bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sans Measurements of Deuterium Trapped at Grain Boundaries in Palladium
Authors: Heuser Brent J. , King John S. , Summerfield George C. 
Published: March 2011

AbstractSmall-angle neutron scattering from grain boundary interfaces has been investigated in polycrystal palladium with and without deuterium dissolved in the solution phase. Polycrystalline samples were prepared using two different procedures: (1) single crystal material was recrystallized at 517°C after 78% cold working, and (2) an extruded polycrystal rod was investigated as received, or recrystallized at 600°C and 680°C. The expected 1/Q2 scattering profile (where Q is the neutron wavevector transfer) from grain boundaries has been observed, and the absolute cross sections permit a determination of the grain boundary surface concentration of missing palladium atoms and of trapped deuterium. The vacancy and trapped deuterium surface concentration determined in these measurements was 0.2-0.3 vacancies/Å2 and 0.4-0.6 deuterons/Å2, respectively. The measurements were extended to the low Q region (Q ≥0.006 1/Å) where the scattering response was dominated by Porod 1/Q4 behavior typical of internal voids. This behavior was especially strong for the samples fabricated from the extruded polycrystal, but was also present in the as-received single crystal. The degradation of the single crystal Porod response after compressional cold working is in reasonable agreement with the calculated effect of flattening a spherical void.
Growth of Grain Boundary Precipitates as a Function of Misorientation in an Al-5 WT% Cu Alloy
Authors: Cantrell M. A. , Shiflet G. J. 
Published: March 2011

AbstractThe size evolution of θ phase (CuAl2) precipitates as a function of time was used to study the growth of grain boundary precipitates in an Al-5 wt % Cu alloy. The kinetics were: modeled using the Brailsford and Aaron treatment of the collector plate mechanism. It was found, for a given time, that the size varied in a reproducible manner as a function of misorientation between the grains. Precipitate size was found to vary from 5 x 10-6 cm to 5 x 10-5 cm, while misorientation varied from 20 to 50 degrees for a given heat treatment period. Grain boundary misorientation was determined to be the most important factor influencing precipitate size for a given grain boundary. The grain boundary plane orientation plays a secondary role in the growth of precipitates. From these data, the relationship between grain boundary misorientation and grain boundary diffusion has been determined.
Diffusion-Induced Grain Boundary Migration and Role of Defects
Authors: Chaki T.K. 
Published: March 2011

AbstractA model is presented to explain various aspects of diffusion-induced grain boundary migration (DIGM). The driving energies of DIGM are identified as the free energy of mixing and the interface free energy, the former being predominant in most cases of DIGM. The grain boundary migrates due to thermally activated motion of atoms across the interface under the influence of the driving energies. An expression for the velocity of migration is derived. It is shown that this depends parabolically on the solute concentration, in agreement with experimental observations in the case of liquid film migration (LFM), which is analogous to DIGM. Furthermore, the velocity is proportional to lattice diffusivity ahead of the boundary. Recent results of enhancement of DIGM by ion bombardment is explained by radiation-enhanced lattice diffusivity due to introduction of point defects by the ions. The model also explains that diffusion-induced recrystallization (DIR) is due to a free energy decrease associated with the transformation from the amorphous phase in the grain boundary layer to the crystalline phase.
Interface Diffusion in Solids
Authors: Grinfeld Michael A. 
Published: March 2011

AbstractSurface diffusion within intergrain space is studied theoretically with the help of the Onsageristic approach of irreversible thermodynamics. The grains are treated as isotropic elastic half solids. It is assumed that species of one of the grains are capable to leave their equilibrium positions in the parent solid body and then they migrate within the inter-grain space along the surface of their parent body. Decrease of the total accumulated energy is postulated to be a driving force of the diffusion processes.
Solid-Phase Epitaxy - Role of Point Defects in Amorphous Solids
Authors: Chaki T.K. 
Published: March 2011

