Elevated Temperature Nanoindentation Creep Study of Plastically Deformed and Spark Plasma Sintered UO2

JOURNAL OF NUCLEAR MATERIALS

卷:545

Article

Frazer, David^1,2  Shaffer, Benjamin³  Gong, Bowen⁴  Peralta, Pedro³  Lian, Jie⁴  Hosemann, Peter^1,5 

[1] Univ Calif Berkeley, Dept Nucl Engn, 4153 Etcheverry Hall, Berkeley, CA 94720 USA

[2] Idaho Natl Lab, Mat & Fuels Complex, 2525 Fremont Ave, Idaho Falls, ID 83415 USA

[3] Arizona State Univ, Sch Engn Matter Transport & Energy, Tempe, AZ 85287 USA

[4] Rensselaer Polytech Inst, Dept Mech Aerosp Nucl Engn, Troy, NY 12180 USA

[5] Lawrence Berkeley Natl Lab, Div Mat Sci, Berkeley, CA USA

关键词: Nanoindentation creep;    High temperature nanoindentation;    Uranium dioxide;   

DOI  :  10.1016/j.jnucmat.2020.152605

来源: Elsevier

【 摘 要 】

Current challenges with uranium dioxide fuel degradation include fuel swelling, cracking and fission gas release, all of which reduce the operational life span of the fuel in commercial reactors. One important factor in prolonging the life span of uranium dioxide (UO2) fuel is developing a good understanding of the mechanical properties of the high burnup structure that forms at the periphery of the fuel pellet during the fuel cycle. Nanoindentation based testing techniques can probe the mechanical properties of small volumes of material and measure properties including hardness, elastic modulus, and creep. In this work, elevated temperature nanoindentation and nanoindentation creep testing is performed on UO2 samples with different microstructures, including nanocrystalline (NC) grains, as well as microcrystalline samples with different grain sizes and creep prestrains introduced at high temperatures. Tests allowed measuring hardness, elastic modulus and creep stress exponents up to 500 degrees C. The test results indicate that for temperatures and stresses used here, NC UO2 had limited to no creep, with stress exponents greater than 10. For UO2 samples with creep prestrain and spark plasma sintered (SPS) UO2 with a 1.8 Am grain size the dominant creep mechanism at the high stresses and relatively low temperatures used is dislocation glide: the creep stress exponents of 3-4 at 500 degrees C also matched well with recent literature values for macro scale compression creep tests. In addition, it was observed that the UO2 samples containing higher dislocation defect densities had lower creep stress exponents than conventional sintered UO2. The stress exponent measured on the conventional sintered UO2 at 500 degrees C was 7, which suggests that the deformation of UO2 at lower temperatures might be hindered by the energetic barriers to dislocation nucleation. (C) 2020 Elsevier B.V. All rights reserved.

【 授权许可】

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