Keywords: impact, dynamic failure, grid, lateral impact load, multi constraints condition, simplified model.

The objective of this research is to propose the methodology that could predict the dynamic failure behaviour on the grid structure for the PWR (Pressurized Water Reactor) fuel assembly. To perform this objective, the two kinds of approach are used in this work. First, in order to obtain the test data on the dynamic failure behaviour of the spacer grid, the impact test is performed with the cell size partial grid specimen, which is made of Zircaloy-4 thin plate. Second, a finite element analysis method for predicting the buckling behaviour on the spacer grid structure is established by a commercial finite element code ABAQUS/Explicit. In this FE analysis method, appropriate boundary conditions and impact loading conditions are applied to simulate the actual test conditions. The dynamic impact analysis is performed for predicting the buckling behaviour of a grid structure under the lateral impact load by finite element method. The grid structure is composed of several thin plates which were inserted each other and then each contact places were welded by laser welding. The finite element model is produced using pre-processor I-DEAS, and solved using nonlinear commercial solver ABAQUS/explicit. In this work, two models are proposed for FE analysis. One is the simplified model and the other is multi constrained one. Applied boundary conditions for dynamic impact analysis were nearly the same with actual boundary conditions for impact test. The dynamic impact parameters of a grid structure such as critical impact acceleration, impact force and buckling mode and so on, are over-estimated with test results. Based on these results, the FE analysis model of the grid structure is needed to modify the stiffness of a grid cell structure. According to these results, the FE model is modified for estimating the buckling behaviour of grid structure. This modified FE model will be compared with test and analysis results using the simplified model. In addition, the finite element analysis model is in good agreement with the impact test results, therefore this finite element model and the analysis procedure will be used as a good tool for predicting the dynamic buckling behaviour of the grid structure.

1

K.H. Yoon and K.N. Song, "Nonlinear Dynamic Buckling Analysis of a Grid Structure", Key Engineering Materials, Vols. 183 187, 451-456, 2000. doi:10.4028/www.scientific.net/KEM.183-187.451

2

"I-DEAS Master Series", Ver. 8m3, Structural Dynamics Research Corporation, OH, USA, 2000.

3

Hibbitt, H.D., Karlsson, G.I. and Sorensen, E.P., "ABAQUS/Explicit User's Manual (version 6.2)", Vol. I and II, Hibbitt, Karlsson & Sorensen Inc., Pawtucket, RI, USA, 2001.

4

ASTM E8M-99, "Standard Test Methods for Tension Testing of Metallic Materials", 1999.

5

K.N. Song et al., "Impact Analysis of Dipper-type and Multi Spring-type Fuel Rod Support Grid Assemblies in PWR", ICONE-10, Paper No. 22177, 2002.

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