Experimental research on thermal-hydraulic characteristics of generation Ⅲ PWR under LOCA conditions

China has developed the HPR1000, an advanced Generation III pressurized water reactor (PWR) that integrates active and passive safety systems to achieve enhanced nuclear power plant safety. Among all design basis accidents (DBAs), the loss of coolant accident (LOCA) represents the most severe challenge for the reactor safety analysis. To investigate LOCA characteristics, the HPR1000 integral test facility (HITE) was designed using the hierarchical two-tiered scaling (H2TS) methodology, accurately simulating the three-loop configuration of the reference reactor. The facility was employed to conduct a LOCA experiment with 4 % cold leg area. Then, the detailed analysis of the resultant system transients and key thermal-hydraulic phenomena were obtained based on the experimental and simulation results. Primary system pressure was effectively reduced during medium pressure rapid cooling (MPRC) operation through steam discharge via VDA under LOCA conditions. The MPRC system achieved a rapid cooldown rate of 500 °C/h and depressurization, enabling timely RIS activation. Both core fluid temperatures and fuel rod cladding temperatures decreased during the accident. The collapsed water level of RS is recovered until reaches the bottom of CL. The experimental results show that the system configuration and capacity is rational in coping with LOCA accident. The thermal stratification phenomenon is observed and discussed in the pipes of primary system. It is evident that the overall variation trend of the pressure obtained from the calculation is generally consistent with the experimental measurements. The findings are expected to improve the understanding of LOCA in HPR1000.