Scaling analysis of coolant spraying process in automatic depressurized system

Abstract

Through the automatic depressurized system of AP1000 reactor, the steam with high temperature and high pressure from the pressurizer sprays into the water tank, and the pressure in the primary coolant system will diminish to protect the reactor. However, as the steam continues to flow into the tank, the water temperature rises rapidly until boiling occurs, which will affect the local heat transfer process. Therefore, it is necessary to understand the corresponding heat transfer mechanism by means of experiment. To ensure that the experimental results with a scale-down model reflect the actual situations of the prototype we analyzed the process of steam jetting from the pipeline into the water tank, and summarized scaling rules based on equation analysis method, including various flow stages. The results show that the phenomena-based similarity between the model and the prototype should meet: (1) geometrically similar model and prototype; (2) equal thermal parameters and identical initial conditions, which can greatly simplify other similarity parameters; (3) at the blowdown stage, keep the steam mass flux and the nozzle diameter consistent; (4) at the natural convection stage with single phase fluid, the equality in terms of Prandtl number and the Grashof number should be met first, while assessing the relative uncertainty.