bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effects of Bacteria on Crystalline Rock
Authors: Ann Brown D. 
Published: March 2011

ABSTRACTMany reactions involving inorganic minerals at water-rock interfaces have now been recognized to be bacterially mediated; these reactions could have a significant effect in the excavation of vaults for toxic and radioactive waste disposal. To investigate the role that bacteria play in the natural aqueous environment of crystalline rock the microbial growth factors of nutrition, energy and environment are described. Microbial activity has been investigated in Atomic Energy of Canada's Underground Research Laboratory (URL), situated in the Archean granitic Lac du Bonnet Batholith, Winnipeg, Manitoba. Faults, initiated in the Early Proterozoic, and later-formed fractures, provide ground-water pathways. Planktonic bacteria, free-swimming in the groundwater, have been observed in over 100 underground borehole samples. The number of bacteria varied from 103to 105mL-1, and appeared to decrease with depth and with increased salinity of the water. However, in the natural environment of deep (100–500 m) crystalline rocks, where nutrition is limited, formation of biofilms by sessile bacteria is a successful survival strategy. Natural biofilms at the URL and biofilms grown in bioreactors have been studied. The biofilms can accumulate different elements, depending upon the local environment. Precipitates of iron have been found in all the biofilms studied, where they are either passively accumulated or utilized as an energy source. Within the biofilm active and extensive biogeochemical immobilization of dissolved elements is controlled by distinct bacterial activities which are sufficiently discrete for hematite and siderite to be precipitated in close proximity.
Sorption Mechanism of Pu, Am and Se on Sodium-Bentonite
Authors: Shibutani Tomoki , Yui Mikazu , Yoshikawa Hideki 
Published: March 2011

ABSTRACTThe distribution coefficients (Kd) were measured for Pu, Am and Se on sodium-bentonite in bentonite-equilibrated distilled water in a pH range 4~ 10. Sodium-bentonite includes sodium-montmorillonite and ferrous minerals such as pyrite. The experiments were carried out by using the batch method under aerobic conditions for Pu, Am and under anaerobic conditions for Se. The distribution coefficients for Pu and Am were in the range 100~ 102m3/kg on sodium-bentonite in the above pH range. The sorption of Pu and Am was modeled by ion exchange of these cationic aqueous species with interlayer cations of sodium-bentonite. The distribution coefficients of Se on sodium-bentonite were interpreted by using a surface complexation model. The model was based on the assumption that the sorption behavior was dominated by ferric-oxyhydroxide, goethite, coating on the surface of pyrite. Sorption behavior of Am in compacted bentonite were also discussed by using cation exchange model.
Influence of Microbiological Activity on the Mobility of Redoxsensitive Radionuclides in Sediments
Authors: Stroetmann Irmgard , Kämpfer P. , Dott W. , Schüle J. , Sokotnejat R. , Winkler A. , Pekdeger A. 
Published: March 2011

ABSTRACTThe influence of microbial activity on the transport and migration behaviour of redox-sensitive radionuclides (e.g. Technetium (Tc) and Selenium (Se)) in groundwater environment were investigated within an interdisciplinarary research program. Soil material and sediments were investigated with batch- and recircu-lation column experiments. The number of microorganisms in the water was determined by counting the colony forming units (CFU) on R2A agar at regular periods.The results of sterile and non sterile recirculation column experiments showed within 80 days a high fixation of the radionuclides in the unsterile samples (80% of Tc, 50% of Se compared with the initial concentration Ao), and no fixation in the sterile samples. There was no difference in the redox values.It could be shown that the immobilisation of the redox-sensitive elements Tc and Se are strongly determined by microbial activity, depending on the different sediments and their microbial live stock. There are indications that the microorganisms found in the non sterile columns are allochthonous bacteria which were dragged into the experimental systems and samples during laboratory work and sampling. The composition of the microbial flora was shown to be very heterogenous and different in each individual column and within the same column at different times. Thus these columns might have been contaminated with microorganisms during sampling and handling of the experimental systems under non sterile conditions, as done generally in most laboratories.
Comparison of International Source-Term Codes
Authors: Zhou W. , Apted M. J. , Robinson P. 
Published: March 2011

