A Vibration Analysis and Test of a 5×5 Rod Bundle

A FE analysis and test has been performed for a 5×5 rod bundle which consists of twenty-three rods that are 2.2 m tall and 9.5 mm in diameter, with two guide tubes and five spacer grids. Two guide tubes were welded to the spacer grids through the medium of guide tube sleeves. Two out of the twenty-three rods were empty, and the rest of them were filled with lead (Pb) rods instead of UO2 pellets. The vibration test was performed for the rod bundle in air, and the test result was compared with the FE analysis that was done by ABAQUS. 6.5 Hz for the first natural frequency, 15 Hz for the second natural frequency and 24 Hz for the third natural frequency were obtained by the vibration test while 4.3 Hz for the first natural frequency, 10.4 Hz for the second natural frequency and 19.2 Hz for the third natural frequency were obtained respectively by the FE analysis. Since two of the first, second and third modes were obtained in two different directions by the FE analysis, tests were carried out in two directions. It is concluded that the lower 6 modes are the bundle vibration modes. The first vibration modes of the rod supported by the springs appeared at 26.9 Hz to 27.0 Hz after the bundle vibration modes, and then several bundle vibration modes followed.