Large-cell model of radiation heat transfer in multiphase flows typical for fuel–coolant interaction

The visible and near-infrared radiative properties of water containing polydisperse steam bubbles and core melt particles are analyzed. The alternative approximate models of radiation heat transfer in the range of water semi-transparency are considered. A new approach based on radiation balance equations for a large computational cell of size about several centimeters is suggested. This approach called large-cell model takes into account not only water heating but also radiation heat transfer between the particles of different temperatures. The latter is important for problems of fuel–coolant interaction in possible severe accident of light water nuclear reactors. The model problems considered in the paper give estimates of nonlocal effects of thermal radiation and confirm the applicability of the large-cell model at parameters typical for fuel–coolant interaction.