bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamics and Kinetics of Crystal-Amorphous Transformation in A1–x Bx Alloys During Reaction with Hydrogen
Authors: Yeh X. L. , Johnson W. L. , Tang J. Y. , Shi C. R. , Keck W. M. 
Published: March 2011

ABSTRACTThe kinetics of amorphous phase formation in polycrystalline A1–xBx (A=Zr, Hf, B=Pd, Rh,.15<x<.25) alloys during reaction with hydrogen has been studied by x-ray diffraction, +19F nuclear reaction depth profiling, TEM and electron diffraction. The formation of the amorphous hydride phase is observed by TEM to begin at grain bounderies of the polycrystalline Zr1–xRhx much in the same manner that “melting” nucleates at grain boundaries. TEM micrographs further show that the phase boundary between the crystalline and amorphous phases remains sharp during the growth of the amorphous phase. Both x-ray diffraction and nuclear depth profiling studies suggest that the overall rate of transformation to the amorphous hydride phase is limited by the rate of hydrogen permeation through the sample surface.Based on the present experiments and an analysis of the relevant free energy curves, we discuss the thermodynamic and kinetic aspects of this effect to explain why an amorphous phase is formed.
Thermal Stability and Phase Transformation in Hfl-xCux Metallic Glasses
Authors: Schulz R. , Leem N. L. , Clemens B. M. 
Published: March 2011

ABSTRACTIn this paper we report the difference in the structures, physical properties and thermal behaviors of two compositions of amorphous Hf-Cu. One (Hf50CU50) is near the eutectic composition and the other (Hf67Cu33) corresponds to an intermetallic compound. Transmission and scanning electron microscopy (TEM, SEM), differential scanning calorimetry (DSC), electrical resistivity and high-angle X-ray diffraction have been used to study these glasses in detail. Amorphous Hf67 Cu33 is structurally stable up to the crystallization temperature, while Hf50 Cu50 undergoes a ductile to brittle transition associated with a chemicai phase segregation at temperatures far below the glass transition. An anomalous behavior in the resistivity is associated with this phase transformation.
The Leaching Behaviour of the Swedish KBS-Glasses ABS 39 and ABS 41
Authors: Hermansson Hans-Peter , Christensen Hilbert , Werme Lars , Ollila Kaija , Lundqwist Rune 
Published: March 2011

ABSTRACTThe planned Swedish KBS glass corrosion investigation program comprises experiments with inactive glasses containing simulated waste, prolonged in-situ tests, the characterization of corrosion products, immiscibility studies, and corrosion experiments with “hot” glass.This presentation gives a short description of the entire program. It focuses thereafter on some recent leaching results with the inactive KBS glass qualities ABS 39 and ABS 41, which were leached in a manner similar to the PNL MCC–1 test procedure.
A Methodology for Characterizing Brittle Fracture of Solid Waste Forms in Accidental Impacts
Authors: Mecham William J. , Jardine Leslie J. , Steindler Martin J. 
Published: March 2011

ABSTRACTA general method for characterizing the major practical effects of accidental impacts on waste packages and for evaluation of scale-model tests has been partially developed. Impact fracture of brittle waste forms has been shown elsewhere to produce particulates whose size distributions are described by the lognormal probability distribution. The model proposed for fragment generation involves the transformation of impact (kinetic) energy into elastic strain energy which is followed by fracture and energy dissipation into heat by the fracture particulates. The peak stresses developing during compressions are approximated as a function of time using elastic theory for a wide range of practical impact conditions for typical (glass) waste forms. The proposed methodology requires experimental validation in terms of correlation of stress and energy parameters with particulate parameters describing the results of fracture. Two kinds of preliminary correlations are presented: (1) calculations of stress parameters for a range of impact conditions; and (2) averages of particulate parameters obtained in standard impact tests.
Processing Effects on the Behavior of Titanate Waste Forms in Aqueous Solutions
Authors: Dosch R. G. 
Published: March 2011

