Numerical investigation of contact treatment methods in the wire-wrapped fuel assembly

The thermal-hydraulic safety of the core assembly is a critical aspect in the development of lead-cooled fast reactors (LFRs). The accuracy of core thermal-hydraulic calculations is significantly influenced by the meshing treatment of the wire-wrapped fuel assembly. The most critical issue in the treatment is the contact point where the tangent of the faces between the wires and the fuel pins meets. The simulation accuracy of common treatment methods is compared through parametric studies of six cases: wire inward indentations, adding materials to connect and different wire diameter enlargements. The benchmark data for the current work is derived from the steady-state experiment conducted on the Natural Circulation Experimental Upgrade (NACIE-UP), specifically regarding boundary conditions and temperature outcomes. The phenomena of heat transfer corresponding to different treatment methods are analyzed to reveal the relationship between the thermal-hydraulic characteristics and the pin-wire contact geometry. The results show that all geometric treatment methods lead to a more uniform temperature distribution across the axial crosssection, thereby losing the original characteristics embodied in the experiment, although R-square values exceed 98 % and the maximum local temperature deviation between different cases is approximately 5 degrees C. Variances in secondary flow intensities, caused by wire disturbances, lead to temperature deviations in the subchannels. Aligning wire-wrapping gaps in CFD simulations to reflect actual conditions significantly improves the accuracy of thermal-hydraulic predictions, representing a practical advancement in reactor design and safety assessment.