bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physical and Electrical Properties of Polycrystalline Silicon Thin Films
Authors: Saraswat Krishna C. 
Published: March 2011

ABSTRACTPhysical and electrical properties of chemically-vapordeposited polycrystalline silicon films have been investigated. Effects of deposition parameters, doping, and high temperature processing on grain size and orientation, carrier concentration, carrier mobility and electrical resistivity, have been studied. By relating the physical and electrical properties to each other it has been shown that electrical conduction is controlled by dopant segregation, carrier tunneling, and trapping at grain boundaries. Models for these three mechanisms have been developed and by combining them a generalized model for electrical conduction has been developed. Presence of grain boundaries has also been shown to strongly influence the thermal oxidation and dopant diffusion in polycrystalline silicon.
Electron Microscopy Study of the Structure of the £ =9, 11 Symmetrical Tilt Grain Boundaries in Germanium
Authors: Papon Anne-Marie , Petit Maurice , Silvestre Georges , Bacmann Jean-Jacques 
Published: March 2011

ABSTRACTThe structure of the £=9 and £=11 tilt grain boundaries about [011] axis is studied by means of complementary electron microscopy techniques. Using α'fringes it is shown that the £=1l boundary translations amount to a large expansion and that the £ =9 is little dilated while the translation along [411] is not accessible. The diffraction technique yields the missing result : there is no translation along [411] : the boundary periodicity is not in both cases that of the coincidence site lattice. A supplementary symmetry occurs in the £ =9 boundary which leads to a shortest periodicity. The observations are consistent with the model of five- and seven-fold rings describing the £ =9 boundary. A model, without dangling bond, which consists in a combination of the £ =9 and £ =3 (coherent twin) patterns, is proposed for the £ =ll boundary.
The Structure of Dislocations in Low-Angle Grain Boundaries in the Diamond Cubic Lattice
Authors: Carter C.B. 
Published: March 2011

ABSTRACTDislocations in low-angle tilt boundaries exhibit a wide variety of Burgers vector including a/2<112> a<001> and a<111>. The dislocations are usually dissociated: Shohkley, stair-rod and Frank partial dislocations may each be formed together with associated intrinsic and extrinsic stackingfaults. Dislocations in low-angle {111} twist boundaries are usually assumed to dissociated by a glide mechanism to give two types of extended nodes, known as P–type and K–type, which contain intrinsic and extrinsic stacking-faults respectively. It is shown that dissociation by climb actually occurs for both types of grain boundary.
Varistor Properties of (Nb,Ba)-Doped TiO2
Authors: Yan M. F. , Rhodes W. W. 
Published: March 2011

ABSTRACTA new varistor based on TiO2 ceramic was developed. TiO2 ceramics with the dopant ranges of 0 < Nb < 2% and 0 < Ba < 2% were prepared and their electrical properties were measured. In these dopant ranges, several compositions were discovered to have useful varistor properties with a voltagecurrent nonlinearity index of α > 3. It was found that Ba dopant which segregates at grain boundaries and an oxidizing atmosphere during cooling are necessary to produce varistor properties in (Nb,Ba)-doped TiO2. Nb was introduced to decrease the TiO2 lattice resistivity to a range useful for device applications. Resistivity data were measured as functions of dopant composition and sintering atmospheres. Data were analyzed in terms of the defect structure in TiO2.
Effects of Surface Layer Defects and Adsorbed Oxygen on TiO2-Rutile Schottky Barriers
Authors: Levinson M. 
Published: March 2011

ABSTRACTThe electronic properties of TiO2 surfaces are of interest to further understanding of grain boundary effects in TiO2 and ZnO based varistor devices. Schottky barriers have been fabricated by Au or Al metallization on Nb doped TiO2-rutile [001] single crystal surfaces. Surface conditions included the presence or absence of either mechanical polishing induced surface defects and/or adsorbed oxygen. I­V measurements on Au samples indicate that surface defects yield ohmic behavior, but the defects may be electrically compensated by adsorbed oxygen to give non-ohmic I­V curves. All Al junctions show ohmic behavior which is interpreted in terms of reaction with surface oxygen. These results explain the necessity of firing varistor materials in an oxidizing atmosphere and suggest that the role of additives in these materials is to stabilize the oxygen concentration at the grain boundaries.
Structure Of Twin Boundaries In Silicon
Authors: Fontaine C. , Smith D.A. 
Published: March 2011

