Design and transient analysis of a novel type passive residual heat removal system

This study introduces an innovative air–water mixed cooling passive residual heat removal (AWMPRHR) system designed to overcome the challenges associated with long-term core cooling under the constraints of weight and space in marine nuclear power plants (MNPPs). By utilizing sub-zero Celsius temperatures air and water tanks as heat sinks, the RELAP5 code was used to assesses the performance differences between series and parallel configurations of air–water-cooled heat exchangers under conditions of short-term constant decay heat power and long-term cooling. The findings reveal that during constant decay heat power, the parallel configuration offers superior heat removal efficiency. However, in long-term cooling scenarios, the performance disparities between the two configurations are minimal. Comparative analysis with water-cooled and air-cooled systems shows that the AWMPRHR system not only significantly reduces the stack height by 89.84 % but also enhances the coolant subcooling following an SBO accident. Conversely, the air-cooled configuration reduces the tank volume by 72.63 % and ensures long-term core cooling. The minimum coolant subcooling at the core outlet was 36.19 K. The AWMPRHR system demonstrates a more efficient capability for long-term cooling of the core with smaller heat sink requirements.