An Integrated Small Modular Reactor is an Integral Pressurized-Water Reactor (iPWR) with a relatively high surface-area-to-volume ratio. It has been hypothesized that a higher surface-area-to-volume ratio aids passive aerosol decontamination through various deposition phenomena, namely thermophoresis, diffusiophoresis and gravitational settling. Accordingly, particle deposition was studied within a range of thermal-hydraulic parameters, namely pressure, temperature and A/V ratios, in the presence as well as the absence of steam. It was found that an overall convective flow exists inside the Containment Vessel (CV) volume, originating due to fluid buoyancy and the temperature gradient between the Reactor Vessel (RV) and Containment Vessel walls. Computational Fluid Dynamics (CFD) simulations confirmed the existence of this convective flow, and it has experimentally been identified as a major particle transport mechanism. The convective flow also aids particle deposition due to turbulent inertial impaction on the walls. The flow velocities are at least an order of magnitude higher than the deposition velocities by phoretic phenomena; this significantly enhances the importance of the convective flow in contributing to particle transport during post-accident conditions in iPWRs.