Online May 8, 2011
Title: Pre Concentration of Impurities in Gaseous Uranium Fluoride and their Characterisation by Mass Spectrometry
Uranium hexafluoride is a volatile compound, which is converted to reactor fuel after enrichment to about 3%. In order that the fuel functions efficiently, the amounts of certain impurities present should be kept within the limits specified by ASTM . Hydrogen fluoride is a major admixture in uranium hexafluoride which has to be removed. This HF reacts with other impurities present to form their fluorides. During the production of UF6 the non-volatile fluorides remain behind as an ash in fluorination reactor while the volatile impuriities volatalise along with uranium hexafluroide . Corrosion of the containers by HF also adds some specific impurities to the material. Howver, the relatively high volatility of UF6 makes its purification possible by distillation, but traces of impurities always remain. Oils, used in pumping system for handling UF6, contaminate the material and their fluorination also takes place in presence of hydrogen fluoride. As reported in literature different hydrocarbons and partially subsituted halohydrocarbons in uranium hexafluoride must not exceed the certified limits …
Although the work presented here is of qualitative nature, it can be concluded from the results obtained that the impurities present in a UF6 sample and having higher boiling or sublimation points than uranium hexafluoride can be pre concentrated by distillation process. Peaks for the fluorides of Cr, Ir, Rb, S, SI, Sr, Ta and Ti have been identified and the intensities of those due to less volatile compounds than uranium hexafluoride, are found to be enhanced after pre-concentration. Fluorine compounds of silicon and sulphyr are more volatile than UF6, resulting in the diminution of peaks of their fluorides in the mass spectrum of pre concentrated samples. Rubidium polyfluoride and their acid compounds have also been identified. Hydrocarbons may contaminate uranium hexafluoride during gas handling and also during experiments A number of hydrocarbon and fluorohydrocarbon peaks observed in the mass spectra of UF6 samples, were characterised.