Helical coiled tube steam generator is the core equipment for energy transfer in a liquid metal fast reactor (LMFR), which transfers the heat released from the core on the primary side to the working mass on the secondary side, generates steam and pushes the turbine to do work. The stability and safety of its operation have a crucial impact on the operational safety, economy and reliability of nuclear power plants.

This study aims to propose a numerical simulation method using computational fluid dynamics (CFD) software for the coupled heat transfer calculation of two-phase fluids in the steam generator of LMFR.

First of all, a three-dimensional numerical model of coupled primary and secondary heat transfer in the steam generator of LMFR was constructed, and the correlation equations of liquid metal and water-vapor variability were established based on the OECD (The Organisation for Economic Co-operation and Development) physical property handbook and the NIST (National Institute of Standards and Technology) database. Then, the Lee phase transition model was used to calculate the mass transfer between the two phases during the evaporation of water-vapor on the secondary side. Finally, the lead-bismuth fast reactor was taken as an object, the coupled heat transfer characteristics between the primary and secondary sides of the steam generator under different primary-side inlet parameters were investigated and compared with the conventional water reactors.

The results show that, under the same conditions, compared with the traditional water reactor, the wall heat flux between the primary and secondary sides is significantly increased when lead-bismuth liquid metal is used in the primary side, and the peak heat flux can reach 1 439.97 kW?m^-2, which is 5~6 times higher than that of the corresponding value of the water reactor, which leads to a significant intensification of the vapor evaporation process in the tube of the secondary side, and the volumetric vapor volume fraction rate rises sharply. Simutaneously, the along-track heat flux distribution between the primary and secondary sides is more heterogeneous, which leads to an increase of the vapor volume fraction rate. Meanwhile, the relative deviation of the heat flux distribution along the heat flux is 3~4 times larger than the corresponding value of water reactor. With the increase of the inlet lead-bismuth temperature on the primary side from 350 ℃ to 450 ℃, the wall heat flux between the primary and secondary sides increases, and the corresponding peak heat flux increases from 950.7 kW?m^-2 to 1 439.97 kW?m^-2. The distribution of the along-range heat flux between the primary and secondary sides is more inhomogeneous, and the inhomogeneity is increased by 20%.