Transactions of the Korean Nuclear Society Virtual Autumn Meeting December 17-18 Experimental Study for Effect of SIP flow rate on Cold Leg 4 inch Upward Break Scenario in ATLAS Facility

The depth of the loop seal of APR1400 (Advanced Power Reactor 1400 MWe) has 0.608 m depth while the U.S.EPR has 0.030 m depth [1]. The deeper loop seal of APR1400 and its impact can be more serious than in other PWRs because the deeper loop seal necessitates longer time to clear the loop seal and partial core uncovery can occur during this time. Therefore, an issue about loop seal and its impact on long term cooling during a postulated loss-of coolant accident (LOCA) was raised for the APR1400. In particular, a top slot break at a cold leg with a medium or small size break was concerned [2]. During this accident, a loop seal reformation after a loop seal clearing can lead a partial core uncover and core temperature excursion may occur. It is possible that the loop seal is reformed by primary steam condensation by steam generator heat transfer or safety injection water flooding (reverse flow to loop seal) after loop seal clearing. And then, pressure increase at the top core region due to the steam released from core. This pressurized steam pushes down the core level and partial core is uncovered. And core temperature excursion may occur. An experimental investigations for the top slot break at a cold leg have been performed as a test item of the 4th ATLAS-Domestic Standard Problem (DSP) [3]. This experiment (ID: LTC-CL-04R) was performed in ATLAS, an integral effect test facility. For this experiment, the safety injection pumps operated with maximum flow rate (about 0.3 kg/sec per pump) during their operating time. This condition is more conservative condition because larger amount of safety injection water increases reverse flow rate to loop seal and loop seal reformation is easily reformed. In the current study, an experiment (ID: LTC-CL-05) for the top slot break at a cold leg was repeated with nominal SIP flow rate to investigate SIP flow rate effect on the loop seal behaviors.