Sodium-cooled fast reactors (SFRs) represent a critical advancement in fourth-generation nuclear technology, where accurate thermal-hydraulic characterization is vital for ensuring operational safety and efficiency. The complex geometry of SFR fuel assemblies presents significant challenges for conventional Computational Fluid Dynamics (CFD) approaches.

This study aims to develop and validate an optimized porous media methodology to facilitate efficient yet precise CFD analysis of SFR core thermal-hydraulics.

The investigation examined the China Experimental Fast Reactor (CEFR) core configuration, comprising 81 hexagonal fuel assemblies. Firstly, the porous media model integrated anisotropic permeability tensors to account for directional flow resistance effects induced by wire-wrap spacers. Momentum source terms were calibrated using experimental pressure drop data. Then, the computational domain was divided into four distinct regions to accommodate spatial variations in power distribution and coolant flow patterns. Additionally, to explore the influence of inter-wrapper flow (IWF) on the core's thermal-hydraulic state, modeling was performed on the inter-wrapper flow and its surrounding components. Finally, the conjugate heat transfer method was employed to calculate the inter-wrapper flow, and results were compared with the conventional CFD approach.

Comparison results demonstrate that the porous media model successfully predicts core thermal-hydraulic behavior with a maximum deviation of 0.7% in pressure drop compared to experimental benchmarks, and computational efficiency is significantly enhanced relative to full-resolution CFD. The inter-assembly gap flow contributes minimally to the total coolant redistribution, confirming its negligible impact on overall core performance.

The proposed porous media model offers a computationally efficient yet accurate alternative for SFR core analysis, demonstrating strong potential for engineering applications. The findings indicate that inter-assembly gaps can be safely disregarded in large-scale simulations without substantial loss of accuracy. This work provides valuable insights for optimizing SFR core design and improving safety assessments.