Neutron and hard X-ray diffraction studies of the isothermal transformation kinetics in the research reactor fuel candidate U-8 wt%Mo

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• 作者：Steffen S&auml ; ubert ; Rainer Jungwirth ; Tobias Zweifel ; Michael Hofmann ; Markus Hoelzel and Winfried Petry
• 关键词：uranium ; nuclear fuels ; uranium&ndash ; molybdenum alloys ; isothermal transformation kinetics ; X-ray diffraction ; neutron diffraction
• 刊名：Journal of Applied Crystallography
• 出版年：2016
• 出版时间：June 2016
• 年：2016
• 卷：49
• 期：3
• 页码：923-933
• 全文大小：1724K
• ISSN：1600-5767

文摘

Exposing uranium–molybdenum alloys (UMo) retained in the γ phase to elevated temperatures leads to transformation reactions during which the γ-UMo phase decomposes into the thermal equilibrium phases, i.e. Ub>2b>Mo and α-U. Since α-U is not suitable for a nuclear fuel exposed to high burn-up, it is necessary to retain the γ-UMo phase during the production process of the fuel elements for modern high-performance research reactors. The present work deals with the isothermal transformation kinetics in U–8 wt%Mo alloys for temperatures between 673 and 798 K and annealing durations of up to 48 h. Annealed samples were examined at room temperature using either X-ray or neutron diffraction to determine the phase composition after thermal treatment, and in situ annealing studies disclosed the onset of phase decomposition. While for temperatures of 698 and 673 K the start of decomposition is delayed, for higher temperatures the first signs of transformation are already observable within 3 h of annealing. The typical C-shaped curves in a time–temperature–transformation (TTT) diagram for both the start and the end of phase decomposition could be determined in the observed temperature regime. Therefore, a revised TTT diagram for U–8 wt%Mo between 673 and 798 K and annealing durations of up to 48 h is proposed.