Orbital Vibratory Motion of a Fuel Rod in a 5X5 Partial Fuel Assembly in a Confined Axial Flow

摘要

An orbital vibratory motion of a fuel rod in a 5X5 partial fuel assembly subjected to a confined axial flow was measured according to a flow variation by an embedded type accelerometer. Two consecutive and independent frequency integrations of the measured accelerations were carried out to obtain the lateral displacement responses of the fuel rod after removing the DC offset in the measured acceleration response. By comparing the integrated displacement to the measured displacement with a non-contacting vibration measurement device, we determined the cutoff frequency for the frequency integration. The differences in the vibration spectrum of the inner and outer rods in the test bundle, the orbital variation during a finite period of time and the orbital loci according to the bundle flow velocity are discussed. The orbital shape of a fuel rod in the test bundle was nearly circular and elliptic; its size increased with a flow velocity increase. The results of this study and methodology will be used for the development and verification of an inserting-type acceleration measurement device which measures a fuel rod vibratory response under a limited environmental test condition. Also, it will be applicable to preparing the test parameters and conditions for fuel fretting experiments.