Experimental investigation of flow-induced vibration in the reactor fuel assembly

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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- This research aims to experimentally investigate the critical flow velocity of light-water coolant in a reactor parallel plate fuel assembly. Coolant flows in between an array of thin, high aspect ratio fuel plates, to remove the heat generated by fission. The critical flow velocity is the speed at which rectangular fuel-plates deflect and collapse onto each other as a result of flow-induced vibration and consequent asymmetric pressure distribution. Although fuel plates do not rupture during plate collapse, the excessive permanent lateral deflection (buckling) of a plate can cause flow blockage in the reactor core, which may lead to over-heating. Destructive testing of a simple aluminium two-plate fuel assembly model resulted in plate collapse at an average flow velocity of 12 m/s, 78% of the theoretical Miller’s Velocity of 15.4 m/s. This difference was attributed to imperfect inlet channel spacing which decreased the collapse velocity of the fuel assembly model. A previously unreported low frequency vibration in the model fuel plate was detected during flow testing. The amplitude of this low frequency vibration increased exponentially with increment flow velocity though its frequency remained constant. It is hypothesized this low frequency vibration was due to a self-exciting mechanism caused by periodic flow redistribution between coolant channels and the hysteretic action of the model fuel plates.
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