"Bubble evolution in Kr-irradiated UO2 during annealing"
Lingfeng He, Xianming Bai, Janne Pakarinen, Brian Jaques, Jian Gan, Andrew Nelson, Anter EL-AZAB, Todd Allen,
Journal of Nuclear Materials
Transmission electron microscopy observation of Kr bubble evolution in polycrystalline UO2 annealed at high temperature was conducted in order to understand the inert gas behavior in oxide nuclear fuel. The average diameter of intragranular bubbles increased gradually from 0.8 nm in as-irradiated sample at room temperature to 2.6 nm at 1600 °C and the bubble size distribution changed from a uniform distribution to a bimodal distribution above 1300 °C. The size of intergranular bubbles increased more rapidly than intragranular ones and bubble denuded zones near grain boundaries formed in all the annealed samples. It was found that high-angle grain boundaries held bigger bubbles than low-angle grain boundaries. Complementary atomistic modeling was conducted to interpret the effects of grain boundary character on the Kr segregation. The area density of strong segregation sites in the high-angle grain boundaries is much higher than that in the low angle grain boundaries.
"In-Situ TEM Observation of Dislocation Evolution in Kr-Irradiated UO2 Single Crystal"
Todd Allen, Jian Gan, Mahima Gupta, Janne Pakarinen, Clarissa Yablinsky, Marquis Kirk, Xianming Bai,
Journal of Nuclear Materials
In situ transmission electron microscopy (TEM) observation of UO2 single crystal irradiated with Kr ions at high temperatures was conducted to understand the dislocation evolution due to high-energy radiation. The dislocation evolution in UO2 single crystal is shown to occur as nucleation and growth of dislocation loops at low-irradiation doses, followed by transformation to extended dislocation segments and networks at high doses, as well as shrinkage and annihilation of some loops and dislocations due to high temperature annealing. Generally the trends of dislocation evolution in UO2 were similar under Kr irradiation at different ion energies and temperatures (150 keV at 600 °C and 1 MeV at 800 °C) used in this work. Interstitial-type dislocation loops with Burgers vector along 〈1 1 0〉 were observed in the Kr-irradiated UO2. The irradiated specimens were denuded of dislocation loops near the surface.
"In-situ TEM study of microstructural evolution in NFA and Cr3C2@SiC-NFA composite during ion irradiation"
Kathy Lu, Xianming Bai, Wei-Ying Chen, Meimei Li, Kaustubh Bawane,
In this work, the ion irradiation responses of a Fe-based nanostructured ferritic alloy or ‘NFA’ (Fe–9Cr–2W–0.2V–0.4Ti–0.3Y2O3) and a Cr3C2@SiC-NFA composite were assessed. In-situ ion irradiation with TEM observation was carried out by using 1 MeV Kr++ ions at doses of 0, 1, 3, 5, 10 dpa and temperatures of 300 °C and 450 °C. Both the NFA and Cr3C2@SiC-NFA samples showed significant dislocation density after 10 dpa at 300 °C. However, the Cr3C2@SiC-NFA composite showed a significantly lower dislocation loop density and a smaller average loop size during the irradiation at 450 °C as opposed to the NFA. At 300 °C, 1/2<111> type dislocation loops were observed in both the NFA and Cr3C2@SiC-NFA samples. Interestingly, at 450 °C, <100> type loops were dominant in the NFA sample while 1/2<111> type loops were still dominant in the Cr3C2@SiC-NFA sample. The results were discussed based on the large surface sink effects and enhanced interstitial-vacancy recombination at higher temperatures. The additional Si element in the Cr3C2@SiC-NFA sample might have played a significant role in determining the dominant loop types.
|"Measurement of grain boundary strength of Inconel X-750 superalloy using in-situ micro-tensile testing techniques in FIB/SEM system" Yachun Wang, Xiang Liu, Daniel Murray, Fei Teng, Wen Jiang, Mukesh Bachhav, Laura Hawkins, Emmanuel Perez, Cheng Sun, Xianming Bai, Jie Lian, Colin Judge, John Jackson, Robert Carter, Lingfeng He, Materials Science & Engineering Vol. 849 2022|
"Microstructure evolution in Xe-irradiated UO2 at room temperature"
Todd Allen, Anter EL-AZAB, Jian Gan, Lingfeng He, Janne Pakarinen, Marquis Kirk, Andrew Nelson, Xianming Bai,
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
In situ Transmission Electron Microscopy was conducted for single crystal UO2 to understand the microstructure evolution during 300 keV Xe irradiation at room temperature. The dislocation microstructure evolution was shown to occur as nucleation and growth of dislocation loops at low irradiation doses, followed by transformation to extended dislocation segments and tangles at higher doses. Xe bubbles with dimensions of 1-2 nm were observed after room-temperature irradiation. Electron Energy Loss Spectroscopy indicated that UO2 remained stoichiometric under room temperature Xe irradiation.
|"Advanced Characterization of Irradiated UO2 Fuel" Lingfeng He, Michael Moorehead, Brandon Miller, Jason Harp, Xianming Bai, TMS 2018 March 11-15, (2018)|
|RTE 2nd Call Awards Announced - Projects total approximately $1.6 million These project awards went to principal investigators from 26 U.S. universities, eight national laboratories, two British universities, and one Canadian laboratory. Tuesday, May 14, 2019 - Calls and Awards|