bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of Icosahedral Al(Mn) by Pulsed Surface Melting
Authors: Follstaedt D. M. , Knapp J. A.
Published: March 2011

Surface melting of alternating Al/Mn layers on Al and Fe substrates by pulsed electron beams and laser is found by TEM to produce icosahedral Al(Mn). Interpreting the observed microstructures in terms of the calculated temperature histories places limits on the melting point of the phase (660 0C < T < 9600C), the time needed for its nucleation from the melt at 6600C (t < 50 ns), and the rate of quenching from thg liquid n needed to suppress formation of the competing T phase (-T > - 1 × 10 K/s).
Fractal Coefficients of An Icosahedral Structure of Quasi-Crystals and Amorphous Alloys
Authors: Levy J.C.S. , Mercier D.
Published: March 2011

Different extended icosahedral structures are obtained from energy minimization and local symmetry Yh. The quasi fractal character of one of these is demonstrated from the quasi algorithm of definition, the gamma density of holes and the measured Hausdorff number ∂. The spectral dimension ∂ is measured and dimensions corresponding to higher derivatives are defined.
The Status and Potential of Rapid Solidification of Magnesium Alloys
Authors: Hehmann F. , Jones H.
Published: March 2011

In spite of giving exceptionally low density and excellent machinability at relatively low cost, magnesium alloys have found only restricted application as engineering materials to date because of limitations in formability, corrosion resistance, strength and creep resistance. Although the very earliest work on record to employ rapid solidification as a means to enhance engineering properties was carried out on magnesium-base alloys, subsequent work employing more modern techniques has not, until very recently, been motivated by the need for alloy development. The present study combines a critical survey of relevant published work with an assessment of the potential of magnesium-base alloys for development by the rapid solidification route.
Mechanical Properties of Rapidly Solidified MG-ZN Alloys
Authors: Themines D. , Riehemann W. , Henning W. , Mordike B.L.
Published: March 2011

Rapidly quenched alloys differ from those that are conventionally solidified in the degree of supersaturation, the microstructure and the grain size. The quenching rate can thus be used to modify the mechanical properties. A fine grain size increases the hardness and ductility. The precipitation behaviour is modified by the high density of heterogeneous nuclei or high density of quenched in defects in that the rate of precipitation is increased. Discontinuous precipitation should make a significant contribution to the increase in strength as a result of the fine grain size.
Plastic Deformation of A Rapidly Solidified Al-Li-Zr Alloy
Authors: Kim N. J. , Das S. K.
Published: March 2011

The deformation behavior of a rapidly solidified Al-3.7%Li-O.5%Zr alloy has been investigated using transmission electron microscopy. Aging of the alloy in a conventional manner produces a homogeneous precipitation of δ' with small amount of heterogeneously distributed composite precipitates. The deformation behavior of the alloy in such aging conditions is dominated by the readily shearable δ', resulting in a pronounced planar slip. A homogeneous distrubution of composite precipitates promoted by double-aging treatment, however, alters the deformation mode to wavy slip by inducing the by-passing of dislocations around the shear resistant composite precipitates.
Effect of Rolling Parameters on the Properties of Al-Fe-V Sheet Rolled on an Experimental Mill
Authors: Brown A. , Raybould D.
Published: March 2011

In recent years, interest in high temperature aluminum alloys has increased. However, nearly all the data available is for simple extrusions. This paper looks at the properties of sheet made from a rapidly solidified Al-10Fe-2.5V-2Si alloy. The sheet is made by direct forging followed by hot rolling, this is readily scalable, so allowing the production of large sheet. The room temperature strength and fracture toughness of the sheet are comparable to those of 2014-T6. The high temperature strength, specific stiffness and corrosion resistance are excellent. Recently, improved thermomechanical processing and new alloys have allowed higher strengths and fracture toughness values to be obtained.
Microstructures and Thermal Properties of Rapidly Solidified Aluminum-Rare Earth Alloys
Authors: Eliezer D. , Savage S. J. , Mahajan Y. R. , Froes F. H.
Published: March 2011

Rapidly solidified (RS) Al-Er, Al-Nd, and Al-Gd ribbons were prepared by pendant drop melt extraction (PDME). The microstructures were studied in detail by optical and transmission electron microscopy. A wide range of microstructures are observed, including “conventional” RS type zones, a cellular structure surrounded by a degenerate eutectic and coupled (lamellar) eutectic structures. A bimodal precipitate distribution is seen in many areas of the ribbons. A series of isochronal heat treatments was conducted to determine the relative thermal stability of these microstructures, which were evaluated by Knoop microhardness measurements.
Recent Developments in Laser Surface Treatment
Authors: Mordike B.L. , Bergmann H.W.
Published: March 2011

Some unrelated examples are given where progress has been made in laser surface treatment in the last few years. These are large scale transformation hardening, reproducible surface melting of cast iron, surface alloying with a reaction with the surrounding atmosphere, fundamental studies of solidification and evaporation cleaning.
Unusual Chemical Composition of Carbides in Rapidly Solidified High Speed Steels
Authors: Tauqir A. , Nowotny H. , Strutt P. R.
Published: March 2011

