Crevice corrosion behavior of type 316L stainless steel in -ray irradiated high-temperature water

Nakahara, Yukio ; Kato, Chiaki   ; Yamamoto, Masahiro ; Tsukada, Takashi ; Watanabe, Atsushi*; Fuse, Motomasa*

Irradiation effects on the corrosion of stainless steel (SS) in high-temperature water have been studied. The corrosion in diffusion-restricted environment was examined with simulated crevice-shape samples. Test specimens were made of Type 316L SS. The specimens have been immersed in deaerated high purity water of 288 C with -ray irradiation for 500 hours. The source of the rays was Co. The maximum absorbed dose rate in the water was estimated to be about 30 kGy h. Characteristics of the surface oxide formed on the tested secimens have been analyzed using SEM, laser Raman Spectrometer (LRS), and TEM/EDX. On the surface of the irradiated specimens immersed as the crevice-shape samples, precipitated particles were observed but the surface was not fully covered with the particles. Besides the particles, bigger particles were observed on the surface. The LRS spectra indicated that the smaller particles were Fe-Ni spinels and the bigger particles were -FeO. In-depth profiles of the surface taken using TEM/EDX showed that the smaller particles were Fe-Ni spinels and the bigger particles were -FeO. The bigger particles of -FeO were only observed in -ray irradiated crevice portion. It indicated that oxidants created by the irradiation changed the potential to nobler direction in the crevice-like environment.