AbstractA model of solid-phase epitaxial growth (SPEG), explaining enhancing effects of ion-irradiation and dopants, is presented. The crystallization is by the adjustment of atomic positions in the amorphous side of the crystalline/amorphous (c-a) interface due to self-diffusion in the amorphous solid, assisted by a freeenergy decrease associated with the transformation from the amorphous (a) to crystalline (c) phase. Irradiation and electrically active dopants increase the selfdiffusivity of a-phase by generating point defects in the amorphous layer and thus enhance crystallization. An expression for the velocity of epitaxial growth is derived. The low activation energy of ion-induced SPEG is due to recombination of point defects in the a-phase.
Laboratory Testing of the Corrosion of Waste Glasses in Aqueous Environments - Effects of Experimental Parameters
Authors: Barkatt AA. , Sang Jing C. , Xing S.-B. , Guo Yan , Pegg I. L. , Barkatt AL. 
Published: March 2011

ABSTRACTMany types of procedures have been developed for testing of the chemical durability of nuclear waste forms. These procedures differ from each other in critical aspects, such as duration, replenishment or non-replenishment of the leachates, and S/V ratio. As a result, different answers to basic questions, such as how waste-form leachability depends on its chemical composition, are obtained when different test methods are used. Furthermore, the possibility that some glasses may exhibit a leach rate excursion within the test period causes the composition dependence to be an even more sensitive function of test duration and of leachant replenishment. These factors also complicate the use of test data for the prediction of long-term waste form behavior.
Applicatons of Hydration Thermodynamics to In-Situ Test Results
Authors: Plodinec M. J. , Wicks G. G. 
Published: March 2011

ABSTRACTAn extremely important question for the eventual disposal of glass in natural environments is the relevance of laboratory testing of glass durability to the long-term performance of glass in geologic environments. The purpose of this study was to attempt to provide an empirical answer to that question, by applying the hydration thermodynamics approach (which has successfully been applied to laboratory tests of glass durability) to the results of longer-term testing in natural environments.The results show that hydration thermodynamics is a useful tool for explaining the effects of glass composition observed in in-situ tests, in several environments. Thus, it appears to provide a link between laboratory tests of glass durability and the results of in-situ tests in natural environments. Perhaps the most important conclusion of this effort is that the in-situ test results emphasize the importance of control of chemical composition during glass production as a means of achieving a durable glass.
High Level Radioactive Waste Glass Production and Product Description
Authors: Sproull James F. , Marra Sharon L. , Jantzen Carol M. 
Published: March 2011

ABSTRACTA summary of the current state of defense high-level radioactive waste in the U.S. is presented. Reasons for the selection of borosilicate glass as the matrix for the waste glass product over other glasses is enunciated. The product and processing requirements which the waste glass must meet are summarized. Finally the effects of crystallization and glass-in-glass phase separation on waste glass durability are discussed. Crystallization, under typical cooling conditions, has minimal effect on durability but glass-in-glass phase separation should be avoided.
Generation of Volatile Organic Compounds by Alpha Particle Degradation of Wipp Plastic and Rubber Material
Authors: Reed Donald T. , Molecke Martin A. 
Published: March 2011

ABSTRACTThe generation of volatile organic compounds (VOCs), hydrogen, and carbon oxides due to alpha particle irradiation of polyethylene, polyvinylchloride, hypalon, and neoprene, is being investigated. A wide diversity of VOCs was found including alkenes, alkanes, alcohols, ketones, benzene derivatives, and nitro compounds. Their yields however, were quite low. The relative amounts of these compounds depended on the material, atmosphere present, and the absorbed dose. This investigation will help evaluate the effect of ionizing radiation on the long-term performance assessment and regulatory compliance issues related to the Waste Isolation Pilot Plant (WIPP).
Development of a Gas-Generation Model for the Waste Isolation Pilot Plant
Authors: Brush L. H. , Garner J. W. , Storz L. J. 
Published: March 2011

