In the core of a molten salt fast reactor (MSFR), heavy metal fuel and fission products can be dissolved in a molten fluoride salt to form a eutectic mixture that acts as both fuel and coolant. Fission energy is released from the fuel salt and transferred to the second loop by fuel salt circulation. Therefore, the MSFR is characterized by strong interaction between the neutronics and the thermal hydraulics. Moreover, recirculation flow occurs, and nuclear heat is accumulated near the fertile blanket, which significantly affects both the flow and the temperature fields in the core. In this work, to further optimize the conceptual geometric design of the MSFR, three geome-tries of the core and fertile blanket are proposed, and the thermal–hydraulic characteristics, including the three-di-mensional flow and temperature fields of the fuel andfertile salts, are simulated and analyzed using a coupling scheme between the open source codes OpenMC and OpenFOAM. The numerical results indicate that a flatter core temperature distribution can be obtained and the hot spot and flow stagnation zones that appear in the upper and lower parts of the core center near the reflector can be eliminated by curving both the top and bottom walls of the core. Moreover, eight cooling loops with a total flow rate of 0.0555 m3 s-1 ensure an acceptable temperature distribu-tion in the fertile blanket.