DISSOLUTION OF SOLID UO2 BY MOLTEN ZIRCALOY

On the basis of different experimental data from separate-effect tests on the kinetics Of UO2 interaction with molten Zircaloy at 1900-degrees-C and exceeding temperatures, a theoretical model is proposed which describes the material behavior during different stages of the chemical interaction process before and after liquid phase saturation. In the first stage dissolution of UO2 and quick saturation of the Zircaloy melt by U and O atoms take place. In the second stage the UO2 dissolution continues with a lower reaction rate and a parabolic time law (is-proportional-to t1/2), and is accompanied by precipitation and growth of a ceramic phase in the liquid. It is shown that the main cause of the discrepancy amongst the different experimental results found in the literature is connected with different dimensions of the UO2 Crucibles and different UO2/Zircaloy mass ratios used in the experiments. The analysis in the present paper leads to recommendations for the application of measured Arrhenius correlations for the kinetics of UO2 dissolution by molten Zircaloy in fuel rods during severe reactor accidents by renormalization of the UO2 dissolution rates.