Thermal Radiation Modeling in Multiphase Flows Typical of Melt-Coolant Interaction

The chapter is concerned with radiation heat transfer modeling in multiphase disperse systems, which are formed in high-temperature melt-coolant interactions. This problem is important for complex interaction of the core melt with water in the case of a hypothetical severe accident in light-water nuclear reactors. A considerable part of thermal radiation emitted by the melt droplets lies in the range of water semi-transparency. As a result, the radiation is not completely absorbed in water and one needs to account for radiation heat transfer between the particles which have different temperatures. The scattering of radiation by steam bubbles and melt droplets separated from ambient water by a thin steam layer is also important. The problem is further complicated by semi-transparency of small oxide droplets and temperature differences between the center and surface of the melt droplets during their solidification. Nevertheless, the specific radiative properties of the multiphase flow components allow for a simplified approach, which is implemented in a problem-oriented CFD code. A more sophisticated approach for visible radiation of the multiphase media is also presented. The latter is expected to be important for optical diagnostics of the flow in small-scale experiments including those using various stimulant melts.