Studies of the elemental composition of carbide phases formed by rapid solidification of a Mo-base high speed steel (M7) have yielded an intriguing finding. Micro-analysis of the extracted carbides (M2C, M23C6 and MC) showea that these were unusually rich in refractory elements with values of Mo in the range 46-53 wt.%, corresponding values for Fe and Cr were low (6-12 wt.% Cr and 1.5-13 wt% Fe). This was in marked contrast with analyses of MC, M6C, M7C3 and M23C6 in the ‘unglazed’ material where Fe and Cr were major constituents. A distinctive feature was M23C6 in the rapidly solidified material which contained large amounts of Mo and W and very little Cr. It is proposed that this phase, initially formed as M6C, underwent solid-state transformation.
Properties of Surface Melted SG Iron
Authors: Mordike B.L. , Bergmann H.W.
Published: March 2011

The surface melting of cast irons is discussed with particular emphasis on composition and effect of impurities. The hardness and wear properties are outstandingly good as shown from tracks under normal working conditions.
Amorphous Cu-Zr and Fe-Ti Compositionally Modulated Films Produced by Sputtering from Elemental Targets
Authors: Chason E. , Kondo H. , Mizoguchi T. , Cammarata R.C. , Spaepen F. , Window B. , Dunlop J.B. , Day R.K.
Published: March 2011

Amorphous compositionally modulated films of Cu-Zr and Fe-Ti have been prepared by sequential sputter deposition of the elemental metals. For Cu-Zr, a critical modulation amplitude has been found, below which the samples are entirely amorphous. The effective interdiffusion coefficient during deposition has been estimated, and found to be assisted by the free energy of mixing and the ion bombardment. X-ray studies of the modulation peaks, using grid scans, reveal a sharp mosaic, and asymmetrical peaks in some samples.
Evidence for the Formation of A Metastable Crystalline Phase During Crystallization of Zr-Ni Metallic Glasses of Approximately 57–63.2 at. % Zr
Authors: McKamey C. G. , Easton D. S. , Kroeger D. M.
Published: March 2011

The crystallization of rapidly solidified Zr-Ni metallic glasses has been studied by differential scanning calorimetry (DSC), x-ray diffraction (XRD), and transmission electronmicroscopy (TEM). Evidence has been found for a metastable phase which is the first crystalline phase to form upon heating in compositions of 57 to 63.2 at. % Zr. This phase seems to be more easily formed and is most stable in the region of 58 to 59 at. % Zr. Uponsubsequent heating to higher temperatures, the metastable phase transforms to the equilibrium phases ZrNi and Zr2Ni. The relationship of this new phase to phase separation at the eutectic composition of 63.5 at. % Zr is discussed in support of the conclusions drawn from low temperature specific heat studies reported previously [1,2].
Respirable Fines Produced by Impacts of Simulated Alternative High-Level Waste Materials
Authors: Jardine Leslie J. , Reedy Gerald T. , Mecham William J.
Published: March 2011

Standardized comparative drop weight impact tests were conducted on solid alternative waste forms under consideration for immobilizing Savannah River Laboratory (SRL) defense wastes. The fragment size distributions were measured in the size ranges of ֮5 to 8000 μm. All waste form fragment size distributions could be described accurately by lognormal plots. Respirable sizes (≤10 μm) were measured. Borosilicate glass and SYNROC specimens yielded the same mass fractions of respirable sizes; FUETAP concrete, high silica and alkoxide glass specimens yielded ֮2–3 times more mass fractions of particles of respirable sizes, whereas tailored (Spinel) ceramic specimens yielded the smallest mass fractions of respirable sizes, ֮2–1/2 times less.
Stability of I and SR Radiophases in Cement Matrices
Authors: Barnes M.W. , Scheetz B.E. , Wakeley L.D. , Atkinson S.D. , Roy D.M.
Published: March 2011

The following study is a portion of a comprehensive research program that is examining the stability of a variety of nuclear waste forms. In addition to the bulk waste forms, important individual radiophases are being studied to obtain a more complete understanding of the behavior of the components of complex multiphase radwaste systems. The stability of the strontium radiophase in supercalcine and an iodine-radiophase will be discussed.

The strontium radiophase in this study was Sr-powellite and the iodine radiophase was I-sodalite. Each radiophase was incorporated into bulk compositionally adjusted portland and aluminate cements. Two processing variables were studied: curing at 60°C and warm pressing at 150°C and 345 MPa.

Sr-powellite in portland cement leaches incongruently; a combination of dissolution and diffusion-controlled exchange of Ca for Sr is demonstrated. In the warm-pressed aluminate cement these reactions are masked by reactions with the curing cement. I-sodalite leaching data indicate dissolution, dominant at long times, combined with diffusion, dominant at short times.
Nuclide Migration Field Experiments in Tuff, G Tunnel, Nevada Test Site
Authors: Erdal B. R. , Rundberg R. S. , Daniels W. R. , Wolfsberg K. , Friedman A. M. , Fried S. , Hines J. J.
Published: March 2011

A project to begin to address the phenomena of flow and element migration in fractured porous rock has recently been started by the Los Alamos National Laboratory, Sandia National Laboratories, and Argonne National Laboratory. The work has three objectives: 1) to develop the experimental, instrumental, and safety techniques necessary to conduct controlled, small-scale, radionuclide migration, field experiments; 2) to use these techniques to define radionuclide migration through rock by performing generic, at-depth experiments under closely controlled conditions in a single fracture in porous rock; and 3) to determine whether available lithologic, geochemical, and hydraulic properties together with existing or developed transport models are sufficient and appropriate to describe real field conditions (i.e., to scale from small-scale laboratory studies to bench-size studies to field studies). The detailed scope of this project and its current status are described.
Transient Hydraulic Tests in Granite: Fissured Porous Medium Analysis and Results
Authors: Black John H. , Barker John A.
Published: March 2011

