Natural Circulate Flow Rate Comparison using Water and Al₂O₃ as Working Fluids Based on Power Control in Medium-scale Passive Cooling Experimental Facility

Abstract The use of natural circulation as a passive cooling safety system in reactors has been implemented by nuclear power plants worldwide, including the AP1000 reactor from Westinghouse and the SMART reactor from KAERI, both featuring the Passive Residual Heat Removal System (PRHRS) to prevent overpressure and overheating in the reactor cooling system during accidents. The type of working fluid used influences the natural circulation flow rate. This research compared the mass flow rate of natural circulation using water and Al 2 O 3 -nanofluid as working fluids under varying heater power for steady-state conditions. The experiment involved varying the heater power in the heating tank at 1400 W, 2800 W, and 4200 W. Data was collected experimentally and analysed to calculate the mass flow rate for both water and nanofluid as working fluids. The results show that nanofluids can increase the mass flow rate compared to water due to differences in density, which affect the flow rate. The highest mass flow rate was observed at 4200 W, where the Al 2 O 3 -nanofluid achieved a mass flow rate of 0.0456 kg/s, compared to 0.0454 kg/s for water.