ABSTRACTSource-term codes to predict the release of radionuclides from nuclear waste packages have been developed and implemented worldwide. A survey and initial comparison of the attributes and capabilities of 13 international source-term codes was recently completed. This preliminary analysis focused on comparison of transport factors/processes and solution methods. This initial comparison is a necessary first step in a properly-conceived, systematic benchmarking of source-term codes. Advantages of such a comparison include assurance of the mathematical correctness of implemented models, comparison and quantification of variances introduced by different types of simplifications, and identification and quantification of the impact of near-field processes.
Three-Diiensional Coupled Ground Water Flow. Thermal Transport and/or Migration of Nuclides Analysis by Boundary Element Method
Authors: Kawamura Ryuji 
Published: March 2011

ABSTRACTIn the safety analyses of radioactive waste disposal, it is important and indispensable to analyze coupled problems of ground water flow, thermal transport and/or migration of nuclides. The three-Dimensional coupled problems is solved by boundary element method in this paper. The results of this method are compared with those experiments of JAERI and STRIPA SWEDEN on the thermal problem, and with those analyses of analytical and FEM results on the migration problem. In this formulation, natural convection is considered by Boussinesq approximation. An example of coupled ground water flow and migration of nuclides with decay chain U2 3 4 → Th2 3 0→ Ra2 2 6 is also tried.
Diffusive Transport of Carbon Dioxide through USW-G4 Topopah Spring Tuffs
Authors: Sarwar Ali M. , King Franklin G. , Ilias Shamsuddin 
Published: March 2011

ABSTRACTThe estimation of diffusive transport of gases through tuffs is important in order to assess whether Yucca Mountain is an environmentally safe and acceptable repository for high-level radioactive waste. The purpose of this study is to provide effective diffusivity data which may be used to calculate the amount of diffusion of carbon dioxide through Yucca Mountain tuff layers to the environment. The effective diffusivity of carbon dioxide was measured for tuff samples from five different layers of the USW-G4 drillhole, which is located in the central part of the proposed repository horizon. The tuff samples studied are from the following layers and depths: Vapor Phase (83.6 m), Upper Lithophysal (130.1 m), Middle Nonlithophysal (224.5 m), Lower Lithophysal (243.9 m, 266.9 m, 297.3 m and 335.2 m), and Lower Nonlithophysal (356.3 m and 371.0 m). A steady-state, counter-diffusion method, using gas chromatographic analysis, was used to determine the effective diffusivity of carbon dioxide through tuff samples. Effective diffusivity increased with temperature between 25°C and 125°C for all layers. The effect of temperature on diffusivity correlated well using second-order polynomials. The porosity, specific surface area and mean pore radius were also determined. In general, diffusivity increased with porosity, specific surface area and mean pore radius, but did not correlate well. From the measured data , it appears that the diffusion takes place primarily in the combined Knudsen and bulk diffusion regimes.
Chemical Implications for the Presence of Introduced Materials in the Post-Emplacement Environment
Authors: Meike Annemarie 
Published: March 2011

ABSTRACTThis paper addresses our ability to predict the chemical consequences of the presence of introduced materials, many of them man-made, in a radioactive waste repository. The chemical modeling ability required to describe this environment over a 10,000 year period is unique and unprecedented. It requires knowledge of parameters that have never been measured, many of them with respect to introduced materials. This paper discusses considerations that are required to establish the potential significance of introduced materials, especially those that could compromise the lifetime of the waste packages or affect the transport of radionuclides from breached containers. The paper presents issues related to the stability of individual compounds, the potential alteration of predicted natural chemical reactions, the potential moderation of those effects by natural zeolites, and the potential for interactions at elevated temperatures between rock, water, water vapor, radiation, waste package, and introduced materials.
Probabilistic Calculations of Groundwater Travel Time in Heterogeneous Three-Dimensional Porous Media
Authors: Bagtzoglou Amvrossios C. , Baca Robert G. 
Published: March 2011

