Transient Numerical Investigation of Direct Vessel Injection for AP1000 under Pressurized Thermal Shock

The transient temperature and the transient mixing characteristics of RPV downcomer in AP1000 under four kinds of operation condition（CMT Hot Functional Test, CMT Injection and ADS, CMT Recirc with ACC / IRWST Injection and Normal RHR Operation） has been investigated using the computational fluid dynamics（CFD） method combined with the conjugate heat transfer computing method. Results show that the coolant mixed strongly at the intersection of DVI-Nozzle and the inner wall surface of RPV under each operating condition. The coolant from the cold leg decide how the distribution of fluid temperature in downcomer of RPV changed. And three typical location of DVI-Nozzle experience a large step change in temperature under each operation condition.