Molten uranium dioxide structure and dynamics

• Published in: Science (American Association for the Advancement of Science) Vol. 346; no. 6212; pp. 984 - 987
• Main Authors: Skinner, L. B., Benmore, C. J., Weber, J. K. R., Williamson, M. A., Tamalonis, A., Hebden, A., Wiencek, T., Alderman, O. L. G., Guthrie, M., Leibowitz, L., Parise, J. B.
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 21.11.2014; The American Association for the Advancement of Science; AAAS
• Subjects: Containers; Coordination numbers; Distribution functions; Ebola virus; Epidemiology; High temperature; Laser beams; Liquids; MATERIALS SCIENCE; Melting; Nuclear fuels; Polyhedrons; Radioactivity; Ronchi; Solids; Synchrotrons; Uranium; Uranium dioxide; X ray diffraction; X-rays
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1259709

Uranium dioxide (UO2) is the major nuclear fuel component of fission power reactors. A key concern during severe accidents is the melting and leakage of radioactive UO2 as it corrodes through its zirconium cladding and steel containment. Yet, the very high temperatures (>3140 kelvin) and chemical reactivity of molten UO2 have prevented structural studies. In this work, we combine laser heating, sample levitation, and synchrotron x-rays to obtain pair distribution function measurements of hot solid and molten UO2. The hot solid shows a substantial increase in oxygen disorder around the lambda transition (2670 K) but negligible U-O coordination change. On melting, the average U-O coordination drops from 8 to 6.7 ± 0.5. Molecular dynamics models refined to this structure predict higher U-U mobility than 8-coordinated melts.