Publications
90 results found
Pavlov T, Vlahovic L, Staicu D, et al., 2016, Experimental evaluation of the high temperature thermo- physical properties of UO2, Top Fuel 2016, Publisher: American Nuclear Society, ISSN: 0003-018X
High temperature properties of UO2 are 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.
Platt P, Lunt D, Polatidis E, et al., 2016, In-situ digital image correlation for fracture analysis of oxides formed on zirconium alloys, Corrosion Science, Vol: 111, Pages: 344-351, ISSN: 0010-938X
Repeated breakdown of the protective oxide layer can be a key factor in the oxidation of zirconium alloys. Hence, accurate measurement of the oxide fracture strength is crucial for simulating the oxidation of these alloys. High resolution digital image correlation was applied to SEM images taken during in-situ tensile loading of oxidised ZIRLOTM. Bi-axial strain measurements obtained during crack formation in the oxide films were converted into stress, and fitted to Weibull distributions to predict the oxide failure strength. Analysis highlights the impact of surface roughness. Samples polished prior to oxidation gave a fracture strength of ∼1.6 GPa.
Scatigno GG, Ryan MP, Giuliani F, et al., 2016, The effect of prior cold work on the chloride stress corrosion cracking of 304L austenitic stainless steel under atmospheric conditions, Materials Science and Engineering: A, Vol: 668, Pages: 20-29, ISSN: 0921-5093
A systematic study of the effect of cold work (CW) on chloride-induced stress corrosion cracking (SCC) in 304L stainless steel was performed. CW between 0% and 40% was applied prior to corrosion of specimens at 75 °C and 70% relative humidity, for 500 h, using MgCl2 (at atmospheric pressure). Samples cracked most readily between 0.5% and 5% CW; at 20% and above no cracks were present. Additionally, above 5% CW, some specific orientation relationships become evident, with cracks primarily aligned along <111> parallel to the transverse direction. The results suggest that at levels of CW >20%, the synergistic effect of micro-mechanisms may hinder SCC in this system.
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
Density functional theory (DFT) and autoclave corrosion tests in 360 °C water were used to investigate the influence of Sb, Sc, Nb and Sn on the corrosion and hydrogen pick-up (HPU) of Zr-alloys. Sc was shown to have a strongly detrimental effect on alloy corrosion resistance. The Nb–Sb–Zr ternary alloy exhibited significantly improved corrosion resistance over Zr–Nb and ZIRLO, and had little measurable HPU after 195 days. The ratio of View the MathML source was shown to transition smoothly with applied space charge, implying Sb can act as a buffer to charge imbalance in the oxide layer.
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.
Haynes T, Shea JH, Ball JA, et al., 2015, Finite element modelling of pellet-clad interaction during operational transients, TOP FUEL 2015, Publisher: European Nuclear Society, Pages: 62-71
A finite element model of pellet-clad interaction in advanced gas cooledreactor fuel experiencing extended reduced power operations ispresented. The model considers a 1/8th segment of fuel and overlayingcladding bonded to it. A radial crack is introduced to the pellet, this isable to open and close, straining a section of cladding above the crack.In addition, circumferential cracks in the fuel pellet result in a sliver offuel being bonded to the cladding; this sliver of fuel contains hairlineradial cracks, known as ladder cracks, the opening and closing of whichare modelled. Finally, the model predicts the creep strain at the tip of anincipient crack in the cladding, ahead of the radial crack in the fuel pellet.Results show that the crack tip creep strain is strongly dependent on themodel of ladder cracking chosen.
