FLOW-INDUCED VIBRATION CHARACTERISTICS ANALYSIS OF EPR FUEL RODS BASED ON POD METHOD

The length of the EPR (European pressurized reactor) fuel rod is longer compared to the M310 fuel rod, resulting in a decrease in frequency and an increase in amplitude compared to the M310 fuel rod. Under the influences of the coolant, grid-to-rod fretting (GTRF) wear may be exacerbated, potentially leading to the leakage of radioactive materials. Here, the EPR fuel rod is simplified as a 3D beam model, where the constraints of dimples and springs on the fuel rod are treated as equivalent elastic constraints. Additionally, the fuel rod with a spacer grid is further simplified as a multi-span continuous simply supported beam model. A finite element model of the EPR fuel rod based on ANSYS-APDL is established, and the fundamental principles of wet mode analysis and vibration response analysis are explained. 12 grid failure conditions have been sorted out, and the influences of grid failure on wet mode and vibration response have been systematically studied. A method for analyzing the vibration characteristics of the EPR fuel rod using the proper orthogonal decomposition (POD) method is proposed, targeting flow-induced vibration (FIV) of the EPR fuel rod. The snapshot matrix is decomposed by POD method to generate the projection subspace, and the responses are projected onto the subspace for model reduction. Finally, the response is reconstructed in the physical space. The results show that the amplitude of vibration responses would increase at the location of grid failure; When the grid structure fails and causes the EPR fuel rod model to become a cantilever beam configuration, the maximum response to turbulent excitation is achieved; For the analysis of response, the first 2 orders POD reduced order model (ROM) can basically reconstruct the response of the fuel rod. The research in this paper will help to the optimization and design of nuclear reactor engineering.