ABSTRACTGroundwater travel time (GWTT) estimation at a potential high-level waste (HLW) repository is subject to various technical uncertainties. These uncertainties stem from model and data uncertainties and cannot be resolved with field tests because of the long time (> 1,000 yr) and large space (> 5,000 m) scales involved. Therefore, computational methods for demonstrating and determining compliance with the GWTT rule will be used. Stochastic theory based approaches constitute a natural framework for performing GWTT estimations under conditions of uncertain and/or limited data.This study employs the generation of spatially correlated hydraulic conductivity fields by the Nearest Neighbor Model (NNM). Repeated (Monte Carlo) realizations of the statistically equivalent random fields are obtained, and the saturated steady-state groundwater flow equation is solved. These results are then used to estimate GWTT along particular paths by releasing a large number of water particles at various starting points. By doing so, path variability is sampled through the realization ensemble space and also through the independent particle “flights” within a specific flow field realization. The uncertainty in predicted GWTT due to parameter variability is assessed for a data set characteristic of the saturated zone at Yucca Mountain at three levels of parameter heterogeneity. However, since several parameters and the boundary conditions of the problem have been arbitrarily assumed, direct conclusions regarding the proposed Yucca Mountain site cannot be drawn from this study.
Water - Compacted Na-Bentonite Interaction in Simulated Nuclear Fuel Disposal Conditions: the Role of Accessory Minerals
Authors: Melamed A. , Pitkänen P. 
Published: March 2011

ABSTRACTIn an earlier laboratory study1, ion exchange processes and smectite alteration were investigated through the interaction between compacted Na-bentonite (Volclay MX-80) and simulated granitic groundwater solutions. The change of montmorillonite from Na- to Ca-rich was found to be the major alteration process in the bentonite. In the water, a concentration decrease in Ca, Mg and K, and an increase in Na, HCO3 and SO4 were recorded. The total amount of Ca available in the water, however, was found insufficient to account for the recorded formation of Ca-smectite, and it is therefore assumed that the accessory Ca-bearing minerals in the bentonite provide the fundamental source of these cations.X-ray powder diffraction analyses and microscope observations of the bentonite samples were re-conducted. Quartz, feldspars, pyrite, calcite and traces of gypsum were revealed as the primary accessories. In reacted samples, goethite and siderite are found as the secondary mineral products in association with corroded pyrite grains, while calcite and gypsum tend to disappear. From these results it is assumed that the oxygen present in the water and bentonite pore space promotes the oxidation of pyrite (dissolved) and the precipitation of goethite. The pore water pH decreases and calcite is partly dissolved. Through the dissolution, the bulk amount of Ca ions in addition to those arising by diffusion from the water is provided. Some of the reaction-released bicarbonate and Fe2+ re-precipitate in the bentonite as siderite, while the rest (as also SO4 ions) diffuse into the water.Though the relative oxygen content in the experiment may be considered higher than that of the repository concept for nuclear fuel disposal (interaction in a semi-closed system with high water/bentonite ratio), the near field geochemistry predictions imply limited oxidizing conditions, which will be characterized by the above-described processes in sulphide-bearing bentonite and occur for some time after the sealing of the repository.
Moisture Movement in a Clay based Buffer Material under Isothermal Conditions
Authors: Mohamed A.M.O. , Shooshpasha I. , Yong R.N. , Onofrei C. 
Published: March 2011

ABSTRACTSeveral series of one dimensional tests were performed to examine the moisture and soil water potential distributions in the buffer material compacted to a dry density of 1.67 Mg/m3 and volumetric water content of 0.28. Diffusivity parameters were calculated using the measured moisture profiles combined with the finite difference method. Powell’s optimization was used to determine the material parameters.It is experimentally demonstrated that the moisture distribution is highly dependent on the test boundary conditions. When volume change was allowed to take place during infiltration process, the buffer material adsorbs more water than in the case of no volume change. This is attributed to an increase in hydraulic conductivity by one order of magnitude. As the volumetric water content increases soil water diffusivity increases and soil water potential decreases.
Reactions of High-Feo Olivine Rock with Groundwater and Redox-Sensitive Elements Studied by Surface-Analytical Methods and Autoradiography
Authors: Hellmuth K-H. , Siitari-Kauppi M. , Rauhala E. , Johanson B. , Zilliacus R. , Gijbels R. , Adriaens A. 
Published: March 2011

