EXAFS studies for atomic structural change induced by ion irradiation of a reactor pressure vessel steel

Iwata, Keiko ; Takamizawa, Hisashi ; Ha, Yoosung  ; Shimodaira, Masaki ; Okamoto, Yoshihiro  ; Honda, Mitsunori   ; Katsuyama, Jinya  ; Nishiyama, Yutaka 

The main causes of the irradiation embrittlement of RPVs are the formation of a solute cluster and the matrix defect. To investigate these embrittlement mechanisms, it is necessary to complementarily apply microstructure analyses. The extended X-ray absorption fine structure (EXAFS) technique can detect changes in the atomic structure because of a vacancy-type defect or interstitial atoms introduced by irradiation around selected atoms. In this study, to investigate such microstructural changes due to irradiation, we performed an EXAFS examination for high-copper RPV steels subjected to ion irradiation. We investigated microstructures of the crystal structure around specific element such as Cu, Mn, and Ni, which are known to be the atoms included in the solute atom clusters and lattice defects such as vacancy-type defects. The results indicated that the solute atoms clusteris thought to aggregate in the Fe matrix while maintaining the bcc structure and that not only a vacancy-type defect but also a tensile configuration-type dumbbell pair could be located around both Cu and Ni atoms.