Investigation of the Turbulent Mass Transport during the Mixing of a Stable Stratification with a Free Jet Using Cfd-methods

During a severe accident, hydrogen can be produced by a chemical reaction between the Zircaloy cladding and water and escape into the containment through a leak in the primary circuit. The prediction of the mass transport of hydrogen is vital for an optimized positioning of countermeasures like recombiners. It is possible that a stable stratification of hydrogen and air occurs, due to the different densities of those fluids. This paper discusses the simulation of mass transport processes during the mixing of such a stable stratification with a free jet. The mixing of a stable stratification with a free jet is characterized by the time dependency of the flow, sharp velocity and density gradients as well as the non-isotropy of Reynolds stresses and turbulent mass fluxes. This paper discusses results of the eddy diffusivity model for the turbulent mass flux as well as improvements with the use of a newly implemented non-isotropic model.