[en] One of the advanced safety features of APR1400 is the SIT (Safety Injection Tank) equipped with fluidic device. The device has a role of extending SIT flow to the later part of a LBLOCA (Large Break Loss-Of- Coolant Accident) to compensate the lack of low head safety injection pumps. The SIT flow going through the device experiences two step flow resistance which increases as the vorticity inside the device increases. In LBLOCA calculations using RELAP5/MOD3, SITs are usually modeled with the ACCUM component. However, the ACCUM component model regards a SIT as a lumped volume so that it can not be applied to the modeling of the SIT of APR1400. As the fluidic device was a kind of newly adopted safety equipment, a full scale test facility, VAPER (Valve Performance Test Rig) was built and various tests were performed by KAERI. Utilizing the results of VAPER tests, a simple and practical RELAP5 modeling method was suggested in this paper