bluuebunny/crossref_metadata_2025 huggingface dataset:
Photo—Conductive Amorphous Silicon Carbide Prepared by Intermediate Species SiF2 and Cf4 Mixture
Authors: Matsumura Hideki , Uesugi Takashi , Ihara Hisanori
Published: March 2011

A new type of hydro—fluorinated amorphous silicon—carbide (a-SiC:F:H) is produced by the glow discharge decomposition of gas mixture of CF4, H2 and intermediate species SiF2. The electrical, optical and structural properties of this a—SiC:F:H are studied and the results are compared with the similar results for a—SiC:F:H produced from gas mixture of CH4, H2 and SiF2 and also for hydrogenated amorphous silicon carbide (a—SiC:H) produced from CH4 and SiH4 gas mixture. It is found that the optical band gap can be increased without degradation of photo—conductive properties only when amorphous silicon carbide is produced from CF4, H2 and SiF2 gas mixture.
Recent Progress of Amorphous Silicon Solar Cell Technology
Authors: Hamakawa Y.
Published: March 2011

A review is given on recent progress in the amorphous silicon solar cells and their technologies. Firstly, some unique advantages of amorphous silicon as a low cost solar cell material are pointed out, and its significant position in the photovoltaic project are discussed. Secondly, newly developed key technologies for improving the photovoltaic performance are demonstrated from the film quality improvement to new junction structure solar cells with a wide and narrow energy gap amorphous silicon alloys. Then, current state of the art in the cell performance are summarized. In the final part, recent feature of the industrializations in both consumer and power application fields are overviewed.
Dual-Chamber Plasma Deposition of a-Si:H Solar Cells at High Rates Using Disilane
Authors: Rajeswaran G. , Vanier P.E. , Corderman R.R. , Kampas F.J.
Published: March 2011

The use of a separated chamber deposition system for the fabrication of a-Si:H solar cells from disilane at high deposition rates results in a substantial improvement in short circuit current compared to that obtained from a single-chamber system. The spectral responses of cells fabricated in the dual-chamber mode are compared to those made in the single-chamber mode. The results are interpreted by assuming that the rate of removal of boron contaminants from the chamber is independent of deposition rate.
Research Progress in the Doe/Seri Amorphous Silicon Research Project
Authors: Sabisky E. , Wallace W. , Stafford B. , Sadlon K. , Luft W.
Published: March 2011

The Amorphous Silicon Research Project (ASRP), established at the Solar Energy Research Institute (SERI) in 1983, is responsible for all U.S. DOE government supported research activities in the field of amorphous silicon photovoltaics. The objectives and research directions of the project have been established by a Five Year Research Plan developed at SERI in cooperation with the Department of Energy in 1984. In order to accomplish project goals, research is performed by a combination of i) multi-year programs consisting of multi-disciplinary research teams based on strong government/industry partnerships and ii) basic research performed in university, government and industrial laboratories. A summary of recent research progress in the ASRP program is presented.
Tunneling Contributions to NiP and Pin Hydrogenated Amorphous Silicon Devices
Authors: McMahon T.J. , Madan A.
Published: March 2011

It is well known that the performance of hydrogenated amorphous silicon (a-Si) p-i-n type devices is determined by the sequence of deposition. For instance, the stainless steel/p-i-n configuration generally shows a larger value of the open circuit voltage (up to 200mV) compared to the n-i-p sequence of deposition \1,2]. Explanations of this phenomena such as the Dember potential \1], self field effect \2], residual doping \3], hydrogen effusion effects associated with the p+ layer deposition process \4, 5] are unable to satisfactorily explain the difference in performance.
Reversible, Light Induced Changes in a-Si:H Films and Solar Cells
Authors: Wronski C. R.
Published: March 2011

Continuous progress is being made in the conversion efficiencies of a- Si:H solar cells and efficiencies in excess of 11% have been achieved. Because of these advances and the development of a-Si:H cell technologies there is an increased interest in the long term performance of a-Si:H cells and the mechanisms responsible for their degradation. The reversible light-induced changes in a-Si:H solar cells are generally associated with the Staebler-Wronski effect (SWE) (1). This effect has been studied on a wide range of a-Si:H materials using a variety of different experimental techniques and this talk reviews the results that have been obtained on a- Si:H films and solar cells (2). It discusses in greater detail recent studies on a-Si:H solar cell structures in which simultanous measurements have been made on the changes in both the photovoltaic properties as well as their electronic properties and densities of gap states. In particular it focuses on several results obtained with semitransparent metal-undoped a-Si:H Schottky barrier solar cell structures (3).
Thermodynamic Study of Silane-hydrogen Chemical System
Authors: Patel Rajendra I.
Published: March 2011

