359 results found
© 2018 The Authors Helium, generated in nuclear fuel, accomodates into bubbles and degrades mechanical stability. Atomic scale simulations were used to study the interaction of He atoms with point defects and defect clusters. The incorporation of a single He atom was unfavourable at an octahedral interstitial site by 0.92 eV compared to the gas phase reference state, by 0.68 eV at an oxygen vacancy and by 0.32 eV at a Th vacancy. The decreasing values reflect the greater space available for the inert He atom. Defect clusters consisting of multiple oxygen and Th vacancies provide more space. Thus, incorporation at a di-vacancy required 0.31 eV, at a neutral tri-vacancy (NTV) 0.25 eV and at a tetra-vacancy 0.01 eV. Clusters formed of two and three NTVs exhibited no energy penalty for the incorporation of multiple He atoms. Relative to incorporation at an interstitial site, clusters offer space for multiple He and may therefore be effective traps to form proto-bubbles. A relationship was generated that describes the incorporation energy of the xth He atom, Ex(n, m), into a cluster consisting of n thorium vacancies and m oxygen vacancies. Solution energies for He, where equilibrium with the solution site is taken into account, were also determined.
Middleburgh SC, Claisse A, Andersson DA, et al., 2018, Solution of hydrogen in accident tolerant fuel candidate material: U₃Si₂, Journal of Nuclear Materials, Vol: 501, Pages: 234-237, ISSN: 0022-3115
Hydrogen uptake and accommodation into U 3 Si 2 , a candidate accident-tolerant fuel system, has been modelled on the atomic scale using the density functional theory. The solution energy of multiple H atoms is computed, reaching a stoichiometry of U 3 Si 2 H 2 which has been experimentally observed in previous work (reported as U 3 Si 2 H 1.8 ). The absorption of hydrogen is found to be favourable up to U 3 Si 2 H 2 and the associated volume change is computed, closely matching experimental data. Entropic effects are considered to assess the dissociation temperature of H 2 , estimated to be at ∼800 K – again in good agreement with the experimentally observed transition temperature.
Pavlov TR, Wangle T, Wenman MR, et al., 2018, High temperature measurements and condensed matter analysis of the thermo-physical properties of ThO2, SCIENTIFIC REPORTS, Vol: 8, ISSN: 2045-2322
Than YR, Wenman MR, Bell BDC, et al., 2018, Modelling and experimental analysis of the effect of solute iron in thermally grown Zircaloy-4 oxides, Journal of Nuclear Materials, Vol: 509, Pages: 114-123, ISSN: 0022-3115
© 2018 Simulations based on density functional theory (DFT) were used to investigate the behaviour of substitutional iron in both tetragonal and monoclinic ZrO2. Brouwer diagrams of predicted defect concentrations, as a function of oxygen partial pressure, suggest that iron behaves as a p-type dopant in monoclinic ZrO2while it binds strongly to oxygen vacancies in tetragonal ZrO2. Analysis of defect relaxation volumes suggest that these results should hold true in thermally grown oxides on zirconium, which is under compressive stresses. X-ray absorption near edge structure (XANES) measurements, performed to determine the oxidation state of iron in Zircaloy-4 oxide samples, revealed that 3 + is the favourable oxidation state but with between a third and half of the iron, still in the metallic Fe0state. The DFT calculations on bulk zirconia agree with the preferred oxidation state of iron if it is a substitutional species but do not predict the presence of metallic iron in the oxide. The implications of these results with respect to the corrosion and hydrogen pick-up of zirconium cladding are discussed.
