Experimental investigation on natural circulation characteristics of emergency passive residual heat removal system in HPR1000

The emergency passive residual heat removal system (EPRHR) in Hualong Pressurized Reactor (HPR1000) adopts natural circulation to remove the core residual heat passively during the event of feed line break or station blackout (SBO) accident. The Emergency Secondary Passive Residual heat removal system Integral Test facility (ESPRIT) was constructed to obtain the natural circulation characteristics of EPRHR under various initial and boundary conditions. Resistance matching was conducted in advance of the experiments, ensuring the same resistance characteristics between the test loop and the prototype. The natural circulation characteristics under different heat exchanger (HX) area, steam generator (SG) liquid level and system resistance were studied experimentally. The test data reveal that the system pressure/temperature rises dramatically with the decline of the HX heat transfer area when the HX heat transfer area is small. The natural circulation flow rate increases with increasing of the SG power, and with decreasing of the HX heat transfer area in the experiment. The natural circulation flow rate oscillates with certain frequency in low power rate conditions. The SG liquid level has no significant effect on system pressure/temperature and natural circulation rate in the experiment. The pressure decline rate decreases with the increase of the resistance coefficients. The condensed water flow rates decrease with the increasing of the resistance.