Microstructural analysis of neutron-irradiated stainless steel weld-overlay claddings of nuclear reactor pressurevessel

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

Microstructure evolutions on two types, namely electroslag (ESW) and submerged-arc (SAW) welding, of stainless overlay claddings of reactor pressure vessel were quantitatively investigated by means of three-dimensional local electrode atom probe (3DAP) in nano-scale. The cladding materials were neutron-irradiated up to about 710n/cm (E 1 MeV) at JMTR. In ferrite phases of cladding materials, 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 between the neutron irradiation and the thermal aging, the ESW and SAW will be reported in presentation.