bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bio-inspired Crystal Growth Induced by Novel Organic Compounds
Authors: Dinsdale Nicholas B. , Heywood Brigid R. 
Published: April 2011

AbstractThe growth of biogenic inorganic crystals demands much attention given the exceptional control of nucleation and growth that is evidenced in biological systems. In many cases the biological mineralization products are crystals engineered to express unique forms and habits; this being linked to the bio-function of minerals. It is acknowledged that the formation of these biogenic minerals is controlled by a complex directory of organic macromolecules which are chemically tailored to mediate the crystallization sequelae. In this study, an homologous series of sulphonated calix[4]arenes (further modified by the addition of an alkyl substituent (R = (CH2)nCH3; n = 0-7)) were selected as chemical and structural mimics for some of the active components in the acidic macromolecules known to be associated with many biogenic mineral phases. Here, these calix[4]arenes were assayed for their ability to control the growth of barium sulphate. Their presence in the crystallization liquor induced the twinning of the barium sulphate crystals; two forms of twinning were observed. Interpenetrant (2-31) twins were noted for substituted calix[4]arenes when R = (CH2)2CH3; and interpenetrant {610} twins when R = (CH2)nCH3; n = 0-7. When R = (CH2)nCH3; n = 0 or 1, the crystals also evidenced a novel acicular growth form. These effects were linked to the chemical properties of the calixarenes and structural recognition motifs created at the calix[4]arene/barium sulphate interface following the adsorption of these sulphonated moieties onto the nascent crystals. The results offer an insight into the mechanisms which may mediate such effects in vivo.
Mechanistic Aspects of Fracture of Human Cortical Bone
Authors: Nalla Ravi K. , Kruzic Jamie J. , Kinney John H. , Ritchie R. O. 
Published: April 2011

AbstractThere has been growing interest of late in the fracture properties of human bone. As understanding such properties in the context of the hierarchical microstructure of bone is of obvious importance, this study addresses the evolution of the in vitro fracture toughness with crack extension (Resistance-curve behavior) in terms of the salient mechanisms involved. Fracture-mechanics based measurements were performed on compact-tension specimens hydrated in Hanks' Balanced Salt Solution using cortical bone from mid-diaphyses of 34-41 year-old human humeri. Post-test observations of the crack path were made by optical microscopy and three-dimensional X-ray computed tomography. The fracture toughness was found to rise linearly with crack extension with a mean crack-initiation toughness of Ko ∼ 2.0 MPa√m for crack growth in the proximal-distal direction. The increasing cracking resistance had its origins in several toughening mechanisms, most notably crack bridging by uncracked ligaments. Uncracked-ligament bridging, which was observed by tomography in the wake of the crack, was identified as the dominant toughening mechanism responsible for the observed Rcurve behavior through compliance-based experiments. The extent and nature of the bridging zone was examined quantitatively using multi-cutting compliance experiments in order to assess the bridging stress distribution. The results obtained in this study provide an improved understanding of the mechanisms associated with the failure of cortical bone, and as such are of importance from the perspective of developing a realistic framework for fracture risk assessment, and for determining how the increasing propensity for fracture with age can be prevented.
Do Natural Silks Make Good Engineering Materials?
Authors: Morrison Natalie A. , Bell Fraser I. , Beautrait Alexandre , Ritchie Joanne , Smith Christopher , McEwen Iain J. , Viney Christopher 
Published: April 2011

AbstractFast relaxation of stresses lower than the yield stress is demonstrated in Bombyx mori(silkworm) cocoon silk and Nephila clavipes (spider) major ampullate silk (MAS; dragline). Stress relaxation and creep make natural silk unsuitable as a long-term load-bearing material. Instead, silk-like materials are better suited to applications in which energy dissipation is important, and in which high loads need to be withstood on a once-off basis for only very short periods of time. Examples might include use as a ballistic material that arrests the penetration of fragments from the explosion of a pressure vessel, an aircraft luggage container, or a tyre. Treatment in a domestic microwave oven is shown to significantly reduce the rate of stress relaxation in both silkworm cocoon and spider MAS. Except for ductility, the tensile properties of cocoon silk measured in constant strain rate experiments are enhanced by this treatment. Initial experiments on MAS suggest that the tensile properties of this material also are enhanced by exposure to microwaves, in this case with the exception of initial modulus.
Use of Soft Lithography for Multi-layer MicroMolding (MMM) of 3-D PCL Scaffolds for Tissue Engineering
Authors: Sun Yang , Ferrell Nicholas , Hansford Derek J. 
Published: April 2011

