Hydrodynamic mass and fluid damping of rod bundles vibrating in confined water and air-water mixtures

In the past few years, a considerable effort has been developed to increasing the understanding of fuel string vibration mechanisms in CANDU (Canadian Deuterium Uranium) reactor channels. Part of the overall program has involved the development of a mathematical model which describes fuel string dynamics in axial flow. Because of the complex bundle geometry, model input parameters such as bundle hydrodynamic mass and associated fluid damping are difficult to determine from theory, and recourse is made to experimental techniques. This paper presents the results of an experimental study conducted to determine these parameters. Assembles of three types of 0.5m long CANDU bundles (with fuel pellets removed to reduce weight), each comprised of two bundles clamped end to end on a central support rod, were tested in flow channels of various inside diameters. An electrodynamic shaker, mounted directly on the flow channel, was used to sinusoidally excite the assembly at its mid-point. A large number of tests was carried out with flow channels filled with air, water, and a range of air-water mixtures (0% to 30% air volume fraction). (Auth.)