Intergranular or intragranular anisotropic pores can be easily observed in the FCC structure of nuclear reactor core structural materials, such as austenitic stainless steel or nickel-based alloys. Austenitic stainless steel contains a certain amount of nickel (Ni), and Ni undergoes transmutation reaction under neutron irradiation to produce helium. Helium combines with vacancy and continuously absorbs more helium and vacancy, evolving into under pressure pores filled with a small amount of helium. The morphology of pores is influenced by both the surface anisotropy of the crystal and grain boundary characteristic because pore nucleation predominantly occurs at grain boundary. The swelling effect caused by pores and the embrittlement effect of high temperature helium are related to the morphology, size and distribution of pores. The phase field method can couple multiple physical fields and accurately describe the effects of material microscopic defects on pores. In this study, we use the phase field method to simulate the evolution and morphology of pores, establishing a free energy functional coupling between crystal plane anisotropy and pore-grain boundary interactions. Our results demonstrate that helium gas induces pore nucleation, with higher concentrations leading to shorter incubation period, faster nucleation rate, and greater growth rate. Grain boundaries act as heterogeneous nucleation sites for helium pores, leading to the formation of pores along these boundaries and high-density diffusion pores within the grains. The intragranular pores exhibit anisotropic characteristics regulated by interfacial energy’s anisotropic modulus, the strength of the anisotropy, and crystal orientation. The high-density intergranular pores interact with each other significantly and are influenced by grain boundaries, while the anisotropic morphology is negligible. Additionally, it has been observed that the pores located in the middle of grain boundaries tend to become an elliptical. The stress inside the pores that contain a small amount of helium gas is negative, which is lower than the value in the matrix. These findings presented herein align well with experimental results, which inspires the prediction of service life of core components and the design of core materials.
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