AbstractTissue engineering scaffolds with precisely controlled geometries, particularly with surface features smaller than typical cell dimensions (1-10μm), can improve cellular adhesion and functionality. In this paper, soft lithography was used to fabricate polydimethylsiloxane (PDMS) stamps of arrays of parallel 5μm wide, 5μm deep grooves separated by 45 μm ridges, and an orthogonal grid of lines with the same geometry. Several methods were compared for the fabrication of 3-D multi-layer polycaprolactone (PCL) scaffolds with precise features. First, micromolding in capillaries (MIMIC) was used to deliver the polymer into the small grooves by capillarity; however the resultant lines were discontinuous and not able to form complete lines. Second, spin coating and oxygen plasma were combined to build 3-D scaffolds with the line pattern. The resultant scaffolds had good alignment and adhesion between layers; however, the upper layer collapsed due to the poor mechanical rigidity. Finally, a new multi-layer micromolding (MMM) method was developed and successfully applied with the grid pattern to fabricate 3-D scaffolds. Scanning electron microscopy (SEM) characterization showed that the multi-layered scaffolds had high porosity and precisely controlled 3-D structures.
Creep testing of thick-wall copper electron beam and friction stir welds
Authors: Andersson Henrik C. M. , Seitisleam Facredin , Sandstr Rolf 
Published: April 2011

Abstract:Thick section copper canisters are planned to be used as a corrosion protection of nuclear waste disposal containers for long term underground deposal in Sweden. The copper canisters will have the top and possibly the bottom lid welded to the canister walls using electron beam or friction stir welding. Due to the high external hydrostatic pressure and the relatively high temperature of the waste during the first one hundred years the copper will creep. The creep process will close the manufacturing gap between the cast iron container and the copper canister. The creep ductility must be sufficient to avoid cracking of the weld.Specimens cut from the friction stir welds and the electron beam welds have been creep tested at temperatures ranging from 75 to 175 °C. Cross-weld specimens were used for both friction stir and electron beam welds. Weld metal, heat affected zone and base metal were also studied for friction stir welds. The results for the electron beam welds show that the main creep deformation is concentrated to the weld metal where the failure takes place. Weld metal and most cross-weld tests of friction stir weld material show similar creep lives and ductility as base metal tests. Ductility at rupture was found to exceed 30% for friction stir weld specimens, and the Norton power law exponent was determined to be between 30 and 50.
Finite Element Modelling of Temperature Distribution in Friction Stir Welding Process and Its Influence on Distortion of Copper Canisters
Authors: Källgren Therese , Jin Lai-Zhe , Sandström Rolf 
Published: April 2011

AbstractIn an effort to enhance safety for long time disposal of waste nuclear fuel, friction stir welding has been developed as one alternative to seal copper canisters. To avoid the formation of voids and cracks during the welding process, an understanding of the heat and material flow andthereby the evolution of the microstructure, is of great importance. Finite element modelling has been used to simulate the heat and material flow as well as thermal expansion during the friction stir welding process. A model involving heat transfer, material flow, and continuum mechanics has been developed. The steady state solutions have been compared with experimental temperature observations as well as analytical solutions, showing good agreement. Temperature distribution is affected by the welding speed. For a given reference pointperpendicular to the welding direction, a lower welding speed corresponds to a higher peak temperature. The plunging position of welding tool influences the temperature distribution and therefore the displacement distribution of the weldment.
The Effect of Fabrication Processes on the Governing Mechanical Failure Criteria for Alloy 22, Ti-Grade 2/7, and Ti-Grade 5/24 Alloys
Authors: Csontos Aladar A. , Dunn Darrell S. , Pan Yi-Ming , Cragnolino Gustavo A. 
Published: April 2011

