Annealing-induced lattice recovery in room-temperature xenon irradiated CeO 2 : X-ray diffraction and electron energy lo
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Lingfeng He Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
Abdel-Rahman Hassan Department of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907, USA
Yongqiang Wang Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
Mahima Gupta Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
Anter El-Azab Department of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907, USA
Todd R. Allen Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA (Received 10 October 2014; accepted 7 January 2015)
A systematic x-ray diffraction (XRD) study was performed on room-temperature Xe-irradiated and postirradiation annealed CeO2. Large scale XRD did not show any additional irradiation-induced phases upon irradiation. Depth profiling the CeO2 (111) diffraction peak over the 150 nm deep Xe-irradiated layer (400 keV, 1 1020 Xe/m2) by grazing incidence XRD indicated a lattice expansion at the irradiated layer. Postirradiation annealing (1 h at 1000 °C) in an oxygen-containing environment removed the observed XRD features. Electron energy loss spectroscopy (EELS) was performed for cross-sectional samples before and after postirradiation annealing. EELS showed that the Ce charge state changed from 14 to 13 at the CeO2 surface indicating the presence of O vacancies in both as-irradiated and annealed samples. EELS also indicated that the amount of O vacancies was reduced at the irradiated region by annealing. The experimental results are discussed based on electronic properties of CeO2, annihilation of oxygen vacancies, and evolution of irradiation damage. I. INTRODUCTION
The structure of UO2 fuel is strongly modified by the production of fission products, irradiation damage, and the high operating temperature and associated decrease in thermal conductivity.1 The low thermal conductivity, in particular, is an important feature of UO2 that has motivated numerous theoretical and experimental studies over the past few decades. Theoretical considerations imply that the main reason for the low thermal conductivity of UO2 crystals, which have a fluorite structure, is the high anharmonicity of certain phonon modes.2
Contributing Editor: Khalid Hattar a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.13 J. Mater. Res., 2015
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In addition to the initially low thermal conductivity of nonirradiated nuclear fuel, irradiation damage resulting in point defects (vacancies, interstitials) and extended defects (dislocations, voids) has a detrimental effect on the UO2 thermal performance.3 Accompanied with the irradiation damage, soluble and nonsoluble fission products populate the matrix forming precipitates and gas bubbles.4 CeO2 has been widely used as a surrogate of UO2 in regard to examining irradiation damage and microstructur
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