• Table 1. Summary of the Produced Thin Film UO 2 Samples.
  • Sample Irradiations.
  • Supplementary Material This manuscript is provided as a supplementary material for the review process only




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    Figure 1. A triangular inverse pole figure for sample AP3 obtained from the EBSD study.

    Film thickness for samples AP1 to AP4 was measured using transverse SEM on a cross section of the sample. Focused ion beam (FIB)-SEM was used to measure film thickness for samples OB6 and OB7 after they have been irradiated. Secondary ion mass spectrometry (SIMS) was performed on sample OB6 (after it has been irradiated) to verify the thickness measured with the FIB-SEM method and on sample AP6 to deduce its thickness, as it was not possible to resolve the UO2 film in the FIB-SEM study, possibly, due to a low electrical conductivity of the film. Film thickness for samples AP5, OB5 and AP7 was estimated based on the growth rate calculated from the measured film thicknesses for samples AP6, OB6 and OB7 and the corresponding deposition times.


    Table 1. Summary of the Produced Thin Film UO2 Samples.

    Sample

    LSAT (AP1-AP4) and YSZ (AP5-AP7, OB5-OB7) substrate crystallographic orientation (hkl)

    UO2 film orientation (hkl)

    UO2 film thickness (nm)

    AP1

    (111)

    (210)a

    110

    AP2

    (001)

    (001)

    140

    AP3

    (001)

    (001)

    120

    AP4

    (110)

    (111)a

    140

    AP5

    (001)

    (001)

    90

    OB5

    (001)

    (001)

    150

    AP6

    (110)

    (110)

    150

    OB6

    (110)

    (110)

    150

    AP7

    (111)

    (111)

    150

    OB7

    (111)

    (111)

    150

    aPreferred crystallographic orientation of the as-produced samples
    Sample Irradiations. Sample irradiations were performed on the IRRSUD beamline at the GANIL accelerator, Caen, France. UO2 films on the LSAT substrates (OB1-4) were irradiated with 129Xe23+ ions of 92 MeV energy to a fluence of 4.8 × 1015 ions/cm2 to simulate the damage produced by fission fragments in nuclear fuel. The energy and mass of the ions used for the irradiation is representative of the typical fission fragments.4,5 The flux was kept at around 1.3 × 1010 ions/(cm2 s) which caused heating of the samples to a temperature not exceeding 150 °C. The samples were allowed to cool down to ambient temperature (around 19 °C) before the beamline was brought to atmospheric pressure using nitrogen gas to minimize surface oxidation of the samples. UO2 films on the YSZ substrates were irradiated with 238U31+ ions of 110 MeV energy to fluences of 5 × 1010 (OB5), 5 × 1011 (OB6) and 5 × 1012 (OB7) ions/cm2 to induce radiation damage. The flux was kept at around 1 × 108 ions/(cm2 s). The irradiation was conducted at an ambient temperature of 16-17 °C. No heating of the samples was observed. The beam line base vacuum was 6 × 10-7 mbar during the irradiations.

    According to the SRIM-2012.03 software,74 the nuclear and electronic stopping, dE/x, for 92 MeV 129Xe23+ ions in UO2 is 0.26 and 24.6 keV/nm, respectively, and the projected range is 6.5 µm and for 110 MeV 238U31+ ions is 0.96 and 27.4 keV/nm, respectively, and the projected range is 6.7 µm. A theoretical UO2 density of 10.96 g/cm3 (ref 5) was assumed in the SRIM calculation. The SRIM results indicate that the 129Xe23+ and 238U31+ ions completely penetrate the UO2 thin films (150 nm max) and the electronic stopping regime dominates the dissipation of ion energy throughout the entire film.





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    Supplementary Material This manuscript is provided as a supplementary material for the review process only

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