which generate together 2000 MW. Angra 3, the third plant of the nuclear station, is under construction and will supply 1405 MW to the electrical grid. The nuclear fuel assemblies, after a work cycle, are removed from the reactor and stored in the respective storage pool. Each one of the NPPs is provided with a spent fuel pool, which has a limited storage capacity, and do not suffice for the whole lifetime of the plants. Thus, a complementary storage facility must be provided for the nuclear station for the NPPs to keep operation. Facilities for storage of spent fuel assemblies (SFAs) which are not "attached" to the reactor building are referred to as "away from reactor" storage facilities. There are two main types of SFA storage in away from reactor facilities: dry storage and wet storage. In both cases, the installation must be provided with a solution to the remove residual heat generated by the spent fuel.Eletronuclear, the company responsible for construction and operation of NPPs in Brazil, has designed a wet SFA storage facility to fulfill the demand for space. According to the design, this storage facility would be provided with a fully passive cooling system for removal of the residual heat. Worldwide, there is only one installation with a similar solution, which is operating in Gösgen, Switzerland. This decision follows the global trend to increase participation of passive systems in nuclear installations, especially after the events of March 11, 2011, in Fukushima. In that occasion three of the six units of Fukushima Daiichi nuclear station suffered a core meltdown caused by a lossof-coolant accident. The unavailability of external energy supply and emergency diesel generators was the cause for the loss of cooling capacity.Passive cooling systems (PCSs) are engineering solutions to perform the function of heat transfer using the temperature difference between hot and cold sources to generate the driving force for the flow. Their advantages