Slug and pulse tests have been used extensively to measure the hydraulic conductivity and specific storage of granitic rocks. After several hundred tests using an I.G.S. design of straddle packer test equipment, it became clear that the conventional methods of test analysis were inadequate. The straddle packer equipment developed by IGS allows the time scale of a test to be altered without repositioning the packers so that a range of tests can be carried out on the same test interval. The new analysis procedure presented here uses a model of fissured rock which incorporates water movement in both the fissures and the rock matrix. A new variable is introduced which includes the parameters matrix hydraulic conductivity, matrix specific storage fissure specific storage and fissure hydraulic conductivity together with the controllable variables, effective casing radius and packer interval length. Examples of analysis using multiple tests in the same interval are presented together with the apparent relationship between measured hydraulic conductivity and specific storage. It would appear that a small number of fissures endow the rock mass with the bulk of its hydraulic conductivity and that many of the higher hydraulic conductivity tests are probably associated with localised “pipe flow”.
Uranium-Lead Radiometric Age Determinations of Naturally Occurring U(VI) Minerals: Application to Radwaste Storage
Authors: Brookins Douglas G.
Published: March 2011

U(VI) bearing species are commonly formed under oxidizing laboratory rock-water-HLW experimental conditions. The experimental stability of artificially produced Na-Cs-Rb weeksite (alkali uranyl hydrosilicate), and other U(VI) species, is uncertain. Naturally occurring U(VI) bearing minerals (uranophane and tyuyamutrite) from the Grants mineral belt, New Mexico, have been studied for their U-Pb systematics as natural analogs to these experimentally produced phases. Samples from highly oxidized rocks and from chemically reducing environments have been studied. The samples from oxidized rocks are mixed with hematite-barite-gypsum-calcite gangue and are close to, but not in contact with, pyritiferous-organic carbon-uraniferous (U(NIV))-chloritic are. The reduced rock uranophane yields nearly concordant238U - 206Pb and 235U - 207Pb ages of 8.32 and 8.33 MYBP (millions of years before the present); the oxidized rock uranophane and tyuyam .nite yield more discordant ages (n=8) between 7.4 and 2.7 MYBP. These data argue for long range stability of U(VI)-rich phases in the geologic environment.
Radiogeological Assessment of Candidate Sites For Nuclear Waste Repositories, Exemplified by Studies of The Stripa Pluton, Sweden
Authors: Wollenberg H. A. , Flexser S. , Andersson L.
Published: March 2011

Investigation of candidate sites for nuclear waste isolation will require an assessment of their radiogeologic settings. Studies at the Stripa research facility in granitic rock of central Sweden incorporated the distribution and abundance of naturally occurring radioelements in rocks encompassing the underground experiments and in the accompanying fracture-controlled groundwater system. These studies showed that besides defining the natural radioactivity baseline upon which the effects of radioactive waste will be superimposed, radioelement distributions can be used to determine the apparent age of the groundwater and its flow paths. In crystalline rocks, where the groundwater systems are confined to the joints and fractures, the uranium daughter element, radon-222 in the water serves as a natural tracer to locate fractures along which significant flow is occurring and to measure the flow rates. The heat production from radioactive decay of uranium-238, thorium-232 and potassium-40 in the rock, combined with measurements of regional and local geothermal heat flow, permit calculation of the apparent size of the rock mass that will encompass the repository. This method is especially useful in terranes such as at Stripa where the contacts between plutons and older rocks are concealed.
Diffusion Measurements in Compacted Bentonite
Authors: Torstenfelt B. , Andersson K. , Kipatsi H. , Allard B. , Olofsson U.
Published: March 2011

The diffusion of Cs, Sr, Am and Tc in compacted bentonite clay has been studied, using a diffusion cell where diffusion takes place axially from the center of a cylinder of the clay. The effect of addition of potential radionuclide getters to the clay (apatite for Am, pyrite, olivine, and Fe(s) for Tc) as well as using complexed (acetate) or colloidal Am has been studied.

The diffusivities obtained for Cs and Sr were very high − 9.0×10−13 m2/s and 2.6×10−12 m2/s, considering that if the effect of sorption on the clay 9is 2 substracted the diffusivities would be 1.8×10−9 m2/s and 3.1×10−8 m2 /s. These diffusivities are, however, maximum values as the concentration profiles do not follow the theoretical form for these nuclides. A small amount of the ions seems to migrate very fast, while the rest moves slower.

For Tc, that may be expected I b2 anionic and thus poorly sorbed, a diffusivity of 5.3×10−11 m2/s was obtained. Addition of Fe(s) decreases the diffusivity by one order of magnitude while olivine and pyrite have no measurable influence during the present contact times (2-3 months). Americium is practically immobile.
Corrosion of Construction Materials in Clay Environments
Authors: Dresselaers Jozef , Casteels Florent , Tas Hugo
Published: March 2011

The corrosion rate and mechanism of construction materials of galleries and casings for boreholes (possibly to be used as consumable overpack of HLW canisters) have been evaluated after a first campaign of corrosion experiments in direct contact with clay, in a humid clay atmosphere and in a gas corrosion chamber. The envisaged construction material is ductile iron (grade 60) and has been tested with and without metallic and organic coatings. The corrosion mechanism is governed by the formation of a rust scale composed of Fe3O4 and C. Preferential attack underneath the surface reaction layer is associated with the progress of a reaction front at the interface between the graphic nodules or flakes and the ferritic or pearlitic structure.

