IRWSTIn-Containment Refueling Water Storage Tank
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Because, in literature [21], the mixing characteristics in the IRWST and the heat transfer calculation of the PRHR HX under the condition of natural convection on the tube outer surface were deeply studied through experiments, the main purpose of this study is to research the mixing characteristic in the IRWST from natural convection to boiling condition, find out the best fit one from several commonly used correlations for PRHR HX saturation boiling heat transfer calculation, and try to come up with a new formula to improve calculation accuracy for the tube outside subcooled boiling.
The IRWST was made by a cylindrical tank filled with water at atmospheric pressure and filled to a level 0.1 m above the top of the heat exchanger tube.
The influence of separation plate and Automatic Depressurization System (ADS) 1-3 sparger in IRWST was also ignored in this experiment.
The PRHR HX located inside the in-containment refueling water storage tank (IRWST) is the major component responsible for heat removal and is shown in Figure 2.
The effect of SBLOCA is reduced through the sequential depressurization of ADS which allows passive injection from the CMTs, the accumulators, and the IRWST [5].
Two direct vessel injection (DVI) nozzles are located in the upper downcomer and safety injection water from CMTs, accumulators, IRWST, and containment sump is supplied through the nozzles.
The SBLOCA transient in AP1000 can be characterized into four (4) different phases which are the blowdown phase, ADS blowdown phase, natural circulation phase, and IRWST injection phase.
With the actuation of all passive safety systems and ADS stages, the primary system finally attains the containment pressure and results in actuation of IRWST. The pressure drop during small break LOCA calculated from RELAP5-MV and NOTRUP is given in Figures 9 and 10, respectively.
Similarly, the IRWST actuation also causes a natural circulation flow.