Cluster Dynamics Prediction of the Microstructure Evolution of 300-Series Austenitic Stainless Steel under Irradiation: Influence of Helium

A cluster dynamics model is being developed for the prediction of the entire microstructure evolution of austenitic stainless steel (SS) under irradiation. The particular features of the model are the description of (i) the creation and evolution of Stacking Fault Tetrahedra (SFT), (ii) the evolution of the Frank loops and network dislocation microstructure, (iii) the influence of helium considering the mean number of helium atoms in cavities. This model was calibrated against 304L austenitic SS data on Frank loops and SFTs after irradiation in the Bor60 fast reactor at 320°C and 9.4×10−7 dpa/s. The predictions of the model were then compared to experimental data (i) from the Ringhals PWR thimble tube CW316 SS irradiated at 315°C, 10−7 dpa/s, and 20 appm He/dpa, and (ii) EBR-II fast breeder reactor SA316 SS irradiated at 470°C and 6×10−7 dpa/s. Results were found to be in good agreement with the experimental data at 315°C, and in poor agreement at 470°C. The heterogeneous nucleation of cavities at the interface of precipitates, which is known to occur at high temperature and is not described in the model, is believed to be responsible for this discrepancy at 470°C. The effect of helium on the cavity microstructure evolution at (i) 315°C and 10−7 dpa/s and (ii) 470°C and 6x10−7 dpa/s was investigated by comparing predictions of the model at 0 and 20 appm He/dpa. Helium was predicted to have no significant influence on the cavity microstructure at 315°C, and a significant influence at 470°C.