ABSTRACTGrain boundaries exert a profound influence on the electrical behavior of semiconductors. First order twin boundaries are the simplest and most common interfaces which occur in polysilicon. We have studied the dislocation structure and preferred boundary plane orientation of such twins by transmission electron microscopy. In addition, we have investigated the atomic structure of twin boundaries on {111} and {112} planes using an interference technique which permits the relative position of two lattices to be determined with a precision of about 0.05Å. Knowing the relative orientation and position of two crystals, together with the interface plane, permits the atomic configuration at the interface to be inferred. We find that the interface structure is surprisingly complex and that more than one atomic configuration is possible for a given grain orientation and interface plane. It is therefore not unexpected that even twin boundaries can show variations in electrical properties.
Effect of Doping and Oxidation on Grain Growth in Polysilicon
Authors: Smith David A. , Tan T.Y. 
Published: March 2011

ABSTRACTWe have studied the influence of doping and oxidation on grain growth of small grain polysilicon. Intrinsic and phosphorus doped (to 1021 /cc pseudo-amorphous layers of Si were prepared by chemical vapor decomposition of SiH4 at 600°C on thermally grown SiO2 on Si wafers. These samples were then annealed in N2 or O2 ambients at 1000°C for 30 minutes. Transmission electron microscopy examination of the samples revealed that grain boundary dislocations were commonly present at high angle boundaries and that there was a remarkable disparity in mean grain size, d, for the different samples. It was found that d was greater for (a) doped poly than intrinsic poly annealed in either N2 or O2, and (b) for the same polysilicon starting materials (doped or undoped) annealed in O2 than in N2. We propose that these phenomena may be explained by the influences of dopant and point defects on grain boundary dislocation mobility which in turn governs grain boundary migration. An atomistic model of grain boundary migration has been developed. A key aspect of the model is the formation and motion of jogs and kinks on grain boundary dislocations. These processes are directly influenced by the behavior of point defects in the material and its electronic properties.
An Assessment of the Long-Term Durability of Concrete in Radioactive Waste Repositories
Authors: Atkinson A. , Goult D. J. , Hearne J. A. 
Published: March 2011

AbstractA preliminary assessment of the long-term durability of concrete in a repository sited in clay is presented. The assessment is based on recorded experience of concrete structures and both field and laboratory studies. It is also supported by results of the examination of a concrete sample which had been buried in clay for 43 years.The enoineering lifetime of a 1 m thick reinforced concrete slab, with one face in contact with clay, and the way in which pH in the repository as a whole is likely to vary with time have both been estimated from available data. The estimates indicate that engineering lifetimes of about 103 years are expected (providing that sulphate resisting cement is used) and that pH is likely to remain above 10.5 for about 106 years.
The Extended Defect as a Mechanism for the Immobilization of HLW Species in Zirconolite, Perovskite and Hollandite
Authors: White T. J. 
Published: March 2011

AbstractHigh resolution electron microscopy, analytical electron microscopy and selected area electron diffraction are used to establish the crystallochemical mechanisms by which simulated high level waste enters Synroc. It is shown that waste species are incorporated largely as a non-continuous solid solution. In other words, simple isomorphic substitution of waste elements in place of matrix cations, i.e. the classical continuous solid solution, does not operate (or is only significant at very low waste levels of radwaste). Usually, substitution is accompanied by the appearance of coherent extended defects which can take the form of antiphase boundaries, unit cell twinning (both mimetic and polysynthetic), or cation ordering. In this manner, a numb~er of closely related phases appear in response to variations in waste composition and loading. It is believed that the mechanism of structural modification will endow Synroc with considerable flexibility to respond to chemical changes in the wastestream. Other ceramic materials currently being evaluated as possible wasteforms (viz. sphene glass-ceramics and APO4 phosphates), are also likely to possess this capacity.
Dissolution of used Candu Fuel at Various Temperatures and Redox Conditions
Authors: Stroes-Gascoyne S. , Johnson L. H. , Beeley P. A. , Sellinger D. M. 
Published: March 2011

