CNPP Fuel Rod Vibration Analysis Using Finite Element Method

The fuel rods in the PWR fuel assembly are continuously supported by spacer grids, which are located at intervals along the axial length of the fuel assembly. The coolant flow induces vibration in fuel rod which can wear away its cladding tube surface in contact with the support structure. Thus, it is important to examine the characteristics of the fuel rod vibrations. In the present study, two different methodologies have been developed to calculate the natural frequencies and mode shapes of the 300 MWe CNPP fuel rod. In the first methodology, a 2D planner flexure modal analysis of the fuel rod is performed using Matlab software, while in the second, a 3D modal analysis is carried out using ANSYS software. In 3D analysis, actual geometry of the CNPP fuel rod and spacer grid spring/dimple support is modeled. The vibration analysis of pre-stressed model is carried out in the modal analysis module of ANSYS. The purpose of this study is not only to compare the 2D and 3D FE models but also to verify the results with the vibration measurements made by the Chinese for CNPP fuel rod. Both the 2D Matlab and 3D ANSYS FE analyses results are found to be in good agreement with the Chinese test results and thus validate the analyses models.