Nanocluster evolution in 9Cr ODS steel after high-dose neutron irradiation in Joyo

Du, Y.*; Toyama, Takeshi*; Inoue, Koji*; Otsuka, Satoshi   ; Yano, Yasuhide  ; Yoshida, Kenta*; Shimada, Yusuke*; Onuma, Masato*; Mitsuhara, Masatoshi*; Nakashima, Hideharu*; Nagai, Yasuyoshi*

Oxide dispersion strengthened (ODS) steels, considered as structural materials in Generation IV fission reactors and fusion reactors, are served in extreme environment, where the neutron radiation doses reach up to 250 dpa while the operation temperature up to 700 deg. C. Thus, understanding the microstructure evolution of ODS steels, especially nanoparticles, at high neutron irradiation levels and high temperature is necessary for the prediction of long-term material degradation. In this study, a detailed investigation of oxide nanoparticles after the neutron irradiation to doses of 16-33 dpa at different temperatures (410 830 deg. C) was performed by the atom probe tomography (APT). The outcome of this investigation brought new insight to the characteristics of oxide nanoparticles formation and evolution under neutron irradiation. It was concluded that the nanoclusters underwent an inverse Ostwald ripening process during the low-temperature irradiation, i.e. neutron irradiation to 16 dpa at 410 deg. C.