AbstractSamples of used UO2 fuel exposed to air-saturated water at 25°C for eight years have been examined using electron microscopy and X-ray diffraction techniques. The results, in conjunction with solution analysis uata, show evidence for a UO3.2H2O precipitate on the fuel surface, and confirm the importance of grain-boundary leaching in controlling Cs-137 release. Studies of useo-fuel dissolution under both oxidizing and reducing conditions at 150°C show significantly lower radionuclide release to solution for reducing conditions, illustrating the potential importance of reoox chemistry in determining the long-term stability of used fuel after disposal.
Review of Progress in the Development of Sphene-Based Glass-Ceramics
Authors: Hayward P. J. 
Published: March 2011

AbstractSince 1980, considerable research has been invested in the development of sphene-based glass-ceramics as hosts for possible future CANDU™ fuel recycle wastes. This paper reviews the fabrication of the glass-ceramics, their detailed microstructure, the partitioning of waste ions between the glassy and crystalline phases, and their resistance to leaching in deionized water and synthetic brines.
Corrosion Behavior of Nodular Cast Iron Casks for Low and Intermediate Level Wastes
Authors: Hauser W. , Köster R. 
Published: March 2011

AbstractIn applying new conditioning methods dehydrated wastes (e.g. concentrates, ion exchange resins) from operation of nuclear power plants and wastes from decommissioning (e.g. highly-activated core components) are conditioned using high integrity nodular cast iron casks without further solidification. Therefore more stringent requirements have to be made for the packaging material. The objective of the investigations was to evaluate the corrosion resistance of the cask material. For this purpose chemical corrosion tests were made applying corrosion media actually considered or postulated in accident scenarios during interim storage or after disposal in the abandoned iron ore mine Konrad or in a salt formation. The conclusion from the corrosion experiments, which have been performed up to now for the basic packaging material, indicates that nodular cast iron casks with wall thicknesses about 200 mm seem to ensure good protection for wastes especially from nuclear power plants with relatively short-lived radionuclides.
Metallographical Study of Hot Isostatically Pressed Copper Encapsulation of Nuclear Fuel Elements
Authors: Loberg B. , Easterling K. E. 
Published: March 2011

AbstractLight optical and electron microscopy have been used to study both laboratory-scale and full scale hot isostatically pressed (HIPed) copper as employed for encapsulation of spent nuclear fuel elements. Particular attention has been paid to the degree of densification achieved, as well as to the status of the joins between the sleeve, lid and the HIPed powder. The work includes the development of computing models for predicting the optimal conditions for HIPing copper and other possible encapsulation materials such as lead and alumina. Mechanical testing of HIPed samples has also been carried out.The current method of using hydrogen to reduce oxides at powder surfaces prior to HIPing is questioned on the basis that metallography reveals definite signs of hydrogen embrittlement. An alternative method of reduction is to use CO/CO2 mixtures instead of hydrogen, and it is suggested that this approach could be strongly advantageous in future.
The Development of Durable Cementitious Materials for Use in a Nuclear Fuel Waste Disposal Facility
Authors: Burnett N. C. , Hooton R. D. , Heimann R. B. , Onofrei M. 
Published: March 2011

AbstractThis paper describes the work on cement paste development and short-term leaching tests in Standard Canadian Shield Saline Solution (SCSSS) in the presence of bentonite at 150°C. It has been found that:-supplementary cementing materials such as silica fume or fly ash could significantly improve the properties of sulphate resistant portland cement (SRPC), in particular, permeability to water and pore size distribution.-the addition of bentonite suppressed the normal tendency of the pH of groundwater to increase rapidly in the presence of cement.-the presence of bentonite increased the release of potassium ions from the cements.-– SRPC blended with 20% silica fume resulted in a groundwater pH lower than that of SRPC, with and without bentonite. Moreover, its cumulative fraction of release of potassium was significantly lower than that of SRPC.
Optimization of Concrete Container Composition in Radioactive Waste Management
Authors: Plecas I. B. , Mihajlovic Li. L. , Kostadinovic A. M. 
Published: March 2011