Mella R, Wenman MR, 2015, Modelling explicit fracture of nuclear fuel pellets using peridynamics, Journal of Nuclear Materials, Vol: 467, Pages: 58-67, ISSN: 0022-3115
Three dimensional models of explicit cracking of nuclear fuel pellets for a variety of power ratings have been explored with peridynamics, a non-local, mesh free, fracture mechanics method. These models were implemented in the explicitly integrated molecular dynamics code LAMMPS, which was modified to include thermal strains in solid bodies. The models of fuel fracture, during initial power transients, are shown to correlate with the mean number of cracks observed on the inner and outer edges of the pellet, by experimental post irradiation examination of fuel, for power ratings of 10 and 15 W g-1 UO2. The models of the pellet show the ability to predict expected features such as the mid-height pellet crack, the correct number of radial cracks and initiation and coalescence of radial cracks. This work presents a modelling alternative to empirical fracture data found in many fuel performance codes and requires just one parameter of fracture strain. Weibull distributions of crack numbers were fitted to both numerical and experimental data using maximum likelihood estimation so that statistical comparison could be made. The findings show P-values of less than 0.5% suggesting an excellent agreement between model and experimental distributions.
Haynes TA, Ball JA, Shea JH, et al., 2015, Modelling pellet-clad mechanical interaction during extended reduced power operation in bonded nuclear fuel, Journal of Nuclear Materials, Vol: 465, Pages: 280-292, ISSN: 0022-3115
A 2D-rӨ model of pellet-clad mechanical interaction in advanced gas-cooled reactor fuel is presented. An incipient 5 μm crack is introduced into the inner surface of cladding bonded to a detachable sliver of fuel. Micro-cracking in the sliver is accounted for through a reduced elastic modulus. A test transient consisting of a hold at 70% power for 720 h was applied to the model. The competing effects of the closure of pellet cracks due to irradiation creep in inner regions of the pellet during extended low power operation, and that of thermal creep in the cladding whilst at reduced power alleviating this are investigated. In colder elements, the effect of irradiation creep dominates. In hotter elements, the effect of cladding creep at low power dominates. It was found that adjusting factors related to the pellet shape were unimportant; the sliver thickness, sliver shape and initial pellet crack width had only a small effect upon the extent of PCMI. Adjusting factors relating to the shape of the incipient crack such as the crack radius and depth had a significant effect; as did adjusting the elastic modulus reduction factor accounting for ladder cracking in the sliver and the coefficient of friction used throughout the model. The resulting model was able to predict the trend in average clad bore crack depth with axial position in the core observed in post irradiation examination.
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.
Spencer DT, Edwards MR, Wenman MR, et al., 2014, The initiation and propagation of chloride-induced transgranular stress-corrosion cracking (TGSCC) of 304L austenitic stainless steel under atmospheric conditions, CORROSION SCIENCE, Vol: 88, Pages: 76-88, ISSN: 0010-938X
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- Citations: 61
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.
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
Beckmann R, Mella R, Wenman MR, 2013, Mesh and timestep sensitivity of fracture from thermal strains using peridynamics implemented in Abaqus, COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING, Vol: 263, Pages: 71-80, ISSN: 0045-7825
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- Citations: 26
Lumley SC, Murphy ST, Burr PA, et al., 2013, The stability of alloying additions in Zirconium, JOURNAL OF NUCLEAR MATERIALS, Vol: 437, Pages: 122-129, ISSN: 0022-3115
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- Citations: 37
Mella R, Wenman MR, 2013, Axisymmetric whole pin life modelling of advanced gas-cooled reactor nuclear fuel, JOURNAL OF NUCLEAR MATERIALS, Vol: 437, Pages: 154-165, ISSN: 0022-3115
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- Citations: 5
Burr PA, Murphy ST, Lumley SC, et al., 2013, Hydrogen accommodation in Zr second phase particles: Implications for H pick-up and hydriding of Zircaloy-2 and Zircaloy-4, Corrosion Science, Vol: 69, Pages: 1-4
Ab-initio computer simulations have been used to predict the energies associated with the accommodation of H atoms at interstitial sites in α, β-Zr and Zr–M intermetallics formed with common alloying additions (M = Cr, Fe, Ni). Intermetallics that relate to the Zr2(Ni,Fe) second phase particles (SPPs) found in Zircaloy-2 exhibit favourable solution enthalpies for H. The intermetallic phases that relate to the Zr(Cr,Fe)2 SPPs, found predominantly in Zircaloy-4, do not offer favourable sites for interstitial H. It is proposed that Zr(Cr,Fe)2 particles may act as bridges for the migration of H through the oxide layer, whilst the Zr2(Ni,Fe)-type particles will trap the migrating H until these are dissolved or fully oxidised.
