The effect of interfacial friction at a high void fraction on the estimation of the dryout heat flux (DHF) of particle beds under co-current two-phase flow conditions is investigated. The objective is to reduce uncertainties in the assessment of debris bed coolability during a severe accident in a light water reactor (LWR). A review of porous media air/water pressure drop experiments and friction models in the literature revealed that the existing models cannot adequately predict the interfacial friction at high void fraction. In this study, interfacial friction at high void fraction is suggested and corresponding modifications to the flow pattern map and other friction terms are presented. The proposed model shows an acceptable agreement with the experimental data of both the air/water two-phase pressure drop and DHF experimental results within the particle size range of 2-4 mm, similar to the average diameter of debris particles (2.5-3.5 mm, Hong and An, 2018) obtained from fuel coolant interaction tests. (C) 2019 Elsevier Ltd. All rights reserved.