The present work investigates buoyancy induced cooling of the vertical rods in an enclosure under the influence of radiative heat transfer using a non-Boussinesq model. The problem consists of seven vertical fuel rods placed in a cylindrical casing which is typically encountered in the nuclear engineering application. Combined convective-radiative heat transfer is studied for uniform heated rod bundle housed in an outer cylindrical casing maintained at a constant temperature. The present study is carried out using an in-house three-dimensional solver by employing a low-Mach number formulation based on unstructured hybrid grids. Simulations considering pure natural convection and combined convection with surface radiation is studied. The heat transfer characteristics concerning temperature distribution inside the enclosure are studied by including the effects of surface radiation. © 2018 International Heat Transfer Conference. All rights reserved.