TY - JOUR
T1 - Reassessment of oxidation-induced amorphization and dissolution of Nb precipitates in Zr−Nb nuclear fuel cladding tubes
AU - Matsukawa, Y.
AU - Kitayama, S.
AU - Murakami, K.
AU - Shinohara, Y.
AU - Yoshida, K.
AU - Maeno, H.
AU - Yang, H. L.
AU - Toyama, T.
AU - Yasuda, K.
AU - Watanabe, H.
AU - Kimura, A.
AU - Muta, H.
AU - Yamanaka, S.
AU - Li, Y. F.
AU - Satoh, Y.
AU - Kano, S.
AU - Abe, H.
N1 - Funding Information:
All the fuel cladding tube samples were supplied by Mitsubishi Nuclear Fuel Co. Ltd. This research was partly sponsored by the Ministry of Education, Culture, Sports, Science & Technology (MEXT) of JAPAN, under the Strategic Promotion Program for Basic Nuclear Research entitled “Study on hydrogenation and radiation effects in advanced nuclear fuel cladding materials”; and a program entitled “R&D of nuclear fuel cladding materials and their environmental degradations for the development of safety standards” entrusted to Tohoku University by the MEXT. This research was carried out partly under the Cooperative Research Program of “the Oarai Center” and “the Cooperative Research & Development Center for Advanced Materials” of the Institute for Materials Research, Tohoku University. This research was also supported in part by the Collaborative Research Program of the Research Institute for Applied Mechanics in Kyushu University; by “Advanced Characterization Nanotechnology Platform, Nanotechnology Platform Program of the MEXT, Japan” at the Research Center for Ultra-High Voltage Electron Microscopy in Osaka University, at the Laboratory of High-Voltage Electron Microscopy in Hokkaido University, at the Ultramicroscopy Research Center in Kyushu University, and at the Center for Nano Technology Support in Tohoku University; and by the Joint Usage/Research Program on Zero-Emission Energy Research, Institute of Advanced Energy, Kyoto University (ZE27C-07 and ZE28C-09). Y.M. was supported by the MEXT Grant-in-Aid for Young Scientists (A) (22686058), by Japan Society for the Promotion of Science (JSPS) KAKENHI (#16K06767), and by The Iron & Steel Institute of JAPAN (ISIJ) the 23rd Research Promotion Grant. Y.M. thanks to Prof. Yoshitsugu Tomokiyo, Dr. Sousuke Kondo, Dr. Kiyohiro Yabuuchi and Dr. Norihiro Sakaguchi for their insightful comments; and Prof. Yasuyoshi Nagai, Mr. Naoki Ebisawa, Ms. Keiko Tomura and Mr. Takaaki Toriyama for their instrumental supports.
Publisher Copyright:
© 2017 Acta Materialia Inc.
PY - 2017/4/1
Y1 - 2017/4/1
N2 - The surface oxide film of a Zr−2.5Nb alloy subjected to long term corrosion at 633 K in simulated primary coolant of pressurized water reactors has been analyzed. The primary concerns were whether Nb precipitates exhibit amorphization upon oxidation, and whether they dissolve into the matrix, as suggested by previous studies. Their behavior is of particular interest, from the viewpoint of engineering, as the mechanism of improving corrosion resistance of Zr fuel cladding by Nb addition, and from the viewpoint of basic materials science, as the critical condition of solid-state amorphization. If amorphization and dissolution proceed simultaneously, it would follow that amorphization occurs at conditions where both O and Nb atoms are mobile; under such conditions diffusion-induced amorphization has never been observed. It was found that the Nb precipitates exhibited amorphization without dissolution. Some of the inconsistencies among the previous studies were found to be artifacts of materials characterization methods. The final configuration of precipitates was amorphous Nb2O5, which is distinct from the other Nb oxides in terms of its dielectric nature with a wide band gap. The matrix initially contained a large amount of Nb greater than the solubility. Although the excess Nb atoms did not precipitate by thermal aging alone, oxidation was found to enhance their precipitation at this temperature. It appears that amorphization can occur even when the motion of atoms is not frozen-in.
AB - The surface oxide film of a Zr−2.5Nb alloy subjected to long term corrosion at 633 K in simulated primary coolant of pressurized water reactors has been analyzed. The primary concerns were whether Nb precipitates exhibit amorphization upon oxidation, and whether they dissolve into the matrix, as suggested by previous studies. Their behavior is of particular interest, from the viewpoint of engineering, as the mechanism of improving corrosion resistance of Zr fuel cladding by Nb addition, and from the viewpoint of basic materials science, as the critical condition of solid-state amorphization. If amorphization and dissolution proceed simultaneously, it would follow that amorphization occurs at conditions where both O and Nb atoms are mobile; under such conditions diffusion-induced amorphization has never been observed. It was found that the Nb precipitates exhibited amorphization without dissolution. Some of the inconsistencies among the previous studies were found to be artifacts of materials characterization methods. The final configuration of precipitates was amorphous Nb2O5, which is distinct from the other Nb oxides in terms of its dielectric nature with a wide band gap. The matrix initially contained a large amount of Nb greater than the solubility. Although the excess Nb atoms did not precipitate by thermal aging alone, oxidation was found to enhance their precipitation at this temperature. It appears that amorphization can occur even when the motion of atoms is not frozen-in.
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U2 - 10.1016/j.actamat.2017.01.032
DO - 10.1016/j.actamat.2017.01.032
M3 - Article
AN - SCOPUS:85010192534
SN - 1359-6454
VL - 127
SP - 153
EP - 164
JO - Acta Materialia
JF - Acta Materialia
ER -