bluuebunny/crossref_metadata_2025_split huggingface dataset:
Grain Boundary Phenomena in ZnO Varistors
Authors: Einzinger Richard 
Published: March 2011

ABSTRACTThe paper resumes essential grain boundary phenomena which were found experimentally by microcontact measurements on adjacent grains. The results suggest a ZnO homojunction model. Calculations of defect equilibria in the Schottky defect model show that homojunctions can be formed during the cooling period under the influence of an extrinsic donor species by a shift of the bulk defect equilibrium and intersecting diffusion profiles of oxygen- and zinc vacancies near the grain boundary.Recent experiments indicate that heterogeneous Bi2O3-segregation layers with a dissolved zinc-antimony-oxide compound are transformed to ZnO epitaxial layers plus a fine grained pyrochlore phase of zinc-bismuth-antimony oxide during the cooling period. Thus epitaxial ZnO layers eliminate thin Bi2O3-films and form homogeneous connections of adjacent grains.
Secondary Ion Images of Impurities at Grain Boundaries in Polycrystalline Silicon
Authors: Pollock Gary A. , Deline V. R. , Furman B. K. 
Published: March 2011

ABSTRACTA CAMECA IMS-3F secondary ion microscope has been used to investigate the presence of impurities in cast polycrystalline silicon wafers and to determine their lateral distribution. Cesium and oxygen ion bombardment were used to selectively detect potential impurities and extract their lateral distribution with submicron lateral resolution.Images of H, C, O, P, and Cu segregated in grain boundaries have been obtained from polycrystalline silicon.
Validation of Hydrogeologic Models to Describe Ground-Water Flow in the Crystalline Basement of Northern Switzerland
Authors: Andrews Robert W. , Kimmeier Francesco , Perrochet Pierre , Kiraly Laszlo 
Published: March 2011

AbstractTwo hydrogeologic conceptual models have been developed to describe the ground-water flow regime in the crystalline rocks of northern Switzerland. The purpose of these models has been to characterize the regional and local ground-water flow systems and to define the groundwater travel paths and velocities from potential waste disposal areas to the biosphere. Several parameters have been used as validation tools in the modeling process. These include potentiometric data, volumetric discharge rates, infiltration rates, bulk and isotopic geochemistry, and temperature distributions. The results of utilizing these validation tools are described.
Confidence in Solutions of Flow Through Stochastically Generated Hard Rock Formations
Authors: Braester Carol , Thunvik Roger 
Published: March 2011

AbstractConfidence in solutions of flow through stochastically generated hard rock formations was studied with the aid of a simplified synthetic model. The formation is conceptualized as a fracture network intersecting an impervious rock mass. The geometrical properties of the fracture network were assumed to be known while fracture transmissivities were considered a stochastic process.First, network fracture transmissivities were generated using a given probability distribution function. This a priori model was considered the “true formation”. In a second step, only a limited amount of information, similar to that obtained in reality from boreholes, was used to construct a conditioned-by-measurement model.Identical flow tests were performed on a formation constructed with limited data and on the “true formation”. The ratio of the rates of flow resulting from these tests was considered a measure of confidence in the stochastically generated formation. The results, with this model and a particular data set, show uncertainty values between 47% to 63%, corresponding to fracture sample sizes of 11% and 2% respectively, from the total number in the network.
The Assessment of Reducing Conditions at Depth in Granitic Rock
Authors: Wikberg Peter 
Published: March 2011

AbstractDeep groundwaters from sites potentially suitable for the disposal of spent nuclear fuel have been chemically characterized. The waters are classified according to their contents of main constituents and pH as shallow or deep groundwaters. New equipment consisting of a mobile field laboratory and downhole pH and Eh probes has been successfully used in the investigations.The deep groundwaters contain appreciable amounts of iron and sulphide and Eh values monitored downhole are more negative than those obtained from calculations based on the ferrous iron ferric hydroxide system. Laboratory simulations of the water rock interaction indicate that the dissolved oxygen is quickly removed when the water is in contact with the rock.
Investigations on the Role of Surface Layers in HLW Glass Leaching
Authors: Conradt R. , Roggendorf H. , Scholze H. 
Published: March 2011