ABSTRACTDesign-basis transuranic (TRU) waste to be emplaced in the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico may generate significant quantities of gas, which may affect the performance of the WIPP with respect to regulations for radioactive and/or chemically hazardous waste constituents. We are developing a model to predict gas generation in WIPP disposal rooms during and after filling and sealing. Currently, the model includes: (1) oxic and anoxic corrosion of steels and other Fe-base alloys, including passivation and depassivation; (2) microbial degradation of cellulosics with O2, NO3-, FeO(OH) , SO42-, or CO2as the electron acceptor; (3) α radiolysis of brine; (4) consumption of CO2and, perhaps, H2S by Ca(OH)2(in cementitious materials) and CaO (a potential backfill additive). The code simulates these processes and interactions among them by converting reactants (steels, cellulosics, etc.) to gases and other products at experimentally observed or estimated rates and plotting temporal reaction paths in three-dimensional phase diagrams for solids in the Fe-H2O-CO2-H2-H2S system.
Laboratory Testing of Waste Glass Aqueous Corrosion; Effects of Experimental Parameters
Authors: Ebert W.L. , Mazer J.J. 
Published: March 2011

ABSTRACTA literature survey has been performed to assess the effects of the temperature, glass surface area/leachate volume ratio, leachant composition, leachant flow rate, and glass composition (actual radioactive vs. simulated glass) used in laboratory tests on the measured glass reaction rate. The effects of these parameters must be accounted for in mechanistic models used to project glass durability over long times. Test parameters can also be used to highlight particular processes in laboratory tests. Waste glass corrosion results as water diffusion, ion exchange, and hydrolysis reactions occur simultaneously to devitrify the glass and release soluble glass components into solution. The rates of these processes are interrelated by the effects of the solution chemistry and glass alteration phases on each process, and the dominant (fastest) process may change as the reaction progresses. Transport of components from the release sites into solution may also affect the observed corrosion rate. The reaction temperature will affect the rate of each process, while other parameters will affect the solution chemistry and the particular processes that are observed during the test. The early stages of corrosion will be observed under test conditions which maintain dilute leachates and the later stages will be observed under conditions that generate more concentrated leachate solutions. Typically, water diffusion and ion exchange reactions dominate the observed glass corrosion in dilute solutions, while hydrolysis reactions are dominant in more concentrated solutions. Which process controls the long-term glass corrosion is not fully understood, and the long-term corrosion rate may be either transport- or reaction-limited.
Densification of Salt-Occluded Zeolite a Powders to a Leach-Resistant Monolith
Authors: Lewis Michele A. , Fischer Donald F. , Murphy Christopher D. 
Published: March 2011

ABSTRACTPyrochemical processing of spent fuel from the Integral Fast Reactor (IFR) yields a salt waste of LiCI-KCI that contains approximately 6 wt% fission products, primarily as CsCI and SrCl2. Past work has shown that zeolite A will preferentially sorb cesium and strontium and will encapsulate the salt waste in a leach-resistant, radiation-resistant aluminosilicate matrix. However, a method is still needed to convert the salt-occluded zeolite powders into a monolith suitable for geologic disposal. We are thus investigating a method that forms bonded zeolite by hot pressing a mixture of glass frit and sait-occluded zeolite powders at 990 K (717°C) and 28 MPa. The leach resistance of the bonded zeolite was measured in static leach tests run for 28 days in 363 K (90°C) deionized water. Normalized release rates of all elements in the bonded zeolite were low, <1 g/m2d. Thus, the bonded zeolite may be a suitable waste form for IFR salt waste.
Expansion of Cementitious Materials Exposed to Sulfate Solutions
Authors: Pommersheim James M. , Clifton James R. 
Published: March 2011

ABSTRACTDisposal of low-level radioactive waste in concrete vaults buried underground is being considered in the United States and a potentially significant degradation process is sulfate attack. The results of experimental studies and of modeling of the kinetics of sulfate attack of cement-based materials are given. It was concluded that the expansion process involves a two-stage mechanism. The first stage is likely to be diffusion controlled and the second stage appears to be acceleratory due to the development and spread of cracks.
Elements Present in Leach Solutions from Unsaturated Spent Fuel Tests
Authors: Finn P. A. , Bates J. K. , Hoh J. C. , Emery J. W. , Hafenrichter L D. , Buck E. C. , Gong M. 
Published: March 2011

