Finite element analysis of the optimized H type grid spring by using gap elements

The optimized H type grid spring of a new design for the Zirconium alloy spacer grids for an advanced LWR fuel assembly is developed. Characterization tests are conducted for this spring and the load vs. displacement curve of the spring characteristics is obtained. Also, four FEM models, which consisted of two 5 × 5 cell models, one 6 × 9 cell model and one 8 × 9 cell model, were developed by the IDEAS code and they were analyzed by the ABAQUS code in order to simulate the newly designed spring characteristics. The results of the FE analysis are compared with those of the spring characterization test and the following conclusions were obtained. First, since a model which includes a lot of cells below the location of the applied load has many gaps due to more slits, the spring characteristics of the model are more flexible. Second, among the four FEM models, the result of the 5 × 5 cell model applied to the displacement load at the top of the model was in good agreement with the test result. Therefore, when a newly designed spring for a spacer grid assembly is developed, its spring characteristics can be estimated by an analysis with an appropriate FEM model without the spring characterization test.