Thermal-hydraulic analysis of rotated wire wrap in LFR assembly under normal operation and flow blockage conditions

This study presents a CFD investigation of thermal-hydraulic behavior in a 19-pin wire-wrapped lead-based fast reactor (LFR) fuel assembly under normal operation and flow blockage conditions. The numerical model is validated against the NACIE-UP ADP10 experiment using the SST k-ω turbulence model, with temperature and pressure drop comparisons confirming grid independence. Two heating modes (uniform and central) and four rotation angles of the central wire wrap (60° and 120° clockwise and counterclockwise) are considered. Results show that wire rotation modifies radial coolant paths and degrades near-wall heat transfer, causing localized temperature rises that are more pronounced under central heating. Subsequently, two blockage cases are simulated under central heating at different axial positions. Although blockage effects on temperature distribution become negligible after flow recovery, at the blockage end, peak temperatures can increase by up to 51 K depending on rotation angle and axial location, and the extent of the disturbed flow region also varies. These findings underscore the need for enhanced attention to local thermal-hydraulic safety when rotated wire wraps and blockage accidents coexist.