Core Liquid Level Depression due to Manometric Effect during PWR Small Break LOCA Effect of Core Bypass

Abstract

In the previous study, it is reported that the core collapsed liquid level was depressed nearly to the core bottom and the dryout of the core was observed in the early stage of the PWR cold leg small break loss-of-coolant accident (LOCA) experiment, The manometric effect due to the liquid seal formation in the loop seal and the difference of the liquid holdup between the steam generator (SG) upflow-side and downflow-side caused a depression of the core collapsed liquid level. The core liquid level was recovered just after the loop seal was cleared.
The bypass between the core side and the downcomer side affects the core liquid depression. Four 5% cold leg break experiments with the different core bypass location, configuration and size were conducted to clarify the bypass effect. When the bypass was relatively small (less than 3% bypass of the initial core flow before the break), the timing of the loop seal clearing delayed with the bypass. When the bypass was relatively large (9, 2% of the core flow), the loop seal clearing took place after the break uncovery and the timing was significantly delayed, In general, the smaller minimum core collapsed liquid level was obtained at the earlier timing of loop seal clearing due to the smaller bypass.