Abstract: A conceptual design of passive containment cooling system (PCCS) with closed-loop configuration was investigated. A set of models were set up and corresponding codes (PCCS-CL) were developed for the prediction of the heat removal capacity of proposed PCCS based on one-dimensional homogeneous two-phase flow model. The genetic algorithm was selected to develop the code for optimization of PCCS. The optimization code was used to conduct the design optimization of PCCS in terms of heat removal capacity along with the PCCS-CL codes. The way to select the geometrical and operational parameters for PCCS was clarified. The results show that the heat removal capacity of PCCS can be enhanced by increasing the diameters of tubes of both internal and external heat exchangers. The optimized number ratio of tube for external heat exchanger and internal heat exchanger is 1.58.