Passive core make-up water tank is used so as to eliminate high pressure safety injection pumps. Transient characteristic research of core make-up water tank in the case of small LOCA were performed. The break sizes are: 2, 6, 12, 18, 30 mm respectively. Thermal hydraulic behaviors of pressurizer and draining flow rate measurement from core make-up water tank to primary coolant system following small LOCA were researched and carried out in the test. A total of 80 sensors were used to measure temperatures, liquid level and flow rate.

The above figures show the pressure curves of CMT for all 5 break sizes. It is evident that there exists a pressure oscillation phase during pressure drop down, especially for f30mm break size and lasts from 50s to end of draining. In general, the blow down phase is longer, steam condensation in CMT is more. The draining behaviors of CMT are complex and change with break size. The draining mass flow rate increases rapidly at the beginning and has a low oscillation phase before stable draining phase. All break sizes have obviously a high flow rate peak. After about 500s, all flow fluxes are nearly the same.