AbstractA corrosion test series was performed to clarify the role of reaction product layers on the corrosion of a simulated HLW borosilicate glass in a salt brine under hydrothermal conditions. The layers were unprotective at 200°C. At 120°C, slight protective effects ocurred when the leachant contained dissolved reaction products. The consequence for the long term behaviour between 120 and 200°C is a constant glass dissolution rate.
U.S. Nuclear Defense Waste Program Current Development and Key Research Areas
Authors: Walton Ray D. , Chacey Kenneth A. 
Published: March 2011

AbstractThe United States has been engaged in defense nuclear activities for over 40 years. The primary goal of the Defense Waste and Byproducts Management Program is to develop technology which ensures the safe, permanent disposal of all defense nuclear waste. Programs are in place at each U.S. Department of Energy site which address long-term strategy for permanent disposal of waste generated as a result of defense operations. Technology is developed for assessing the hazards, environmental impact, and cost of each long-term disposition alternative for selection and implementation. This paper addresses the key research areas and major facilities associated with the long-term management of defense nuclear waste.
Crystallization Behavior of a Ferri-Silicate α-Waste Glass
Authors: Stalios A. D. , De Batist R. 
Published: March 2011

AbstractThe crystallization behavior of a ferri-silicate α-waste glass was studied by means of several experimental techniques. The main crystal phase showed a plate-like morphology and was identified as a monoclinic pyroxene. The Johnson-Mehl-Avrami equation was used for the determination of the kinetic parameters of the process. Following both isothermal and non-isothermal techniques, the Avrami exponent, n, was found to be nearly one. The activation energy for crystal growth is Eg = 356 kJ mole−1. The crystallization process is governed by instantaneous nucleation and diffusion controlled two dimensional growth.
French High Level Nuclear Waste Program — Key Research Areas
Authors: Sombret Claude G. 
Published: March 2011

AbstractThe most important aspects of this research program concern disposal safety: the long-term behavior and sensitivity of the materials to the variability inherent in industrial processes, and the characterization of the final product. This research required different investigations involving various scientific fields, and implements radioactive and non-radioactive glass samples as well as industrial scale glass blocks. Certain studies have now been completed; others are still in progress.
Alpha-Recoil Effect on the Dissolution of Betafite: Rapid Natural Annealing of Radiation Damage Within A Metamict Phase
Authors: Eyal Y. , Lumpkin G. R. , Ewing R. C. 
Published: March 2011

AbstractBetafite, a radioactive mineral, is the Ti-rich member of the pyrochlore group, A1–2B2X6Y0–1, (Fd3m, Z = 8), where A = Ca, Na, U, Th, REE (rare earth elements), Y, Ba, Sr, Bi, Pb; B = Nb, Ti, Ta, Zr, Sn, Fe: X = oxygen; Y = 0, OH and F. The pyrochlore structure (or structural derivatives, e.g. zirconolite in SYNROC) is a common constituent of polyphase, crystalline radioactive waste forms. Naturally occurring minerals with this structure often occur in the metamict state. Therefore, a principal concern is the effect of alpha-recoil damage on the structure and dissolution behavior of synthetic, analogue, waste-form phases which contain actinides.We describe the dissolution behavior of 238U, 234U, 232Th, 230Th and 228Th in betafite during leaching in a bicarbonate-carbonate solution. Results indicate enhanced leaching of recently produced alpha-recoil damage as evidenced by the more rapid dissolution rate of 228Th relative to 232Th and 230Th, and only slightly enhanced leaching of older damage as evidenced by a small increase in the dissolution rate of 234U relative to 238U. These experiments demonstrate that individual alpha-recoil tracks are preserved for some time as disordered regions of higher chemical reactivity in already fully-damaged, aperiodic structures. We estimate an annealing time for the alpha-recoil tracks of 2,000 ± 1,300 yr in the metastable, aperiodic structure. Similar alpha-recoil tracks should be formed and annealed in other aperiodic nuclear waste forms, such as borosilicate glass.
An Investigation of Uranium L-Edges of Metamict and Annealed Betafite
Authors: Greegor R. B. , Lytle F. W. , Chakoumakos B. C. , Lumpkin G. R. , Ewing R. C. 
Published: March 2011

