Nanostructure of metallic particles in light water reactor used nuclear fuel

• Published in: Journal of nuclear materials Vol. 461; pp. 236 - 243
• Main Authors: Buck, Edgar C., Mausolf, Edward J., McNamara, Bruce K., Soderquist, Chuck Z., Schwantes, Jon M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier B.V 01-06-2015; Elsevier
• Subjects: Crystallites; Light water reactors; Metal particles; Molybdenum; Nanostructure; Neutron irradiation; NUCLEAR FUEL CYCLE AND FUEL MATERIALS; Nuclear fuels; Uranium
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2015.03.001

[Display omitted]
•An extraordinary nano-structure has been observed in the noble metal particles that form in UO2 reactor fuels.•The composition of the particles was highly variable with low levels of uranium and plutonium present in the particles.•This nano-structure may play an important role in the behavior of nuclear fuels under accident conditions.
An extraordinary nano-structure has been observed in the metallic (Mo–Tc–Ru–Rh–Pd) particles that are known to form during irradiated in light water nuclear reactor fuels. This structure points possible high catalytic reactivity through the occurrence of a very high surface area as well as defect sites. We have analyzed separated metallic particles from dissolved high burn-up spent nuclear fuel using scanning and transmission electron microscopy. The larger particles vary in diameter between ∼10 and ∼300nm and possess a hexagonally close packed epsilon-ruthenium structure. These particles are not always single crystals but often consist of much smaller crystallites on the order of 1–3nm in diameter with evidence suggesting the occurrence of some amorphous regions. It is possible that neutron irradiation and fission product recoils generated the unusual small crystallite size. The composition of the metallic particles was variable with low levels of uranium present in some of the particles. We hypothesize that the uranium may have induced the formation of the amorphous (or frustrated) metal structure. This unique nano-structure may play an important role in the environmental behavior of nuclear fuels.