Status of Natural Circulation Experiments in Multiple Channel RD-14M Test Facility
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Abstract
This paper presents an analysis of the results of a series of natural circulation tests conducted in the multiple channel RD-14M test facility. The RD-14M loop components are arranged in a figure-of-eight configuration similar to that in a CANDU heat transport system. The paper also presents physical explanations for the phenomena observed in the tests. The tests were conducted to enhance the understanding of the flow behaviour in a multiple channel test facility. The tests were also conducted to provide data for development and verification of thermohydraulics codes used in simulation of postulated reactor accident scenarios. The tests were conducted over a range of flow conditions and using various test procedures, The tests exhibited the following phenomena: oscillations in the total circuit and individual channel flows including in- and out-of-phase circuit flow oscillations, and reversal in the direction of channel flows. Some of the tests exhibited bifurcations in channel flow oscillations leading, as a result, to possible chaos. Following channel flow reversal, the
following phenomena were observed in the various tests: (i) thermosyphoning flow reversal, (ii) thermosyphoning breakdown with the channel flows circulating through the headers below the steam generators and with the system heat removed by reflux condensation, (iii) thermosyphoning breakdown with periods of limited reflux condensation and, hence, system heatup and pressurization at various rates, (iv) standing start, and (v) stratification in the channel flows. It is theorized, with experimental evidence, that: (i) oscillations in a channel flow could either increase or decrease the flow sufficiently to result in force imbalance on the channel fluid and, hence, reverse the channel flow, (ii) flow reversal in a sufficient number of channels causes thermosyphoning breakdown, and (iii) phase separation in the outlet headers causes channel flow stratification. The results of a two-fluid code simulation of one of the tests support one of the mechanisms proposed for the channel flow reversal phenomenon. Presently, the test procedures are being reviewed.
following phenomena were observed in the various tests: (i) thermosyphoning flow reversal, (ii) thermosyphoning breakdown with the channel flows circulating through the headers below the steam generators and with the system heat removed by reflux condensation, (iii) thermosyphoning breakdown with periods of limited reflux condensation and, hence, system heatup and pressurization at various rates, (iv) standing start, and (v) stratification in the channel flows. It is theorized, with experimental evidence, that: (i) oscillations in a channel flow could either increase or decrease the flow sufficiently to result in force imbalance on the channel fluid and, hence, reverse the channel flow, (ii) flow reversal in a sufficient number of channels causes thermosyphoning breakdown, and (iii) phase separation in the outlet headers causes channel flow stratification. The results of a two-fluid code simulation of one of the tests support one of the mechanisms proposed for the channel flow reversal phenomenon. Presently, the test procedures are being reviewed.
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