ABSTRACTTitanate processing parameters including temperature, waste loading, redox conditions, and additives used to promote specific phases were evaluated with respect to their effect on leaching of Cs, Mo, Ca, Sr, Ba, U, Gd, and Ti in the range of 22°-150°C in leachates which included deionized water, acidic (pH 2), and basic (pH 12) solutions. Surface analyses and microstructural characterization were used to relate observed leaching behavior to processing parameters. Redox conditions were found to be very important with respect to Cs (and Mo) retention. Two Cs-bearing phases were found in titanate prepared under oxidizing conditions. One had a hollandite structure and the other contained Cs, Mo, Ca, and Fe as major constituents. The latter phase, which was more susceptible to leaching, was not observed in titanates prepared using adequate reducing conditions. Where applicable, a reference glass (PNL 76–68) was included in the leaching tests. Comparative leach rates for elements common to both waste forms were generally one to four orders of magnitude lower for the titanates within the range of conditions used.
The Use Of 222Rn as a Flow Path Monitor for Studies of Radionuclide Transport in Fissures
Authors: Hines J. , Cohen D. , Fried S. , Friedman A. M. 
Published: March 2011

ABSTRACTA technique has been developed using 222Rn as a flow path monitor. Its principle advantage over other radiotracers or dyes is that while the Kd of Rn gas in water solution is zero and hence follows the water path, its 210Pb daughter is retained strongly by rock. The immobilized 210Pb is not subject to diffusion, an important consideration in the proposed Nevada Field Test. To evaluate the technique, a series of laboratory scale experiments have been performed. Artificial fissures consisting of glass plates and prepared flat surfaces were coupled to insure well characterized fissures. Water solutions of radiotracer were metered through these fissures and the discharge monitored to produce breakthrough curves as a function of flow rate. The rock surfaces were analysed for radionuclide concentration and the rock sectioned for diffusion profile into the rock.
Formation and Properties of Americium Colloids in Aqueous Systems
Authors: Olofsson U. , Allard B. , Andersson K. , Torstenfelt B. 
Published: March 2011

ABSTRACTThe formation and sorption properties of colloidal americium in aqueous solutions have been studied with variations of pH (2–12), ionic strength (0.01–1.0 M NaClO4), americium concentration (10−7 −10−11 M) and storage time (6 h–6 months). A large fraction of the americium is sorbed on the container walls or on Al2O3 in the pH-range 7–11. Around pH 5–8 and at pH above 12 centrifugable fractions (particle sizes greater than 100 nm) are obtained. The fraction formed at pH above 12, which seems to be a true hydroxide colloid, migrates through an A12O3-filled column with very little retention. The average charge of americium species in solution changes from positive values at pH below 7–8 to negative values at pH above 10–11, as indicated from electromigration studies.
Iron-Enriched Basalt for Containment of Nuclear Wastes
Authors: Welch J M. , Schuman R. P. , Sill C. W. , Kelsey P. V. , Henslee S. P. , Tallman R. L. , Horton R. M. , Owen D. E. , Flinn J. E. , Idaho Eg&g 
Published: March 2011

ABSTRACTIron-enriched basalt (IEB) has been investigated as a containment medium for defense transuranic (TRU) and defense high-level wastes (HLW). IEB samples have been fabricated incorporating simulated and actual defense TRU wastes generated at the Rocky Flats Plant (RFP), and simulated defense high-level wastes. These samples were tested for leaching resistance and fracture toughness. Cesium and strontium volatility from an IEB melt was also assessed, using radioactively spiked samples.
Radionuclide Migration: Laboratory Experiments with Isolated Fractures
Authors: Rundberg R. S. , Thompson J. L. , Maestas S. 
Published: March 2011

ABSTRACTLaboratory experiments examining flow and element migration in rocks containing isolated fractures have been initiated at the Los Alamos National Laboratory. Techniques are being developed to establish simple fracture flow systems which are appropriate to models using analytical solutions to the matrix diffusion - flow equations, such as those of I. Neretnieks [1]. These experiments are intended to be intermediate steps toward larger scale field experiments where it may become more difficult to establish and control the parameters important to nuclide migration in fractured media.Laboratory experiments have been run on fractures ranging in size from 1 to 20 cm in length. The hydraulic flow in these fractures was studied to provide the effective apertures. The flows established in these fracture systems are similar to those in the granite fracture flow experiments of Witherspoon et al. [2]. Traced solutions containing 85Sr and 137Cs were flowed through fractures in Climax Stock granite and welded tuff (Bullfrog and Tram members, Yucca Mountain, Nevada Test Site). The results of the elutions through granite agree with the matrix diffusion calculations based on independent measurements of Kd. The results of the elutions through tuff, however, agree only if the Kd values used in the calculations are lower than the Kd values measured using a batch technique. This trend has been previously observed in chromatographic column experiments with tuff.
Zirconolites from Sri Lanka, South Africa and Brazil
Authors: Ewing Rodney C. , Haaker Richard F. , Headley Thomas J. , Hlava Paul F. 
Published: March 2011

