Numerical investigation on the thermal-hydraulic performance of LFR fuel assemblies with multi-parameter wire wrap geometries

Lead-cooled fast reactors (LFRs) represent a highly promising fourth-generation nuclear technology, characterized by low operating pressures, inherent safety, and compact core configurations. Within LFRs, hexagonal fuel assemblies rely heavily on wire-wrapped structures to ensure subchannel stability and enhance thermal-hydraulic performance. However, existing studies predominantly focus on isolated geometric variations, leaving the synergistic multi-parameter effects in heavy liquid metals insufficiently explored. Addressing this gap, this study conducts a comprehensive computational fluid dynamics (CFD) investigation on the Lead-Bismuth Eutectic (LBE) cooled 19-pin wire-wrapped assemblies based on the MYRRHA core. Following a rigorous validation against experimental benchmark data, a systematic parametric analysis is executed to evaluate the coupled effects of wire pitch, wire diameter, and the number of wires. Utilizing the field synergy angle and Performance Evaluation Criteria (PEC), the underlying fluid-structure interactions are explicitly elucidated to identify thermally optimized configurations. Furthermore, drawing upon the extensive CFD dataset, a new multivariate non-linear empirical model—designated as the UCTD-L correlation—is developed to predict the friction resistance coefficient. By incorporating coupled structural correction factors, the UCTD-L model reliably captures the drag characteristics of diverse geometries. Validated against an independent out-of-sample test dataset, the proposed correlation restricts the Mean Relative Error (MRE) strictly below 20%.