Study on microstructural changes in neutron-irradiated stainless steel weld-overlay cladding of nuclear reactor pressure vessels by atom probe tomography

Takeuchi, Tomoaki   ; Nishiyama, Yutaka ; Katsuyama, Jinya  ; Onizawa, Kunio ; Matsukawa, Yoshitaka*; Toyama, Takeshi*; Nagai, Yasuyoshi*; Kameda, Jun*

Microstructure evolution on stainless overlay cladding of reactor pressure vessel was quantitatively investigated by means of three-dimensional local electrode atom probe (3DAP) in nano-scale. The cladding material was neutron-irradiated up to 710n/cm (E 1 MeV)at JMTR. In ferrite phases of cladding material, a 12% of Cr concentration fluctuation, which was arisen through a spinodal decomposition, observed before the irradiation was progressed to 20% after the irradiation while the wave length of the fluctuation was almost not changed about 8-10 nm before and after the irradiation. In addition, Ni, Si and Mn concentration fluctuations were also observed. Correlation between Cr concentration fluctuation and hardness, other elements concentration fluctuation and differences from the thermal aging will be reported in presentation.