Spectrophotometric determination of the oxygen to uranium ratio in uranium oxides based on dissolution in sulphuric acid

The oxygen to uranium ratio in uranium oxides such as U3O8, UO2+x powders and UO2 fuel pellets has been determined by a new spectrophotometric method. The method can be used for determination of O/U ratio in UO2 pellets and powders on a routine basis. In the described method, uranium oxides in the powder form are dissolved in 2M sulphuric acid containing a few drops of HF. The concentrations of U(IV) and U(VI) are directly determined by means of the absorbances of these species at different wavelengths. For determination of the O/U ratio in U3O8 powder samples, 630 and 310 nm are the wavelengths chosen for U(IV) and U(VI), respectively. For UO2+x powder, where the O/U ratio lies between 2.04 to 2.15, U(IV) and U(VI) are determined at 630 and 300 nm respectively, whereas for UO2 fuel pellets, where the O/U ratio is less than 2.01, 535 and 285 nm are used. (author)