ABSTRACTZirconolites, CaZrTi2O7, from Sri Lanka and Pala Bora, South Africa, and a calzirtite, CaZr3 TiO9, from Jacupiranga, Brazil, were examined using the electron microprobe, x-ray diffraction (annealing study), transmission electron microscopy, scanning electron microscopy and optical microscopy. The x-ray data indicate that all three zirconolites are metamict. Both Sri Lanka zirconolites are amorphous to the limits of resolution of the electron microscope (֮10 A). The Pala Bora zirconolite is largely amorphous but contains isolated domains (50–200 A) of crystalline material which may be the result of post—metamict recrystallization and alteration. The only other significant evidence for chemical alteration was the lower Th concentration (1–2 weight percent) and slightly lower analytic totals for the rims of the Sri Lanka zirconolites. Upon annealing at 1130°C for 5 hours, all three zirconolites recrystallized as microcrystalline aggregates. Refined unit cell parameters and volumes are consistent with published data for synthetic zirconolites. Both Sri Lanka zirconolites contain microvoids, spherical in shape, and 200 Angstroms to 2 microns in size. This porosity may be the result of helium accumulation arising from the decay of U and Th. The calzirtite was highly crystalline, exhibited no porosity, and was unchanged by the annealing treatment.
Permeability, Swelling and Radionuclide Retardation Properties of Candidate Backfill Materials
Authors: Westsik J. H. , Bray L. A. , Hodges F. N. , Wheelwright E. J. 
Published: March 2011

ABSTRACTA backfill placed between a nuclear waste canister and the host geology of a nuclear waste repository can impede the migration of water through the waste package and retard the movement of radionuclides into the geologic formation. Hydraulic conductivities and swelling pressures are being determined as functions of the density of the compacted backfill, temperature, radiation dose, hydraulic head and the chemical composition of the permeating fluid. Bentonite clays and bentonite/sand mixtures have received initial emphasis. Sodium bentonite and calcium bentonite samples compacted to a dry density of 2.1 g/cm3 had hydraulic conductivities in the range of 10−12 to 10−13 cm/s. In addition, batch distribution ratios (Rd) for Sr, Cs, Am, Np, I, U and Tc have been measured for a number of candidatebackfill materials. Both initial permeability and sorption studies have used a synthetic basaltic ground water.
PNL-Sandia HLW Package Interactions Test: Phase One
Authors: Molecke Martin A. , Bradley Donald J. , Shade John W. 
Published: March 2011

ABSTRACTThe first phase of a complex high-level waste (HLW) package interactions test in a salt environment has been completed. The test system consisted of PNL 76–68 HLW glass (loaded with inactive fission products and 238U) surrounded by a stainless steel waste canister, a TiCode- 12 overpack, a bentonite/sand backfill, excess brine leachant, and a bedded rock salt container, all heldwithin a 19-liter autoclave. All components were physically compromised in order to force wasteform-barrier-salt interactions to occur during this 95-day, 250°C overtest. Analyses of leachant, wasteform, and all barrier surfaces were performed. Test data included the synergistic effects between barriers and confirmed previous analyses of simpler systems. The glass wasteform exhibited some surface alteration but was not dissolved to any significant degree. The TiCode-12 overpack showed minimal uniform corrosion and no localized attack. Observed mineralogical alteration of the backfill was minimal.
Implantation and Industrial Metal Processing
Authors: Fromson Robert E. , Kossowsky Ram 
Published: March 2011

ABSTRACTThe potential for reducing indirect manufacturing costs and the challenge to improve component performance justify active consideration of ion implantation in industrial metal processing. The need for interaction between the scientific community and the industrial community is shown with specific examples of methods employed by Westinghouse for accelerating this interaction.A review of implantation activities at Westinghouse include basic technology studies, equipment considerations, material evaluation capabilities, factory trial results, and some of the planned areas of future interest. The preferred characteristics of targets of opportunity are identified and needed advances in technology and equipment are discussed.
Experimental and Theoretical Analyses of Small-Scale Radionuclide Migration Field Experiments
Authors: Erickson K. L. , Fortney D. R. 
Published: March 2011