ABSTRACTPreliminary results for the composition of the leachate from unsaturated tests at 90°C with spent fuel for two successive periods of ~60 days each with pretreated J-13 groundwater are reported. The pH of the leachate solutions ranged from 4 to 7. The americium concentration was 104 to 105 greater than that reported for saturated spent fuel tests in which the leachate pH was 8. The major fraction of material in the leachate was present as colloids containing both americium and curium. The presence of actinides in a form not currently directly included in repository radionuclide transport models provides information that can be used in spent fuel reaction modeling, the performance assessment of the repository and the design of the engineering barrier system.
Comparison of the Dissolution Behaviour of Various UO2Samples in Saline Solution at 100°C Under Reducing Conditions
Authors: Stroes-Gascoyne S. , Tait J.C. , Porth R.J. , McConnell J.L. , Duclos A.M. 
Published: March 2011

ABSTRACTThe separate effects of alpha- and gamma-radiolysis on UO2dissolution can be studied with unirradiated UO2, whereas studies vith used nuclear fuel necessarily always include both alpha- and gamma-radiolysis effects. This paper attempts to separate these effects by comparing the leaching behaviour in saline solution of a number of UO2samples (each vith a particular radiation characteristic or chemical property inherent to used fuel) vith the leaching behaviour of used fuel. Data from leaching experiments vith lov- and high-burnup CANDU (CANada Deuterium Uranium) fuels are also compared. The results indicate that the presence of an alpha field at 100°C under reducing conditions does not increase UO2dissolution but suggest that the combined effects of the beta and gamma fields in used CANDU fuel may enhance UO2dissolution.
A Comparative Study of the Natural and Experimental Corrosion of Poorly Durable Potash-Lime-Silica Glasses
Authors: Cooper G.I. , Cox G.A. 
Published: March 2011

ABSTRACTNaturally corroded, poorly durable glasses are compared with results from MCC-4 leach tests on similar glasses. It is suggested that different corrosion products are formed at different temperatures; therefore, care should be taken when interpreting experimental leach rates. Solution composition, pH and flow around the sample can also have a profound effect on corrosion rates.
Effect of Surface Layers on the Dissolution of Nuclear Waste Glasses
Authors: Xing Shi-Ben , Buechele Andrew C. , Pegg Ian L. 
Published: March 2011

ABSTRACTExplanation of the striking non-linear effect of glass composition on the aqueous dissolution represents an important challenge to existing dissolution mechanisms. Surface layers that are formed during glass dissolution may play an important role in this effect. One chemically reactive and one less-reactive nuclear waste glass (leachate concentrations differ by about a factor of 10) were reacted in deionized water. Two types of glass powders were used: Type A powders were pristine glass powders; Type B powders were the glass powders which had been reacted for 120 days to develop the surface layers. Both the solution concentrations and the surface layers were investigated. The experimental observations indicate that: (i) There is a range of glass compositions over which small differences in composition lead to large changes in both reaction rates and surface layer thickness; and (ii) The reaction rate is strongly affected by the formation of the surface layer (the layer appears to be protective) and cannot be explained in terms of saturation effects alone. The findings are contrary to the conclusion of a previous study and serve to highlight the inadequacy of existing dissolution models predicated on an overly simplistic mechanism, especially with regard to glass composition effects.
Non-Linearity in Glass Composition Dependence of Dissolution Rates: Effect of Solution pH
Authors: Xing Shi-Ben , Muller Isabelle S. , Pegg Ian L. 
Published: March 2011

