Analysis of heat energy changes during steady-state condition based on heater power variation at the FASSIP-03 NT loop

The station blackout (SBO) incident at the Fukushima Daiichi nuclear power plant in March 2011 in Japan became an essential background for research activities on the passive cooling system in nuclear reactor safety technology. The effect of changes in fluid density in hot areas causes a buoyancy force, and changes in fluid density in cold conditions cause a gravitational pull so that natural circulation occurs in the working fluid (water) long inside the loop. The research aims to analyze heat energy changes during steady-state conditions based on the variation of heater powers using FASSIP-03 NT Loop. The study has been done experimentally based on variations in water temperature settings in the heating tank and electric power in the heater. The analysis was carried out based on the graph calculating the heat energy rate so that the thermal energy balance that occurred in the loop could be known. The thermal energy balance analysis results provide data on the number of energy changes in each part of the loop, i.e., in the cooling, heating, and piping. For example, the value of magnitude differences between the rate of change of energy in the helical heat exchanger in the heating tank (qH) and the rate of change of heat energy in the cooling tank (qC) ranges from 6.77% - 15.26%, with an average difference of 12.07%. So in this study, the thermal energy balance is considered fulfilled because the heat received in the HTS component is close to the same as the heat released in the CTS component.