Post-corrosion analyses of old gray iron coal mine shafts exposed for 60 and 90 years in well defined conditions are included to validate the use of the results of the short-time tests for very long exposure times.
The Dissolution of Irradiated Fuel Under Hydrothermal Conditions
Authors: Johnson Lawrence H. , Joling Henry H.
Published: March 2011

Uranium dioxide, the major component of irradiated CANDU fuel, shows good hydrothermal stability under the appropriate redox conditions. The thermodynamic stability of UO2in low ionic strength granite groundwater at 150°C under oxidizing and reducing conditions is briefly reviewed in order to provide a basis for discussion of the results of irradiated fuel dissolution experiments. Fuel chemistry characteristics that influence the kinetics of fission product release are also discussed.

Experimental studies demonstrate the influence of redox chemistry on irradiated fuel dissolution behaviour. Undero9 trongly reducing conditions, both uranium and99Tcconcentrations in solution decrease to the detection limit, whereas appreciable concentrations of both elements accumulate under oxidizing conditions. The release of some fission products, such as90Sr and137Cs, does not seem to be strongly affected by changes in redox chemistry. Under oxidizing conditions, the rate of90Sr release to solution increases by a factor of ten to twenty between 25 and 150°C.

These studies indicate the need for further work in certain areas, in particular on the relative amounts of important fission productsreleased by leaching versus matrix dissolution, and on the effect of the products of α–radiolysis of water on the dissolution of irradiated fuel.
Dod Applications of Implantation-Modified Materials
Authors: Hubler G. K.
Published: March 2011

This paper reviews areas under investigation within DoD involving the application of ion implantation to problems in wear, friction, corrosion, and fatigue. Specific results on the modification of metal fatigue in Ti turbine blade alloys and the modification of sliding wear of steels are reviewed and discussed in terms of the mechanisms which are thought to be acting to improve the metal properties.
Development of Engineered Structural Barriers For Nuclear Waste Packages
Authors: Westerman R. E. , Pitman S. G. , Elmore R. P. , Nelson J. L.
Published: March 2011

The development of structural barriers for nuclear waste packages involves selection of candidate materials, their screening by mechanical and corrosion testing, rigorous accelerated testing, and evaluation and comparison with other package elements. This document presents results from work conducted on titanium and cast steels.
Strontium-Basalt Reactions Under Nuclear Waste Repository Conditions
Authors: Komarneni Sridhar
Published: March 2011

Hydrothermal interactions of Sr as strontium chloride or hydroxide with basalts or basalt phases were investigated at 300°C for 4 and/or 12 weeks under a confining pressure of 30MPa. The nature and extent of Sr immobilization varied with the Sr source and with the basalt or basalt phase which immobilized up to 99.99% of the added Sr. The main mechanism of Sr fixation with basalts seems to be ion exchange when SrCl2 was the Sr source. Among the basalt phases, basalt glass was the most effective for SrCl2 immobilization by probably forming new strontium mineral phases. However, when Sr(OH)2 reacted with basalts or basalt phases Sr was immobilized by the crystallization of strontium aluminosilicates such as SrAl2Si2O8 . These results of Sr-nearfield interactions in a basalt repository indicate that basalt can be a good barrier for Sr migration from nuclear wastes.
Chemical, Physical and Engineering Characterization Of Candidate Backfill Clays and Clay Admixtures for a Nuclear Waste Respository-Part I
Authors: Singh Sudesh K.
Published: March 2011

Fourteen Canadian clays and clay admixtures were subjected to simulated nuclear waste repository environments. The present work is concerned with the montmorillonite-dominant materials only. The montmorillonite-dominant samples showed significant leaching on interaction with deionized water. On heating the samples at 200°C for 500 hours, montmorillomites lost intermicellar water completely and acquired cusp-like to cylindrical morphologies. The loss of water and the morphological changes in montmorillonites significantly altered the engineering characteristics. Permeability, shrinkage limits, compactability and shear strength varied in response to the dominant exchange cation in the structure of montmorillonites and the presence of other mineral components in the materials. The synthetic granite water reacted with montmorillonites and led to changes in chemical and mineralogical compositions, crystalline state and engineering properties.
Stochastic Analysis of Groundwater Flow and Contaminant Transport in a fractured Rock System
Authors: Schwartz F.W. , Smith L. , Crowe A.S.
Published: March 2011

It has been possible to develop a stochastic model for groundwater flow and mass transport in a fractured rock system. A large number of statistically independent realizations of a fracture network are generated from a set of probability distributions for parameters defining the fracture geometry. By solving for hydraulic head at the fracture intersections and using data on apertures and porosities, seepage velocities may be calculated and the transport equation solved for each trial of a Monte Carlo simulation. Model output consists of distributions of moving particles and various mass exit times. Applications illustrate the types of model results and the skewed character of particle distributions.
Performance of Asphalt and Clay Liners as a Uranium Mill Tailings Leachate Barrier
Authors: Buelt James , Barnes Steve
Published: March 2011

