Electrochemical Studies of Corrosion of Sinfuel: Simulated Used UO2 Fuel

Abstract

ABSTRACTThe corrosion of SIMFUEL, simulated high-burnup CANDU (CANadian Deuterium Uranium) fuel, was investigated in 0.1 mol·dm−3 NaClO4 solution (pH ∼ 9.5) as a function of dissolved oxygen concentration using electrochemical techniques and X-ray photoelectron spectroscopy (XPS). Electrodes were constructed of SIMFUEL pellets with compositions close to those of a natural UO2 fuel that has undergone burnup of 3 at% and 6 at%. The XPS analysis of freshly polished SIMFUEL pellets showed that the extent of uranium oxidation in SIMFUEL was equivalent to that in stoichiometric UO2. The SIMFUEL electrodes showed higher conductivity and electrochemical reactivity than the pure UO2 electrodes. A comparison of the open circuit corrosion potentials of the SIMFUEL electrodes with that of a pure UO2 electrode in oxygenated solutions showed a much faster increase in the potential for the SIMFUEL electrodes at short times. This suggests that the initial stages of UO2 oxidation, i.e., UO2 → UO2+x → UO2.33, are facilitated by fission product impurities in the UO2 matrix. However, the “steady-state” oxidation of uranium in SIMFUEL by the dissolved O2 was similar to that observed in pure UO2 under similar conditions.