Development of CUPID-Heat Exchanger Model for the Simulation of the Condensation Phenomena inside the PCCS

The pressurization of reactor containment during number of design basis and severe accidents is a major safety concern in nuclear power plants. To prevent pressure buildup inside the containment. Steam released during accidents should be removed. The development of passive safety systems to guarantee the integrity of the containment in case of accidents have drawn much attention recently. Among these systems is the Passive Containment Cooling System (PCCS). The PCCS consists of number of vertical tube banks acting as a heat exchanger. The condensation process occurs on the outer surface of the tubes. The coolant inside the tubes comes from the Passive Containment Cooling Tank (PCCT) which is located outside the containment and acts as a heat sink. The working fluid circulates between the PCCT and PCCS tubes passively, relying on buoyancy force. Condensation inside the containment takes place in the presence of non-condensable gases such as air and hydrogen which can be generated from core damage. Many experimental [1] and analytical studies [2] showed that the presence of the non-condensable gases sharply degrades heat transfer. Thus, decreasing the rate of steam condensation. Therefore, predicating the condensation rate in the presence of the non-condensable gases is of great importance. In the present work, the CUPID code has been utilized to develop a one tube heat exchanger model in order to simulate the condensation of the steam in the presence of air over vertical tube inside the PCCS. A component scale approach based on empirical heat transfer correlations is adapted. This approach is applicable for large reactor containment application since it allows the usage of coarse meshes. Thus, shorter computational time is needed. Wall heat transfer models are applied inside and outside of the condensing tube. Heat transferred through the tube wall is calculated solving 1D heat conduction equation. Finally. The model is validated against a small scale PCCS experiment