In this study considered is the buckling of spacer grids in the nuclear fuel assembly, which are required to have a sufficient strength against an accident like earthquake. Linearized buckling analysis is carried out for obtaining the eigenmodes, and followed by a full nonlinear analysis to find the load-deflection curve. Special attention is given to the modeling of the spot-welding and the constraints between the unit spacers assembled together : it is found that a proper treatment of the constraints is critical for accurate assessment of the buckling behavior including strain localization at the point of spot welding. The buckling strength of the 17x17 spacer grid, which is difficult to analyze due to a large number of degrees of freedom, is obtained from analysis for the smaller models 3x3, 5x5, 7x7, and 9x9 spacer grids.
