Effect of Grain Boundaries on Krypton Segregation Behavior in Irradiated Uranium Dioxide
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Fission products, such as krypton (Kr), are known to be insoluble within UO2, segregating toward grain boundaries and eventually leading to a lowering in thermal conductivity and fuel swelling. Recent computational studies have identified that differences in grain boundary structure have a significant effect on the segregation behavior of fission products. However, experimental work supporting these simulations is lacking. Atom probe tomography was used to measure the Kr distribution across grain boundaries in UO2. Polycrystalline depleted UO2 samples were irradiated with 0.7 MeV and 1.8 MeV Kr-ions and annealed to 1000°C, 1300°C, and 1600°C for 1 h to produce a Kr-bubble dominated microstructure. The results of this work indicate a strong dependence of Kr concentration as a function of grain boundary structure. Temperature also influences grain boundary chemistry with greater Kr concentration evident at higher temperatures, resulting in a reduced Kr concentration in the bulk. Although Kr segregation takes place at elevated temperatures, no change in grain size or texture was observed in the irradiated UO2 samples.
KeywordsScanning Transmission Electron Microscope Atom Probe Tomography Segregation Behavior Nonirradiated Sample Postirradiation Annealing
This work is supported as part of the Center for Materials Science of Nuclear Fuel, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number FWP 1356. Use of the FIB and atom probe instrumentation at the Center for Advanced Energy Studies was supported by the U.S. Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07-051D14517. The authors would also like to thank Dr. Andrew Nelson for providing the UO2 samples used in this study and Dr. Yaqaio Wu for assistance in running the atom probe. The Kr irradiation was carried out in the Frederick Seitz Materials Research Laboratory Central Facilities at the University of Illinois-Urbana Champaign, and the authors would like to thank Doug Jeffers for his assistance in performing the irradiation.
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