AbstractThe effect of fabrication processes on the governing mechanical failure criteria for Alloy 22, Ti-Grade 2/7, and Ti-Grade 5/24 has been evaluated through the development of material specific failure assessment diagrams (FAD). The Barsom and Rolfe Charpy V-Notch (CVN) energy to KICempirical relationship was shown to be conservative when compared to experimental KJC data for Alloy 600 and 690, which indicates that the KIC derivation is most likely conservative for Alloy 22 as well. In contrast, the CVN to KICH2 relationship was found to be non-conservative for Ti-Grade 2/7 and Ti-Grade 5/24. The derived KIC value for Alloy 22 was then used to construct a K-based FAD, which indicated that the governing mechanical failure theory was the Tresca criterion for plastic collapse. Both the derived KIC and experimental KQ values were used in the development of the Ti-Grade 2/7 and Ti-Grade 5/24 FADs. The Ti-Grade 2/7 FAD indicated that the governing mechanical failure theory is also plastic collapse while the Ti-Grade 5/24 FADsuggested mixed mode failure processes where neither linear-elastic fracture mechanics (LEFM) nor Tresca can accurately predict.
Technetium and Molybdenum in Oxide Spent Nuclear Fuel: Impact on Release Estimates
Authors: Fortner Jeffrey A. , Kropf A. Jeremy , Finch Robert J. , Cunnane James C. 
Published: April 2011

AbstractTechnetium-99 99Tc) is an important radionuclide in repository models owing to its relatively long half-life and the high aqueous solubility of compounds where it is inthe heptavalent state. The vast majority of the 99Tc inventory presently slatedfor disposal is contained in oxide commercial spent nuclear fuel (CSNF), where it is divided (along with its cohort, molybdenum) betweenexsolved, intermetallic “epsilon” particles and isolated, likely oxidized, atoms distributed in the uranium dioxide matrix. We present recent evidence from synchrotron x-ray fluorescence spectroscopy, electron microscopy, and fuel dissolution testing on the likely oxidation state, coordination environment, and physical disposition of technetium and molybdenum in CSNF. Effects of the relative proportioningof technetium and molybdenum among the metallic and oxidized states in CSNF, andtheir distribution in or near grain boundaries and gaps on release during CSNF corrosion testing are discussed.
An Experimental Basis for a Mixed Potential Model for Nuclear Fuel Corrosion within a Failed Waste Container
Authors: Shoesmith D.W. , Noël J.J. , Garisto F. 
Published: April 2011

AbstractA mixed-potential model to predict the corrosion behaviour of nuclear fuel inside a failed carbon steel-lined copper waste container in a granitic repository is briefly described. A number of experiments underway to improve the mechanistic form of the model and to provide the necessary input data are discussed. A primary emphasis is placed on the consequences of the accumulation of corrosion product deposits on the fuel surface on the development of aggressive local chemistries, the cathodic reduction of H2O2 and potential for scavenging of H2O2 by the products of carbon steel corrosion (in particular H2).
Uncertainties in geochemical models of natural systems: Implications for performance assessments
Authors: Palenik Christopher S. , Jensen Keld A. , Ewing Rodney C. 
Published: April 2011

AbstractLicensing a geologic repository for nuclear waste will be based primarily upon the results of a performance assessment (PA), which evaluates compliance of the repository with radiation exposure limits by modeling the engineered and natural barrier systems over extended periods (104 to 106 years). The properly completed PA must include an analysis of the sources of uncertainty, as well as the range of input parameter values, in order to determine whether the analysis is “robust”, “realistic” or “conservative”. This paper examines the sources of uncertainty that may be encountered in source-term and near-field models in a performance assessment of a repository for spent nuclear fuel by examining the uncertainties in modeling the geochemical behavior of the Bangombé natural reactor in Gabon.
Preferential Radionuclide Release Due to Alpha Decay: Effects on Repository Performance
Authors: Pickett David A. , Murphy William M. 
Published: April 2011

AbstractWe model preferential release of 237Np, 234U, 230Th, 226Ra, and 210Pb from disposed commercial spent nuclear fuel as a result of alpha recoil damage, using the U.S. Nuclear Regulatory Commission (NRC) Total-system Performance Assessment (TPA) model for the potential repository at Yucca Mountain. Time-dependent augmentation of the ingrown component is simulated by increasing the initial parent inventory; we have used a factor of five increase, based on natural system observations. For 237Np, the magnitude of preferential release is subject to solubility limits. Stochastic TPA runs show a significant effect on modeled dose of preferential 237Np release, but low impact from the other four radionuclides. The mechanism could be ineffective if 237Np is incorporated into secondary phases. While our results are exploratory in nature, this approach to modeling decay-related enhancement of release can be applied in other nuclear waste disposal settings.
Application of the TSPA Glass Degradation Model to Non-Conforming Waste Forms
Authors: Ebert W. L. 
Published: April 2011

