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A model for a fully-flexible fuel bundle dynamics
Osama Elbanhawy, Marwan Hassan, Atef Mohany

Last modified: 2018-04-21


Fuel bundles are subjected to axial high flow rates. This flow through the fuel bundle can induce significant vibration levels.  Such vibrations can compromise the integrity of the fuel bundles in the form cracking at endplates or fretting damage on the inside surfaces of the pressure tube.

A comprehensive numerical framework is proposed to model the flow-induced vibrations of a fully-flexible fuel bundle.  The model includes the representations of 37 fuel rods and two endplates.  Each fuel rod is modelled by 30 beams elements each of which has 12 degrees of freedom.  Each of the endplates is discretized into a number of plate elements.

Each of the outer rods can potentially be in contact with the pressure tube at three locations via bearing pads. In addition, there are six side spacers and six tall spacers with gaps to separate the rod from the neighbouring rods. For the internal rods there are at least 9 locations of potential contact points. The fuel-to-pressure tube as well as fuel-to-fuel contacts are treated with the pseudo force approach.  In addition, at all contact sites the force-balance friction model with a velocity feedback technique is used to represent the stick/slip friction phenomenon.  Using this technique simulations of the dynamics of a fully flexible fuel bundle including the flexibility of the endplates were conducted.  The simulations consider three excitation mechanisms including turbulence, pressure pulsation, and motion-dependent fluid forces.


Fuel Bundles, Impact, Fretting wear

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