The nuclear power plant's containment is the final barrier that prevents harmful radioactive material from entering the outside environment if a reactor core damage occurs, e.g., after a Loss Of Coolant Accident (LOCA). In the event of such a severe accident, steam, hydrogen, and other non-condensable gases are released into the containment of a nuclear power plant. Possible detonation and deflagration of the released hydrogen gas may result in containment failure, thereby paving the way to release harmful radioactive material. Accurate prediction of hydrogen gas distribution in the containment atmosphere is necessary for effective accident management. The flow prevailing in a nuclear reactor containment is turbulent, buoyancy-driven, and governed by the steam condensation on containment structures. Radioactive aerosols and noble gases, released into the containment atmosphere from the reactor pressure vessel, have a "decay-heat" associated with them and behave as heat source terms, which cause local buoyancy effects, thereby influencing gas distribution. The present work is divided into two parts: The first part deals with the modeling of multi-component buoyant gas flow, turbulence, steam condensation on walls, and conjugate heat transfer. The second part concerns aerosol transport modeling and its influence on the local gas distribution through decay-heat. A simplified "drift-flux" approach is chosen for the aerosol transport, considering the computational limits imposed by the size of a nuclear reactor containment. The containmentFoam solver, based on OpenFOAM (v6), is used for all model implementations. The ultimate objective of the current work is to quantify the effect of the decay-heat released by the radioactive aerosol on the local hydrogen gas distribution.