Browsing by Author "Cooper, MWD"

Now showing 1 - 6 of 6
  • No Thumbnail Available
    Item
    Formation of (Cr,Al)UO4 from doped UO2 and its influence on partition of soluble fission products
    (Elsevier, 2013-11-01) Cooper, MWD; Gregg, DJ; Zhang, YJ; Thorogood, GJ; Lumpkin, GR; Grimes, RW; Middleburgh, SC
    CrUO4 and (Cr, Al)UO4 have been fabricated by a sol–gel method, studied using diffraction techniques and modelled using empirical pair potentials. Cr2O3 was predicted to preferentially form CrUO4 over entering solution into hyper-stoichiometric UO2+x by atomic scale simulation. Further, it was predicted that the formation of CrUO4 can proceed by removing excess oxygen from the UO2 lattice. Attempts to synthesise AlUO4 failed, instead forming U3O8 and Al2O3. X-ray diffraction confirmed the structure of CrUO4 and identifies the existence of a (Cr, Al)UO4 phase for the first time (with a maximum Al to Cr mole ratio of 1:3). Simulation was subsequently used to predict the partition energies for the removal of fission products or fuel additives from hyper-stoichiometric UO2+x and their incorporation into the secondary phase. The partition energies are consistent only with smaller cations (e.g. Zr4+, Mo4+ and Fe3+) residing in CrUO4, while all divalent cations are predicted to remain in UO2+x. Additions of Al had little effect on partition behaviour. The reduction of UO2+x due to the formation of CrUO4 has important implications for the solution limits of other fission products as many species are less soluble in UO2 than UO2+x. © 2013, Elsevier B.V.
  • No Thumbnail Available
    Item
    Partition of soluble fission products between the grey phase, ZrO2 and uranium dioxide
    (Elsevier, 2013-07-01) Cooper, MWD; Middleburgh, SC; Grimes, RW
    The energies to remove fission products from UO2 or UO2+x and incorporate them into BaZrO3, SrZrO3 (grey phase constituent phases) and ZrO2 have been calculated using atomistic scale simulation. These energies provide the thermodynamic drive for partition of soluble fission products between UO2 or UO2+x and these secondary oxide constituents of the fuel system. Tetravalent cation partition into BaZrO3, SrZrO3 and ZrO2 was only preferable for species with smaller radii than Zr4+, regardless of uranium dioxide stoichiometry. Under stoichiometric conditions both the larger and the smaller trivalent cations were found to segregate to BaZrO3 but only the smaller fuel additive elements Cr3+ and Fe3+ segregate to SrZrO3. Partition from UO2+x was always unfavourable for trivalent cations. Additions of excess Cr3+ (as a fuel additive) are predicted make the partition into BaZrO3 and SrZrO3 more favourable from UO2 for the larger trivalent cations. Trivalent fission products with radii smaller than or equal to that of Sm3+ were identified to segregate into ZrO2 only from UO2. No segregation to SrO or BaO is predicted. © 2013, Elsevier B.V.
  • No Thumbnail Available
    Item
    Swelling due to the partition of soluble fission products between the grey phase and uranium dioxide
    (Elsevier, 2014-04-01) Cooper, MWD; Middleburgh, SC; Grimes, RW
    The change in volume associated with the partition of soluble cations from uranium dioxide into the (Ba,Sr)ZrO3 grey phase has been investigated using atomic scale simulations. Here past work on the thermodynamic drive for the segregation of trivalent and tetravalent cations from uranium dioxide is built upon in the context of fuel swelling. Only small tetravalent cations segregate into the grey phase and this is predicted to result in an overall reduction in fuel volume. Individual trivalent cations that segregate, can cause either a contraction or an expansion of the overall fuel volume. Cr2O3 doped UO2 promotes co-partition forming mixed cation clusters in the grey phase and causing an overall reduction in fuel volume for all trivalent cations. This may have implications for fuel performance and may alter other fuel swelling mechanisms.© 2013 Elsevier Ltd.
  • No Thumbnail Available
    Item
    Thermal conductivity and energetic recoils in UO2 using a many-body potential model
    (IOP Science, 2014-11-14) Qin, MJ; Cooper, MWD; Kuo, EY; Rushton, MJD; Grimes, RW; Lumpkin, GR; Middleburgh, SC
    Classical molecular dynamics simulations have been performed on uranium dioxide (UO2) employing a recently developed many-body potential model. Thermal conductivities are computed for a defect free UO2 lattice and a radiation-damaged, defect containing lattice at 300 K, 1000K and 1500 K. Defects significantly degrade the thermal conductivity of UO2 as does the presence of amorphous UO2, which has a largely temperature independent thermal conductivity of ∼1.4Wm−1 K−1. The model yields a pre-melting superionic transition temperature at 2600 K, very close to the experimental value and the mechanical melting temperature of 3600 K, slightly lower than those generated with other empirical potentials. The average threshold displacement energy was calculated to be 37 eV. Although the spatial extent of a 1 keV U cascade is very similar to those generated with other empirical potentials and the number of Frenkel pairs generated is close to that from the Basak potential, the vacancy and interstitial cluster distribution is different. © 2014, IOP Publishing Ltd.
  • No Thumbnail Available
    Item
    Thermal conductivity variation in uranium dioxide with gadolinia additions
    (Elsevier, 2020-11) Qin, MJ; Middleburgh, SC; Cooper, MWD; Rushton, MJD; Puide, M; Kuo, EY; Grimes, RW; Lumpkin, GR
    By combining experimental observations on Gd doped fuel with a theoretical understanding, the variation in thermal conductivity with Gd concentration and accommodation mechanism has been modelled. Four types of Gd accommodation mechanisms have been studied. In UO2−x, isolated substitutional Gd3+ ions are compensated by oxygen vacancies and {2Gd'u:V"o}x defect clusters. In UO2, isolated substitutional Gd3+ ions are compensated by U5+ ions and {Gd'u:U'u}x defect clusters. The results indicate that defect clusters can be considered as less effective phonon scatterers and therefore result in less thermal conductivity degradation. The thermal conductivity predicted for UO2 with {Gd/u:U'u}x defect clusters is in good agreement with experimental data for UO2 with 5 wt% Gd2O3. This supports the previous theoretical results that Gd is accommodated through defect clusters {Gd'u:U'u}x in UO2 in the presence of excess oxygen. © 2020 Elsevier B.V.
  • Thumbnail Image
    Item
    Thermodynamic properties at the rim in high burnup UO2 fuels
    (The Minerals, Metals & Materials Society, 2020-02-23) Frost, D; Veliscek-Carolan, J; Galvin, C; Obbard, EG; Cooper, MWD; Burr, PA
    Not available