Publications
390 results found
Cooper MWD, Grimes RW, Fitzpatrick ME, et al., 2015, Modeling oxygen self-diffusion in UO2 under pressure, Solid State Ionics, Vol: 282, Pages: 26-30, ISSN: 0167-2738
Access to values for oxygen self-diffusion over a range of temperatures and pressures in UO2 is important to nuclear fuel applications. Here, elastic and expansivity data are used in the framework of a thermodynamic model, the cBΩ model, to derive the oxygen self-diffusion coefficient in UO2 over a range of pressures (0–10 GPa) and temperatures (300–1900 K). The significant reduction in oxygen self-diffusion as a function of increasing hydrostatic pressure, and the associated increase in activation energy, is identified.
Middleburgh SC, Burr PA, King DJM, et al., 2015, Structural stability and fission product behaviour in U3Si, JOURNAL OF NUCLEAR MATERIALS, Vol: 466, Pages: 739-744, ISSN: 0022-3115
Hodgson APJ, Grimes RW, Rushton MJD, et al., 2015, The Impact of Neutron Cross Section Group Structures on the Accuracy of Radiological Source Models, NUCLEAR SCIENCE AND ENGINEERING, Vol: 181, Pages: 302-309, ISSN: 0029-5639
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- Citations: 4
Burr PA, Wenman MR, Gault B, et al., 2015, From solid solution to cluster formation of Fe and Cr in α-Zr, Journal of Nuclear Materials, Vol: 467, Pages: 320-331, ISSN: 1873-4820
To understand the mechanisms by which the re-solution of Fe and Cr additions increase the corrosion rate of irradiated Zr alloys, the solubility and clustering of Fe and Cr in model binary Zr alloys was investigated using a combination of experimental and modelling techniques — atom probe tomography (APT), x-ray diffraction (XRD), thermoelectric power (TEP) and density functional theory (DFT). Cr occupies both interstitial and substitutional sites in the α-Zr lattice; Fe favours interstitial sites, and a low-symmetry site that was not previously modelled is found to be the most favourable for Fe. Lattice expansion as a function of Fe and Cr content in the α-Zr matrix deviates from Vegard's law and is strongly anisotropic for Fe additions, expanding the c-axis while contracting the a-axis. Matrix content of solutes cannot be reliably estimated from lattice parameter measurements, instead a combination of TEP and APT was employed. Defect clusters form at higher solution concentrations, which induce a smaller lattice strain compared to the dilute defects. In the presence of a Zr vacancy, all two-atom clusters are more soluble than individual point defects and as many as four Fe or three Cr atoms could be accommodated in a single Zr vacancy. The Zr vacancy is critical for the increased apparent solubility of defect clusters; the implications for irradiation induced microstructure changes in Zr alloys are discussed.
Jaem R, Nakayama M, Manalastas W, et al., 2015, Insights into the Lithium-Ion Conduction Mechanism of Garnet-Type Cubic Li5La3Ta2O12 by ab-Initio Calculations, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 119, Pages: 20783-20791, ISSN: 1932-7447
Murphy ST, Fossati PCM, Grimes RW, 2015, Xe diffusion and bubble nucleation around edge dislocations in UO2, Journal of Nuclear Materials, Vol: 466, Pages: 634-637, ISSN: 1873-4820
Recently it has been suggested that dislocations, generated by radiationdamage, may increase the rate of fission gas diffusion from the fuel grains,an affect which is at present not incorporated into fuel performance codes.Therefore, we perform molecular dynamics simulations employing empiricalpotentials to investigate the diffusion of Xe atoms around edge dislocationsin UO2 to establish the importance of this pathway for fission gas release.The results suggest that for isolated atoms near the dislocation the activationenergy for Xe diffusion is dramatically reduced relative to the bulk. However,Xe atoms diffusing along the dislocation cluster together to form small bubbles,these bubbles incorporate all of the isolated mobile Xe atoms therebyinhibiting fast diffusion of Xe along the dislocation core.
