The spacer grid is one of the main structural components in fuel assembly which supports the fuel rods, guides cooling water, and protects the fuel assembly from the external impact load such as earthquakes. Therefore, the mechanical and the structural properties of the spacer grid must be extensively examined while designing it. In this paper, a numerical method for reliably predicting the buckling strength of the spacer grid is presented. Numerical analyses on the buckling behavior of the spacer grid are performed for a various array of grid sizes, considering that the spacer grids are an assembled structure of thin-walled plates. The nonlinear dynamic impact analysis is conducted by using the finite element code ABAQUS/Explicit. Buckling tests are also carried out for several kinds of the specimens of the spacer grids in order to compare the results between the test and the simulation. This test is accomplished by a free fall dummy weight onto the specimen. From this test, only the uppermost and lowermost layers of the multi-cell are buckled, which implies the local buckling at the weakest point of the grid structure. Simulation results also similarly predict the local buckling phenomena. It is found to corresponde well with the test results. In addition, a correlation that can predict the maximum impact strength is empirically derived from the simulation results in the case of the grids having the larger number of cells.
