Experimental Investigation on the Optimization of ADS Sparger Arrangement in IRWST of AP1000 Plant

In AP1000 plant, the Automatic Depressurization System (ADS) works to discharge the high-temperature and high-pressure steam from the Reactor Coolant System (RCS) primary side to the In-containment Refueling Water Storage Tank (IRWST) in the LOCA conditions, which is very important to the safety of the reactor. In our previous work, an overall scaled-down IRWST and ADS sparger experimental bench has been built to study the special condensation and mixing phenomena in the accidental depressurization events in IRWST of AP1000 plant. Based on the research results, the thermal stratification is very obvious in the steam spraying process, which is not efficient for the condensation of the spraying steam. In the present work, an optimized ADS sparger arrangement design is recommended to enhance the convection effect and reduce the thermal stratification, and the effects of the new design are validated by the experiment. The Stratification number (Str) is employed to evaluate the thermal stratification extent. The experimental results indicate that the modification of the sparger elevation can indeed change the velocity distributions in IRWST, and further reduce the thermal stratification significantly, which is beneficial for the safety of the reactor under the accident conditions.