AbstractIn this paper an optimization of concrete container composition, used for storing low and intermediate level radioactive waste from nuclear power plants in Yugoslavia, is presented.Mechanical properties 37−52 MPa, permeability 1.07. 10−13 - 1.50. 10−11cm2 and leakage rate 3.66. 10−6 - 1.77. 10−4 cm/d for concrete made of commercial materials, were tested.
The Corrosion of Steel and Zirconium in Anaerobic Concrete
Authors: Hansson Carolyn M. 
Published: March 2011

AbstractAn experimental investigation has been made of the corrosion behaviour of steel and Zircalloy 2 in deaerated synthetic pore solution and of steel in deaerated mortar. Zircalloy 2 was found to be passivated at all values of pH and electrochemical potentials investigated. Its passive corrosion rate was of the order of <0.01 μm/year. The steel exhibited active corrosion rates of a few μm/year with hydrogen evolution as the corresponding cathodic reaction. The measured free potentials indicated, however, that the hydrogen partial pressures were less than 1 atm.
ESCA Investigation of the Reaction Products Formed on Titanium Exposed to Water Saturated Bentonite Clay
Authors: Mattsson Håkan , Olefjord Ingemar 
Published: March 2011

AbstractTitanium is one of the materials proposed in the Swedish programme for the final containment of spent nuclear fuel. In the present investigation, the final repository environment was simulated on the laboratory scale by embedding titanium and a Ti-Pd alloy in dense, water-saturated bentonite clay. The temperature was 95°C and the exposures lasted between 4 months and 2 years. Analysis was performed using ESCA combined with ion etching.The reaction products formed on the surface consists of TiO2 Montmorillonite - the main constituent of bentonite - is incorporated in the oxide. Suboxides exist near the oxide/metal interface.The oxide thickness is in the range 70–100 Å. The oxide growth between 4 months and 2 years is small. No significant influence of Pd could be noted. If it is assumed, that the oxide growth follows a logarithmic law, the expression giving the thickest oxide is y = 5.5 In t (where y is the oxide thickness (Å) and t is the exposure time (s)).
The “Source Term” for Safety Assessments of the Disposal of Vitrified High-Level Radioactive Waste
Authors: Hough A. , Marples J. A. C. , Handyside I. 
Published: March 2011

AbstractTwo series of experiments have been carried out In an attempt to derive a source term for the release of some radioisotopes from vitrified high-level waste after disposal In hard rock. In the first type of experiment, the repository was modelled In miniature and the release of the isotopes was measured after they had leached from the glass and diffused through the backfill. In the second type. the “solubilities” of the isotopes were measured In the presence of the constituents of the repository.
Americium Speciation and Distribution Coefficients in a Granitic Ground Water
Authors: Beall Gary W. , Lee William W.-L. , Van Luik Abraham E. 
Published: March 2011

AbstractWe call attention to the possible importance of pH-dependent speciation in determining the distribution coefficient of americium in a granitic ground water. We obtained experimental distribution coefficients for americium. We used the geochemical code PHREEQE to calculate the amount present of americium complexes with hydroxides and carbonates over a range of pH, using formation constants taken from the literature and one estimated for AmOHCO3, a neutral complex suspected of playing an important role in the aqueous chemistry of americium, although not experimentally evaluated. Combining the above inputs, we calculated individual distribution coefficients for americium complexes. We are able to show that the batch distribution coefficient for americium can be seen as the sum of individual distribution coefficients of various complexes.
Humic Substances in Ground Waters
Authors: Paxéus N. , Allard B. , Olofsson U. , Bengtsson M. 
Published: March 2011

AbstractThe humic materials isolated from ground waters of a borehole in Fjällveden (Sweden) were characterized by elemental and functional group analyses. Spectroscopic properties, molecular weight distributions as well as acid-base properties of the fulvic and humic fractions were also studied. The ground water humic substances were found to be quite similar in many respects (but not identical) to the Swedish surface water humics concentrated from the Gτ(b, A)öta River but appeared to be quite different from the American ground water humics from Biscayne Florida Aquifer or Laramie Fox-Hills in Colorado. The physico-chemical properties of the isolated humic materials are discussed.
A Review of Progress in the Canadian Nuclear Fuel Waste Management Program
Authors: Lyon R. B. , Johnson L. H. 
Published: March 2011

