ECC Bypass in the ATLAS Separate Effect Test for a Low Reflooding Rate

KAERI (Korea Atomic Energy Research Institute) has recently started the operation of the ATLAS (Advanced Thermal-Hydraulic Test Loop for Accident Simulation), which is a thermal-hydraulic integral effect test facility for evolutionary pressurized water reactors. As the first phase of the ATLAS program, a series of large break loss of coolant accident (LBLOCA) reflood tests have been performed to resolve the safety issues related with thermal-hydraulic phenomena during the LBLOCA late reflood period in the APR1400. After completion of the integral LBLOCA reflood tests, separate effect test named as LB-CL-15 was performed to help validate the RELAP5 reflood models for a core quench phenomenon under a low flow rate ECC injection condition. A separate effect test data peculiar to the APR1400 could be obtained, which has the DVI injection, reverse heat transfer from steam generators and steam binding effect, etc. In this paper, among the typical thermal-hydraulic phenomena during the LBLOCA reflood period, the emergency core cooling (ECC) bypass is focused and a fraction of the direct ECC bypass in the LB-CL-15 test is evaluated