ABSTRACTIn our previous studies on the optimization of glass compositions for high-level nuclear waste vitrification it was found that, over certain composition ranges, PCT leachate concentrations increased dramatically with very small changes in glass composition. The large differences that are observed between the leachate pH values for the “durable” and the “less-durable” glasses is one possible cause for this strongly non-linear glass composition effect; conversely, the pH difference may be merely another symptom. In this study, four simulated nuclear waste glasses (two of the less-durable and two of the durable types), were leached in both zwitterionic and inorganic buffer solutions, at fixed pH-values in the ranges of 7 to 12. The very different leaching behaviors of the two types of glasses persisted and, furthermore, different pH-dependence was found despite their very similar glass composition. This study suggests that the leachate pH difference observed between the less-durable and the durable glasses under uncontrolled pH conditions is not the major cause of the large difference of leaching behavior between those glasses. The normalized release ratios of soluble components (B, Li, Na) to Si show significant differences for the two types of glasses.
RBS and PIXE Analysis of Alteration Layers on Waste Glass in a Leaching Test Under Reducing Condition
Authors: Sasakawa Kaoru , Imakita Tsuyoshi , Wada Ryutaro , Matsuda Fumio 
Published: March 2011

ABSTRACTA corrosion test of model waste glass was carried out with and without a carbon steel under reducing condition in a glove box purged with nitrogen gas, and then the characteristics of alteration layers of the glass were examined.On the glass surfaces corroded under reducing condition with carbon steel, a thick precipitated layer was observed by Scanning Electron Microscopy (SEM). In this layer concentrated iron was observed by Particle Induced X-ray Emission Spectrometry (PIXE) and Rutherford Backseattering Spectrometry (RBS). Such a thick precipitated layer was not observed on the corroded glass under oxidizing conditions with and without carbon steel and reducing condition without carbon steel.
XPS and XRD Studies of Samples from the Natural Fission Reactors in the Oklo Uranium Deposits
Authors: Sunder S. , Miller N.H. , Duclos A.M. 
Published: March 2011

ABSTRACTMineral samples from the natural fission reactors 10 and 13 in the Oklo uranium deposits were studied using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) to gain information about the long-term behaviour of UO2 fuel in a geological disposal vault. Two samples from reactor zone 10 (samples # D81N-190292 and D73-88) and one sample from reactor zone 13 (sample # SD37-S2/CD) were analysed. Low-resolution XPS spectra were recorded to determine the major elements present in the ore. High-resolution spectra were recorded to gain information about the chemical state of the elements present in the mineral samples. The samples show low values for the U6+/U4+ ratio. The oxidation state of uranium in these samples is even lower than that in U409. The binding energies of the Pb 4f bands indicate most of the Pb is in the +2 oxidation state in these samples. The C Is band indicates the presence of organic carbon. XRD analysis shows that the main uranium-bearing phase is uraninite and lead is present mainly as galena. The significance of the results for nuclear fuel waste management is discussed.
Significance of the Effect of Mineral Alteration on Nuclide Migration
Authors: Murakami Takashi , Ohnuki Toshihiko , Isobe Hiroshi , Sato Tsutomu , Yanase Nobuyuki , Kimura Hideo 
Published: March 2011

ABSTRACTIn order to clarify the effect of mineral alteration on nuclide migration, we examined the processes, mechanisms, and kinetics of chlorite weathering, and the uranium concentrations in minerals and rocks at Koongarra, Australia. The observed concentrations of uranium in rocks were compared to those calculated. The sequence of chlorite weathering may be simply expressed as a chlorite → vermiculite → kaolinite conversion. These minerals occur as a function of depth, which corresponds well to uranium concentrations on the meter scale. Iron minerals, closely related to the uranium redistribution, are released during the weathering. The first-order kinetic model of the weathering process suggests that the weathering rate is not constant but time-dependent. The uranium concentrations are qualitatively proportional to the extent of the weathering; the weathered part having higher uranium concentration. Uranium mainly occurs with iron minerals, and sub micron sized saléeite, a uranyl phosphate, is one of the most probable uranyl phases associated with the iron minerals. The uranium fixation mechanisms are probably saléeite microcrystal coprecipitation and sorption to the iron minerals. Our model, which describes uranium concentrations in rocks as a function of time, shows that the transition zone (a vermiculite dominant area) plays an important role in the uranium migration. We have established that weathering of chlorite has affected the redistribution of uranium for more than one million years. The present study demonstrates the significance of mineral alteration when we estimate nuclide migration for geologic time.