Abstract In this study a thermal-hydraulic analysis is performed of nanofluids as a coolants in subchannels in hot fuel assembly of VVER-1000 reactor by subchannel method. Water-based nanofluids containing various volume fractions of Al2O3 nanoparticles are analyzed. The conservation equations and conduction heat transfer equation for fuel and clad have been derived and discretized by finite volume method. The transfer of mass, momentum and energy between adjacent subchannels are split into diversion crossflow and turbulent mixing components. The governing non linear algebraic equations are solved by numerical iteration methods. Finally the nanofluids analysis results are compared with the pure water results. To validate the applied approach, the model and COBRA-EN code results are compared for the case of pure water. Results show that the heat transfer increases with nanoparticles volume concentration in the subchannel geometry.