Coolant Flows And Influence Analysis In Fuel Rod Bundle With Grid Spacer

Pressurized water reactor(PWR)nuclear power plants(NPPs)transfer nuclear fission energy out of reactor core by coolant flows through the fuel assembly.The thermal hydraulic and structural deformation characteristics of the coolant and fuel assembly are directly related to the safety of reactor and efficiency of NPPs.It is of great significance to study the characteristics of the two and their interact ions.The paper sets up a 5X5 fuel rod bundle with grid spacer and coolant flow geometric models and divides mixed grid in high-quality.In this paper,the model simulation adaptive verification is conducted with the experimental results.The flow characteristics of the coolant at normal operating condition and single tunnel chock condition are first studied.And then the multi-field coupling simulation of interaction and influence between coolant and fuel rod bundle with grid spacer is conducted in unidirectional and bidirectional ways,which provides a reference for the reactor core safety analysis and the fuel assembly design optimization.The research results show that the grid spacer structures such as the mixing vanes,springs and protrusions disturb coolant causing lateral flow and diagonal flow between the rod bundle tunnels at normal operating condition.The diagonal flow across rods significantly enhance the convective heat transfer between coolant and fuel rod.The local flow coolant velocity decreases in single tunnel chock condition,which results in a decrease of convective heat transfer efficiency,a rise in the temperature of fuel rod,and a decrease in the thermal margin.But the peak temperature is still about 34.3K below the saturation temperature.According to the results of the unidirectional heat-fluid-solid coupling analysis,grid spacer makes the coolant flow unevenly distributed,which induces rod bundle deformation non-uniformly.The lateral coolant flow and thermal stress of the fuel rod make rod bundle deformation reaches hundreds of um.Compared unidirectional simulation results with bidirectional multi-field coupling results,average and peak temperature,coolant secondary flow velocity and fuel rod bundle deformation are all smaller than those in the unidirectional coupling analysis.The bidirectional multi-field coupling analysis is closer to the actual situation of coolant and fuel rod bundle in the reactor,which can avoid overly optimistic estimates of coolant flow and heat transfer enhancement.Fuel rod bundle can keep its structure stable at both conditions.It’s a certain reference significance that the research provides the implementation method,relevant data and a closer multi physical field coupling simulation to a real situation.