The SCDAP/RELAP5 3.2 model of AP1000 on SBLOCA

One of innovation design of both the AP600 and AP1000 from conventional Westinghouse PWRs is that they includes passive safety features to prevent or minimize core uncovery during small break loss of coolant accidents (SBLOCAs). This paper uses the best estimate code SCDAP/RELAP5 3.2 to build the numerical model of AP1000. Several SBLOCAs are simulated and analyzed. RELAP5 predictions are also compared to the simulation results of NOTRUMP code. The comparison shows good agreement. The sensitivity analysis of liquid entrainment model of RELAP5 on the pressure-balance-line (PBL), which connecting core makeup tank (CMT) and cold leg in AP1000 is done. Comparisons of the system pressure decreasing, the level of CMT, and actuation time of ADS all indicate that the existing horizontal stratification entrainment model of RELAP5 is very sensitive and important to the short-term of LOCA, and has significant impact on the entire SBLOCA process.

► The best estimate code SCDAP/RELAP5 3.2 is employed to build the model of AP1000.
► RELAP5 predictions are compared to the simulation results of NOTRUMP code.
► The sensitivity analysis of stratification entrainment model of RELAP5 is done.
► It is found that the model is very sensitive to the short-term of LOCA.
► It is also found that the model has significant impact on the entire process.