The thermodynamic calculations of chemical equilibrium compositions of various species were performed for silane-hydrogen system at different temperatUres [500-6000K], pressures [0.01-10 Torr], and mixing ratios [various silane fractions]. The effect of dopant impurities such as diborane and phosphine on equilibrium concentration profiles of various gaseous, tonic, and condensed species was also investigated. These data will be very useful in understanding the deposition chemistry of silane chemical systems and will be a valuable aid in optimization studies.
Capacitance Studies of Light-Induced Effects in Undoped Hydrogenated Amorphous Silicon
Authors: Zellama K. , Cohen J.D. , Harbison J.P.
Published: March 2011

The effects of light saturation on the properties of undoped a-Si:H films were studied by a new capacitance profiling technique which can be used to directly determine changes in the dangling bond density of states near midgap. Coplanar conductivity and capacitance vs. temperature measurements save the changes in activation energies for electrical conductivity. These studies indicate that, while substantial increases in the dangling bond densities are observed for most samples, the detailed behavior of the light induced changes in these films are inconsistent with the creation of such defects by breaking weak valence band tail states.
Amorphous Silicon Films and Solar Cells Prepared by Mercury-Sensitized Photo-CVD of Silane and Disilane
Authors: Delahoy Alan E. , Doele B. , Ellis F.B. , Ramaprasad K.R. , Tonon T. , Dine J. Van
Published: March 2011

The low temperature deposition of a-Si:H films and devices by mercurysensitized photo-decomposition of silanes is described. The problem of window deposition is ameliorated by the use of a perfluoropolyether coating to give deposition rates of 0.3 Å s−1. Highly photosensitive undoped layers can be produced. These films exhibit many properties in common with glow discharge films including thermal quenching of photoconductivity between 125-200°K and the Staebler-Wronski effect. A wide gap silicon carbide p layer is described, and is usefully employed in p-i-n structures to give 6% efficient solar cells. SIMS analysis of these devices shows that it is possible to achieve sharp p-i interfaces in a single chamber reactor. Deposition rates greater than 2 As−1 have recently been achieved.
Short Channel Amorphous Silicon MOS Structures with Reduced Capacitance
Authors: Yaniv Z. , Cannella V. , Hansell G. , Vijan M.
Published: March 2011

We report improvements in device structures by the reduction of capacitance in short channel length thin film transistors of amorphous silicon alloy materials. Employing techniques similar to those previously reported [1,2], these MOS structures are fabricated with channel lengths of 1 to 2 micrometers using standard photolithography with 10 micrometer minimum feature size. Significant reductions in capacitance over earlier reported device designs were achieved by improvements in device geometry and innovative use of shadowing techniques utilizing oblique angle deposition to minimize overlap between electrodes. Theses reduced capacitance short channel length TFTs enhance the possibility of fabricating on-board drivers for active matrix liquid crystal displays using amorphous silicon alloy devices. Despite the relatively low mobility of amorphous silicon (∼ 1 cm2 /V-sec) these short channel length TFTs can provide currents large enough for operation in the megahertz regime when these reductions in capacitance are incorporated. The noncritical photolithography assures that devices may be fabricated over large area substrates (8" × 8") with acceptable yields. Computer simulations predict that these TFTs will be able to provide the necessary speed for on-substrate drivers. We will present experimental results from the new TFT structures and describe modeling methods and results for amorphous silicon TFT ring oscillators. We will discuss the significance of these results as they pertain to drive circuitry for large area liquid crystal displays.
A High-Speed Amorphous-Silicon Dytamic Circuit
Authors: Okada H. , Nara Y. , Uchida Y. , Watanabe Y. , Matsumura M.
Published: March 2011

