COUNTERCURRENT GAS-LIQUID FLOW IN A PRESSURIZED-WATER REACTOR HOT LEG

The objective of this analysis is to obtain an algebraic correlation f or flooding and unflooding in a pressurized water reactor (PWR) hot le g during reflux core cooling. This correlation may be used in loss-of- coolant accident analysis codes such as RELAP5. The one-dimensional tw o-fluid model equations are solved to obtain a void fraction profile a long the pipe. A jump condition is included in the model to account fo r the possibility of a hydraulic jump. The flooding correlation by Mis hima and Ishii is used to determine the flooding point. The model is v alidated against the scaled-down data of Krolewski and the full-scale data of Ohnuki, Adachi, and Murao. Reducing the coefficient of the flo oding correlation to match the full-scale data is necessary to account for the effect of diameter size. Based on the validated model, a floo ding correlation is obtained along the lines of the Wallis flooding cr iterion. It is further shown that under the conditions prevalent durin g PWR refluxing, the hysteresis between flooding and unflooding is not relevant, so the same correlation is valid for both.