FLUID DYNAMIC EFFECTS IN THE FUEL ELEMENT TOP NOZZLE AREA DURING REFILLING AND REFLOODING
Countercurrent flow of a gas and a liquid occurs during emergency cooling conditions in the region of downcomer and the core of lightwater cooled nuclear reactors. In order to identify the flooding mechanisms, investigations of countercurrent flow were performed under a large variety of test conditions. As internals to the flow duct, perforated plates, a 4 x 4 rod bundle with tie plate and a complete fuel element dummy, were used to simulate hydraulically a section of the upper part of a PWR fuel element. The selected fluid systems were air - water and steam - water. During the steam - water tests the effects of subcooled water injection were also investigated. Droplet photographies of entrainment mechanisms above the tie plate are evaluated by a digital image analysing system. The results of the experiments indicate similar mechanisms for countercurrent flow in tubes and square ducts with and without internals. In all cases there is a distinct gradient in pressure drop and a remarkable appearance of flow instabilities near the countercurrent flow limitation. The mathematical methods leading to a flooding model are outlined. The model is based on the stability condition of the wavy interfaces. The own experimental data and those from the literature are well represented by the derived model.
Bibliographic Reference: EUR 10165 EN (1985) MF, 309 P., BFR 600, BLOW-UP COPY BFR 1545, EUROFFICE, LUXEMBOURG, POB 1003
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Record Number: 1989124011400 / Last updated on: 1987-01-01
Available languages: en