Optimized Design Of Holddown Springs With Bending Leaves

摘要

The function of the holddown springs is to guarantee the axial holddown of the fuel assemblies throughout their inreactorrnoperation up to their final unloading.rnIn order to minimise the height of the top nozzle on which they are mounted, these springs are made up of a stack ofrnbending leaves whose tilt guarantees the necessary stroke to accomodate the gap variations between the top of the assembliesrnand the upper core plate.rnGiven the required holddown forces and the available space, the spring leaves undergo plastic strains in normal servicernduring the vessel closure and cold return phases. Analyses of the stresses and strains in the leaf material is necessary tornrule out the risks raised by such loadings under PWR conditions. A dedicated computational tool is used to conduct these analyses;rnthis module integrates the following non-linear behaviour models:rn- large displacements and rotations,rn- elastic-plastic strains,rn- one-sided contacts with sliding and friction.rnThis software enables rapid simulation of the behaviour of leaf springs in the preliminary design phase, and analysisrnof the loadings experienced by the material. With this tool, spring geometry can be optimized by minimizing the stresses andrnplastic strains on the material, while maintaining the required level of holddown force.