Determination of the stoicheiometry of uranium dioxide by differential-pulse polarography

Uranium dioxide is widely used as a nuclear fuel and usually it exists as a non-stoicheiometric hyperstate UO2+x because of the oxygen interstitial arrangement. The proposed method for determining the oxygen to uranium ratio in uranium oxides is based on the dissolution of the nuclear fuel in concentrated phosphoric acid under an inert atmosphere, to preserve the uranium oxidation states. After complete dissolution, sulphuric acid is added in order to obtain a 1.47 M H3PO4–1.5 M H2SO4 supporting electrolyte. Differentialpulse polarographic determination of uranium(VI) directly follows at –0.09 V versus S.C.E. An aliquot of this solution is then oxidised with an almost equivalent amount of cerium(IV) sulphate solution, converting all uranium(IV) into uranium (VI); the total uranium content is then determined in the same way. The proposed method permits determinations of uranium(VI) levels as low as 0.2 µg ml–1 with a relative standard deviation of about 2%.The oxygen to uranium ratio is calculated by the equation O/U = 2.000 0 + U(VI)/total U and a result of 0.001 unit is obtainable with a coefficient of variation of about ±0.1%.