Pacific Northwest Laboratory is evaluating the long-term effectiveness of various asphalt and clay liner materials as a radionuclide and process chemical barrier from uranium mill tailings. A field test is being conducted by monitoring asphalt and clay liners installed at the Grand Junction, Colorado tailings site. In addition eight prospective liners have undergone three months exposure to accelerated conditions to predict their behavior over a 1000 year period. High calcium leachates have been forced through thin layers of clay to determine the ability of the clay to resist ion exchange, which reduces its swelling capabilities. Asphalt liners have been exposed to elevated temperatures and increased strengths of oxidizing agents to accelerate their aging process. The permeability coefficients measured during this exposure were then used to predict each liners stability with time. The analyses thus far show that clay soils with bentonite amendments and most asphalt compositions have good long-term performance characteristics.
A Comparative Assessment of Tru Waste Forms and Immobilization Processes
Authors: Ross W. A. , Harvey C. O. , Lokken R. O. , May R. P. , Roberts F. P. , Timmerman C. L. , Treat R. L. , Westsik J. H.
Published: March 2011

Six alternative TRU waste forms and seven waste immobilization processes are comparatively assessed on the basis of both product properties and process costs and risks. The waste forms are characterized for their leachability, mechanical strength, and thermal and radiation stability. The processes are evaluated in terms of costs (for processing, transportation, and repository disposal) and in terms of occupational exposure, industrial hazard, and quality assurance. Cast cement is recommended for immobilization of defense TRU wastes. A glass system, either borosilicate or aluminosilicate, is recommended for immobilization of commercial TRU wastes.
Low-Level Waste Disposal Analysis
Authors: Ensminger Daniel , Koplik Charles , Oston Steven , Kaplan Maureen , Nalbandian James
Published: March 2011

The safety of low-level radioactive waste disposal sites is analyzed using the computer code LOTRAN. Radiation doses to off-site individuals and to future land reclaimers are computed for a generic disposal site located in a humid Eastern environment. The predicted doses are compared to illustrative performance criteria developed under this project. Results provide insight into those characteristics of low-level waste disposal systems most important to public safety and will allow analyses of tradeoffs among natural and engineered features.
Immobilization and Leakage of Krypton Encapsulated in Zeolite or Glass
Authors: Christensen A. B. , Del Debbio J. A. , Knecht D. A. , Tanner J. E.
Published: March 2011

Krypton and other gases are readily adsorbed in zeolite 5A molecular sieve or porous Vycor “thirsty glass” and may be trapped there by sintering 2–4 hours at 700° or 900°C, respectively. Encapsulation in these materials is the basis of a method to “immobilize” krypton-85 for storage. Amounts of gas trapped are approximately proportional to gas density, and are about 50 and 40 cc(standard conditions = STP)/cc of solid at 1000 atm, for zeolite 5A and glass, respectively. Based on tests of a few months duration a leakage of 0.3% of the krypton is predicted for 10 years at 400°C for either material.
Cementitious Radioactive Waste Hosts Formed Under Elevated Temperatures and Pressures (Fuetap Concretes)
Authors: Dole L. R. , Moore J. G. , Rogers G. C. , West G. A. , Devaney H. E. , Morgan M. T. , Mcdaniel E. W. , Kessler J. H.
Published: March 2011

Concretes formed under elevated temperatures and pressures (FUETAP concretes) are effective hosts for transuranic (TRU) and high-level defense and commercial wastes.

Tailored cement formulations developed at Oak Ridge National Laboratory (ORNL) use Portland cement, fly ash, sand, and clay additives. These FUETAP concretes are cured under mild autoclave conditions, then the unbound water is removed.

This paper summarizes the FUETAP development program. These continuous studies address the major questions concerning the performance of radioactive waste forms.
Mercury Reduction and Removal During High-Level Radioactive Waste Processing and Vitrification
Authors: Eibling Russell E. , fowler John R.
Published: March 2011

A reference process for immobilizing the high-level radioactive waste in borosilicate glass has been developed at the Savannah River Plant. This waste contains a substantial amount of mercury from separations processing. Because mercury will not remain in borosilicate glass at the processing temperature, mercury must be removed before vitrification or must be handled in the off-gas system. A process has been developed to remove mercury by reduction with formic acid prior to vitrification. Additional benefits of formic acid treatment include improved sludge handling and glass melter redox control.
Leaching Behaviour of Ion-Implanted Simulated Hlw Glasses and Tentative Prediction of their Alpha-Recoil Aging.
Authors: Dran J.C. , Langevin Y. , Maurette M. , Petit J.C. , Vassent B.
Published: March 2011

The ion implantation-based simulation of α-recoil aging in radwaste glasses has been applied to several simulated HLW glasses. The results are qualitatively described by a new model of leaching for the implanted glasses although several specific features of irradiated surfaces are not clearly understood. This model suggests that for the most likely case of diffusion-controlled corrosion, where the reaction scheme involves several steps (hydration, dissolution of hydrated silica gel, etc…), the kinetics-controlling one would not necessarily be radiation sensitive. Indeed for these more representative glasses, no evidence for a drastic increase in the dissolution rate of the silica gel, induced by ion implantation has been so far detected, whereas the hydration rate seems in some cases more significantly enhanced. However the implications of these observations for the durability of the glasses remain to be assessed.
The Effect of Radiolysis on Leachability of Plutonium and Americium from 76–101 Glass
Authors: Nash K. L. , Fried S. , Friedman A. M. , Susak N. , Rickert P. , Sullivan J. C. , Karim D. P. , Lam D. J.
Published: March 2011

