Molecular Orbital Approach to the Design of Corrosion Resistant Zirconiuim Alloys for Nuclear Applications

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 07555500
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 試験
• Research Field: Structural/Functional materials
• Research Institution: Nagoya University
• Principal Investigator: MORINAGA Masahiko Nagoya Univ., Dept.of Materials Sci.and Eng., Professor, 工学部, 教授 (50126950)
• Co-Investigator(Kenkyū-buntansha): HIGASHINAKAGAWA Emiko Toshiba Co.Ltd., Materials Device Research Lab., Chief Researcher, 研究開発センター・材料デバイス研究所, 主幹研究員 ; EZAKI Hisakazu Suzuka Technical College, Associate Professor, 助教授 (80160357) ; MURATA Yoshinori Nagoya Univ., Dept.of Materials Sci.and Eng., Associate Professor, 工学部, 助教授 (10144213)
• Project Period (FY): 1995 – 1996
• Keywords: Corrosion / Zirconiium alloys / Electronic structure / Molecular orbital method / Alloy design

Research Abstract

The present study aims to elucidate corrosion mechanism of zirconium alloys in a fundamental manner, and also to get information for the design and development of new cladding materials which is in great demand for realizing higher burn-ups of nuclear fuels in the advanced reactors.
A series of corrosion experiments were carried out with a variety of binary Zr-M alloys where M's are Ti, V,Cr, Mn, Fe, Co Ni, Cu and Sn. The auto-clave corrosion tests were performed under the steam conditions of 673 K and 10.3 MPa, and the corrosion time used was 259.2ks. The chemical composition and the electronic structure of the zirconia film formed on the specimen surface were investigated in details using the X-ray photoelectron spectroscopy (XPS). It was found that there was a clear difference in the XPS spectra between highly corrosion-resistant alloys and poorly corrosion-resistant alloys. Also, the observed corrosion resistance depended strongly on the alloying elements, and it changed periodically following the position of elements in the peridic table. Furthermore, it was shown that the alloying elements were not uniformly distributed in the zirconia film, but instead there was a concentrational gradient in it.
In addition to these experiments, the DV-Xalpha molecular orbital calculations were performed. Simulated was the nature of the chemical bond between atoms in the zirconia. On the basis of these calculations as well as the experiments, a new model for the corrosion mechanism was proposed for zirconiium alloys. This will provide us a good indication for the design of highly corrosion-resistant zirconium alloys