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

David Frazer, Benjamin Shaffer, Bowen Gong, Pedro Peralta, Jie Lian, Peter Hosemann

Research output: Contribution to journalArticlepeer-review

Abstract

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°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 μm 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°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°C was ~ 7, which suggests that the deformation of UO2 at lower temperatures might be hindered by the energetic barriers to dislocation nucleation.

Original languageEnglish (US)
Article number152605
JournalJournal of Nuclear Materials
Volume545
DOIs
StatePublished - Mar 2021

Keywords

  • High temperature nanoindentation
  • Nanoindentation creep
  • Uranium dioxide

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Materials Science(all)
  • Nuclear Energy and Engineering

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