Mechanisms of Leaching and Dissolution of UO₂ Fuel

An integrated experimental approach to mechanistic studies of the leaching and dissolution of irradiated UO₂fuel is described. The program includes an investigation of the solubility of the UO₂ matrix under thermodynamically well-defined conditions, detailed measurements of the leaching and dissolution of irradiated fuel under simulated disposal conditions, and electrochemical measurements with a novel UO₂ electrode to elucidate dissolution mechanisms. Initial experiments show that the solubility of UO₂ under alkaline reducing conditions is relatively insensitive to temperature changes, that the leach rates of irradiated fuel are also not strongly temperature dependent, and that surface films on the UO₂ fuel may play an important role in the dissolution process. Several aspects of the UO₂ matrix dissolution process are now understood, and the approach taken has indicated where future work is needed.