Since the design of Advanced Power Reactor 1400MWe (APR1400) has a deep loop seal geometry, loop seal reformation during Small Break Loss-Of-Coolant Accident (SBLOCA) has been concerned due to its possible effect on core uncovery and significant cladding temperature rise. Therefore it has been an important safety issue of SBLOCA and it has been vital to understand the effect of loop seal clearing and reformation on the core uncovery and cladding temperature.

In this study, SBLOCA of APR1400 was analyzed with MARS-KS (KINS Standard version of Multi-dimensional Analysis of Reactor Safety) code to investigate the thermal-hydraulic behavior including loop seal clearing and reformation. The break spectrum analysis was performed to identify the effect of break size to confirm the limiting case leading to Peak Cladding Temperature (PCT). The limiting case of MARS-KS calculation was compared with that of SPACE (Safety and Performance Analysis CodE). Particularly the thermal-hydraulic parameters including the system pressure and the water level of core and downcomer were identified in detail.