Determination of oxygen/uranium ratio in irradiated uranium dioxide based on dissolution with strong phosphoric acid

Applicability of a chemical method to the determination of O/U ratio in irradiated uranium dioxide, UO/sub 2+x/, was investigated. A sample piece was taken from the irradiated UO/sub 2+x/ pellet with a diamond cutter and dissolved in strong phosphoric acid (SPA). The O/U ratio was calculated from the amounts of U(IV) and U(VI) in the solution. Oxidation states of uranium after sampling and dissolution were confirmed to be the same as those in the pellet. The stability of U(IV) and U(VI) in the SPA solution with radioactivity was investigated. For the determination of U(IV) and U(VI), two methods based on different principles, flow coulometry and spectrophotometry, were employed to avoid unexpected error. The interference from plutonium and fission products in the determination was reduced by preelectrolysis. The O/U ratio of > 2.001 in UO/sub 2+X/ with < 1 x 104 MW days/ton burnup was determined with flow coulometric detection. Reliability of the results was verified by spectrophotometry. 23 references, 4 figures, 4 tables