A RANS simulation of cold leg buoyant mixing

Computational fluid dynamics (CFD) simulations were conducted using Star CCM+ in order to investigate the mixing characteristics in the cold leg injection region of a pressurized water reactor (PWR) pressure vessel. Through the use of CFD codes, this present work seeks to characterize the mixing in this region in order to pro- vide information capable of impacting the reactor life- time. The flow in the domain is driven solely by buoy- ancy, through the use of two vary- ing density fluids in an isothermal setup. The fluids used in the experiment were a salt-water and ethanol-water mixture, for both the heavy fluid and light fluid respectively. The simu- lated density difference was chosen to be 10% and the cold tank fluid height was adjusted such that the static pressure across the initial fluid-fluid interface would be zero. The simulation was conducted in the Reynolds Av- eraged Navier-Stokes (RANS) framework, with focus on K-epsilon model. Turbulent parameters and values for densities, velocities and Reynolds stresses were gath- ered at locations of interest. These quantities of interest were compared with the experimental data, where pos- sible, and the results are presented here.