Browsing by Author "Obbard, EG"

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    Anisotropy in the thermal expansion of uranium silicide measured by neutron diffraction
    (Elsevier, 2018-09) Obbard, EG; Johnson, KD; Burr, PA; Lopes, DA; Liss, KD; Griffiths, GJ; Scales, N; Middleburgh, SC
    In-situ neutron diffraction patterns were collected for a sample of as-cast U3Si2 during heating to 1600 °C. Anomalous changes were observed above 1000 °C, including the formation of a new diffraction peak not belonging to P4/mbm U3Si2, unequal changes in the peak intensities and onset of anisotropic lattice expansion. The large data-set enabled derivation of a function-fitted isotropic thermal expansion coefficient to high precision, in close agreement with previous dilatometry results but reducing linearly with temperature over the studied interval. Anisotropy in the instantaneous lattice thermal expansion corresponded to anomalies reported by White et al. (2015) at a similar temperature. © Elsevier B.V
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    A combined DFT and NPD approach to determine the structure and composition of the ε-phase of tungsten boride
    (Elsevier, 2023-10-15) Setayandeh, SS; Stansby, JH; Obbard, EG; Brand, MI; Miskovic, DM; Laws, KJ; Peterson, VK; Astbury, JO; Wilson, CL; Irukuvarghula, S; Burr, PA
    The ε-phase of tungsten boride, conventionally labelled as W2B5, has been identified as a promising candidate for shielding application in spherical tokamak fusion reactors. However, further research has been hindered by a lack of agreement on the structure and even composition of the ε-phase. Here, we identify the stable crystal structure and stoichiometry range of ε tungsten borides through a combination of ab initio simulations and neutron diffraction of isotopically enriched samples. We considered the ability to accommodate hypo-stoichiometry in six published structures of the ε phase. Chemical disorder was modelled using configurational ensembles to account for entropy of non-stoichiometry. We show that two W2B4-x structures (with x=∼0.25 − 0.5), with space group symmetry P63/mmc and P63/mcm, appear to be thermodynamically stable. These candidate compounds have 6.2 − 7.8 at.% less B than the W2B5 composition reported in exiting phase diagrams. We confirm these findings by means of neutron powder diffraction, performed on 11B-enriched arc-melted and crushed samples. Rietveld refinement using the neutron data shows the ε-phase to be better described as W2B3.60(2) (P63/mcm), in keeping with density functional theory (DFT) calculations. Linear change in DFT-derived lattice parameters of the candidates for the ε-phase proposes a simple model to assess the tungsten boride composition by measuring the lattice parameter (e.g. by X-ray diffraction. The simulations also reveal that the material can accommodate a range of stoichiometric variations (via B vacancies) with relatively small stored energy, which is a desirable feature for neutron shielding application. © 2023 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. Open Access CC-NC-ND
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    Crystallographic characterization of U2CrN3: a neutron diffraction and transmission electron microscopy approach
    (Elsevier, 2023-06) Patnaik, S; Mishchenko, Y; Stansby, JH; Fazi, A; Peterson, VK; Jädernäs, D; Thuvander, M; Johnson, KD; Obbard, EG; Lopes, DA
    In this study, neutron diffraction and transmission electron microscopy (TEM) have been implemented to study the crystallographic structure of the ternary phase U2CrN3 from pellet to nano scale respectively. Recently microstructural evaluation of this ternary phase has been performed for the first time in pellet condition, overcoming the Cr evaporation issue during the conventional sintering process. In this work for the first time, the crystallographic structure of the ordered ternary U2CrN3 phase, stabilized in pellet condition, has been obtained by implementing neutron diffraction. For this study, pellets of the composite material UN with 20 vol% CrN were fabricated by powder metallurgy by mixing UN and CrN powders followed by Spark Plasma Sintering (SPS). TEM was used to investigate the nanoscale structure with a thin lamella of the order of 100–140 nm produced by focused ion beam (FIB). The neutron data revealed the phase composition of the pellet to be primarily 54(8) wt.% U2CrN3, in good agreement with the stoichiometry of starting reagents (UN and CrN powder) and metallographic analysis. Neutron data analysis confirms that all the crystallographic sites in U2CrN3 phase are fully occupied reinforcing the fully stoichiometric composition of this phase, however, the position of the N at the 4i site was found to be closer to the Cr than previously thought. TEM and selected area electron diffraction rendered nano-level information and revealed the presence of nano domains along grain boundaries of UN and U2CrN3, indicating a formation mechanism of the ternary phase, where the phase likely nucleates as nano domains in UN grains from migration of Cr. © 2023 The Author(s). Published by Elsevier Ltd. Open access article under the CC BY licence.
