Resolving hydrogen related safety issues, pertaining to nuclear reactor safety have been an important area of research world over for the past decade. Studies on hydrogen transport behavior and development of hydrogen mitigation systems are still being pursued actively in various research labs, including Bhabha Atomic Research Centre (BARC), in India. The Passive Catalytic Recombiner is one of such hydrogen mitigating devices consisting of catalyst surfaces arranged in an open-ended enclosure. In the presence of hydrogen with available oxygen, a catalytic reaction occurs spontaneously at the catalyst surfaces and the heat of the reaction produces a natural convection flow through the enclosure. The present study aims for performing a CFD simulation to obtain the temperature distribution inside the recombiner, A 3D CFD model has been developed to study the mechanism of catalytic recombination and has been tested for literature quoted experiments. A parametric study has been performed for a particular recombiner geometry for various inlet conditions. Salient features of the simplified CFD model developed at BARC and results of the present model calculations are presented in this paper.