Among the advanced nuclear technologies, high-temperature gas-cooled reactors (HTGRs) stand out due to their co-generation capabilities and exceptional passive safety systems. The HTGR’s exceptional passive safety feature is demonstrated with the HTR-PM nuclear power plant. The loss of cooling tests validated that these reactors can be cooled down by the laws of nature, without depending on the emergency core cooling system during accident conditions. HTGRs rely on a reactor cavity cooling system (RCCS) to remove decay heat from the reactor pressure vessel (RPV) over long-term transients. The RCCS receives heat from the RPV through convection and radiative heat transfers. In RCCS designs, radiative and convective heat transfer strongly influence each other, and this interaction becomes even more pronounced due to the system?s reliance on natural convection. Thermal-hydraulic experiments and simulations are essential for characterizing the complex thermal-hydraulic behavior of the RCCS. There are several studies focused on the experimental and numerical modeling of the RCCS. However, a notable gap exists in the literature when it comes to high-fidelity simulations such as DNS or LES of the RCCS. Combining high-fidelity approaches promises to deliver more accurate and reliable numerical data, thus improving the understanding of the thermal-hydraulic characteristics of RCCS designs. Large Eddy Simulation (LES) model has been developed for forced convection inside the RCCS to obtain a high-fidelity representation of the RCCS at a scale that has not been attempted before. The LES model is utilized to compare with the RANS model. This comparison verifies the robustness and accuracy of the turbulence modeling approach of the RANS model for the RCCS. Finally, based on the comparison between the LES and RANS models, the RANS model of the experimental facility is developed and compared with the available experimental data.
