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Synthesis and characterization of Nd2SnxZr2−xO7 pyrochlore ceramics
No full textPyrochlore structured Nd2SnxZr2−xO7 (x=0–2) ceramics were prepared by a new chemical synthesis route in an aqueous media. Raman spectra and X-ray diffraction patterns confirmed the formation of the pyrochlore structure after sintering at 1400 °C. SEM results showed pelletized materials became dense with increasing Zr/Sn mole ratio and sintering temperature. These candidate materials have characteristic structures for the development of nuclear waste forms or inert matrix nuclear fuels.© 2013, Elsevier Ltd and Techna Group S.r.l
Microstructural and mechanical factors influencing high pH stress corrosion cracking susceptibility of low carbon line pipe steel
No full textSeveral adjacent gas pipe sections were obtained from the field. These pipe sections had nominally identical manufacturing, construction, coating and operational conditions. Some sections were unaffected by stress corrosion cracking (SCC), whereas surrounding sections were affected by SCC. Slight differences in mechanical and microstructural properties were found between the two types of section. Residual stress/strain and hardness close to the outer surface of the pipes and high angle boundary fraction values were lower for the non-cracked pipe sections. Predominant 〈1 1 0〉//ND texture was also found at the outer surface of the non-cracked pipe sections. These characteristics lead to a lower crack growth rate in laboratory SCC experiments. These features being mainly a result of the line pipe steel manufacturing operations, appropriate metallurgical processes leading to low residual stress (6.2%YS), relatively low fraction of high angle boundaries (about 0.75) and predominant {1 1 0}〈1 1 0〉 texture in the material (or in the near surface) are expected to greatly improve the stress corrosion cracking resistance of line pipe steels on the field. © 2014, Elsevier Ltd
Thermal conductivity and energetic recoils in UO2 using a many-body potential model
No full textClassical 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
Synthesis, properties, water and solute permeability of MWNT buckypapers
No full textHigh power tip sonication was used to prepare dispersions containing multi-walled carbon nanotubes (MWNTs), or multi-walled carbon nanotubes functionalised with carboxylic acid groups (MWNT-COOH) or amine groups (MWNT-NH2). The dispersion of carbon nanotubes was facilitated by the presence of a surfactant (Triton X-100) or various macrocyclic ligands (derivatised porphyrin, phthalocyanine or calixarene) in the solution. Vacuum filtration of the dispersions afforded self-supporting membranes known as buckypapers. Microanalysis provided evidence for retention of the surfactant or macrocyclic ligands in the buckypapers, which were also characterised by measurement of their electrical conductivities (24±16 to 58±11 S/cm), contact angles (28±1° to 55±10°) and mechanical properties (tensile strengths varied between 1.6±0.7 and 13±2 MPa). The surface and internal morphologies of the buckypapers were similar to each other, which correlates with the lack of variation observed in their permeability's towards water. The ability of selected buckypapers to remove trace organic contaminants (TrOCs) was also examined. A buckypaper prepared using Triton X-100 as the dispersant showed more than 80% removal efficiency for 11 out of the 12 TrOCs investigated in this study. On the other hand, a buckypaper prepared from MWNTs and phthalocyaninetetrasulfonic acid exhibited lower removal efficiencies for these TrOCs, possibly due to their smaller specific surface area. © 2014, Elsevier B.V
Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases
No full textApatite-type oxides ([AI4][AII6][(BO4)6]O2), particularly those of the rare-earth silicate and germanate systems, are among the more promising materials being considered as alternative solid oxide fuel cell electrolytes. Nonstoichiometric lanthanum silicate and germanate apatites display pure ionic conductivities exceeding those of yttria-stabilized zirconia at moderate temperatures (500–700 °C). In this study, mixed Si/Ge-based apatites were prepared by hydrothermal synthesis under mild conditions rather than the conventional solid-state method at high temperatures. Single-phase and highly crystalline nanosized apatite powders were obtained with the morphology changing across the series from spheres for the Si-based end member to hexagonal rods for the Ge-based end member. Powder X-ray and neutron analysis found all of these apatites to be hexagonal (P63/m). Quantitative X-ray microanalysis established the partial (<15 at%) substitution of La3+ by Na+ (introduced from the NaOH hydrothermal reagent), which showed a slight preference to enter the AI 4f framework position over the AII 6h tunnel site. Moreover, retention of hydroxide (OH–) was confirmed by IR spectroscopy and thermogravimetric analysis, and these apatites are best described as oxyhydroxyapatites. To prepare dense pellets for conductivity measurements, both conventional heat treatment and spark plasma sintering methods were compared, with the peculiar features of hydrothermally synthesized apatites and the influence of sodium on the ionic conductivity considered.© 2014, American Chemical Society
Using X-ray fluorescence core scanning to assess acid sulfate soils