ABSTRACTAnalyses have been completed which provide guidance for conducting radionuclide migration field experiments. Characterization of nonwelded tuffs and laboratory experiments defining dominant chemical phenomena were used to develop a model for describing migration in fractured porous rock. Criteria for obtaining optimum experimental conditions were developed in terms of the key variables dominating migration in a given rock type, namely the fracture aperture, distribution coefficient, and average fluid velocity. For simple dissolved species, which are reversibly sorbed, variations in fracture aperture and fluid velocity affect experiment results much more than variations in distribution coefficient. Therefore, the experiment should be designed to optimize hydrogeologic conditions rather than sorption properties.
Radiation Induced Sodium Metal Colloid Formation in Natural Rock Salt From Different Geological Localities
Authors: Loman J. M. , Levy P. W. , Swylertt K. J. 
Published: March 2011

ABSTRACTRadiation damage has been studied in natural rock salt from various localities, including potential repository sites. In the 100 to 300 C range the damage consists of point defects, primarily F-centers, and colloidal metal sodium particles. With increasing dose the F-centers grow to a saturation level, reached at 107 –108 rad, that decreases with increasing temperature to a negligible level at 300 C. Colloid concentration vs. irradiation-time curves follow nucleation and growth curves accurately described by C tn, or C(dose)n, relations at large irradiation times. For fourteen samples,n = 1.85± 0.18 but the values of C vary by a factor of more than 103. The constant C is related to the sample strain, the impurity and void content, dose rate, and possibly other factors. The currently available data indicate that rock salt adjacent to radioactive waste canisters, at a temperature of 150 C, will contain between 0.01 and 10 mole percent of sodium metal when the total dose reaches 1010 rad.
Novel Experiments for Understanding the Shallow Land Burial of Low-Level Radioactive Wastes
Authors: Depoorter G. L. , Hakonson T. E. 
Published: March 2011

ABSTRACTData on the basic processes that occur in the shallow land burial of low-level radioactive wastes are needed to engineer facilities with guaranteed performance, to validate models for system predictions, and to provide input to models that consider contaminant pathways out of the facility. Two types of novel experiments that will provide experimental data on the basic processes in shallow land burial facilities are described in this paper. Generic experiments that give data on the movement of water and radionuclides and an experiment that is particularly important for semi-arid sites are described.
Nuclear Waste Disposal: The Interface Between Performance Assessment and Research
Authors: Lyon R.B. 
Published: March 2011

ABSTRACTThe potential impact of the post-closure phase of a nuclear fuel waste disposal project is radiation dose to man. Radiation dose is estimated as the end product of a total systems analysis. Field and laboratory research must be assimilated in a form that can be accepted by the total systems analysis procedure. A central focus of this assimilation must be the consideration of uncertainties in the analysis and data used. Irreducible uncertainty arises because of the wide variability in natural systems and the unprecedented extrapolation into the distant future. The SYVAC computer program provides a framework for assimilation of the results of the field and laboratory research with a systematic treatment of uncertainty. A SYVAC assessment of the post-closure performance of a Canadian nuclear waste disposal facility is presented with particular illustrations of the interface between the assessment models and data and the field and laboratory research.
Photoinduced Paramagnetic Defects in Amorphous Silicon Dioxide
Authors: Stathis J. H. , Kastner M. A. 
Published: March 2011

ABSTRACTSeveral paramagnetic defects are created by exposure of amorphous SiO2 to sub-band-gap light. The spectra of the dominant centers can be isolated by using their annealing, microwave power, and excitation-photonenergy dependence. The results are discussed in terms of specific models for the intrinsic defects in a-SiO2.
Electron Paramagnetic Resonance and Optical Study of Radiation-Induced Defect Centers in Doped Silica Glasses
Authors: Schwartz Robert N. , Tangonan Gregory L. , Blair G. Richard , Chamulitrat Walee , Kevan Larry 
Published: March 2011

