EXTENDED ABSTRACT: Tristructural isotropic(TRISO)fuel pellets, with intrinsic safety properties, are an important fuel element component for high-temperature gas-cooled reactors(HTGR) and modular microreactors(MMR), where the SiC coating is used to withstand the pressure of the fission gas and further prevent the diffusion of fission products, providing an important safety barrier for reactors. SiC coatings are prepared by fluidized bed-chemical vapor deposition (FB-CVD), and the growth kinetics is difficult to obtain directly due to the reaction characteristics of high temperatures.In order to study the crystal nucleation and growth mechanism of SiC during the coating process, the phase field simulation method was used to simulate the dynamic behavior of SiC deposition on solid surfaces during multiphase vapor deposition by establishing a multiphase deposition model and coupling the Smoothed boundary method (SBM). Through simulation, it was found that the early stage of SiC coating growth followed the VolmerWeber growth pattern, which means the nucleation island grows until the island core junction, and finally forms a continuous polycrystalline thin film. At the same time, with the introduction of more complex heterogeneous phase shapes and distributions, the multi-scale effects and interfacial interaction behaviors of crystal growth during deposition were further studied. The relationship between diffusion and sedimentation in the process of polycrystalline competitive growth was investment, and the parameters related to diffusion including the influence of gas phase diffusion coefficient, gas phase impact rate, surface diffusion coefficient, deposition rate, and the influence of parameters related to diffusion and deposition (gas phase concentration) were explored. In addition, the effect of surface flatness of sedimentary substrate (amorphous carbon) on the growth process of polycrystalline competition is also explored.

Keywords：Phase field simulation; SiC coating layer; Smoothed boundary method; Grain growth.