In this paper, the effect of the confinement on the vibration of rods within nuclear fuel bundle is analyzed and discussed. Differential added damping of the rods depending on their position within the bundle adds to the classical development of modal and spectral analysis. This is accomplished by coupling the classical modeling of the variable-mass, Euler-Bernoulli beam on elastic supports with the two-dimensional computational fluid dynamics (CFD) estimation of motion-dependent effects, with the viscous effects integrally modeled. A 5×5 reduced-scale (shortened) rod bundle subject to room-temperature single-phase nominally axial flow within a square confinement is used to illustrate the response to a harmonically varying excitation. The harmonic analysis showed that there are significant differences in the response of the rods, depending on their position within the bundle.

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