Sodium to air heat exchangers (AHX) with finned tubes is used in fast breeder reactors for decay heat removal. The aim of decay heat removal is to maintain the fuel, clad, coolant, and structural temperatures within safety limits. To investigate the thermal hydraulic features of AHX, a robust porous body based computational fluid dynamics (CFD) model has been developed and validated against the experimental data obtained from a model AHX of 2 MW capacity in Steam Generator Test Facility at the Indira Gandhi Centre for Atomic Research, Kalpakkam. In the present paper, the developed porous body model is used to study the sodium and air temperature distribution and the influence of various parameters that affect the heat removal rate and sodium outlet temperature in full-size AHX used in the fast breeder reactors. The parameters include mass flow rates and inlet temperatures of sodium and air. The focus of the study has been to identify conditions that can pose the risk of sodium freezing.