Research Of Thermal Stratification Mechanism In Passive Containment Cooling System(SMR)

The containment of SMR,such as NuScale,is immersed in the reactor cooling pool which provides a passive heat sink for containment heat removal under LOCA conditions.The heat transfer efficiency of passive safety systems is affected by thermal stratification in the cooling pool.Therefore,it is of a great significance to study thermal stratification in the reactor cooling pool.Experimental and numerical study were conducted to study thermal stratification in the reactor pool of NuScale power modular.The experiment benchmark was built depending on the dimensions of NuScale reactor at the ratio of 1/20.Four heating rods were uniformly arranged inside the stainless-steel containment to simulate the decay heat during LOCA accident.The temperature at key locations was measured by thermocouples and the velocity field was obtained by Particle Image Velocimetry technique PIV.The instantaneous velocity and temperature field in the water pool changed with four different heating powers.Moreover,four turbulent model cases were developed using ANSYS FLUENT to simulate the transient velocity and temperature field in the water pool.The experiment results showed that the fluid near the vertical wall of the containment flows upwards,when it reaches upper water surface then it flows horizontally towards pool walls.Simultaneously,temperature gradient appears in the containment cooling pool.The mechanism of thermal stratification conditions for different heating power during different times was analyzed to obtain the effects of thermal power and time on thermal stratification.It is found that thermal stratification gradually becomes stronger and mixing interface position moves up when heating time increases.Similarly,the degree of thermal stratification increases with power increase for the same calculation time.Numerical simulation results show that the k-? model are in good agreement with the experimental results.