Characteristics of Natural Circulation Flow and CHF under External Reactor Vessel Cooling within Surface Saturated Conditions

Based on the one-dimensional conservation equations, the numerical calculation model has been established for the analysis of the characteristics of natural circulation flow on the outer surface of reactor pressure vessel utilizing the net vapor generation model in low-flow subcooled boiling and drift flux model. Combined with the SULTAN correlation, a comprehensive study of the effects of heating power, flow channel clearance, loss coefficient of inlet area and flooding levels on the outer cooling process of lower head under in-vessel condition has been conducted in this study.