Experimental investigation of flow-induced vibration in a parallel plate reactor fuel assembly

Full text of publication follows: A model of a parallel-plate fuel assembly is tested for plate collapse. The model comprises of two Aluminium plates of dimensions 1.2 mm x 78 mm x 780 mm, rigidly clamped in a fuel-assembly model. The plates are clamped on the two longest sides with the two shorter side free. The two plates sit inside the fuel-assembly model, separated by three channels: 78 mm in width and 4.3 mm in height. The mock fuel assembly is mounted vertically in a water tunnel and is set on a rectangular channel acting as a flow straightener. There is no stabilizing comb installed on the leading edge. One of the two plates is instrumented with strain gauges at three positions: the leading edge, the middle of the plate and the trailing edge. These strain gauges detect vibration and deflection in the plate at different flow speeds. Also, the mock fuel assembly is equipped to measure static pressure at 100 mm intervals along the axis of the plate. Aggregate flow through the fuel assembly model is measured by a flowmeter mounted in the water tunnel, whilst flow through individual channels is measured by LDV. Preliminary results shows plate collapse occurs between an average velocity of 11.5 m/s and 12 m/s in 25 deg. C light-water. This was determined by simultaneously measuring deflection of the strain gauge and the mass flow through the fuel-assembly model. The shape of the plate collapse seems random, either with both plates collapsing onto each other or with both plates collapsing away from each other. In the case of the plates collapsing away from each other, cavitation was observed. The frequency of the plate remained constant at 4 Hz at all flow speeds. The results attained in the experiment compare well with the calculated Miller's (1960) Critical Velocity of 15.4 m/s for the conditions described above. Also, many phenomena observed in the experiments agrees with similar experiments in the past, as outlined by Kim et al. (1995). Further details of experiments are provided in the paper. References: - Kim, G. and Davis, D. C., Hydraulic Instabilities in Flat-Plate-Type Fuel Assemblies, Nuc. Sci. Eng., 158 (1995), 1-17; - Miller, D. R., Critical Flow Velocities for Collapse of Reactor Parallel-Plate Fuel Assemblies, J. Eng. Power, April (1960) 83-95. (authors)