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F321 austenitic stainless steel is used in high-temperature, high-pressure, and severe irradiation conditions at high-temperature gas reactors, leading to the formation of irradiation defects such as point defect in the matrix. This study explores the displacement cascade process in F321 austenitic stainless steel based on molecular dynamics (MD) simulations with the aim of investigating the effect of PKA energy, PKA direction and temperature. MD results show that irradiation-induced Frenkel pairs (FPs) number increases with increasing PKA energy. The effect of different PKA directions is not significant when energy is lower than 30 keV, which becomes obviously at 50 keV and 100 keV. In addition, the increasing temperature leads to lower FPs. When it comes to defect cluster, both size and number of clusters increase with increasing PKA energy, which is consistent with the trend with FPs. Vacancy cluster is larger than that of interstitial cluster and the irradiation-induced defect cluster is not significantly dependent on PKA directions. Furthermore, five typical dislocation loops (1/2 < 110>, 1/6 < 112>, 1/3 < 111>, 1/6 < 110 > and 1/3 < 100>) are observed in samples after displacement cascade, especially high-energy PKA cascades. More interestingly, 1/6 < 112 > dislocation loop is formed first in the displacement cascade process due to its high mobility. These insights reveal systematic irradiation defect formation mechanism during displacement cascade under varied irradiation conditions, offering a new perspective for novel understanding irradiation effect in F321 stainless steel. Based on that, the effect of various factors could be quantified precisely, governing the study of irradiation defects' generation. [ABSTRACT FROM AUTHOR]

The brittle–ductile transition temperature (BDTT) and fracture toughness are useful indicators of the brittleness of reactor pressure vessel materials. However, current methods to analyze these parameters are expensive and time-consuming; moreover, the relevant mechanism is not very clear. Thus, in this study, a body-centered cubic crystal plasticity finite element model (CPFEM) based on the densities of dislocation and irradiation defects, which are full- and partial-absorption dislocation loops, was numerically implemented on A508-3 steel. Irradiation embrittlement was investigated in the CPFEM framework. The cleavage failure model for a representative volume element was proposed to calculate the BDTT, the results of which agreed well with experimental results in the literature for both unirradiated and irradiated samples. The risk for brittle failure is higher for irradiated samples at constant temperature. Furthermore, the proposed model combined with the Beremin cleavage fracture local approach, could estimate the fracture toughness of A508-3 steel at different temperatures before and after irradiation. The results obtained were consistent with reported experimental data, indicating that irradiation exacerbates the embrittlement. This work is beneficial to the calculation and evaluation of irradiation effect of RPV steel, providing reference for the research of reactor life extension. [ABSTRACT FROM AUTHOR]