Materials chemistry and transport modeling for severe accident analyses in light-water reactors III. Fuel dissolution by molten cladding Original Research Article

The rate of fuel dissolution by melting cladding during a severe fuel damage accident is shown to be controlled by the flow of fission product decay heat to the interaction zone, which supplies the endothermic enthalpy changes accompanying UO2 dissolution and αZr(O) melting. Diffusion in the growing U-Zr-O melt is rapid and the liquid-phase concentrations remain at saturation. Reduction of the fuel by oxygen diffusion affects both the amount of oxygen in the melt and the heat balance in the melting region. Over a wide range of conditions, the time required to melt the cladding completely is approximately 100 s and the amount of fuel dissolved is approximately 5% of the pellet content of uranium. Detailed modeling of this process may not be critical to severe accident analyses.