AbstractThe Canadian Nuclear Fuel Waste Management Program is reviewed, illustrating the progress that has been made in assessing the concept of disposal of nuclear fuel waste in plutonic rock of the Canadian Shield. Research is being conducted into used fuel storage and transportation, fuel waste immobilization, site characterization and selection methods, and performance assessment modelling. Details of achievements in these areas are outlined, and results of the most recent interim assessment are discussed.
Natural, Thermal and Radiolytical Gas Liberation in Rock Salt as a Result of Disposed High-Level Radioactive Waste
Authors: Jockwer Norbert , Gross Sabine 
Published: March 2011

AbstractRock salt contains crystal water of the hydrated minerals, water in the form of brine inclusions or adsorbed to the crystal boundaries, as well as primary gases. Further gases are produced or liberated due to the disposed high-level, heat producing wastes resulting from the thermal and radiolytic decomposition of the main and secondary constituents.All volatile components which are present in a final repository have an influence on the disposal horizon, promote the spreading of possibly liberated radionuclides, increase corrosion of the containment and may lead to a pressure increase in a disposal borehole. Therefore a qualita-tive and quantitative determination of the components which could be lib-erated from the rock salt as a result of the disposal of high-level wastes is of significance for a final repository.
Radionuclide Transport Modelling in Fissured Zones and Channels
Authors: Rasmuson Anders , Neretnieks Ivars 
Published: March 2011

AbstractRadionuclides escaping from a repository for high level nuclear waste in crystalline rock may eventually be carried by the flowing water in fissure zones. In such zones the rock is broken in blocks of varying sizes and shapes. Also, the water velocity may vary very much along the flow path. The integrated finite difference method (IFDM) is proposed for numerical calculations of radionuclide transport in such zones. A method for lumping blocks of various sizes and shapes into a single PSEUDOBODY is tested by comparing it with an exact analytical solution which can account for the diffusion into blocks of any size distribution. The errors obtained in using the PSEUDOBODY-approach are found to be small. Furthermore, a method for determining an “average” Peclet number in a strongly varying velocity field is tested and found to give comparatively small errors.
Experimentation and Modelling of U, Th and Lanthanides Transport in Fissured Rocks: Influence of Complexation
Authors: Toulhoat Pierre 
Published: March 2011

AbstractThree circulation experiments have been carried out between two drill-holes in a granite after hydraulic fracturation (Le Mayet de Montagne, France). We have injected together uranyl carbonate and Th, La, Sm, Eu, Dy and Yb EDTA complexes. Amounts of tracers were different in each run. Recovery curves are similar for Th and lanthanides, but have a delayed peak and an increased tailing for uranium. For rare earth elements, recovery rates increase with increasing stability of the complex used as tracer. Recovery rates increase also with increasing amount of tracer. Those features are explained by non linear and non reversible sorption. The importance of complexation is demonstrated. Strong organic complexing agents enhance trace elements mobility.
Development of the Code Melodie for Long Term Risk Assessment of Nuclear Waste Repositories
Authors: Goblet P. , Guetat P. , Lewi J. , Mangin J-P , Marsily G. De , Raimbault P. 
Published: March 2011

AbstractMELODIE is a computer code developed at the CEA/IPSN for risk assessment of nuclear waste repositories in geological formations. The interactive evolution of the source, geosphere and biosphere is studied for periods of time longer than 100 000 years. In its first version, the code can describe a repository in granite rock located at a specific site.The code is built in a modular form which allows to use different versions of the sub-system models.The basic model for radionuclide migration and hydrpgeology is a subroutine version of the METIS code developed by ENSMP. METIS is a 2D finite element code which solves the advection-dispersion equation for porous media with explicit fracture representation. Linear adsorption kinetics is included as well as matrix diffusion and radionuclide decay chains.The source model developed at CEA/DRDD**** is derived from CONDIMENT which is a 1D finite difference code describing the behaviour of high level waste packages. Four axisymetric layers are individualized: glass matrix, container, bentonite and granite. The glass leaching is modelled as a dissolution and diffusion process of the individual chemical components.The biosphere model ABRICOT developed at the CEA/DPT** is based on a detailed description of agricultural activities defined in individual systems.MELODIE is tested by participation to international exercices such as Pagis [1], Intracoin [2] and Hydrocoin [3]. Future developments will include introduction of scenarios constructed from geoprospective studies and algorithms for sensitivity studies.