THERMAL-HYDRAULIC PHENOMENA DURING REFLUX CONDENSATION COOLING IN STEAM-GENERATOR TUBES

The transitions of cooling mechanism in steam generator tubes during r eflux condensation are studied. It is found that the transitions are c losely related to the occurrence of flooding or counter-current flow l imitation phenomena in steam generator tubes. As shown in the previous studies of other researchers, the transition from filmwise reflux con densation into total reflux condensation occurs when the flooding crit erion suggested by Wallis is met. In this study, it is suggested that the transition from total reflux condensation to complete carry-over o ccurs depending on the tube height and cooling conditions. It is also shown that the flooding at SG tubes occurs before the flooding at hot leg when a reflux condensation mode is existing in steam generator. Th ough the thermal-hydraulic conditions during reflux condensation after a small-break loss-of-coolant accident have enough margin to the tran sition into carry-over, considerations for the prevention of primary c oolant relocation should be provided. (C) 1998 Elsevier Science Ltd. A ll rights reserved.