Abstract: Liquid lead-bismuth is considered as the core coolant of the fourth-generation lead-cooled fast reactors, and its compatibility with structural steels is one of the focuses of current researches. In this paper, the aggregation process of iron atoms in liquid lead-bismuth and the diffusion behavior of iron clusters were simulated by using the molecular dynamics method. The influence laws and microscopic mechanisms of the temperature of the system, the size and mass concentration of iron clusters on the coalescence process between iron clusters and the diffusion behavior of iron clusters were analyzed. The results show that iron atoms tend to form clusters in liquid lead-bismuth and that high temperatures can accelerate the aggregation process. In addition, it is found that the coalescence between iron clusters in liquid lead-bismuth needs to overcome energy barriers, the energy barrier to be overcome for the coalescence of two iron clusters of radii 10 Å at 473 K is about 2.14 eV, and the increase of system temperature and the increase of iron clusters size are favorable for the occurrence of coalescence between iron clusters. Furthermore, the diffusion coefficients of iron clusters were calculated, and found to increase with the decrease of their mass concentration, decrease with the increase of their size, and increase with the increase of the temperature of the system. The effect of iron clusters size on the diffusion activation energies was not significant, and the diffusion activation energies of iron clusters with radii of 10 Å, 12.5 Å, and 15 Å were 0.128 eV, 0.140 eV, and 0.134 eV, respectively.

Key words: molecular dynamics, iron clusters, liquid lead-bismuth, diffusion coefficient