Numerical Model Development of Dummy Fuel Rod Under New Spacer Grids and End Constraints Using Experimental Modal Analysis

One of the most important parameters in the analysis of the vibration behavior of the fuel rod is the elastic properties of spacer grids. In this research the combination of laboratory tests and theoretical formula was used to determine the elastic coefficients of these spacers that is related to fuel assembly with circular design. In order to validate the numerical model a spatial modal test set-up has been designed, constructed and set up to perform the modal test. The modal test results indicate that equivalent density of the dummy fuel rod depends on the natural mode of the rod. Then, the spring coefficients of the middle spacers and end constraints have been modified by comparing the results of numerical simulation with the results of modal tests defined in different supporting states of the hollow rod. The simulation results show that in addition to the middle spacers, also the end constraints have a significant effect on the natural frequencies of the rod. The Sensitivity Analysis results show that these coefficients depend on the natural mode of the rod. In addition, the results show that by updating the spring coefficients of the middle spacers and end constraints the estimation error of natural frequencies has been significantly reduced and the estimation of natural mode shapes based on the modal assurance criterion has been significantly improved.