Radiative Heat Transfer in Molten UO₂ Based on the Rosseland Diffusion Method

Radiant heat transfer in a horizontal molten UO₂ pool that is about to boil has been analyzed using the Rosseland diffusion approximation and radiative slip boundary conditions. When superimposed on the free convection heat transfer, internal thermal radiation increases the heat loss through both the upper and lower pool surfaces. This increase is significant at the lower Rayleigh numbers where the radiant transfer dominates the free convection. At the higher Rayleigh numbers, radiant heat loss is small compared to the convective heat loss. Internal thermal radiation also tends to equalize the heat removed through the upper and lower boundaries, and to increase the pool depth required for fuel boiling. Since the internal radiative transfer has been shown to alter the heat loss from the pool, and therefore melt-through and cooldown rates as well as boiling, it should be incorporated into postaccident heat removal analysis.