A novel dynamic circuit composed of amorphous-silicon Schottkybarrier diodes and field-effect transistors has been proposed. The circuit response time is as short as the discharging time of a load capacitor through the driver transistor. The circuit having 1µm-long, self-aligned transistors has been predicted theoretically to be able to be operated at multi-MHz rates. Preliminary experimental results are also presented.
Influence of Transparent Electrodes on Image Sensor Performance
Authors: Kempter K. , Wieczrek H. , Hoheisel M.
Published: March 2011

The short response times required for image sensors demand blocking contacts at the sensor cell. It was found that the junctions between transparent electrodes (ITO or a thin palladium film) and the metallic back electrode with a-Si:H form blocking contacts yielding photocurrent decay times of the order of some microseconds. The two different time regimes observed for the decay are interpreted as being limited by the drift and the release of holes respectively.
The Use of Amorphous Silicon Emitters in Bipolar Transistors
Authors: Ghannam M. , Nijs J. , Keersmaecker R. De , Mertens R.
Published: March 2011

For the first time an operating heterojunction bipolar silicon transistor has been realized with phosphorous doped amorphous silicon (a-Si) emitter. The deposition of a-Si is a relatively simple technique. The current gain (β) of 14 at a base Gummel Number (G.N.) of 1.35 1013 s/cm4 is higher than that obtained with normal diffused emitter bipolar transistors with the same G.N. for the base. This adds a degree of freedom to the design of bipolar structures according to the compromise between base resistance and current gainCrucial points that have to be looked at further are interface recombination at the a-Si/c-Si transition and emitter resistance.
Recombination Under Double Injection Conditions in a-Si:H Based Diodes.
Authors: Konenkamp R. , Madan Arun
Published: March 2011

The junction recovery technique is used to investigate recombination parameters and kinetics in thin film a-Si:H diodes. It is found that double injection occurs in most of the p-i-n type samples at sufficient forward bias and that the recovery currents are dominated by the extraction of trapped holes from the valence bandtail. The mobility-lifetime product of the recovered carriers is seen to be strongly dependent on the dopant concentration in the active layers of the devices.
Steady State and Transient Capacitance Measurements of the Energy Levels of a Low Angle Tilt Boundary in a Germanium Bicrystal
Authors: Broniatowski A. , Bourgoin J.C.
Published: March 2011

Steady state and transient capacitance (DLTS) measurements have been performed on a low angle tilt boundary in a germanium bicrystal, in combination with an electron microscope study of the boundary dislocation structure. A characteristic level has been found at 0.42 eV below the bottom of the conduction band, with a density about 109 cm-2 and an electronic capture cross-section about 5 × 10-12 cm2.
Experimental Study of the Relative Energy of Symmetrical <110> Tilt Boundaries in a Semi-Conducting F.C.C. Oxide (NiO).
Authors: Dhalenne Guy , Dechamps Michel , Revcolevschi Alexandre
Published: March 2011

Large size bicrystalline samples of NiO corresponding to tilt configurations around a < 110 > axis have been grown by the flame fusion technique, the misorientation angles varying from 0 to 180°. The variation of the relative energy of the grain boundary with misorientation has been studied and has indicated a very different behaviour from that previously observed by the authors on <100> tilt boundaries. High relative energy values and deep cusps on the energy curve at high coincidence angles are observed. The results are discussed in terms of interface energy.
Identification of Arsenic Surface Species on the Si (100) Surface
Authors: Perino S. C. , Helms C. R.
Published: March 2011

The molecular character of arsenic adsorbed on the Si (100) surface has been investigated using thermal desorption spectroscopy (TDS) and Auger electron spectroscopy (AES). A variety of arsenic surface species were deposited on the silicon surface by employing different evaporation sources, including metallic arsenic, arsine gas, and chips of GaAs crystals. We present coverage dependent spectra showing the desorption of As4 tetramers at 350°C and As2 dimers at 900°C. The loosely bound arsenic is adsorbed from the solid evaporation sources only and resides on the surface as tetramers. The tightly bound arsenic does not form multiple layers and the high desorption temperatures suggests the adsorbed arsenic exists as monomers.
The Effect of Heat Treatment on Grain Boundary Properties in Cast Polycrystalline Silicon
Authors: Russell P.E. , Herrington C.R. , Burke D.E. , Holloway P.H.
Published: March 2011