ABSTRACTGamma- and UV-induced defect centers in germanium and fluorine doped silica have been studied by electron paramagnetic resonance (EPR) spectroscopy. The complex spectrum at g≃2 in γ-irradiated germanium doped glass corresponds to a superposition of resonances from several germanium E′-centers. In UV-irradiated samples, however, the EPR spectrum is dominated by only one type of germanium E′-centers. Significant spectral simplification of γ-irradiated germanium doped silica can be achieved by heating or broadband photoirradiation. Similar results are observed in multimode germanium doped core optical fibers. UV-induced optical loss spectra in the 0.5–1.5 μm wavelength range were also measured in these core fibers as well as the growth kinetics of the UL-induced absorption. Gamma-irradiation of fluorine doped silica generated two different types of silicon E′-centers, Ea1. At lower radiation dose one sees a mixture of Ea1 and Ea2, but at higher radiation dose Ea2 dominates. A spectrum dominated by the Ea2 variant is also observed in LW-irradiated samples and in photobleached low gamma dose samples.
Transition Metal Ion Species in Glass: A Comparison of Optical Absorption and Luminescence Evidence
Authors: White William B. , Knight Diane S. 
Published: March 2011

ABSTRACTOptical absorption spectra of d-d transitions can be interpreted through crystal field theory as evidence for at least four kinds of species: traditional network modifier ions (Mn2+, Fe2+, and Ni2+), octahedral complexes (Cr3+, Mn3+), tetrahedral complexes (Co2+, Fe3+), and network-forming ions (Ti4+, Fe3+). Absorption spectra measure only majority species since crystal field bands are broad and overlapping. Luminescence spectra reveal minority species if these species happen to be efficient emitters under laser excitation. Doublet-quartet emission bands (Cr3+) are independent of crystal field but allow the distinction between species because of small differences in bonding which shifts the Racah B parameter. Quartet-sextet emission (Mn2+, Fe3+) is strongly dependent on coordination number and bond lengths. Qualitative, but not quantitative, changes in speciation can be followed as glass composition is varied. Conceptually, the complexation of transition metal ions in insulator glasses results from a competition between the transition metal and the glass-forming framework for p-orbital electrons of non-bridging oxygens. Complexation is further enhanced in clustered glasses where the ions segregate into the more depolymerized units.
Surface Structure of Silica Glasses by Molecular Dynamics Simulations
Authors: Levine S. M. , Garofalini S. H. 
Published: March 2011

ABSTRACTMolecular dynamics computer simulations were used to study surfaces of pure silica glass. The potentials used here were those previously established to model bulk silica and have been extended to study surface relaxation in a perfect vacuum. A large number of surfaces were made using different starting configurations; system sizes, and cooling procedures. Following “fracture”, many broken bonds rearranged in response to the changes in the net forces in the surface region. After this reconstruction, the simulations showed the expected general features observed experimentally, such as a prevalence of oxygen atoms at the outermost surface, non-bridging oxygens, and strained siloxane bonds. Three fold silicons (similar to e’ centers) were initially present in the “fractured” surfaces but most often were incorporated into the network tetrahedrally after reconstruction. Other defects produced during the reconstruction were five coordinated silicons and more importantly, edge sharing tetrahedra, forming the strained siloxane bonds. Bond angles and bond lengths for each defect were determined, showing good agreement with previously published results as well as providing new information. Finally, estimations for silanol concentrations were made which compare well with experimentally determined coverages. The computer simulation technique used here adequately reproduces many of the structural and dynamic characteristics of silica glass surfaces.
Time Resolved Fluorescence Line Narrowing in Ytterbium-Doped Inorganic Glasses
Authors: Brundage R. T. , Yen W. M. 
Published: March 2011

ABSTRACTWe have used time resolved fluorescence line narrowing to study optical dephasing and energy transfer among Yb3+ ions doped in inorganic glasses. We observe for the first time in any rare earth doped glass system a change in the power of the temperature dependence of the homogeneous linewidth of the 2F5/2(1)-2F7/2(1) transition of Yb, 3+ as well as an efficient one-phonon assisted energy transfer process occuring among Yb3+ ions at higher concentration due to a quadrupole-quadrupole coupling of the ions. In this paper we review past studies in rare earth doped gla s systems of these topics and compare them to our observations of Yb3+ in silicate and phesphate glasses.