One aspect of the leachability of actinide bearing glass which has not been adequately addressed is the effect of radiolysis of the system (glass-water) on the amount of actinides liberated from the glass. In the present study, we have investigated the leaching of plutonium and americium from 76–101 glass samples (containing 2 mole % plutonium) in the presence of a one megaRad/hour gamma radiation field. The presence of the radiation field was found to increase the leaching rate of both plutonium and americium by a factor of five. Speciation studies of the plutonium in the leachate indicate that the plutonium is present predominantly in the higher oxidation states, Pu(V) and Pu(VI) and that it is significantly associated with colloidal particles. Examination of the glass surfaces with X-ray photoemission spectroscopy, XPS, both before and after leaching was carried out; these studies showed lower surface concentrations of plutonium in the samples of glass leached in the radiation field.
Ion Implantation Studies of Nuclear Waste Forms
Authors: Northrup Clyde J. M. , Arnold George W. , Headley Thomas J.
Published: March 2011

The first observations of physical and chemical changes induced by lead implantation damage and leaching are reported for two proposed U.S. nuclear waste forms (PNL 76–68 borosilicate glass and Sandia titanate ceramics) for commercial wastes. To simulate the effects of recoil nucleii due to alpha decay, the materials were implanted with lead ions at equivalent doses up to approximately 1 × 1019 a decays/cm3 . In the titanate waste form, the zirconolite, perovskite, hollandite, and rutile phases all exhibited a mottled appearance in the transmission electron microscope (TEM) typical of defect clusters in radiation damaged, crystalline solids. One titanate phase containing uranium was found by TEM to be amorphous after implantation at the highest dose. No enhanced leaching (deionized water, room temperature, 24 hours) of the irradiated titanate waste form, including the amorphous phase, was detected by TEM, but Rutherford backscattering (RBS) suggested a loss of cesium and calcium after 21 hours of leaching. The RBS spectra also indicated enhanced leaching from the PNL 76–68 borosilicate glass after implantation with lead ions, in general agreement with the observations of Dran, et al. [6,7] on other irradiated materials. Elastic recoil detection spectroscopy (ERD), used to profile hydrogen after leaching, showed penetration of the hydrogen to several thousand angstroms for both the implanted and unimplanted materials. These basic studies identified techniques to follow the changes that occur on implantation and leaching of complex amorphous and crystalline waste forms. These studies were not designed to produce comparisons between waste forms of gross leach rates.
Study of the Metamict Transformation in α-Quartz Using High-Resolution Electron Microscopy and Convergent Beam Electron Diffraction
Authors: Pascucci M. R. , Hutchison J. L. , Hobbs L. W.
Published: March 2011

The metamict transformation under electron irradiation has been studied in α-quartz using transmission electron microscopy (TEM) and convergent-beam electron diffraction (CBD). The transformation occurs in two stages: heterogeneous nucleation of discrete disordered inclusions and a slower homogeneous loss of crystalline order in the surrounding matrix. Both features are attributable to solidstate radiolysis, a mechanism for which is proposed. Ultrahigh resolution TEM structure images and information from zeroth and high order Laue zones in CBD confirm that shortrange correlations are the first to be lost and that longerrange correlations persist well into the metamict transformation. A transformation model is advanced in which progressive disorder evolves from small displacements of individual [SiO4] coordination units, made possible by lowered connectivity, within a framework of long-range ordered material.
Materials Research for the Canadian Nuclear Fuel Waste Management Program
Authors: Cameron Donald J.
Published: March 2011

Nuclear fuel waste disposal research in Canada is concentrating on hard-rock disposal. The research programs concerned with the man-made components of the disposal system are reviewed. Irradiated fuel and solidified reprocessing wastes are both being researched, as are durable containers, and buffer and backfill materials. This review concentrates mainly on the more scientific aspects of the research, which contribute to the selection of preferred options for the various components of the system, and which support directly or indirectly the safety analysis of the disposal concept. Some technology development is included in the program now, and this is expected to expand as confidence in the acceptability of the disposal concept grows.
The Development and Testing of Synroc C as a High Level Nuclear Waste Form
Authors: Reeve K.D. , Levins D.M. , Ramm E.J. , Woolfrey J.L. , Buykx W.J.
Published: March 2011

The current status of SYNROC C research and development by the Australian Atomic Energy Commission is reviewed. A non-radioactive fabrication demonstration line designed to produce 10 cm o.d., 90 cm long, cylinders of SYNROC canned in stainless steel by the method of in-can hot pressing is being commissioned. Leach tests are proving the excellent leach resistance of SYNROC. Accelerated radiation damage testing using fast neutrons has simulated storage times of up to 6.7×105 years. Thermophysical properties of SYNROC have been measured over the temperature range 20–650°C.
Percolation Transition and Accumulation of Strain in Chalcogenide Glasses
Authors: Murase Kazuo , Fukunaga T.
Published: March 2011

Network structures and glass forming tendency of g-(Ge1−ySny)1−x(Se, or S)xare discussed in connection with the percolation transition near the Phillips critical composition xc= 0.8, and local or extended topological transitions due to strains induced by compositional changes or applied pressures.
Defect Levels in the Gap of Arsenic Selenide Glasses
Authors: Adriaenssens Guy J.
Published: March 2011

