Experimental investigation on the temperature distribution in the cavity pool of ex-vessel cooling system

Highlights: ► The temperature profiles in the tank mainly vary in the gravity direction. ► Increasing in flow rate will decrease the stratification and enhance the mixing effect. ► The initial temperature and heat loss rate shows a negligible effect on stratification. ► Pe number could qualitatively reveal the control mechanisms of the stratification. - Abstract: During the external reactor vessel cooling process, the cavity pool might be stratified due to the buoyancy effect. The purpose of this study is to investigate the temperature distribution and the effect of main factors on the thermal stratification phenomena in the cavity pool. A large rectangular tank of the REPEC test facility, with a dimension of 2 m in length, 1.5 m in width and 1.5 m in height, is used to simulate the cavity pool. And the water level of the tank can be set to any value in the range of 0.9–1.5 m. In the experiment, the hot water enters into the tank through the top inlet, while the relative cold water withdraws from the bottom outlet. 24 T type thermocouples are used to measure the temperature profiles in the tank. The experiment investigation mainly focuses on the temporal and spatial temperature distribution, heat loss rate to the ambient, the effect of initial tank temperature and charging flow rate on the thermal stratification phenomena in the tank. The experiment results indicate that thermal stratification occurs spontaneously when the flow rate is low, but the thermal stratification phenomenon weakens with the increase of flow rate. It is demonstrated that the initial water temperature has little effect on the thermal stratification process. The temperature distribution varies in the gravity direction and is almost uniform in the horizontal direction. Consequently, a simplified 1D analytical model is proposed and Pe number is derived from the model to qualitatively characterize the stratification in the tank