Numerical investigation on the performance of the combined passive and spray cooling system under nuclear severe accident

The process of heat removal and depressurization is one of the most significant issues in nuclear safety design. The spray system and the passive containment cooling system (PCCS) are two essential safety arrangements to protect the integrity of the containment and the apparatus. In the present study, the performance of the combined cooling system is investigated by using three-dimensional CFD simulations. The interactions between spray system and external PCCS are analyzed. The numerical results reveal that neither the single passive containment cooling nor the spray system can remove heat and depressurize the containment efficiently under all circumstances. Whereas the combined passive and spray cooling system proposed in this paper can overcome the insufficiency and take the advantages of both the two systems. The mechanism for the superiority of the combined system is explained through the droplets phase change, vapor transportation, wall condensation and film cooling heat transfer processes.