Evaluation of mechanical properties of (Ce,Gd)O<sub>2-x</sub> as a surrogate for (U,Gd)O<sub>2-x</sub> solid solutions

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Abstract

The mechanical properties of CeO<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> solid solutions as a surrogate for UO<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> burnable poison fuel were evaluated by both experimental and molecular dynamics (MD) analyses. Surface observation and X-ray diffraction measurement showed that Gd<sub>2</sub>O<sub>3</sub> doping into CeO<sub>2</sub> depressed the grain size of CeO<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> solid solution and caused the expansion of the lattice parameter up to 15 wt% of Gd<sub>2</sub>O<sub>3</sub> content. The mechanical properties were estimated from the sound velocities measured by the ultrasonic pulse-echo method. The sound velocities in CeO<sub>2</sub>- Gd<sub>2</sub>O<sub>3</sub> were found to decrease with increasing Gd<sub>2</sub>O<sub>3</sub> content, which caused the reduction in the elastic moduli and Debye temperature. On the other hand, the results obtained from MD analyses showed the lattice expansion of CeO<sub>2</sub>- Gd<sub>2</sub>O<sub>3</sub>, the decrease of the average nearest distance between Ce (or Gd) and O ions, and the decrease of oxygen coordination number around each cation while the Gd<sub>2</sub>O<sub>3</sub> content was increasing. It was, therefore, found that the bond valence sum considered to be the effective cation charge slightly decreased with increasing Gd<sub>2</sub>O<sub>3</sub> content. Thus, the crystal binding energy decreased and consequently, the elastic moduli decreased. In addition, the lower value of experimental elastic moduli may be partly caused by crystal imperfection, e.g. grain boundaries, pores, and cracks.
Original languageEnglish
Pages (from-to)1927
JournalThe Proceedings of the International Conference on Nuclear Engineering (ICONE)
Volume2019
Issue number0
DOIs
Publication statusPublished - 2019

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