08-16-2017, 08:44 PM
Presented by:
Jeong Sik Yim
Heong Kook Joo
Dong Seong Sohn
ABSTRACT
The holddown Spring is one of the major components of a fuel assembly for PWR. It holds the fuel assembly firmly seated down on the lower core plate and allows the FA axial movement caused from the irradiation growth of guide thimbles. Depending on the up-lift force of a fuel assembly, from 2 to 4 leaves are assembled to be a set of a spring pack and it is fixed on the frame of the top end piece by screw. The spring can deflect so greatly during operation that consequently it would have non-linear characteristics. It is important to know the characteristics exactly in the design of the FA, especially for the estimation of the performance of the FA. Here, the non-linear force-displacement of each leaf spring as well as the spring characteristics of a pack consist of two to four leaves are obtained by ANSYS. Large deformation and stiffening effect as well as friction between each leaf are included. The results from ANSYS were compared with those from the test, which showed a fairly good agreement with each other. Using this method, the characteristics of a spring set can be predetermined prior to the final decision of a spring dimension.
Considering the performance of the spring behavior, it is desirable that the spring set has a large linear displacement range in order not to lose the spring force. Thus, to make a spring set have a large linear range, optimization of the spring, mainly concerned the spring thickness and yield stress, are done. It is shown that the optimized spring set, which has even less than one leaf, could have the same spring characteristics as a normal set.
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