The effects of heat treatment at temperatures appropriate for solar cell device fabrication on grain boundaries in cast poicrystalline silicon have been studied. An MIS device structure using a 200° C heating was used for fabricating test devices on heat treated samples for EBIC studies. Grain boundary effective surface recombination velocities (Seffgb ) and effective mid-grain diffusion lengths were measured. Seffgb was found to increase after heat treatment. Segregation of oxygen to grain boundaries has been observed in heat treated samples.
Grain Boundary Shunt Currents Across a pn Junction
Authors: Roy Morrison S.
Published: March 2011

The effect on the diode characteristics when a conducting grain boundary intersects a pn junction is analyzed. The possibilities of conducting grain boundaries are related to the levels associated with precipitates at the grain boundary. The effect of the grain boundary on the diode characteristics is found particularly degrading when donor impurities precipitate in the n region while simultaneously acceptor impurities precipitate in the p region. Both solar cell characteristics and the dark diode characteristics are analyzed.
Chemical and Ion Beam Etch Studies of Polycrystalline Silicon
Authors: Lester P. A. , Singh R. , Rice D.A. , Pangborn R. N. , Ashok S. , Fonash S. J.
Published: March 2011

MS and MIS solar cell performance as a function of wet chemical etching history has been studied and correlated with lattice strain obtained from x-ray double-crystal diffraction technique and intragranular surface topography. Dry ion beam etching from a Kaufman ion source is found to damage the surface and radically alter the electrical barrier by introducing donor-like states in the damaged region.
Grain Boundary Passivation and Analysis for Solar Cell Applications
Authors: Rao V. J. , Anderson W. A. , Kai F.
Published: March 2011

Grain boundaries in Wacker poly-Si are shown to contribute mid-gap interface states, a greater frequency dependence in a.c. conductance, and lesser frequency dependence in capacitance. H-passivation was shown to be effective in reducing grain boundary effects as evidenced by 4-point probe resistance and IR studies.
Physical and Electrical Properties of Polycrystalline Silicon Thin Films
Authors: Saraswat Krishna C.
Published: March 2011

Physical 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

The 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

Dislocations 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

A 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

The 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

Grain 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

We 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.
Results from the Long-Term Interaction and Modeling of SRL-131 Glass with Aqueous Solutions
Authors: Strachan Denis M. , Pederson L. R. , Lokken R. O.
Published: March 2011

During the various processing activities in the production of plutonium for the U.S. national defense programs, waste by-products were generated. These wastes, which have been generated over about the past 40 years at sites such as Savannah River Plant in South Carolina and Hanford in Washington, have been stored in underground tanks. Plans for the final disposal of the Savannah River Plan waste have now been documented [1] and call for the decontaminated soluble fraction of the waste to be mixed with cementitious materials and disposed of in near-surface trenches [2]. The radionuclide fraction of the soluble waste and the insoluble fraction of the waste will be converted to glass and sent to a geologic repository. In order for the repository to accept the glass, certain performance criteria must be met. Although not fully defined, it is certain that these criteria will include some specification on the rate of release of nuclides from the glass waste form when contacted by water.
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

A 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

High 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

Samples 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

Since 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

In 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

Light 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

This 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

In 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

An 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

Titanium 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

Two 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

We 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

The 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.
Laboratory and Modelling Studies of Microbial Activity in the Near Field of a HLW Repository
Authors: West Julia M , McKinley Ian G , Grogan Helen A , Arme Susan C
Published: March 2011

Microbial effects are one of the possible perturbations to the expect-ed performance of a deep geological repository which must be examined as part of a comprehensive safety analysis. Recent literature surveys (eg [1, 2] ) and reconnaisance sampling studies [3, 4] have concluded that: a) microbial contamination of a repository is inevitable b) even for high level nuclear waste, conditions in the near-field are insufficiently extreme to ensure complete sterilisation.
A Review of Progress in the Canadian Nuclear Fuel Waste Management Program
Authors: Lyon R. B. , Johnson L. H.
Published: March 2011

The 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

Rock 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

Radionuclides 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

Three 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

MELODIE 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.
Estimations Of Changes in Microcrack-Population, Elastic Modulus, and Permeability, Due to Differential-Thermal Expansion in Plutonic Rock Surrounding A Nuclear Fuel Waste Disposal Vault
Authors: Wilkins B. J. , Liner Y. , Rigby G. L.
Published: March 2011