Jalem R, Nakayama M, Manalastas W, et al., 2015, Insights into the lithium-ion conduction mechanism of garnet-type cubic Li5La3Ta2O12 by ab-initio calculations, Journal of Physical Chemistry C, Vol: 119, Pages: 20783-20791, ISSN: 1932-7455
Burr PA, Middleburgh SC, Grimes RW, 2015, Crystal structure, thermodynamics, magnetics and disorder properties of Be-Fe-Al intermetallics, Journal of Alloys and Compounds, Vol: 639, Pages: 111-122, ISSN: 0925-8388
The elastic and magnetic properties, thermodynamical stability, deviation from stoichiometry and order/disorder transformations of phases that are relevant to Be alloys were investigated using density functional theory simulations coupled with phonon density of states calculations to capture temperature effects. A novel structure and composition were identified for the Be–Fe binary ε phase. In absence of Al, FeBe5 is predicted to form at equilibrium above ∼1100 K, while the ε phase is stable only below ∼1500 K, and FeBe2 is stable at all temperatures below melting. Small additions of Al are found to stabilise FeBe5 over FeBe2 and ε, while at high Al content, AlFeBe4 is predicted to form. Deviations from stoichiometric compositions are also considered and found to be important in the case of FeBe5 and ε. The propensity for disordered vs ordered structures is also important for AlFeBe4 (which exhibits complete Al–Fe disordered at all temperatures) and FeBe5 (which exhibits an order–disorder transition at ∼950 K).
Cooper MWD, Middleburgh SC, Grimes RW, 2015, Modelling the thermal conductivity of (UₓTh₁-ₓ)O₂ and (UₓPu₁-ₓ)O₂, Journal of Nuclear Materials, Vol: 466, Pages: 29-35, ISSN: 0022-3115
The degradation of thermal conductivity due to the non-uniform cation lattice of (UₓTh₁-ₓ)O₂ and (UₓPu₁-ₓ)O₂ solid solutions has been investigated by molecular dynamics, using the non-equilibrium method, from 300 to 2000 K. Degradation of thermal conductivity is predicted in (UₓTh₁-ₓ)O₂ and (UₓPu₁-ₓ)O₂ as compositions deviate from the pure end members: UO₂, PuO₂ and ThO₂. The reduction in thermal conductivity is most apparent at low temperatures where phonon-defect scattering dominates over phonon–phonon interactions. The effect is greater for (UₓTh₁-ₓ)O₂ than for (UₓPu₁-ₓ)O₂ due to the greater mismatch in cation size and mass. Parameters for analytical expressions have been developed that describe the predicted thermal conductivities over the full temperature and compositional ranges. These expressions may be used in higher level fuel performance codes.
Bertolus M, Freyss M, Dorado B, et al., 2015, Linking atomic and mesoscopic scales for the modelling of the transport properties of uranium dioxide under irradiation, JOURNAL OF NUCLEAR MATERIALS, Vol: 462, Pages: 475-495, ISSN: 0022-3115
Jalem R, Rushton MJD, Manalastas W, et al., 2015, Effects of Gallium Doping in Garnet-Type Li7La3Zr2O12 Solid Electrolytes, Chemistry of Materials, Vol: 27, Pages: 2821-2831, ISSN: 1520-5002
Garnet-type Li7La3Zr2O12 (LLZrO) is a candidate solid electrolyte material that is now being intensively optimized for application in commercially competitive solid state Li+ ion batteries. In this study we investigate, by force-field-based simulations, the effects of Ga3+ doping in LLZrO. We confirm the stabilizing effect of Ga3+ on the cubic phase. We also determine that Ga3+ addition does not lead to any appreciable structural distortion. Li site connectivity is not significantly deteriorated by the Ga3+ addition (>90% connectivity retained up to x = 0.30 in Li7–3xGaxLa3Zr2O12). Interestingly, two compositional regions are predicted for bulk Li+ ion conductivity in the cubic phase: (i) a decreasing trend for 0 ≤ x ≤ 0.10 and (ii) a relatively flat trend for 0.10 < x ≤ 0.30. This conductivity behavior is explained by combining analyses using percolation theory, van Hove space time correlation, the radial distribution function, and trajectory density.
