Numerical Study On Flow And Boiling Heat Transfer Characteristics In Rod Bundle Fuel Assembly Of Pressurized Water Reactor

As a clean new energy,nuclear power has made great strides on the road of global energy development.Nuclear reactor contains fuel assemblies,whose safety is one of the basic conditions to maintain the normal operation of nuclear power plant.When the fluid flows between the rod bundle channels of the fuel assembly and fully exchanges heat with the heating rod,subcooled boiling may occur,which can strengthen the heat exchange.Therefore,by simulating the flow and heat transfer in the rod bundle single and multi-channel model（with a positioning grid）,the author simulates and analyzes the internal flow and heat transfer characteristics,such as transverse velocity,wall temperature and other parameters.In the first place,by analyzing the heating conditions and other parameters,the author obtains the distribution law of flow field characteristics in the channel by Rensselaer Polytechnic Institute wall boiling model（RPI wall boiling model）,finds that the greater the inlet velocity is,the greater the onset of subcooled boiling（ONB）value is;The higher the inlet temperature,the smaller the ONB value;The higher the heat flux,the lower the ONB value.Through the comparison between simulation and experiment,the prediction formula of subcooled boiling starting point suitable for this working condition is obtained;The heat transfer coefficient is independent of heating conditions.The greater the inlet velocity,the greater the heat transfer coefficient.The transverse velocity of gas phase and liquid phase in any section in the flow direction presents different distribution characteristics.Secondly,the multi-channel model of rod bundle fuel assembly is numerically simulated by using the numerical model and boiling model applied in single channel.Conditions in the research such as heating conditions,flow fluctuation,inlet flow velocity and other operating parameters on the flow boiling characteristics in the rod bundle channel were analyzed.A conclusion is drawn through the research that the fuel element frame has a benign effect on the flowing and thermal interaction characteristics in the channel.The mixing wing in the positioning grid is the main factor of the transverse velocity fluctuation.It can increase the disturbance velocity of liquid movement and improve the heat transfer capacity between the fluid and the heat source;The flow between rod bundles at different positions is also affected,which causes the non-uniformity of flow;The circumferential boiling heat transfer characteristics of rod bundles at different positions are analyzed.The results show that the size of ONB points of rod bundles at different positions is different under different heating conditions and flow fluctuation conditions,and the circumferential ONB points of each rod bundle are asymmetric.The obtained ONB point prediction structure relationship is still applicable to the multi-channel model.