Study On Flow And Heat Transfer Characteristics Of Coolant In Helical Cruciform Fuel Bundles

Fuel assembly is one of the significant components in reactor design and safety analysis.Its structure and flow and heat transfer performance are very important to the safety,reliability and economy of nuclear power plants.The structural design of fuel assemblies has an important influence on the thermophysical and hydraulic performance in the rod bundle channels and plays a key role in whether the coolant can safely and efficiently carry the heat away from the core.Helical cruciform structure has been adopted in the helical cruciform fuel assembly,due to the self-positioning of the rod bundle,larger heat exchange area and stronger the energy exchange between the channels.Understanding the influence of the helical cruciform structure on the flow and heat transfer characteristics in the rod bundle channels is an important basis for developing new efficient fuel assemblies.In this paper,domestic and abroad researches on PWR fuel assembly structure and thermal-hydraulic performance have been reviewed the SST k-ω turbulence model was adopted to simulate the flow and heat transfer characteristics of coolant in the helical cruciform fuel assembly.The effects of the helical cruciform structure,Reynolds number and fuel rod arrangement on the flow and heat transfer characteristics were studied.Furthermore,the influences of two fuel rod placement modes(square placement and hexagonal placement)on flow and heat transfer were compared and analyzed.The results show that the helical cruciform structure can cause the coolant to generate the transverse velocity,enhence the mixing intensity in the beam channel,and improve the heat transfer efficiency.The Reynolds number significantly affects the resistance and heat transfer characteristics.With the increase of Reynolds number,the coefficient of friction resistance decreases,while increasesing the Nussel number enhances the heat transfer.The effect of the screw pitch on the flow and heat transfer performance is particularly significant.With the decrease of the screw pitch,the cross flow intensity increases,the Nussel number of the rod bundle channel increases,and the mudding and heat transfer performance are enhanced.In the hexagonal channel,the velocity and temperature distribution of coolant are more uniform,and the thermal-hydraulic performance is excellent.Based on the research of the flow and heat transfer processes of the coolant in the helical cruciform fuel assembly,the flow characteristics,resistance and heat transfer characteristics in the bundle channels are obtained,and the inlet parameters,structure parameters and arrangement affect of the bundle are explored.The influence of the above-mentioned performance is further analyzed for the importance of the fuel assembly structure to the safe,stable and efficient operation of the PWR.This study provides a certain theoretical basis for the design of a new type of high-efficiency fuel assembly in a nuclear reactor.