No full textDuring the formation of acid sulfate soils (ASS), several chemical elements in the sediment are mobilised. These elements are removed from the sediment or become enriched as precipitates in distinct horizons. The stratigraphic depth in which these precipitates accumulate is element-specific and is located either within the oxidised or in a transitional zone between the oxidised and the reduced zone. Aim of this study is to demonstrate how X-ray fluorescence core scanning, together with detailed sediment descriptions, can be used to perform an initial assessment of these different zones in ASS in a fast and cost-effective manner. We measured the chemical element signatures of K, Fe, Pb, Sr, Zn, Ni, Y, Mn and Ca in two sediment cores from Western Australia where ASS are suspected to occur. The oxidised zone in both cores is characterised by the occurrence of jarosite, which is indicated by pale straw yellow mottling and synchronous peaks in Fe/Ti, K/Ti, Pb/Ti and Sr/Ti, and of other secondary Fe-oxides, which are indicated by reddish mottling and synchronous peaks in Fe/Ti and Pb/Ti. The transition zone into reduced material is marked by synchronous peaks in Zn/Ti, Ni/Ti, Y/Ti and Mn/Ti. Based on these characteristic signatures, we broadly estimated the depth of the oxidised and the transitional zone at both sites. © 2014, CSIRO
Photocatalytic properties of TiO2: effect of niobium and oxygen activity on partial water oxidation
No full textThis work reports the effect of niobium (0–1 at%) on photocatalytic activity and the band gap of TiO2 with controlled oxygen activity in the range 10−12 Pa < p(O2) < 105 Pa. It is shown that maximum of photocatalytic performance in partial water oxidation is observed for Nb-doped TiO2 containing 1 at% Nb that is processed at 1273 K in pure oxygen, p(O2) = 105 Pa. The mechanism of photocatalytic water oxidation is considered in terms of a predominant effect of photocatalytically active surface sites corresponding to titanium vacancies. It is shown that the niobium-induced increase of the band gap, surface potential and charge transport have a minor influence on photoreactivity of Nb-doped TiO2 with water. © 2016 Elsevier B.V
Mitigating cutting-induced plasticity in the contour method. Part 2: Numerical analysis
No full textCutting-induced plasticity can have a significant effect on the measurement accuracy of the contour method. The present study examines the benefit of a double-embedded cutting configuration that relies on self-restraint of the specimen, relative to conventional edge-crack cutting configurations. A series of finite element analyses are used to simulate the planar sectioning performed during double-embedded and conventional edge-crack contour cutting configurations. The results of numerical analyses are first compared to measured results to validate the cutting simulations. The simulations are then used to compare the efficacy of different cutting configurations by predicting the deviation of the residual stress profile from an original (pre-cutting) reference stress field, and the extent of cutting-induced plasticity. Comparisons reveal that while the double-embedded cutting configuration produces the most accurate residual stress measurements, the highest levels of plastic flow are generated in this process. This cutting-induced plastic deformation is, however, largely confined to small ligaments formed as a consequence of the sample sectioning process, and as such it does not significantly affect the back-calculated residual stress field. © 2016 Elsevier Ltd
Fabrication and testing of U–7Mo monolithic plate fuel with Zircaloy cladding
No full textNuclear fuel designs are being developed to replace highly enriched fuel used in research and test reactors with fuels of low enrichment. In the most challenging cases, U–(7–10 wt%)Mo monolithic plate fuels are proposed. One of the considered designs includes aluminum-alloy cladding, which provides some challenges in fabrication and fuel/cladding interaction during service. Zircaloy cladding, specifically Zry–4, was investigated as an alternative cladding, and development of a fabrication method was performed by researchers with the Comisión Nacionalde Energia Atómica (CNEA) in Argentina, resulting in test fuel plates (Zry–4 clad U–7Mo) which were subsequently tested in the Advanced Test Reactor in Idaho. Because Zry–4 and U–(7–10)Mo have similar high-temperature mechanical properties, fabrication was simplified in that the fuel foil and cladding could be co-rolled and bonded. The challenge was to prevent a thermal-expansion mismatch, which could destroy the fuel/cladding bond before complete bonding was achieved; the solution was to prevent the composites from cooling significantly during or between roll passes. The final product performed very well in-reactor, showing good bonding, very little fuel/cladding interaction—either from fabrication or in-reactor testing—and little swelling, especially no detectable heterogeneous bubble formation at the fuel/cladding interface tested to a fission density of up to 2.7E+21 (average) fissions/cm3, 3.8E+21 (peak). © 2016 Elsevier B.V
Measurement of 233U/234U ratios in contaminated groundwater using alpha spectrometry.
No full textThe uranium isotope 233U is not usually observed in alpha spectra from environmental samples due to its low natural and fallout abundance. It may be present in samples from sites in the vicinity of nuclear operations such as reactors or fuel reprocessing facilities, radioactive waste disposal sites or sites affected by clandestine nuclear operations. On an alpha spectrum, the two most abundant alpha emissions of 233U (4.784 MeV, 13.2%; and 4.824 MeV, 84.3%) will overlap with the 234U doublet peak (4.722 MeV, 28.4%; and 4.775 MeV, 71.4%), if present, resulting in a combined 233+234U multiplet.
A technique for quantifying both 233U and 234U from alpha spectra was investigated. A series of groundwater samples were measured both by accelerator mass spectrometry (AMS) to determine 233U/234U atom and activity ratios and by alpha spectrometry in order to establish a reliable 233U estimation technique using alpha spectra.
The Genie™ 2000 Alpha Analysis and Interactive Peak Fitting (IPF) software packages were used and it was found that IPF with identification of three peaks (234U minor, combined 234U major and 233U minor, and 233U major) followed by interference correction on the combined peak and a weighted average activity calculation gave satisfactory agreement with the AMS data across the 233U/234U activity ratio range (0.1–20) and 233U activity range (2–300 mBq) investigated. Correlation between the AMS 233U and alpha spectrometry 233U was r2 = 0.996 (n = 10). © 2015, Elsevier Ltd