Experimental Research And Numerical Simulation On Flow Distribution Characteristics Of Seven-Box Assembly In Small Grid Plate Of Fast Reactor

The internal structure of the primary loop of the pool-type sodium-cooled fast reactor is complex,with a wide variety of components,including grid plate and a variety of core assemblies,resulting in a complicated flow of coolant.In addition,there are many types of core assemlies,and their heating power and distribution positions are different,especially for fuel assemly.If the coolant flow through it is too large,the temperature of the coolant at the core outlet is low,which affects the reactor economy;If the coolant flow rate is too small,the fuel assembly will not be sufficiently cooled,threatening the safety of the reactor.Therefore,reasonable flow distribution is critical to reactor safety and economy.Current research work mostly focuses on the fast reactor internal components,such as grid plate,fuel assembly,and wire-wrapped rod bundle.There are few studies on the flow distribution characteristics of fast reactor cores.Most of these studies have performed numerical simulations on the flow distribution in the grid plate,but the entry tube type is single,and the numerical results lack diversity and have not been fully experimentally verified.Therefore,it is necessary to further investigate the flow distribution characteristics of fast reactor core components,with adopting complete assembly and increase assembly types.In this paper,a core sub-channel experimental section is established based on the structure of the fast reactor primary loop,which is composed of a large grid plate sleeve,a small grid plate and seven fuel assemblies.In this experimental section,the flow of coolant in the reactor core was considered comprehensively.And the flow-characteristics hydraulic experiments are conducted for this experimental section.Based on the experimental results,the mechanism research on the flow distribution characteristics of the seven-box assembly in the small grid plate is carried out.The calculation of the CFD software is verified according to the experimental results,which proves the rationality and validity of the k-ε model and the porous media parameters are verified under the high Reynolds number of the seven-box assembly model.Subsequently,the calculation of the seven-box assembly model for different component types and pin leakage conditions was carried out.The flow distribution characteristics of the fast reactor core seven-box assembly are experimentally and numerically investigated.The influence of factors such as the type,installation position and pin leakage of the seven-box fuel assembly on the flow characteristics of the sub-channel is carefully analyzed.Providing technical support for calculation and experiment of fast reactor full core flow distribution.The research results show that:The difference in the flow characteristics of the fuel assembly at different positions(middle and peripheral positions)is less than 2%,which proves that the installation position has a small influence on the flow characteristics of the assembly;Changing the combination type of the seven assmblies of the model,the flow characteristics of the fuel assembly are limited impact by the coupling between the assmblies,and are consistent under different combinations;The entry tube leakage has no obvious influence on the flow characteristics of the assembly,but it can significantly reduce the force on the pin connector,which is beneficial to the stable of the assembly.The experimental flow distribution coefficient of seven-box assembly is between 0.96-1.08,and the numerical simulation flow distribution coefficient is between 0.97-1.01,both show that the existing small grid plate structure design is reasonable and the flow distribution result is relatively uniform.