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Three-Dimensional Characterization of Sintered UO2+x: Effects of Oxygen Content on Microstructure and Its Evolution

Karin Rudman, Patricia Dickerson, Darrin Byler, Robert McDonald, Harn Lim, Pedro Peralta, Chris Stanek, Kenneth McClellan

Nuclear Technology / Volume 182 / Number 2 / May 2013 / Pages 145-154

Technical Paper / Special Issue on the Symposium on Radiation Effects in Ceramic Oxide and Novel LWR Fuels / Fuel Cycle and Management /

The oxygen content during the intermediate and final stages of sintering can have a strong effect on the microstructural evolution of oxide fuels. Two depleted urania (d-UO2.0 and d-UO2.14) samples, sintered up to a theoretical density of 90%, were serial sectioned using a focused ion beam and characterized with electron backscatter diffraction (EBSD). The EBSD data were used to make three-dimensional reconstructions of the microstructures to evaluate their characteristics at an intermediate stage of sintering. The oxygen content was found to affect grain shape and grain boundary (GB) mobility, as curved and elongated grains were observed in UO2.0, as well as stronger pore-GB interactions, which is an indication that microstructure was less evolved in UO2.0. Both samples presented a similar fraction ([approximate]20%) of special, coincident site lattice boundaries, with larger amounts of Σ3n GBs, and a rather large fraction of Σ11 GBs for UO2.14. Crystallographic GB planes were also determined to study the distributions of all GB parameters. The UO2.0 sample had a large fraction of GB planes close to the Σ3 twinning planes, which suggests that lower-energy interfaces are used to minimize energy in this sample, potentially due to lower overall GB mobility as compared to UO2.14.

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