Atomic Energy of Canada Limited is studying the disposal of nuclear fuel-waste in a vault in plutonic rock. An important part of this study is to develop models to assess the rate of escape of waste components to the biosphere. In these models time-dependent changes in the system are important. One such change is the increase in temperature of the rock mass immediately surrounding the vault, and in the far-field. Differential- thermal expansion between rock constituents (crystals), and the expansion of trapped water, will produce microcracking and, hence, possibly changes in intact-rock elastic modulus and permeability. This paper describes the model devised to estimate the extent of microcracking in rock surrounding a vault, and the anticipated changes in rock elastic modulus and permeability. The model is applied to a possible vault, located at various depths in plutonic rock typical of the Canadian Shield. It estimates the dimensions of an envelope outside of which the influence of the vault on microcracking will be negligible.
Characteristics of Laser/Energy Beam-Melted Silicon Mechanical Damages
Authors: Lee El-Hang
Published: March 2011

We describe what appears to be a first attempt to melt and recrystallize macroscopic (10-20 μm deep) silicon mechanical damage that is induced from wafer modification such as slicing and lapping. Recrystallized surfaces appear mirror shiny, with significantly improved surface smoothness, as compared to the coarse texture of damaged surfaces. The crystallinity also appears good in general. Through the depth of melt were observed indications of impurity migration, probably caused by accumulated segregation at the advancing solid-liquid interface. Recrystallized surfaces, despite their smoothness, remain topologically uneven as a result of lateral mass transport. In addition, the extensive heat required to melt thick layers of silicon causes slip dislocations.
Time-Resolved Picosecond Optical Study of Laser-Excited Graphite
Authors: Huang C. Y. , Malvezzi A. M. , Liu J. N. , Bloembergen N.
Published: March 2011

The pump-and-probe technique is employed to perform picosecond timeresolved measurements of the reflectivity changes in highly oriented pyrolitic graphite excited by 0.532-μm pump pulses. At low pump fluences, the presence of a short-lived plasma and a high-temperature gradient gives rise to an increase in the reflectivity probed at 1.9 μm but causes a decrease at 1.064 μm. At the threshold fluence, 140 mJ/cm2, the reflectivity drops abruptly, marking a phase transformation. Above the threshold, the reflectivity drops to -0.2 from its original value of 0.42 at 1.064 μm and to -0.4 from its ambient value of 0.50 at 1.9 μm. This new phase persists only for a few nanoseconds.
Transient Conductance Measurements And Heat-Flow Analysis of Pulsed-Laser-Induced Melting of Aluminum Thin Films
Authors: Tsao J. Y. , Picraux S. T. , Peercy P. S. , Thompson Michael O.
Published: March 2011

We report time-resolved electrical-resistance measurements during pulsed-laser melting of a metal, aluminum. The resistances are correlated with the thresholds for partial and full melting. We describe a semianalytic solution, based on an impulse-response function, for the response, to a heating pulse, of a thin film of good thermal conductor supported by an infinite substrate. The results agree well with the resistance measurements, and confirm our interpretation of the data. In addition, time-resolved reflectance measurements establish that, in this geometry, melting and solidification proceed via the motion of a well-defined, planar liquid/solid interface, whose position can be deduced from the resistance measurements. These measurements permit the first real-time determinations of melt-depths and quenching histories during rapid-solidification processing of metals.
The Crystalline-To-Amorphous Phase Transition In Irradiated Silicon
Authors: Seidman D.N. , Averback R.S. , Okamoto P.R. , Baily A.C.
Published: March 2011

The amorphous(a)-to-crystalline (c) phase transition has been studied in electron(e-) and/or ion irradiated silicon (Si). The irradiations were performed in i n the Argonne High Voltage Microscope-Tandem Facility The irradia ion of Si, at <10 K, with 1-MeV e- to a fluence of 14 dpa failed to induce the c-to-a transition. Whereas an irradiation, at <10 K, with 1.0 or 1.5-MeV Kr+ ions induced the c-to-a transition by a fluence of ≈0.37 dpa. Alternatively a dual irradiation, at 10 K, with 1.0-MeV e and 1.0 or 1.5-MeV Kr+ to a Kr+ fluence of 1.5 dpa -- where the ratio of the displacement rates for e- to ions was ≈0.5--resulted in the Si specimen retaining a degree of crystallinity. These results are discussed in terms of the degree of dispersion of point defects in the primary state of radiation damage and the mobilities of point defects.