Experimental study on transient heat transfer characteristics during the dropping of containment pressure

The reactor containment integrity and the pressure inside the containment are the most concern in the practical running process. To evaluate the transient heat transfer, non-equilibrium fraction (NEF) is proposed to represent the completed degree of transient condensation. An empirical correlation for NEF is developed and the fit error is within ±25% for 97% of results. Based on this, a simplified calculation model for transient heat transfer rate is also developed, then the transient condensation heat transfer coefficient (HTC) is obtained to characterize the intensity of transient heat transfer. The effect of mixed gas pressure, air mass fraction and temperature of cooling water on NEF and transient condensation HTC are discussed. The result indicates that the initial air mass fraction and initial gas-mixture pressure play an important role in transient-state heat transfer, and the influence of initial cooling water temperature can be ignored. This study aims to improve the understanding of transient-state heat transfer and provide guidance to practical engineering.