The ideas and energy diagrams of the valence alternation pair model (also: negative-U model) are introduced and matched to the classical steady-state photoconductivity analysis in terms of two discrete recombination levels in the gap. Data from bulk a-As47Se53 serve as example. Negative effective correlation energies Ueff = -0.72 eV for a-As2Se3, −0.61 eV for a-As2Se4 and -0.58 eV for a-As47Se53 are obtained. The positively charged defects are found to be Se3+ with relaxation energies W+ ≃ 0.1 to 0.2 eV, and the negatively charged defects are As2− with relaxation energies W− ≃ 0.3 to 0.6 eV.
The Relation Between Defects and Relaxation in Viscous Liquids
Authors: Brawer S.
Published: March 2011

It is shown that defects can be identified in liquids, that they are related to atomic diffusion, and a model is described whereby defects give rise to the observed relaxation behavior of viscous liquids. A review is presented of defects in silicate and fluoroberyllate liquids, as studied by computer simulation. It is found that defects have the form of overcoordinated or undercoordinated atoms, and that atomic diffusion occurs only at the site of defects. The manner in which an Ising model can represent the detect structure of viscous liquids to a first approximation is presented. The results of Monte Carlo simulations of a 2-dimensional kinetic Ising model are described. The behavior of this model is qualitatively the same as that of viscous liquids.
Defects and the Photodarkening Process in the Chalcogenide Glasses
Authors: Taylor P. C. , Liu J. Z.
Published: March 2011

In the chalcogenide glasses the primary defects are thought to involve under- and over-coordinated chalcogen atoms which are diamagnetic under quasiequilibrium conditions because of the presence of a strong electron-lattice interaction. These defects can be optically, or in some cases thermally, excited into metastable paramagnetic configurations which are well described as chalcogen “dangling bonds.” Alloying the chalcogenide elements with group V or group IV atoms produces additional diamagnetic defects which in their excited paramagnetic configurations also appear to be well described as dangling bonds. Some of these defects may play a role in the photodarkening (PD) process which is a metastable shift of the absorption edge to lower energies after irradiation with light of energy greater than or equal to that of the band gap. The PD process requires the presence of a non-bonding plike valence band. The microscopic description of the PD process may involve the creation of defects or the tunneling of chalcogen atoms.
UV-Radiation Induced Color Centers in Optical Fibers
Authors: Simpson J. , Ritger J. , DiMarcello F.
Published: March 2011

Paramagnetic color centers have been observed in germanium silicate and germanium phosphosilicate multimode optical fiber exposed to broadband ultraviolet light (2–5 eV). These centers are characterized by an ESR and optical absorption similar to 1 meV and 100 keV radiation induced defects and show an apparent saturation as the UV dose approaches 100 J/cm2. The UV induced ESR spectra are not identical to that induced by 60Co radiation however, similar Ge(2) and Ge(3) germanium defect signatures are apparent. For both compositions these centers are characterized by a rapidly increasing loss from 1.0 to 0.5 µm with an additional broad absorption peak at 1.5 µm for the phosphorus containing cores. We suggest that the UV induced optical absorptions for both compositions in the short wavelength range are due in part to the Ge(2) germanium substitutional sites and expect that the 1.5 µm absorption is due to the P1 phosphorus oxygen vacancy.
Electron Paramagnetic Resonance Studies of Intrinsic Bonding Defects and Impurities in SiO2 Thin Solid Films
Authors: Schwartz Robert N. , Clark Marion D. , Chamulitrat Walee , Kevan Larry
Published: March 2011

Electron paramagnetic resonance (EPR) spectroscopy has been used to identify paramagnetic intrinsic bonding defects and impurities in as-deposited thin solid SiO2 films. Thin films grown by E-beam vacuum deposition, RF sputtering, thermal oxidation of polysilicon, plasma enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD) techniques have been examined. Some of the growth techniques yield films that have paramagnetic centers similar to those found in bulk radiation-damaged vitreous SiO2. A new temperature dependent EPR center was observed in PECVD SiO2 films and has been assigned to trapped NO2. Slow-motional EPR lineshape theory was used to analyze the temperature dependent spectra.
Cross Sectional Transmission Electron Microscopy Study of Obliquely Evaporated Silicon Oxide thin Films
Authors: Barna A. , Geszti O. , Gosztola L. , Seyfried E.
Published: March 2011

The columnar structure in obliquely evaporated silicon oxide layers was investigated by transmission electron microscope (TEM). For TEM studies of these layers, samples were made by low angle ion-beam thinning of cross-sections, the planes of which were determined by the normal of the film and the direction of evaporation. Increasing the angle of evaporation from 5° to 30° (measured from the plane of the substrate), a change from a well–defined columnar structure to a striated structure was observed, for layers evaporated both under “low-rate” and “high-rate” conditions. There is a clear-cut dependence of the orientation of columns (αc) upon the angle of evaporation (α), however deviating from the “tangent rule” (tanαc=2tanα).
Impurity Effects of Metal Ions in Chalcogenide Glass Films
Authors: Suzuki M. , Okano S. , Machi S. , Yamakawa H.
Published: March 2011

Doping effects of metal ions in chalcogenide glass films were studied. Doped impurities were found to act as donor or acceptor centers, when impurity ions were introduced in chalcogenide glass films below the glass transition temperature. Rectifying effects were realized in chalcogenide glass films doped with Al, Cd and Mg, so it is certain that the p-n junction was formed by the impurity doping. The tunneling of electrons through gap states, however, appeared to increase the reverse current of heavily doped diodes, so that large rectifying effects were not attained. A high density of defect states especially in the surface region would be responsible for low temperature diffusion of metal ions.
Defects in Gel-Derived Glasses
Authors: Brinker C. J. , Tallant D. R. , Roth E. P. , Ashley C. S.
Published: March 2011

