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

本文的研究旨在从根本上阐明锆合金的腐蚀机理，并为设计和开发新型包层材料提供信息，这些材料在先进反应堆中实现核燃料的高燃耗量是非常需要的。用Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Sn等多种Zr-M二元合金进行了一系列腐蚀实验。在673 K和10.3 MPa的蒸汽条件下进行了自蒸釜腐蚀试验，腐蚀时间为259.2ks。利用x射线光电子能谱（XPS）对样品表面形成的氧化锆膜的化学成分和电子结构进行了详细的研究。结果表明，高耐蚀合金与低耐蚀合金的XPS谱有明显差异。此外，合金元素的耐蚀性与合金元素的耐蚀性密切相关，并随元素在元素周期表中位置的变化而周期性变化。此外，合金元素在氧化锆膜中的分布并不均匀，而是存在浓度梯度。除了这些实验外，还进行了dv - x - α分子轨道的计算。模拟了氧化锆原子间化学键的性质。在计算和实验的基础上，提出了锆合金腐蚀机理的新模型。这将为高耐蚀锆合金的设计提供良好的指导

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