Study on the thermal hydraulic characteristics of a simulated pressurizer during the blowdown process

Abstract The small break loss of coolant accident (SBLOCA) is a typical accident studied by many researchers. However, blowdown characteristics of the SBLOCA have not received sufficient attention. In this study, an experimental system for simulating the inherent characteristics of a pressurizer during the blowdown process is built under a low-pressure condition, and a mathematical model for predicting the thermal–hydraulic characteristics during this blowdown process is established. The simulation results are compared with experimental results to verify the accuracy of the mathematical model; the simulation and experimental results were in good agreement. The effects of different nozzle diameters and different initial pressures on the thermal–hydraulic characteristics are analyzed according to these simulation and experimental results. The results show that the steam temperature and pressure in the heating container have a high decline rate during the early stage of the blowdown process, and the decline rate subsequently decreases and remains steady, while the water temperature during the blowdown process decreases steadily. During the blowdown process, the nozzle diameter and initial pressure have little effect on the steam temperature, water temperature, and pressure, but the decline rates of both the liquid level and mass flow exhibit an increasing trend as the nozzle diameter and initial pressure increase. Compared to the water temperature, steam temperature, and container pressure, the liquid level and mass flow are more appropriate parameters for predicting the characteristic parameters of the blowdown process.