Numerical investigation for the heat transfer mechanisms between subchannels of bar rod bundles cooled by liquid sodium

The flow field in the fuel assembly of Sodium cooled Fast Reactor (SFR) is highly non-uniformed which results in quite complex heat transfer phenomena between subchannels of rod bundles.From the design and safety purpose of the reactor core, mechanisms behind these heat transfer phenomena must be analysed thoroughly under all working conditions. However, due to the decrease of the fast reactor activity and the huge experimental costs with liquid sodium, few researches have been conducted to deepen the understanding of the heat transfer mechanisms after the 1980’s in spite of the large uncertainty and limited parameter ranges of existing empirical correlations. In this paper, a Computational Fluid Dynamic (CFD) model of two subchannels with adjacent fuel rods is used to investigate the heat transfer mechanisms under a wide range of geometry and flow conditions. The turbulent heat transfer of the liquid metal is resolved through the SST k-ω turbulent model with modified turbulent Prandtl number, and the CFD model is verified with experimental data. Data analysis of the simulation results shows clearly dependence of the heat transfer mechanisms on the geometry parameters and the flow parameters. By fitting of the numerical results with the least square method, new correlations for the turbulent mixing and the rod conduction are developed.