Numerical Study on the Influence of Double-Wire Spacers on Coolant Flow Within a Fuel Assembly of Lead-Cooled Fast Reactors Based on LBE4EqnFoam

Spacer wires are widely employed in lead-cooled fast reactor fuel assemblies to maintain rod positioning. The helical spacer structure induces rotational flow and enhances transverse mixing between subchannels, thereby significantly influencing thermo-hydraulic performance. To further regulate coolant mixing intensity and reconstruct internal flow structures, a double-wire configuration with variable radial phase differences is proposed. Three-dimensional steady RANS simulations of liquid lead–bismuth flow in a 19-pin double-wire fuel assembly are conducted using a four-equation turbulent heat transfer model. Results indicate that pressure and velocity fields exhibit periodic distributions along the helical direction, with a clear inverse correlation between high-pressure and high-velocity regions. Transverse secondary flow intensity shows pronounced axial periodicity and attains a maximum value of 0.32, with stronger mixing observed in the vicinity of the spacer wires. Peripheral and corner subchannels maintain lower average coolant temperatures, whereas peak temperatures are concentrated within internal subchannels. The overall convective heat transfer coefficient decreases gradually along the axial direction and presents a localized enhancement in the mid-axial region. The axially averaged convective heat transfer coefficient of DP60 is approximately 4.58% higher than that of DP90. This difference is a thermal comparison and does not establish overall thermo-hydraulic superiority. Peak modeled coolant temperature fluctuations are observed at the interface between peripheral and outer internal subchannels, while maximum turbulent Prandtl numbers are concentrated within internal subchannels.