Potentiometric determination of hexavalent uranium in uranium silicide samples

The Chilean Nuclear Energy Commission's Department of Nuclear Materials has among its projects the production of fuels elements for nuclear reactors, and, therefore, the Chemical Analysis Laboratory must have a rapid and reliable method for uranium analysis, to control the uranium concentration during each stage of the production process. For this reason the Chilean Nuclear Energy Commission's Chemical Analysis Laboratory has validated a potentiometric method, which is a modification of the Davies and Gray method proposed by A.R. Eberle. This method uses the Potentiometric Titration Technique and is based on the direct and rapid reduction of uranium (VI) to Uranium (IV), in a concentrated phosphoric acid medium, with excess iron (II) used as a reducing agent. In this medium the excess iron (II) selectively oxidizes to iron (III) with nitric acid, using molybdenum (IV) as a catalyzer, the nitrous acid that is produced is eliminated by adding amidosulfuric acid. The solution is diluted with 1M sulfuric acid and the uranium (IV) obtained is titrated potentiometrically with potassium dichromate in the presence of vanadilic sulfate to obtain a better defined final titration point. The samples were softened with hydrochloric acid and nitric acid and later 50 ml were estimated in a 20% sulfuric acid medium. The analytical method was validated by comparing it with Certified Reference Material (C.R.M.) from the New Brunswick Laboratory (NBL), Metallic Uranium, CRM 112-A. The F Test and the T Test show that the value calculated is less than the tabulated value so the result is traceable to the reference material. The quantification limit, sensitivity, precision and accuracy were quantified for the method