ABSTRACTThe reaction of unaltered olivine rock with groundwater and redox-sensitive elements (Tc, Re, and U) was investigated at elevated temperatures in the laboratory. Olivine was found to react easily with water taking up trace elements in alteration products. The alteration products were characterized using Rutherford backscattering, secondary ion mass spectrometry and electron microprobe analysis. The sample surfaces were studied by autoradiography and digital image processing techniques.
Equilibria in Saturated Bentonite
Authors: Arthur R. C. 
Published: March 2011

ABSTRACTIt has been proposed that smectite clays, the predominant minerals in bentonite, are metastable solid solutions whose compositional heterogeneity prevents strict adherence to fixed ion activities and activity ratios characterizing invariant equilibria among stoichiometric phases [1,2]. This is qualitatively confirmed in the present analysis of exceptionally well-constrained experimental data [3] using a solid-solution model defined by the phase rule and estimated ideal site-mixing parameters. The results suggest that equilibria are approached among smectite solid solutions and kaolinite or halloysite, and that these minerals coexist metastably with respect to asiO2(aq)· Irreducible uncertainties are generated in the model by analytical and conceptual deficiencies in understanding compositional variability in smectite. However, their estimated effects on smectite’s stability are relatively small, and are comparable to the effects of experimental uncertainty in standard Gibbs energies on the stabilities of stoichiometric minerals.An alternate analysis of the data further confirms that smectite does not behave like a stoichiometric phase [3]. Ion-exchange models for this clay mineral may therefore be thermodynamically ill defined because stoichiometric behavior is assumed implicitly under limiting conditions of fixed proportions of cations on exchange sites. Ion exchange is a pragmatic simplification enabling empirical analysis of some experimental data. However, its empirical, rather than thermodynamic, basis should not be overextended to conditions that are beyond an experimentally calibrated range.
Characterization of a Lignite Ash from the Metc Gasifier II. Scanning Electron Microscopy
Authors: Stevenson R. J. , Larsen R. A. 
Published: March 2011

AbstractLignite coal ash produced in a stirred, fixed-bed gasifier at the Morgantown Energy Technology Center (METC) has been studied by scanning electron microscopy using both morphologic and chemical analyses. Detailed chemical analyses of phases, grains, and traverses across grains illustrate the heterogeneous nature of the ash. These data support the concept that most of the ash was formed by partial melting and subsequent crystallization and agglomeration.
Disposal of Western Fly Ash in the Northern Great Plains
Authors: Groenewold Gerald F. , Hassett David J. , Koor Robert D. , Manz Oscar E. 
Published: March 2011

AbstractLeachates from western fly ashes are typirally alkaline. Our studies indicate a strong correlation between alkalinity of western fly ash leachate and trace element concentrations. Elements of particular concern include As, Se, and Mo. A base neutralization mechanism is operative in all of the overburden types found at mine disposal sites in western North Dakota. Regional geological similarity suggests that this mechanism is operative throughout the Northern Great Plains. Although the mechanisms of neutralizatioti are speculative, laboratory experiments indicate significant neutralization at all levels of base above background levels. Long-term monitoring of fly ash disposal-sites indicates that alkaline neutralization of fly ash leachate is occurring. Further, field data indicate that toxic trace elements (particularly As and Se) in disposal site leachates decrease in concentration as the pH of the learhate is neutralized. Thus, the intrinsic corditions at Northern Great Plains fly ash disposal sites appear to promote significant attenuation of critical toxic elements found in fly ash leachates. Regardless of the pH, leachates in those settings have high concentrations of sodium and sulfate. Western fly ashes are commonly cementitious. Our studies indicate that fly ashes comnoniy develop significant strength after several months of burial, particularly if emplaced in an unsaturated disposal setting. Once cementitious reactions have occurred, the fly ashes show little potential for leaching. Thus, a combination of intrinsic disposal-site conditions and the cementitious behavior of the fly ashes suggests that surface-mine disposal of western fly ashes in the Northern Great Plains, assuming proper disposal-site selection, may not cause long-term environmental problems associated with toxic trace elements.
The Characterization of Alloyed NiGeAuAgAu Ohmic Contacts to AlInAs/GaInAs Heterostructure by Auger Electron Spectroscopy and Wavelength Dispersive X-Ray Analysis
Authors: Capani P. M. , Mukerjee S. D. , Rathbun L. , Griem H. T. , Wicks G. W. , Eastman L. F. , Hunt J. 
Published: March 2011