AbstractThe uranium site in naturally occurring metamict minerals of the pyrochlore group (A1–2B2O6Y0–1) has been investigated using x-ray absorption spectroscopy (XAS). Pyrochlore structures are common phases in proposed polycrystalline waste forms. Betafite, a member of the pyrochlore group (B = 2Ti ≥ Nb+Ta), exhibits U-O bond lengths of 1.94 and 2.37 A for the metamict state, and 2.03 and 2.51 A for the crystalline (annealed) state. The U-O bond lengths decrease (∼0.1 A) and there is a disruption in the second nearest neighbor periodicidy as material is converted from the crystalline to the metamict state.
German Nuclear High-Level Waste Program - Key Research Areas
Authors: Geipel Helmut 
Published: March 2011

AbstractBased on more than 10 years of research and development, vitrification and high level waste disposal have reached the status of demonstration projects in the Federal Republic of Germany: hot operation of the PAMELA vitrification plant is scheduled for october 1985, and a disposal test with 30 canisters of high active glass is being prepared in the ASSE salt mine. Safety studies for a model repository led to a good understanding of the relevant phenomena; they will continue using sitespezific parameters. Modelling and computer codes will be further developed in international cooperation. In addition to reprocessing, the technology for direct disposal of spent fuel will be developed and demonstrated in the next years.
Hard Clay as Host Medium Thermo-Mechanical Experiments and Model
Authors: Baldi G. , Borsetto M. , Hueckel T. , Peano A. , Tassoni E. 
Published: March 2011

AbstractClay's impermeability is an essential feature for the quality of a possible repository. However it results in a substantial pore water pressure rise induced by heating whose magnitude and dissipation rate depend on the clay's deformational response to heating. Experiments on thermal strains and effective stress are reported and the mathematical model implemented in a computer code is described. It allows study of a repository performance due to waste heating in both continental and subseabed clay formation.
The Effects of Simultaneous Heat and Mass Transport on Radionuclide Migration
Authors: Walton Frank B. , Ross J. P. M. , Juhnke D. G. 
Published: March 2011

AbstractFive thermal-convection loops, constructed of granite, were operated for 350 d with a hot-side temperature of 60°C and a cold-side temperature of 20°C, to examine the effects of a thermal gradient on the convective transport of seven radionuclides. Radionuclide concentrations on the surface of the loop flow channels indicated that 125Sb, 60Co and 54Mn and precipitated iron oxyhydroxides were concentrated in the hot side of the loops. Concentrations of 144Ce and 99Tc were higher in the cold side of the loops. Both of these patterns were exhibited by 75Se. The concentration of 137Cs was not significantly affected by the thermal gradient. Radionuclide solubility and sorption were affected by variations in pH, Eh and ionic strength. Incorporation of the radionuclide into mineral lattices was found to play a key role in retarding the transport of all radionuclides tested.
Investigations Into the Mobilization of Actinides From ILW Conditioned in Cement and Bitumen and Studies of their Sorptive and Migration Behaviour in Both the Near- and Far-Fields for a Repository Contained in a Deep Salt Environment
Authors: Flambard A. R. , Fusban H.-U. , Keiling Ch. , Marx G. 
Published: March 2011

AbstractExperiments have been carried out into the leaching of ILW conditioned in cement and bitumen in concentrated salt solutions. Although difficult to observe with real waste leachates, investigations into the leaching of a simulated waste in cement have indicated leached transuranic levels of ca. 10−9 M ; the amount of activity leached by a quinary salt solution being 102 - 103 times higher . This has been interpreted in terms of a pH effect. For the real waste, spectroscopy has indicated a significantly larger release of Cs from cement than from bitumen. For all waste samples a notable absence of colloidal material was observed ; an observation which can be explained in terms of the high solution ionic strengths and the corresponding influence upon radionuclide solvation.Transuranic mobility studies through salt and sand from a salt dome in Northern Germany have shown the presence of at least two types of species of wildly differing mobility ; one migrating with approximately the same velocity as that of the solvent front and the other strongly retarded. Actinide recoveries (i.e. that passing through the columns) could be strongly influenced by either changing the system pH or by the addition of a competitor such as Ce ; the latter effect pointing to a competitive sorption.
Diffusivities in Crystalline Rock Materials
Authors: Skagius Kristina , Neretnieks Ivars 
Published: March 2011