Defects in gel-derived glasses were reviewed for the three principal stages of the sol-gel process: solution, porous gel, and consolidated glass. The most prominent defects in gel-derived SiO2 are Raman active defects characterized by sharp bands at 490 cm−1(D1) and 608 cm−1(D2) 18O enrichment, experimental estimates of heats of formation, and structural studies of cyclic model compounds were used to identify the structural origins of D1 and D2 in gels. We conclude that D1 and D2 in gel-derived SiO2 are the oxygen breathing modes of 4- and 3-fold siloxane rings, respectively, as originally proposed by Galeener to explain these Raman-active defects in conventional vitreous silica (v-SiO2). During heat treatments near Tg (defined by n = 1013.5 poises), the gel-derived SiO2 structure rapidly approaches that of conventional v-SiO2.
The Nature of the Paramagnetic States in SiO2-GeO2-Sol-Gel Glasses
Authors: Kordas George , Mukherjee S. P.
Published: March 2011

The 9.5 GHz ESR-spectra of gamma-ray irradiated 94 SiO2 6 GeO2 (mol%) aero gels heat treated at 462°C were recorded at 300 K. The ESR-spectrum of this gel consisted of an asymmetric line (g1 = 2.001, g2 = 1.995, and g3 = 1.994) attributed to the Ge(3)-center and other components which have not yet been identified. The 94 SiO2 6 GeO2 gel was treated at 1000 and 1280°C and then exposed to gamma-ray radiation. The Ge(1)- and Ge(3)-centers were identified in the 94 SiO2 6 GeO2 gel with TH = 1000°C. At TH = 1280°C the signal of the Ge(1)-center dominated the spectrum of this sample. The spectra of the 58 SiO2 42 GeO2 gels with TH = 1200 and 1400°C can be described by the Ge(3)-center. The Ge(1)-center was of minor importance in these samples.
The Thermal Conductivity of Several Fluoride Glasses
Authors: McCarthy K. A. , Sample H. H. , Koss M. B.
Published: March 2011

The thermal conductivities of beryllium fluoride glass and a fluoroberyllate glass have been measured in the 2–100K temperature range. These results are compared with earlier results on fluorozirconate glasses. The “plateau” region is well-defined for both materials. The plateau-center conductivity for BeF2 glass is the lowest yet recorded for any glass; it is some three times lower than the fluoroberyllate glass and four times lower than the fluorozirconates. A preliminary analysis of the data show a strong correlation between plateau-center conductivity and average cation mass of the material.
Structural, Electronic, and Magnetic Properties of Surfaces, Interfaces, and Superlattices
Authors: Freeman Arthur J. , Fu C. L. , Oguchi T.
Published: March 2011

Advances in all-electron local density functional theory approaches to complex materials structure and properties made possible by the implementation of new computational/theoretical algorithms on supercomputers are exemplified in our full potential linearized augmented plane wave (FLAPW) method. In this total energy self-consistent approach, high numerical stability and precision (to 10 in the total energy) have been demonstrated in a study of the relaxation and reconstruction of transition metal surfaces. Here we demonstrate the predictive power of this method for describing the structural, magnetic and electronic properties of several systems (surfaces, overlayers, sandwiches, and superlattices).
Pseudopotential Calculations of Structural Properties of Solids
Authors: Cohen Marvin L.
Published: March 2011

Through the development of a total energy pseudopotential approach, it has become possible to compute structural, electronic, and vibrational properties of solids using only the atomic numbers and atomic masses of the constituent atoms as input. The method has been applied to semiconductors, insulators, and metals; and agreement with experiment for most properties is usually within a few percent.

Applications include the determination of lattice constants for specific structural phases, properties of structural phase transitions, cohesive energies, bulk moduli, lattice vibrational spectra, electron-lattice interaction parameters, and electronic and superconducting properties. A recent example is the prediction of superconductivity in highly condensed hexagonal silicon which was subsequently found experimentally.
Fracture and Flow Via Nonequilibrium Molecular Dynamics
Authors: Hoover W. G. , De Lorenzi G. , Moran B. , Moriarty J. A. , Ladd A. J. C.
Published: March 2011

The scope of molecular dynamics problems designed to simulate materials properties is described, focussing on the limits computation imposes on space and time scales, as well as the limits theoretical understanding imposes on our knowledge of interatomic forces. Five strategies for improving the efficiency of the simulations are described. Shock-induced solid-solid phase transformations are discussed to illustrate these ideas.
Electronic Properties of Liquid Silicon
Authors: Broughton J. Q. , Allen P. B.
Published: March 2011

The electronic properties of liquid silicon were computed by coupling molecular dynamics and tight binding methods. By employing the Stillinger-Weber potential, atomic configurations of liquid Si at 1740°C were generated by molecular dynamics. Tight binding parameters chosen to fit fcc,bcc, simple cubic and diamond cubic band structures of silicon, were then used to obtain the electronic properties of the system. All states within 10eV of the Fermi level are found to be delocalized, the density of states spectrum similar (but much broadened) to that of diamond cubic silicon and the optical conductivity is found to be almost featureless with no Drude behavior.