Performance Analysis of Passive Residual Heat Removal System

The core heat in the RCS is transferred to secondary system through the Steam Generator (SG) with the boiling and the heat of secondary system is transferred to the coolant in the ECT through the PRHRS heat exchanger with the condensation. Because boiling and condensing heat transfer coefficients (HTC) are larger than single-phase liquid HTC, the boiling-condensation nature circulation is most efficient mechanism. It is optimal condition that the saturated vapor exists in SG outlet to ECT inlet and the saturated water exists in ECT outlet to SG inlet. If the pressure increases, the saturation temperature would be increased and the single phase heat transfer would occur. The numerical analysis using MARS-KS code under reactor trip accident and sensitivity analysis according to charging time was conducted. As a result of analysis it has been observed that the PRHRS performance could be degraded depending on the operation conditions. If the working fluid (i.e., water inventory) is over-charged, the natural circulation could not be established sufficiently and the heat transfer would be deteriorated. For optimal PRHRS performance the uncertainty factor (e.g., signal delay) should be eliminated.