Local hot spot formation of the wire-wrapped pin bundles under forced convection in liquid metal cooled reactors

Helical wire-wrap spacers are a common structural element in liquid metal–cooled fast reactors (LMFRs), where they promote coolant mixing and improve heat transfer in densely packed fuel assemblies. Nevertheless, the wire spacers introduce additional thermal resistance which can result in localized peak temperature. An experiment was performed to measure local temperature distributions associated with wire contact in a simple rectangular channel under forced convection. Galinstan was employed as a working fluid to emulate the thermal–hydraulic behavior of low–Prandtl-number coolants. The results indicate that hotspot formation occurs when the Biot number exceeds unity, whereas for Biot numbers below one, a cold spot occurs due to the fin effect of the wire. The magnitude of the temperature peaks proportionally increases with applied heat flux. An empirical correlation was presented to estimate hotspot formation over a broad range of material properties and flow conditions and extensive parametric studies were performed using complementary computational fluid dynamics (CFD) simulations. The outcomes of this study provide valuable guidance for optimizing wire-wrap spacer designs to mitigate localized thermal hotspots in LMFR systems. • Localized hotspots in wire wrapped bundles occur when the Biot number exceeds unity. • An empirical correlation was developed to estimate the peak temperature. • Minimizing contact area and enhancing coolant bypass mitigate hotspot formation.