Investigation of AP1000 containment pressure and temperature transient under station black out accident with different pressure set-points

AP1000 reactor applying external cooling concept to anticipate the increase in pressure due to Station Black Out (SBO). Disposal mechanism of decay heat conducted through the Passive Residual Heat Removal System (PRHRS) to In-containment Refueling Water Storage Tank (IRWST) and subsequently forwarded to the reactor containment. Containment is externally cooled through natural convection in the air gap and through evaporation cooling water poured on the outer surface of the containment wall when the pressure attaints 1.7 bars according to the applied pressure set-point. With this mechanism, the pressure will increase until it reaches certain maximum value and then decrease when containment cooling already begun effectively. The purpose of this study was to determine the effect of the set-point to the maximum pressure and temperature reached. The utilized method is to perform simulations using Matlab-07 model of analytical calculations based on a transient state that is capable of estimating the power of heat evacuated and the pressure in the containment. The simulation results show the pattern of pressure and temperature transient rises to a maximum and drops back to a value that is relatively constant. With the set-point variation ranging from 1.7 bars to 5 bars, the maximum pressure varies from 3.5 bars to 5 bars and the maximum temperature varies from 117 °C to 125 °C. It can be concluded that with increasing the set-point pressure of starting the external cooling with water, the maximum pressure and temperature increase. (author)