Development of Sweepout Model in APR1400 During an LBLOCA

As a result of experiments with the Upper Plenum Test Facility and the 1400-MW(electric) Advanced Power Reactor (APR1400), sweepout in the downcomer has been identified as playing an important role in the depletion of the core coolant inventory during a large-break loss-of-coolant accident. In order to identify the sweepout mechanism and estimate the amount of coolant discharged during sweepout, separate-effects tests were performed in a rectangular-type test apparatus 1/5 the scale of the APR1400 downcomer. The experimental results showed that the sweepout was dominantly influenced by the hydraulic behaviors of coolant and steam near the intact cold leg. A sweepout model was developed by correlating the experimental results to analytically derived nondimensional parameters. The developed model showed applicability to the prototype, as the experimental results of the counterpart tests were in good agreement, within <25.0% of the uncertainty band.