranium samples from high bumup fuels to eliminate trace amounts of short lived 224Ra produced during the decay of 232U and its daughters as they interfere in the estimation of 90Sr.

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