Numerical Analysis Of Flow-induced Vibration Of PWR Fuel Rod Assembly

The PWR fuel assembly consists of rod bundles.The high flow rate of coolant in the core and unsteady coolant flow may cause flow-induced vibration,which will cause wear and fretting in PWR fuel assembly.The lateral flow caused by the mixing wing can cause the deformation and the vibration of the fuel rods.Wear and the leakage of radioactive materials endanger the integrity of the reactor's first safety barrier.Previous research of public literatures on the flow-induced vibration issues of the fuel assembly tends to focus on three aspects:one is only study the coolant flow in reactor core;the second is to study the flow-induced vibration without heat transfer;the third is making mechanical analysis of fuel rod.In this paper,the ANSYS CFD software is used performing CFD simulation analysis on fluid-structure coupling vibration characteristics of the PWR fuel rod assembly with the influence of heat transfer.Calculate the natural frequency of the fuel rod and the mixing wing,under the influences of heat transfer.Firstly,calculate the coolant flow in the fuel rod assembly under the influence of the lateral flow flushing caused by the mixing wing.Secondly calculate the stress distribution and deformation distribution of the fuel rod assembly by using the flow field data as the initial condition,and finally calculate the vibration frequency of the mixing wing and fuel rods.The results show that the mixing wing can greatly enhance the lateral flow of the coolant and increase the heat exchange between water and fuel rod,but also increase the flow resistance greatly.The flow resistance caused by spring is much larger than rigid protrusion.Because the spring which incident face was larger and made a strong block affect that caused axial velocity fluctuation largely.The spring is order to reduce the vibration of the rod.Different constraints had a great influence on the vibration characteristics of the fuel rod.The natural frequency of the mixing wing is much larger than that of the fuel rods,and the wing is hard to be effect.When the flow rate of the coolant and the core condition changed,the frequency of the fuel rods and the mixing wing changed.Considering the influence of heat transfer of the fuel rods,the natural-frequency of the fuel rods and mixing wing increased with the increase of the flow rate.When the reactor thermal power changed,the natural-frequency of the fuel rods and mixing wing changed.The results and conclusions in this paper have certain significance for the analysis of flow-induced vibration.It also can provide some references and basis in the future and be useful in future thermal-hydraulic design.