Evaluation of Fuel Rod Response Using Principal Component Analysis

Abstract

This study pertains to an experimental analysis on the effects of the transverse jet flow geometry on the stability of a 6 × 6 square rod bundle. The experimental work represents a reduced scale fuel assembly subjected to localized cross flow conditions. This type of complex system is typically found in the nuclear industry (pressurized water reactor cores). The goal of the experimental study is to investigate the onset and characterize rod instability as it relates to the intensity and diameter of the jet cross-flow. The rod response was recorded using a high-speed camera in the vibration plane. From image processing, rod vibration amplitudes, and power spectral densities are acquired in both stream-wise and transverse directions. The results indicate that by increasing the jet nozzle diameter ratio, the critical flow velocity is reduced, however, the maximum vibration amplitude in the bundle decreases as the jet diameter ratio increases. The experimental datasets produced by all three sets of experiments were analyzed by Principal Component Analysis (PCA). The method obtained the orbit plots of the rod bundle undergoing fluid-elastic instability due to the transverse jet flow penetration for each set of experiments. A significant outcome of this research is the relation of acceleration ratio when the nozzle diameter is increased.