An evaluation and revision of the gravimetric determination of uranium in uranium hexafluoride

An evaluation of the indirect gravimetric determination of uranium in uranium hexafluoride has been made, and the accuracy has been established by comparison to a direct titration of uranium using potassium dichromate (SRM-136c). From this study the gravimetric method has been revised to increase accuracy. The revised method is biased less than 0.01 percent low as compared to 0.02 percent with the unrevised method. It was found that the gravimetric factor must be based on the stoichiometry of the U/sub 3/O/sub 8/ which varies with pyrohydrolysis conditions. The low bias was caused by volatilization loss of uranium as uranium hexafluoride during pyrohydrolysis and very small errors in the determination of the sample weight. Because of the volatilization loss the use of a bias correction factor with the revised method is justified. 5 refs., 7 tabs.