Rushton MJD, Wenman MR, Mella R, et al., 2013, Providing skilled graduates to the nuclear industry, Nuclear Future, Vol: 9, Pages: 44-49, ISSN: 1745-2058
Wenman MR, 2013, Fitting small data sets in the lower ductile-to-brittle transition region and lower shelf of ferritic steels, ENGINEERING FRACTURE MECHANICS, Vol: 98, Pages: 350-364, ISSN: 0013-7944
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- Citations: 5
Mella R, Wenman MR, 2012, Finite element modelling of advanced gas-cooled reactor fuel performance and cladding structural integrity, TOP FUEL
Sudworth C, Smith C, Ahearn A, et al., 2012, The nuclear island, RAEng Publications
Wenman MR, Chard-Tuckey PR, 2010, Modelling and experimental characterisation of the Luders strain in complex loaded ferritic steel compact tension specimens, INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 26, Pages: 1013-1028, ISSN: 0749-6419
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- Citations: 36
Parfitt DC, Bishop CL, Wenman MR, et al., 2010, Strain fields and line energies of dislocations in uranium dioxide, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 22, ISSN: 0953-8984
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- Citations: 28
Wenman MR, Price AJ, Steuwer A, et al., 2009, Modelling and experimental characterisation of a residual stress field in a ferritic compact tension specimen, INTERNATIONAL JOURNAL OF PRESSURE VESSELS AND PIPING, Vol: 86, Pages: 830-837, ISSN: 0308-0161
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- Citations: 4
Garrity DJ, Wenman MR, Jenneson PM, et al., 2009, Development of a transmission geometry X-ray diffraction system for measuring the austenite to martensite phase transformation in 304 L stainless steel, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, Vol: 607, Pages: 695-699, ISSN: 0168-9002
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- Citations: 2
Wenman M, Barton J, Trethewey K, et al., 2009, FINITE ELEMENT MODELLING OF TRANSGRANULAR CHLORIDE STRESS CORROSION CRACKING IN 304L AUSTENITIC STAINLESS STEEL, Pressure Vessels and Piping Conference of the American-Society-of-Mechanical-Engineers, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 975-985
Wenman MR, Trethewey KR, Jarman SE, et al., 2008, A finite-element computational model of chloride-induced transgranular stress-corrosion cracking of austenitic stainless steel, ACTA MATERIALIA, Vol: 56, Pages: 4125-4136, ISSN: 1359-6454
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- Citations: 34
Trethewey KR, Wenman M, Chard-Tuckey P, et al., 2008, Correlation of meso- and micro-scale hardness measurements with the pitting of plastically-deformed Type 304L stainless steel, CORROSION SCIENCE, Vol: 50, Pages: 1132-1141, ISSN: 0010-938X
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- Citations: 23
Wenman MR, 2006, A simple model of Lüders behaviour in a novel compact tension specimen for investigation of residual stress effects., ASME Pressure vessels and piping conference
Price AJ, Wenman MR, Tsakiropoulos P, et al., 2006, Modelling fatigue crack growth in a residual stress field, ASME Pressure vessels and piping conference
Wenman MR, Novovic M, Bowen P, 2000, The effect of microstructure on the fracture toughness of a C-Mn weld metal, European Conference on Advances in Mechanical Behaviour, Plasticity and Damage (EUROMAT 2000), Publisher: ELSEVIER SCIENCE BV, Pages: 1421-1426
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