Experimental Study On Direct Contact Condensation Regime And Thermal Stratification Under Rocking Condition

Floating nuclear power plants(FNPPS)usually adopt small reactors,with high inherent safety of the system.Due to the disturbance and attack of wind and waves at sea,the design of FNPPS should not only comply with the basic safety requirements of onshore mode reactors,but also meet the safety requirements of floating platforms.The pressure suppression system of floating nuclear power plants uses the experience of onshore boiling water reactors for reference.A pressure suppression pool is arranged at the bottom of the containment to suppress the pressure rise in the containment by injeting steam into supercooled water and directly contacting condensation.Direct contact condensation in suppression pools with different condensation flow patterns can induce thermal stratification,greatly weakening the suppression performance of the pool,potentially causing overpressure and damaging the integrity of the containment.Therefore,it is necessary to study the phenomenon of direct contact condensation and thermal stratification in the suppression pool of floating nuclear power plants.This article relies on a six degree of freedom rocking platform to build a downward immersion direct contact condensation experimental platform under floating conditions.A comparative experiment of static and rocking was conducted under low mass flow rates,and the steam condensation process under different temperature conditions in the suppression pool was recorded using a high-speed camera,and collecting temperature data.According to the location of the steam-water interface and the shape of the steam bubble,four condensation regimes were studied:chugging,external necking,spheroidal upward bubble and T-shaped upward bubble.The influence of various regimes on thermal stratification in the suppression pool was studied.The experimental results show that the regime of chugging and external necking cause a large downward circulation of subcooled water,which enhance the flow mixing around the discharge tube and the bottom of the pressure suppression pool.Consequently,the thermal stratification phenomenon does not happen in those condensation regimes.However,the regimes like spheroidal upward bubble and T-shaped upward bubble cause the upward circulation of subcooled water in pressure suppression pool,which cause the thermal stratification.The Richardson number(Ri)can be used as a dimensionless number for the regime transition.when the Ri is smaller than 1,the condensation regime is external necking.Besides,when the Ri is greater than I,the condensation regimes are spheroidal upward bubble and T-shaped upward bubble.The starting point of thermal stratification under rocking conditions is basically the same as that under static conditions,but there are significant differences in the performance of the condensation regimes and the temperature response of the suppression pool,which are mainly determined by the rocking motion.