AbstractAn approach is presented for determining if the models used to calculate the release of radionuclides from defense high-level radioactive waste (HLW) glass for total system performance assessment (TSPA) calculations can be used to account for the release of radionuclides from waste forms other than standard borosilicate glasses. The fractional release rates of radionuclides due to waste form degradation, the available surface area, and the radionuclide inventory in an alternative waste form can be compared with the corresponding models used in TSPA for HLW glasses to determine if those models adequately represent the waste form. This approach is demonstrated for the ceramic and metallic waste forms developed for electrometallurgically treated spent sodium-bonded nuclear fuel. Depending on the waste form, comparisons made with aspects of the HLW glass model may be based on similarities in degradation mechanisms or purely empirical.
Modelling of the Dounreay Recovered Spent Nuclear Fuel Database
Authors: Baikie I.D. , Dennis Frank , Scirea Massimo , Crawford Ron 
Published: April 2011

AbstractWe report the initial results of modelling studies performed on the Dounreay Database of Spent Nuclear fuel particles recovered from the marine environment and coastal foreshore adjacent to the Dounreay Fast Reactor Complex located in the North East coast of Scotland. We demonstrate how interrogation of the fuel-particle frequency versus 137Cs isotopic distribution allows us to generate particle behaviour models and residence lifetimes of various particle subgroups. Similarly we find the recovered fuel particle's spatial distribution and shape characteristics are determined by environmental selection rules governed by properties of adjacent sediment and sediment transport mechanisms.Analysis of the Spent Fuel particle database allows us to speculate on the original Site discharge pathways and fuel composition at the time of discharge. Further such studies correlate well with other sample morphology and compositional data and allow us to speculate upon the ultimate fate of different spent fuel types.
Influence of the Near-Field Conditions on the Mobile Concentrations of Np and Tc Leached from Vitrified HLW
Authors: Pirlet Véra , Lemmens Karel , Iseghem Pierre Van 
Published: April 2011

AbstractThe solubility values usually used in Belgium for Performance Assessment of the disposal of HLW in deep geological formations are based on migration experiments in the far-field and, thus, can be considered as "far-field solubilities". The particular chemistry in the near-field of the repository will also influence the solubility of the released radionuclides. Therefore, the determination of maximum concentrations of the radionuclides in the near-field is also useful. This was approached by leach tests with doped glass in near-field conditions. The experiment consisted of static leach tests with the french R7T7 reference glass doped with 237Np (0.34 wt%) and 99Tc (0.12 wt%), two key radionuclides in the performance assessment of the disposal system. The glass was put in contact with FoCa7-clay together with pyrite, metallic iron and Boom clay water to simulate the near-field conditions under reducing conditions. The interpretation of the results is based on the measurement of the steady-state Np and Tc concentrations in the leachates after ultrafiltration through 100,000 MWCO membranes and on the activity measured on the clay after different test durations. Most of the Np and Tc activity (99.5%) was found associated to the clay and increasing as a function of time while the Np and Tc concentration in the leachates were stable and extremely low with a mean value of 1.5×10−10M for Np and 5.6×10−10M for Tc. This is due at least partially to sorption on the clay, but there are indications for precipitation as well.
Field-Scale Migration of99Tc and129I at the Nevada Test Site
Authors: Hu Qinhong , Smith David K. 
Published: April 2011