ABSTRACTIn a lattice-matched <100> InP/Ga0.47In0.53As/Al0.48In0.52As system used for modulation-doped field effect transistors (MODFETs), low resistance ohmic contacts to the two-dimensional electron gas have been fabricated using alloyed NiGeAuAgAu metallization. In this work we examine the use of Auger electron spectroscopy (AES) and wavelength dispersive x-ray spectroscopy (WDX) analyses for studying the metal-semiconductor interactions and their correlation with measured ohmic contact resistance.
The Use of Leed for the Characterization of Surface Damage from Pulsed Laser Irradiation
Authors: Helms Aubrey L. , Cho Chin-Chen , Bernasek Steven L. , Draper Clifton W. 
Published: March 2011

ABSTRACTLow Energy Electron Diffraction (LEED)-Spot Profile Analysis and Auger Electron Spectroscopy (AES) have been used to study the response of Mo(100) single crystal surfaces to Q-switched, frequency doubled Nd:YAG laser pulses. The experiments were conducted in a special ultra-high vacuum (UHV) system which allowed the surfaces to be irradiated under controlled conditions. Laser fluences both above and below the melt threshold were employed. For the melted surfaces, good epitaxial regrowth was observed. The spot profile analysis indicates the formation of random islands on the surfaces. Surfaces which had been previously disordered by 3 KeV Ar+ implantation were laser surface melted and observed to regrow epitaxially as has been observed in the case of ion implanted silicon. The formation of the islands and stepped structures is explained by considering the activation of dislocation sources by the induced thermal stresses resulting in slip.
Ultrasensitive Elemental Analysis of Materials Using Sputter Initiated Resonance Ionization Spectroscopy
Authors: Parks J. E. , Beekman D. W. , Schmitt H. W. , Spaar M. T. 
Published: March 2011

ABSTRACTSputter Initiated Resonance Ionization Spectroscopy (SIRIS) is a technique being developed by Atom Sciences, Inc. to perform ultrasensitive elemental analysis of materials. SIRIS uses sputtering to atomize a solid sample and resonance ionization (RIS) to selectively ionize an element of interest. The SIRIS technique is capable of detecting impurities at the 0.1 ppb level (5 × 1012/cm 3) in a routine analysis time of 5 minutes. RIS and the SIRIS technique are briefly reviewed. We report a detection efficiency for SIRIS of 2 ppb sensitivity and recent results are given for standard well-characterized samples of boron-doped silicon. Current progress is described for the development of depth profiling and the analysis of silicon in gallium arsenide. The SIRIS detection of silicon in standard reference materials certified by NBS is presented.
Characterization of Thin Metal Films by SIMS, AUGER, and TEM
Authors: Furman B. K. , Benedict J. P. , Granato K. L. , Prestipino R. M. , Shih D. Y. 
Published: March 2011

ABSTRACTSecondary ion mass spectrometry (SIMS), Auger spectroscopy, and transmission electron microscopy (TEM) were applied to study Au, Cu, Ti, Ti-W, Cr, Al-Cu, and Al metal films deposited on both Si and ceramic substrates.SIMS analysis of as-deposited metal films was used to characterize impurity levels, both metallic and gaseous, incorporated during deposition. The results revealed that the levels varied under generally accepted deposition conditions. As-deposited and annealed films were examined with SIMS, Auger, and TEM to study interdiffusion, grain growth, and impurity segregation as a function of processing conditions. Metallic impurities were observed to modify Au/Ti interdiffusion. Large variations in residual H, C, O, and N were observed in as-deposited Al and Al-Cu films.Hydrogen, incorporated during deposition of Ti films, was observed to redistribute after thermal annealing in N2 or thermal cycling in forming gas (N2-10% H2). Samples thermally cycled in forming gas absorbed additional H into the Ti layer. SIMS/ion imaging was used to study the incorporation and segregation of H. Differences in H behavior were observed to be dependent upon metal structure, composition, and substrate material.