Abstract: In the event of a severe nuclear reactor accident, the radioactive fission products in the form of aerosols will be released in large quantities into the containment along with steam, hydrogen, and other gases. The transport and deposition of aerosols in the nuclear containment are significantly influenced by the thermal-hydraulic conditions of the containment. The development approach of a three-dimensional computational fluid dynamics (CFD) code called GASFLOW is outlined, specifically tailored to analyze the thermal-hydraulics and behavior of aerosols in the containment during severe accidents. The Eulerian-Lagrangian approach enables the mass, momentum, and energy two-way coupling between the continuous gas and the dispersed particles. This approach is promising to model the behaviors of aerosols/droplets in 3D simulations of a full-scale nuclear containment. The particle group method is applied in the Lagrangian approach to track the particle trajectory. The ordinary differential equations, which couple the local heat and mass transfer between particles and the surrounding gas mixtures, are solved by the Runge-Kutta method. The GASFLOW aerosol analysis module is extensively validated by experiments, such as Gunn-Kinzer, Ranz-Marshall, CARAIDAS, and TOSQAN experiments, which respectively demonstrate good agreement with respect to each phenomenon: free-falling particles without heat and mass transfer, evaporation dynamics of an isolated stagnant droplet in dry air, the momentum and heat transfers of a single droplet under typical post-accident atmosphere conditions, and the gas mixing and depressurization in the containment by water spray. The validated program can accurately evaluate the three-dimensional distribution of aerosol transportation and deposition in the containment. The three-dimensional CFD analysis of aerosol behavior in the containment during a typical severe accident of a large advanced pressurized water reactor indicates that the CFD calculation time is acceptable and has good engineering practicality for large dry nuclear containment. The total deposited and suspended aerosol mass is in good agreement with the results predicted by the lumped parameter code MELCOR. The three-dimensional distribution of aerosols is influenced by the flow field, concentration field, and temperature field. Hygroscopic growth of aerosols is a key factor affecting the natural removal of aerosols. This aerosol analysis module in GASFLOW can be extended to study aerosol behavior in other complex thermal-hydraulic conditions, such as aerosol removal by containment spray and aerosol entrainment by intensive convection or hydrogen explosion.