Cooper MWD, Murphy ST, Rushton MJD, et al., 2015, Thermophysical properties and oxygen transport in the (Ux,Pu1−x)O2 lattice, Journal of Nuclear Materials, Vol: 461, Pages: 206-214, ISSN: 1873-4820
Bell BDC, Murphy ST, Burr PA, et al., 2015, Accommodation of tin in tetragonal ZrO2, Journal of Applied Physics, Vol: 117, Pages: 1-7, ISSN: 0021-8979
Atomic scale computer simulations using density functional theory were used to investigate the behaviour of tin in the tetragonal phase oxide layer on Zr-based alloys. The Sn×ZrSnZr× defect was shown to be dominant across most oxygen partial pressures, with Sn′′ZrSnZr″ charge compensated by V∙∙OVO•• occurring at partial pressures below 10−31 atm. Insertion of additional positive charge into the system was shown to significantly increase the critical partial pressure at which Sn′′ZrSnZr″ is stable. Recently developed low-Sn nuclear fuel cladding alloys have demonstrated an improved corrosion resistance and a delayed transition compared to Sn-containing alloys, such as Zircaloy-4. The interaction between the positive charge and the tin defect is discussed in the context of alloying additions, such as niobium and their influence on corrosion of cladding alloys.
Jay EE, Fossati PCM, Rushton MJD, et al., 2015, Prediction and characterisation of radiation damage in fluorapatite, Journal of Materials Chemistry A, Vol: 3, Pages: 1164-1173, ISSN: 2050-7496
Tahini HA, Chroneos A, Middleburgh SC, et al., 2015, Ultrafast palladium diffusion in germanium, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 3, Pages: 3832-3838, ISSN: 2050-7488
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- Citations: 11
Jay EE, Rushton MJD, Chroneos A, et al., 2015, Genetics of superionic conductivity in lithium lanthanum titanates, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 178-183, ISSN: 1463-9076
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- Citations: 79
Qin MJ, Cooper MWD, Kuo EY, et al., 2014, Thermal conductivity and energetic recoils in UO<sub>2</sub> using a many-body potential model, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 26, ISSN: 0953-8984
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- Citations: 36
Murphy ST, Cooper MWD, Grimes RW, 2014, Point defects and non-stoichiometry in thoria, SOLID STATE IONICS, Vol: 267, Pages: 80-87, ISSN: 0167-2738
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- Citations: 36
Cooper MWD, Middleburgh SC, Grimes RW, 2014, Vacancy mediated cation migration in uranium dioxide: The influence of cluster configuration, SOLID STATE IONICS, Vol: 266, Pages: 68-72, ISSN: 0167-2738
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- Citations: 12
Cooper MWD, Murphy ST, Fossati PCM, et al., 2014, Thermophysical and anion diffusion properties of (U-x,Th1-x)O-2, Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 470, ISSN: 1471-2946
Using molecular dynamics, the thermophysicalproperties of the (Ux,Th1−x)O2 system have beeninvestigated between 300 and 3600 K. The thermaldependence of lattice parameter, linear thermalexpansion coefficient, enthalpy and specific heat atconstant pressure is explained in terms of defectformation and diffusivity on the oxygen sublattice.Vegard’s law is approximately observed for solidsolution thermal expansion below 2000 K. Differentdeviations from Vegard’s law above this temperatureoccur owing to the different temperatures at whichthe solid solutions undergo the superionic transition(2500–3300 K). Similarly, a spike in the specificheat, associated with the superionic transition,occurs at lower temperatures in solid solutions thathave a high U content. Correspondingly, oxygendiffusivity is higher in pure UO2 than in pure ThO2.Furthermore, at temperatures below the superionictransition, oxygen mobility is notably higher insolid solutions than in the end members. Enhanceddiffusivity is promoted by lower oxygen-defectenthalpies in (Ux,Th1−x)O2 solid solutions. Unlikein UO2 and ThO2, there is considerable variety ofoxygen vacancy and oxygen interstitial sites in solidsolutions generating a wide range of property values.Trends in the defect enthalpies are discussed interms of composition and the lattice parameter of(Ux,Th1−x)O2.
