Numerical analysis of thermal-hydraulic characteristics of grid positioned triangular fuel assemblies in lead-cooled fast reactor under ocean conditions

The lead-based fast reactor is a promising fourth generation reactor type, which has good natural circulation capability, great fuel proliferation potential, high safety, and easy miniaturization. The design of miniaturized lead-based reactors is expected to become a potential choice for ocean energy supply or ship propulsion. This study is based on CFD(FLUENT) method to investigate the influence of ocean conditions (i.e. rolling motion) on the thermal-hydraulic characteristics of liquid lead cooled grid positioned triangle fuel assemblies. The modeling of liquid lead in triangular channels based on FLUENT has been clarified, the SST k-ω turbulence model and the Cheng et.al turbulent heat transfer models (Prt) indicate that has the highest accuracy in simulating the flow & heat transfer of liquid lead coolant. Based on this, the impact characteristics of rolling on a single channel were analyzed. Research has shown that an increase in rolling amplitude and a decrease in rolling period have an increased impact on the Nusselt number and friction resistance coefficient. And rolling can enhance heat transfer capability, where the heat transfer capacity is more sensitive to rolling amplitude changes and less sensitive to rolling periods. The influence of rolling on the friction resistance coefficient is not significant, with a change amplitude of less than 2%. Finally, research on typical 7-rod bundles shows that the rolling motion has the greatest impact on the longitudinal pressure of the liquid lead, with an average increase of about 10%. The impact of rolling on velocity is smaller than the pressure, and the effect varies upstream and downstream of the grid, and the impact on fluid temperature is not significant. The rolling motion increased the Nusselt number value within the rod bundles, with an average increase of about 5%,and reduced the friction resistance coefficient, with an average decrease of about 10%. This study demonstrates the influence of rolling motion on the thermal-hydraulic characteristics of the core under a typical fast reactor triangular component arrangement, which has important reference significance for the miniaturization design of marine lead-based fast reactors.