Validation of RELAP5 MOD3.3 code for entrainment phenomenon against FATE test facility

The fourth stage of Automatic Depressurization System(ADS4) is a crucial part in the passive core cooling system. During LOCA transient or long-term cooling period, entrainment/offtake phenomenon will take place at the ADS4 branch. This phenomenon may affect the depressurization process or boric acid balancing. The RELAP5 mod3.3 is expected to be useful and effective for analyzing the thermal-hydraulic behaviors in design, licensing and safety analysis of nuclear power plant. In this case, accurately evaluating the entrainment/offtake model in RELAP5 is quite important for safety analysis of passive nuclear power plant. A Full scAle Test facility for liquid Entrainment (FATE) is designed and fabricated to give a better understanding of entrainment's scaling effect and quantify the uncertainty of existing models. The geometry of upper plenum, hot leg and ADS4 pipe are all the same with CAP1400. Test data of both onset of liquid entrainment (OLE) and entrainment rate for different gas and liquid flow rate are achieved. Calculation results are compared with the experiment data and existing entrainment models. The differences are discussed and analyzed.