Lumley SC, Grimes RW, Murphy ST, et al., 2014, The thermodynamics of hydride precipitation: the importance of entropy, enthalpy and disorder, Acta Materialia, Vol: 79, Pages: 351-362, ISSN: 1359-6454
The precipitation of zirconium hydrides from Zr solid solution was investigated using first-principles lattice dynamics simulations. These included the temperature-dependent vibrational enthalpy and vibrational entropy combined with the configurational entropy terms. In contrast with previous approaches, it was found that the latent enthalpy alone is not sufficient to fully describe precipitation of hydrides; a full thermodynamic assessment is required. In particular, the vibrational enthalpy of precipitation assists in stabilizing hexagonal close-packed hydrides and is especially important in forming the metastable zeta phase. The configurational entropy change during precipitation favours face-centred cubic hydrides. Given this, at concentrations below 300 ppm H, no hydride precipitation is predicted, suggesting that when hydrides are seen in those materials it is because the local concentration of H is greater than that measured globally. While gamma hydride is the most stable phase, it is very close in energy to the delta phase.
Jackson ML, Jay EE, Rushton MJD, et al., 2014, A concerted mechanism for Cl- migration in chlorapatite, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 2, Pages: 16157-16164, ISSN: 2050-7488
Chroneos A, Tahini HA, Schwingenschloegl U, et al., 2014, Antisites in III-V semiconductors: Density functional theory calculations, JOURNAL OF APPLIED PHYSICS, Vol: 116, ISSN: 0021-8979
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- Citations: 9
Cooper MWD, Middleburgh S, Grimes RW, 2014, Swelling due to the partition of soluble fission products between the grey phase and uranium dioxide, PROGRESS IN NUCLEAR ENERGY, Vol: 72, Pages: 33-37, ISSN: 0149-1970
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- Citations: 7
Murphy ST, Rushton MJD, Grimes RW, 2014, A comparison of empirical potential models for the simulation of dislocations in uranium dioxide, PROGRESS IN NUCLEAR ENERGY, Vol: 72, Pages: 27-32, ISSN: 0149-1970
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- Citations: 13
Murphy ST, Jay EE, Grimes RW, 2014, Pipe diffusion at dislocations in UO<sub>2</sub>, JOURNAL OF NUCLEAR MATERIALS, Vol: 447, Pages: 143-149, ISSN: 0022-3115
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- Citations: 24
Cooper MWD, Rushton MJD, Grimes RW, 2014, A many-body potential approach to modelling the thermomechanical properties of actinide oxides, Journal of Physics: Condensed Matter, Vol: 26, ISSN: 0953-8984
A many-body potential model for the description of actinide oxide systems, which is robust at high temperatures, is reported for the first time. The embedded atom method is used to describe many-body interactions ensuring good reproduction of a range of thermophysical properties (lattice parameter, bulk modulus, enthalpy and specific heat) between 300 and 3000 K for AmO2, CeO2, CmO2, NpO2, ThO2, PuO2 and UO2. Additionally, the model predicts a melting point for UO2 between 3000 and 3100 K, in close agreement with experiment. Oxygen–oxygen interactions are fixed across the actinide oxide series because it facilitates the modelling of oxide solid solutions. The new potential is also used to predict the energies of Schottky and Frenkel pair disorder processes.
Middleburgh SC, Karatchevtseva I, Kennedy BJ, et al., 2014, Peroxide defect formation in zirconate perovskites, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 2, Pages: 15883-15888, ISSN: 2050-7488
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- Citations: 23
Middleburgh SC, Lumpkin GR, Grimes RW, 2013, Accommodation of excess oxygen in fluorite dioxides, SOLID STATE IONICS, Vol: 253, Pages: 119-122, ISSN: 0167-2738
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- Citations: 24
Burr PA, Murphy ST, Lumley SC, et al., 2013, Hydrogen solubility in zirconium intermetallic second phase particles, JOURNAL OF NUCLEAR MATERIALS, Vol: 443, Pages: 502-506, ISSN: 0022-3115
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- Citations: 21
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