The interaction and dissolution of solid UO2 by molten Zircaloy-4 cladding in an inert atmosphere or steam

The dissolution of solid UO2 by molten Zircaloy-4 cladding, and structural changes in the UO2 matrix, have been investigated at ≅ 2000 degrees Celsius, using internally heated fuel-element simulators. Tests were carried out in an inert atmosphere or steam. Post-test examinations showed that the molten cladding contains varying proportions of uranium and oxygen that com from the partial dissolution of the UO2. In the presence of steam, the external cladding surface also reacts to form zirconium oxide, the formation of which is a function of heating rate, time and temperature. The maximum amount of UO2 dissolved by the molten Zircaloy-4 cladding was 6 vol.% in the inert atmosphere; the typical amount was 0.5 to 1 vol.%. In steam, the maximum amount was 0.5 vol.%