A RANS Analysis of Pressurized Thermal Shock Phenomena in Nuclear Reactor Geometries Using Star CCM+

Abstract

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 provide information capable of impacting the reactor lifetime. The flow in the domain is driven solely by buoyancy, through the use of two varying 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 simulated 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 Averaged Navier-Stokes (RANS) framework, with focus on K-epsilon model. Turbulent parameters and values for densities, velocities and Reynolds stresses were gathered at locations of interest. These quantities of interest were gathered with the intent on guiding the experimental analysis in preparation for a future verification and validation study for the committee on the safety of nuclear installations. The simulated results deviate from the available experimental data, this is due to a change in the material properties and the solutions used in the experimental analysis. Despite this, the simulations of the cold-leg mixing experiment behave physically as expected.