The Importance of High-fidelity Numerical Simulations for Nuclear Reactor Design and Safety

Large-scale computations play a crucial role in numerous engineering and scientific applications, especially in the nuclear field, where the demand for accurate simulations and reliable reference data for validation purposes underscores the significance of high-fidelity simulations. Given the substantial computational resources required, these simulations necessitate dedicated computational facilities. This presentation will highlight the vital role of high-fidelity numerical simulations, specifically Direct Numerical Simulation (DNS), in facilitating the design and safety analyses of nuclear fission reactors.

To exemplify this, a Direct Numerical Simulation (DNS) is conducted using a high-order spectral element method to analyze flow and thermal fields in a Pressurized Thermal Shock (PTS) scenario. The chosen configuration represents a simplified reactor pressure vessel. Cold water is introduced from a square duct, impacting the downcomer wall containing the hot water. Mixing between the cold and hot water occurs in the downcomer. The friction Reynolds number in the inlet duct is 180, with a unitary Prandtl number for the fluid. The thermal field is addressed by imposing two different boundary conditions: isothermal and adiabatic, representing extreme scenarios of a conjugate heat transfer problem. A meticulous meshing strategy is employed, and post-analysis verification ensures the mesh resolution meets high-quality DNS. These simulations are performed using the HPC facility at the Świerk Computing Centre (CIŚ), NCBJ, Poland.