Vibration analysis of a dummy fuel rod continuously supported by spacer grids

The fuel rods in the pressurized water reactor are continuously supported by a spring system called a spacer grid (SG), which is one of the main structural components for the fuel rod cluster (fuel assembly). The fuel rods have a vibration behavior within the reactor due to coolant flow. Since the vibration, which is called flow-induced vibration, can wear away the surface of the fuel rod, it is important to understand its vibration characteristics. In this paper, a modal testing and a finite element (FE) analysis using ABAQUS on a dummy fuel rod continuously supported by Optimized H Type (OHT) and New Doublet (ND) spacer grids are performed to obtain the vibration characteristics such as natural frequencies and mode shapes and to verify the FE model used. The results from the test and the FE analysis are compared according to modal assurance criteria. values. The natural frequency differences between the two methods as well as the mode comparison results for the rod with the OHT SG are better than those with the ND SG. That is, in the case of the ND grid model using beam-spring elements, there was a large discrepancy between the two methods. Thus, we tried to modify the FE model for the ND SG considering the contact phenomena between the fuel rod and the SG. The results of the new model showed a good agreement with the experiment compared with those of a beam-spring model. (C) 2004 Elsevier B.V. All rights reserved.