AbstractThe groundwater at the Nevada Test Site (NTS) contains many long-lived radionuclides, including99Tc (technetium) and129I (iodine), as a result of 828 underground nuclear weapons tests conducted between 1951 and 1992. We synthesized a body of data collected on the distribution of99Tc and129I in groundwater to assess their migration at NTS, at field scales over distances of hundreds of meters and for durations up to forty years and under hydrogeologic conditions very similar to the proposed geological repository at Yucca Mountain. The results of our study show that Tc does not necessarily exist as a mobile and conservative species TcO4−, as has been commonly assumed. This conclusion is corroborated by recent in situ redox potential measurements, which show that groundwaters at multiple locations of the NTS are not oxidizing, and mobility of reduced Tc species (TcO2·nH2O) is greatly decreased. Speciation of iodine and its associated reactivity is also complex in the groundwater at the NTS, and its effect on the mobility of iodine should be the subject of future studies.
Distributions of Concentration Limits for the Source Term in Performance Assessments
Authors: Murphy William M. , Soldavini Steve , Gallagher Colin M. 
Published: April 2011

AbstractRadionuclide concentration limits are important parameters in performance assessments for geologic disposal of nuclear waste, but their statistical distributions are challenging to define. Thermodynamic solubilities provide an attractive theoretical constraint, but solubilities do not provide a basis for distribution functions, and concentration limits can exceed solubilities in irreversible systems. Distributions of natural concentrations are broad and do not correspond to distributions of concentration limits. Interpretations of natural nickel and lead concentrations suggest that they do not represent concentration limit distributions. Interpretation of groundwater data for dissolved calcium indicates a bimodal distribution, which hypothetically corresponds to a solubility-limited population and a population of values below the solubility limits.
HTO Diffusion in Oxfordian Limestone and Callovo-Oxfordian Argillite Formations
Authors: Descostes M. , Blin V. , Grenut B. , Meier P. , Tevissen E. 
Published: April 2011

AbstractDiffusion coefficients and accessible porosities for HTO were measured on 30 samples from the Andra Underground Rock Laboratory in Meuse/Haute-Marne (France) using the through diffusion technique. Two distinct geological formations were studied: Oxfordian limestone and Callovo-oxfordian argillite between 166 and 477 m depth. The experiences were carried out with synthetic pore-water from each formation. The measured values of the effective diffusion coefficients (De) are ranging from 2.6× 10-12 to 12.4 × 10-11 m2 s-1 while accessible porosities (ε) are between 2.4 and 24%. Good correlations are found between these two parameters.
Experimental study of colloid interactions with rock surfaces
Authors: Alonso U. , Missana T. , Patelli A. , Ravagnan J. , Rigato V. 
Published: April 2011

AbstractIn subsurface environments, colloids may play a role in the transport of contaminants to the biosphere because of their high capacity to adsorb them. The electrostatic interactions between colloids and the heterogeneous rock surfaces will determine the fate and transport of both colloids and contaminants adsorbed on the particles. Thus, the aim of the present work was to study the electrostatic interactions between colloidal particles and a crystalline rock surface. Since different minerals are expected to act as preferential reactive areas, the spatial distribution of colloids on the mineral surfaces was studied, accounting several conditions, by means of the nuclear ion beam technique μ-Particle Induced X-ray Emission (μPIXE).
Behavior of UO2 in the RBMK-1000 Spent Fuel under Oxidizing Conditions
Authors: Kolyadin A. B. , Mishin V. Ya. , Mishin K. Ya. , Aloy A. S. , Koltsova T. I. 
Published: April 2011

AbstractThe oxidation of UO2–type spent nuclear fuel (SNF) in gaseousmedia was studied at different temperatures and oxygen contents using gravimetric and powder X-ray diffraction (XRD) techniques. The aim of the study was to determine the mechanism(s) of thermal-oxidation alteration of SNF during long-term dry storage. The samples used in the experiments were chips of RBMK-1000 fuel rods.Oxidation of UO2with a mean burn-up of 10.7 and 19.73 MW d/kg in humid air was observed at a temperature as low as 150°C. At 200°C nearly all of the UO2was transformed into U3O8 between 3500-4000 hours. In a humid nitrogen environment containing of 0.05-1.3 vol. % oxygen at 300°C, the UO2 completely transformed to U3O8 between 2500-3000 hours. Oxidation of UO2in samples with small amounts of jacket damage (e.g., <0.04 MM2)ll progresses more slowly and after â3000 hours the oxygen-to-uranium ratio was 2.56.Stabilization of the oxidation process was not observed in the fuel samples upto an O/U ratio of 2.4, which may be attributed to the smallburn-up of the fuel under investigation.