Neutronic-coupled thermal hydraulic analysis of flow blockage in the hottest wire-wrapped LBE-cooled fuel assembly

Abstract

Flow blockage in lead-cooled fast reactors is considered a realistic accident for fuel assemblies, whereas reactivity feedback and axial power profiles are considered in few studies due to the complexity and lack of neutronic modules in commercial computational fluid dynamic software. This study proposes a neutronic-coupled thermal–hydraulic model to analyze the coupling effect on flow blockage in a 19-pin wire-wrapped fuel assembly. Neutronic and thermal hydraulics were validated by comparing the reported benchmark and experimental data, respectively. Simulation results with and without neutronic coupling schemes were compared, and case studies of different reactivity insertions were conducted. The wall overheating of blockages with coupling schemes is more conservative than the constant heat source condition with the lower dimensionless temperature T¯. After a step change of cross-section, the response of Rw and T¯ shows synchronous behavior. For a larger reactivity insertion, it leads to higher wall heat flux, lower wall thermal resistance and lower dimensionless temperature for blockage regions.