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Journal Articles

Effect of water radiolysis on surface oxide film formed on SUS316L in $$gamma$$-ray irradiated high temperature water

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

Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2013) (CD-ROM), 5 Pages, 2013/09

Major corrosion problems of light water reactor (LWR) which are represented by stress corrosion cracking are affected by dissolved oxygen (DO) concentration in feed water. Many corrosion tests were conducted with the parameter of DO values. Oxygen source of an actual LWR is radiolysis of cooling water and also H$$_{2}$$O$$_{2}$$ is generated. The effect of these species created by water radiolysis to corrosion of structural material was not sufficiently examined. $$gamma$$-ray irradiated experiments were conducted in high temperature water condition using type 316L stainless steels with crevice. The calculation of radiolysis products was not estimated by the effect of radiolysis products. From these results, much complicated reaction seemed to occur at the $$gamma$$-ray irradiated crevice portion.

Journal Articles

Effects of $$gamma$$-ray irradiation and crevice-like shape on the corrosion of type 316L stainless steel in high-temperature water

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

Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2009 (CD-ROM), p.226 - 231, 2009/10

The irradiation effect to high-temperature water in nuclear power plant has been regarded as one of important issues for preventing corrosion and stress corrosion cracking of plant materials. However, the effects of surface reaction and configurations of material on irradiated high-temperature water chemistry have been studied little because of the difficulty of measuring the environment. In this work, we have done a series of corrosion tests of Type 316L stainless steel in high-temperature water in order to estimate the effects of $$gamma$$-ray irradiation and crevice-like shape on the water chemistry. Test specimens immersed in high-temperature water of 288 $$^{circ}$$C were $$gamma$$-ray irradiated for 500 hours. The absorbed dose rate of $$gamma$$-ray irradiation was estimated to be 30 kGy h$$^{-1}$$. The dimensions of the disk-like specimens were 16 mm in diameter by 0.5 mm in thickness. The surfaces of the specimens were mechanically finished with #800 emery paper. Sets of two specimens attached closely in order to simulate a crevice-like environment were also immersed. The surfaces of the specimens were analyzed using SEM, TEM, and laser Raman spectrometer. The results of surface analyses indicated that $$gamma$$-ray irradiation enhanced the precipitation of iron oxide on the surface and the thickness of inner oxide layer became thicker by $$gamma$$-ray irradiation. $$gamma$$-ray irradiation also changed the morphology of oxide on the surface faced to the crevice-like environment.

Oral presentation

$$gamma$$-ray irradiation effects on the corrosion of type 316L stainless steel in a gap filled with high-tempertaure water

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

no journal, , 

no abstracts in English

Oral presentation

Effect of $$gamma$$-ray irradiation on corrosion of crevice portion of stainless steel in high temperature water

Yamamoto, Masahiro; Nakahara, Yukio; Kato, Chiaki; Tsukada, Takashi; Wada, Yoichi*; Fuse, Motomasa*

no journal, , 

Oxidants, such as hydrogen peroxide, are created by radiolysis of water in the light water reactor. It is easily estimated that the reactions are accelerated rather on the metal surface than the bulk water. Furthermore, a crevice portion concentrates more oxidants because of retardation of diffusion of them. Stainless steel samples having crevices were examined to clarify the effects of $$gamma$$ ray irradiation on corrosion at crevice portion. Difference of corrosion features were determined by some surface analytical techniques. And the effect of diffusion process of oxidants in the crevice was evaluated by calculation using FEM method.

Oral presentation

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

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

no journal, , 

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 $$^{circ}$$C with $$gamma$$-ray irradiation for 500 hours. The source of the $$gamma$$ rays was $$^{60}$$Co. The maximum absorbed dose rate in the water was estimated to be about 30 kGy h$$^{-1}$$. 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 $$alpha$$-Fe$$_{2}$$O$$_{3}$$. In-depth profiles of the surface taken using TEM/EDX showed that the smaller particles were Fe-Ni spinels and the bigger particles were $$alpha$$-Fe$$_{2}$$O$$_{3}$$. The bigger particles of $$alpha$$-Fe$$_{2}$$O$$_{3}$$ were only observed in $$gamma$$-ray irradiated crevice portion. It indicated that oxidants created by the irradiation changed the potential to nobler direction in the crevice-like environment.

Oral presentation

Research for the improvement of SCC evaluation method including the effect of radiation on water, 3; Influence of materials and dissolved oxygen related to oxide film structures on stainless steel under $$gamma$$-ray irradiation in high temperature water

Yamamoto, Masahiro; Nakahara, Yukio; Kato, Chiaki; Tsukada, Takashi; Suzuki, Kazuhiro; Hatakeyama, Yuichi; Watanabe, Atsushi*; Fuse, Motomasa*

no journal, , 

It is well known that the decomposition of water by irradiation results in the formation of oxidants, such as hydrogen peroxide (H$$_{2}$$O$$_{2}$$) and radical species. The oxidant such as H$$_{2}$$O$$_{2}$$ promote nobler electrochemical corrosion potential (ECP) of stainless steels (SSs) and change oxide instructors as corrosion products on stainless steels surface. In this work, the effects of $$gamma$$-ray irradiation and structure on the corrosion of Type 316L SS and 304L SS in high-temperature water of 288C were examined. We also consider structures of the oxide film on the stainless steel using transmission electron microscope (TEM) and Raman spectroscope in order to show the differences made by the irradiation and structure. In addition, the effect of diffusion restriction and surface reactions may become more significant Inside crevices, so that the environments are expected to be different from those in the outsides.

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