The numerical simulation was carried out to investigate the local entropy generation in turbulent mixed convection heat transfer of supercritical water within the inner sub-channel of SCWR. The SSG Reynolds stress model with enhanced wall treatment was used as a turbulence model. The circumferential heterogeneity of heat transfer was introduced into the entropy generation analysis. The mechanisms of entropy generation in the near wall region within the boundary layer and the region away from the wall were discussed in detail. The results show that the buffer layer has great influence on heat transfer enhancement, and both the viscous sub-layer and buffer layer act significantly in the entropy generation with respect to circumferential heterogeneity. Usually, the entropy generation in the narrow gap is relatively larger than that in the sub-channel center when comparing the contribution of entropy production caused by heat transfer to that caused by energy dissipation. The simulation findings may provide a theoretical direction for the conceptual design of SCWR. (C) 2017 Elsevier Ltd. All rights reserved.