Investigation of Grid Strap Vibration Subjected to Axial Flow Condition

It is important to identify static and dynamic characteristics for every structure from the viewpoint of structural evaluation. In addition, when the structure is subjected to special design conditions, the mechanical performance should be evaluated for safety operation. Especially, the fuel assembly is exposed to turbulent flow condition. Therefore, the dynamic behavior of the fuel rods including grid strap should be examined. Grid strap vibration caused by flow induced is one of the critical elements to fuel cladding wear. To analyze these phenomena, grid strap are examined under the free and forced vibrations. Grid configuration is pretty complex, since the spring and dimple design should be implemented within the limited space. This paper measures local vibration on the strap in one cell. For full sized spacer grid, the dynamic characteristics will be different from that of the small scale grid in the view point of global geometry. Therefore, one cell vibration is considered rather than a global vibration. And one cell of the strap has one spring and two dimples. This paper presents dynamic characteristics of the strap in a grid at several conditions. First, modal analysis of the strap is performed by Finite Element Method(FEM). And modal testing is followed with a 5x5 grid to identify the dynamic characteristic considering real conditions in air. Finally, flow induced vibration for 5x5 small scale fuel bundle is completed in INFINTTM facility that is a test facility to evaluate flow induced random vibration