Influence of spray characteristics on local light gas mixing in nuclear containment reactor applications

The action of spray on the mixing of different gases is used in numerous industrial applications, such as the chemical industry or the nuclear containment. The present paper concerns the impact of a spray on the break-up of a light gas layer (helium) initially confined in the top of a closed volume. Numerical calculations were performed in order to simulate the evolution of the helium concentration when the spray is activated. The objective of the paper is to show how the boundary conditions used for describing the spray can be important on the local gas mixing. Several sensitivity studies were performed that show the importance of the droplet boundary conditions: droplet size distribution, droplet velocity profiles, number of droplet classes, etc. Influence of these parameters on local gas concentration can be even higher than the one induced by a different turbulence model or some numerical parameters. Influence of the nozzle position inside the vessel is also analyzed. Extrapolation to an industrial application based on nuclear reactor containment is then discussed and recommendations are given for CFD simulations on the impact of spray systems on the gas mixing in nuclear reactors.