Bell BDC, Murphy ST, Grimes RW, et al., 2017, The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys, ACTA MATERIALIA, Vol: 132, Pages: 425-431, ISSN: 1359-6454
Fossati PCM, Grimes RW, 2017, Cation ordering and oxygen transport behaviour in Sr1-3x/2LaxTiO3 perovskites, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 5, Pages: 5321-5331, ISSN: 2050-7488
Hodgson APJ, Jarvis KE, Grimes RW, et al., 2017, Advances in the development of a dissolution method for the attribution of iridium source materials, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY, Vol: 311, Pages: 1193-1199, ISSN: 0236-5731
Jackson ML, Burr PA, Grimes RW, 2017, Defect processes in Be12X (X = Ti, Mo, V, W), NUCLEAR FUSION, Vol: 57, ISSN: 0029-5515
Kuganathan N, Ghosh PS, Arya AK, et al., 2017, Energetics of halogen impurities in thorium dioxide, JOURNAL OF NUCLEAR MATERIALS, Vol: 495, Pages: 192-201, ISSN: 0022-3115
Pavlov T, Vlahovic L, Staicu D, et al., 2017, A new numerical method and modified apparatus for the simultaneous evaluation of thermo-physical properties above 1500 K: A case study on isostatically pressed graphite, THERMOCHIMICA ACTA, Vol: 652, Pages: 39-52, ISSN: 0040-6031
Pavlov TR, Wenman MR, Vlahovic L, et al., 2017, Measurement and interpretation of the thermo-physical properties of UO2 at high temperatures: The viral effect of oxygen defects, ACTA MATERIALIA, Vol: 139, Pages: 138-154, ISSN: 1359-6454
Pilania G, Whittle KR, Jiang C, et al., 2017, Using Machine Learning To Identify Factors That Govern Amorphization of Irradiated Pyrochlores, CHEMISTRY OF MATERIALS, Vol: 29, Pages: 2574-2583, ISSN: 0897-4756
Valu SO, Benes O, Manara D, et al., 2017, The high-temperature heat capacity of the (Th,U)O-2 and (U,Pu)O-2 solid solutions, JOURNAL OF NUCLEAR MATERIALS, Vol: 484, Pages: 1-6, ISSN: 0022-3115
Bell BDC, Murphy ST, Burr PA, et al., 2016, The influence of alloying elements on the corrosion of Zr alloys, CORROSION SCIENCE, Vol: 105, Pages: 36-43, ISSN: 0010-938X
Burr PA, Middleburgh SC, Grimes RW, 2016, Solubility and partitioning of impurities in Be alloys, JOURNAL OF ALLOYS AND COMPOUNDS, Vol: 688, Pages: 382-385, ISSN: 0925-8388
Chernatynskiy A, Auguste A, Steele B, et al., 2016, Elastic and thermal properties of hexagonal perovskites, COMPUTATIONAL MATERIALS SCIENCE, Vol: 122, Pages: 139-145, ISSN: 0927-0256
Cooper MWD, Kuganathan N, Burr PA, et al., 2016, Development of Xe and Kr empirical potentials for CeO2, ThO2, UO2 and PuO2, combining DFT with high temperature MD, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 28, ISSN: 0953-8984
Galvin COT, Cooper MWD, Rushton MJD, et al., 2016, Thermophysical properties and oxygen transport in (Th-x, Pu1-x)O-2, SCIENTIFIC REPORTS, Vol: 6, ISSN: 2045-2322
Ghosh PS, Arya A, Dey GK, et al., 2016, A computational study on the superionic behaviour of ThO2, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 18, Pages: 31494-31504, ISSN: 1463-9076
Ghosh PS, Kuganathan N, Galvin COT, et al., 2016, Melting behavior of (Th,U)O-2 and (Th,Pu)O-2 mixed oxides, JOURNAL OF NUCLEAR MATERIALS, Vol: 479, Pages: 112-122, ISSN: 0022-3115
Hodgson APJ, Jarvis KE, Grimes RW, et al., 2016, Development of an iridium dissolution method for the evaluation of potential radiological device materials, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY, Vol: 307, Pages: 2181-2186, ISSN: 0236-5731
Jackson ML, Burr PA, Grimes RW, 2016, Resolving the structure of TiBe12, ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, Vol: 72, Pages: 277-280, ISSN: 2052-5206
Jackson ML, Fossati PCM, Grimes RW, 2016, Simulations of threshold displacement in beryllium, JOURNAL OF APPLIED PHYSICS, Vol: 120, ISSN: 0021-8979
Liu X-Y, Cooper MWD, McClellan KJ, et al., 2016, Molecular Dynamics Simulation of Thermal Transport in UO2 Containing Uranium, Oxygen, and Fission-product Defects, PHYSICAL REVIEW APPLIED, Vol: 6, ISSN: 2331-7019
Pavlov T, Vlahovic L, Staicu D, et al., 2016, Experimental evaluation of the high temperature thermophysical properties of UO<inf>2</inf>, Pages: 1227-1235
High temperature properties of UO2are reported, in particular thermal conductivity, specific heat capacity, thermal diffusivity and melting point. All are measured with a single laser flash apparatus coupled with a numerical inverse method. The thermal conductivity, spectral emissivity, specific heat capacity, thermal diffusivity and melting point are in very good agreement with established literature values indicating the validity of the methodology and its potential for measuring these properties up to melting. The melting point was identified to be 3118 K ± 28 K. The thermal conductivity exhibits a minimum between 1800 K and 2100 K due to the competition between phonon scattering and an increase in the concentration of free charge carriers. The substantial increase in specific heat can be predominantly attributed to the formation of oxygen Frenkel pairs.
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