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    Gamma radiation effects on the performance of FIR-based fiber-optic temperature sensors
    (Institute of Electrical and Electronics Engineers, 2019-11-02) Fan, D; Xiao, G; Chu, Y; Ma, Z; Wei, S; Zhang, B; Tian, Y; Fu, X; Obbard, EG; Davies, JB; Luo, Y; Peng, GD
    The gamma radiation effect on the performance of fluorescence intensity ratio-based fiber-optic temperature sensors is studied. The results indicate such temperature sensors are promising for integration in gamma radiation environment.
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    In-situ neutron characterization of advanced nuclear ruels - the road to a new neutron irradiation testing capability
    (The Minerals, Metals & Materials Society, 2020-02-23) Obbard, EG; Gasparrini, C; Burr, PA; Johnson, KD; Lopes, DA; Anghel, C; Middleburgh, SC; Gregg, DJ; Liss, KD; Griffiths, GJ; Scales, N; Thorogood, GJ; Lumprin, GR
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    A review on the development of nuclear power reactors
    (Elsevier, 2019-02) Ho, M; Obbard, EG; Burr, PA; Yeoh, GH
    Nuclear power can solve the energy trilemma of supplying baseload, clean and affordable power. However, a review of nuclear power plant (NPP) builds show mixed results, with delays in Finland and in the US offset by successes in China, South Korea and the UAE. In the West, financing for new builds has been difficult in the face of a deregulated energy market, billion-dollar upfront investments, long build times and in the case of the US historically low gas prices. We explore how the nuclear industry is innovating in facing these challenges through a review of nuclear power developments in the past, present and future. Early developments in nuclear power in the 1950s resulted in a variety of designs, out of which the pressurised water reactor (PWR) became dominant for its compactness and overall economy. Over the next 10 years, several PWR-based small modular reactor (SMR) designs are expected to come online within an eight-year timeframe. Their modular construction and fabrication in a controlled factory setting aims to shorten build times from 8 to 3 years. However, the lack of established regulatory approval pathways may be a time-limiting challenge that needs to be overcome by the first fleet of SMRs. The passive safety and a smaller fuel loading of SMRs will allow them to be deployed at more potential sites, including brownfield replacements of old coal-fired power plants or power unconventional, remote or islanded grids. Some SMRs are also designed to load follow which will allow them to work harmoniously with intermittent renewables sources with the promise of an affordable, truly carbon-neutral grid. In the longer term, advanced nuclear reactors in the form of sodium cooled, molten salt cooled, and high temperature gas cooled reactors hold the promise of providing efficient electricity production, industrial heat for heavy industry as well as the generation of hydrogen for synthetic fuel. © 2019 The Author(s). Creative Commons Published by Elsevier Ltd.
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    Thermal expansion and steam oxidation of uranium mononitride analysed via in situ neutron diffraction
    (Elsevier B. V., 2023-03) Liu, J; Gasparrini, C; White, JT; Johnson, KD; Lopes, DA; Peterson, VK; Studer, AJ; Griffiths, GJ; Lumpkin, GR; Wenman, MR; Burr, PA; Sooby, ES; Obbard, EG
    In situ neutron powder diffraction experiments are applied to physical, kinetic, and microstructural characterization of uranium mononitride as a promising light water reactor fuel material. The temperature-variable coefficient of thermal expansion and isotropic Debye Waller factors are obtained by sequential Rietveld refinement over 499–1873 K. Oxidation of a UN pellet (95.2% density) under flow of 11 mg/min D2O is observed to initiate above 623 K and the rate increases by a factor of approximately 10 from 673 to 773 K, with activation energy 50.6 ± 1.3 kJ/mol; uranium oxide is the only solid corrosion product. Crown Copyright © 2022 Published by Elsevier B.V.
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    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
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