OpenFOAM modeling of beryllium melt motion and splashing from first wall in ITER

Abstract

Beryllium (Be) is a material which will be used as a plasma facing component in ITER due to its unique properties of high thermal conductivity, low density, and high strength. However, under extreme conditions of high temperature and pressure, Be can melt at the surface of tiles and molten droplets can be ejected into the reactor leading to disruption of fusion plasma. The pressure, mass density, velocity of Be vapor, and variations of temperature at the melt layer interface can influence the splashing of Be melt. The Computational Fluid Dynamics (CFD) model based on the OpenFOAM toolbox, a free open source CFD software package, was developed to treat the coupled flow of liquid Be metal and its vapor. The vapor-melt interface is modeled using the volume of fluid (VOF) approach implemented in the interCondensatingEvaporatingFoam solver that solves the continuity, momentum, heat conduction, and VOF equations. This CFD model is capable to predict the hydrodynamic effects of Be vapor on the melt layer motion, splashing, non-linear growth of melt waves, and ejection of molten droplets. The modeling accounts for the effects of thermal, viscous, gravitational, and surface tension forces at the vapor-melt interface. In this research, we used the interCondensatingEvaporatingFoam solver to simulate the effects of Be phase change and the development of melt motion with the droplets ejected from the surface. The CFD model accounts for inter-phase change between Be liquid and Be vapor. The evaporation model was validated against the Stefan phase-change problems. The influence of heat and mass transfer across the vapor-melt interface on melt layer stability is also investigated. The results provide an understanding of how the rate of phase change affects the development of melt structures and waves at the vapor-melt interface.