In-depth understanding of sodium heat transfer characteristics with low Prandtl number in wire-wrapped fuel assemblies using high-fidelity CFD technique

Understanding the thermal-hydraulic behavior of sodium-cooled fast reactors is crucial for optimizing their performance and safety. This study investigates the unique low Prandtl number properties of liquid sodium coolant, which influence heat transfer and fluid dynamics in turbulent flows within wire-wrapped fuel bundles. Using a combination of experimental data and high-fidelity Computational Fluid Dynamics (CFD) simulations, we analyzed key thermal-hydraulic characteristics for the ORNL 19-pin, Toshiba 37-pin, WARD 61-pin, and KAERI 61-pin fuel bundles under various heating and flow conditions. CFD simulations were conducted in STAR-CCM+ and ANSYS CFX and examined mass flow rates, pressure drops, and temperature distributions, validated against experimental data. Sensitivity analyses of turbulence models (SST, k-ε, and k-ω) indicated that the SST model best captured complex flow and three-dimensional vortical structures in SFR conditions, with edge subchannels exhibiting enhanced heat transfer due to higher axial velocities. Code-to-code comparisons confirmed strong agreement in predicted results, with STAR-CCM+ aligning more closely with experimental data in some cases. The study underscores the importance of advanced CFD techniques in accurately modeling thermal management in wire-wrapped fuel bundles, contributing to improved safety and efficiency in SFR systems