Study On Transient Numerical Simulation Of Direct Injection Of AP1000 Pressure Vessel Under Pressure Penetration

Reactor pressure vessel(PRV) is the only main equipment which can’t be instead.When the loss of coolant accident(LOCA) occurs in the pressurized water reactor (PWR)primary coolant system, RPV will have serious pressurized thermal shock (PTS) which iscaused by the injection of the emergency core cooling system. The safety injection ofsecond-generation PWR generally is connect to the mainline, and the change of stress andtemperature in the nozzle region is much higher than other regions of RPV. AP1000advanced pressurized water reactor uses direct vessel injection(DVI) so that the coolant inthe accumulator(ACC), the core makeup tank(CMT) and the in-containment refuelingwater storage tank(IRWST) are injected into the RPV by the same pipeline. PTS of theDVI nozzle is more intense when LOCA happens.In order to investigate the phenomena of PTS, the transient temperature and thetransient mixing characteristic of RPV downcomer in AP1000under four kinds ofoperating condition (CMT Hot Functional Test, CMT Injection&ADS, CMT Recirc withAcc/IRWST Injection and Normal RHR Operation) has been investigated by usingcomputational fluid dynamics (CFD) method combined with conjugate heat transfercomputing method. And the transient temperature sensitivity analysis of DVI in differentheight and circumferential angle of DVI nozzle is developed. All the results above showthat:(1) The coolant mixed strongly at the intersection of DVI-Nozzle and the inner wallsurface of RPV under four kinds of operating condition. The coolant form the cold leg hasa great impact on the distribution of fluid temperature in downcomer of RPV. And the localof DVI-Nozzle experience a large step change in temperature.(2) The relative height between DVI nozzle and cold leg and the circumferential angledetermine the flow resistance of safety injection water from the fluid in RPV downcomer.The bigger the flow resistance of safety injection suffers, more slowly the temperature ofthe slope between the DVI nozzle and inner wall of RPV drops, but more fast the temperature of wall in Venturi tube region falls. And the transient temperature of thedrainage component and the RPV wall under DVI nozzle is not sensitive to the flowresistance which the safety injection water is suffered.The research results can be technical support for the improvement of DVI nozzlelayout and the structural design and mechanical analysis of RRV.