AbstractThe diffusion of non-sorbing species in different crystalline rocks and fissure coating materials has been studied. The results show that the effective diffusivity of iodide, Uranine and Cr-EDTA in rock materials with fissure coating material is of the same magnitude or higher than in granites and gneisses. The results also show that it is not possible to assign one value to the diffusivity of a rock from a given area. The variations in properties are too large. The estimated effective diffusivity of iodide in rocks without fissure coating material was found to be in the range 1.10-14 m2/s to 70.10-14 m2/s.To simulate the stress that exists in the bedrock at large depths, diffusion experiments with iodide and electrical resistivity measurements in rock materials under mechanical stress have been performed. It was found that the diffusivity in rock samples at 300–350 bars stress was reduced to 20–70% of the value in samples under atmospheric pressure.
Sorption and Diffusion of Radionuclides in Rock Matrix and Natural Fracture Surfaces Studied by Autoradiography
Authors: Muuronen S. , Kämäräinen E-L. , Jaakkola T. , Pinnioja S. , Lindberg A. 
Published: March 2011

AbstractA method based on autoradiography was developed to determine the sorption and diffusion of cesium, strontium, cobalt, nickel, iodine and americium into rock matrix. Samples chosen for this study were filled and unfilled natural fracture surfaces and drill cores having a central drilled hole (”). Rock types were mica gneiss, tonalite and rapakivi granite, which were selected to represent the common rocks and minerals in Finnish bedrock. Distribution coefficients (Ka-values) of cesium and strontium determined for fissure surfaces and drill core cups were of the same order of magnitude. After three months contact time the greatest penetration depth for cesium was 2.5 mm, for a natural fissure surface sample of rapakivi granite. For strontium the penetration depths of 11 mm in three months and 35 mm in twelve months were found for filled natural fissure surface samples of rapakivi granite. The range of Da-values was 1.5 × 10−15 - 3.2 × 10−14 m2/s and 1.4 × 10−14 - 2.1 × 10−13 m2/s for cesium and strontium, resp. For cobalt the Da-values of 5 × 1016 m2/s in tonalite was obtained. In six months the penetration depths of nickel, iodine and americium were too low (< 0.5 mm) to allow calculation of Da.
Migration Behavior of U(VI) in Tuff
Authors: Sato Seichi , Furuya Hirotaka , Araya Sadao , Matsuo Kazumori 
Published: March 2011

AbstractAdsorption coefficient and penetration behavior of U(VI) in Itado tuff were measured. The migration behavior of U(VI) in the tuff was discussed.Adsorption coefficient of U(VI) was measured by a batch method using a wafer specimen and a powder specimen in pH region from 2 to 7. Adsorption coefficient was 17000 m1/g at the pH value of 5.5.Penetration behavior of U2− (VI) in Itado tuff was studied as a function of pH, concentration of CO32− and temperature by contacting the rock specimen with U(VI) solution. The concentration profile and fractional amount of U(VI) penetrating into the rock specimen Mt/M were measured. The penetration behavior of U(VI) was seen to be diffusion accompanied by adsorption/desorption process. In the pH region from 3 to 4, it is likely that the penetration process of U(VI) is not sufficiently reversible but is competitive process consisting of diffusion and adsorption. In the pH region above 6, penetration depth was very thin because of both large adsorption coefficient and large adsorption rate constant.The sectioning method was found to have an advantage to see the penetration behavior directly. But in the pH region from 6 to 7, the method has a shortage that diffusion coefficient, and adsorption and desorption rate constant could not be determined, because of small penetration depth of U(VI). From this point of view, the measurement of the fractional amount of penetration as a function of time should be carried out as well as that of concentration profile.
Ocean Floor Sediment as a Repository Barrier: Comparative Diffusion Data for Selected Radionuclides in Sediments from the Atlantic and Pacific Oceans
Authors: Schreiner F. , Sabau C. , Friedman A. , Fried S. 
Published: March 2011

AbstractEffective diffusion coefficients for selected radionuclides have been measured in ocean floor sediments to provide data for the assessment of barrier effectiveness in subseabed repositories for nuclear waste. The sediments tested include illite-rich and smectite-rich red clays from the mid plate gyre region of the Pacific Ocean, reducing sediment from the continental shelf of the northwest coast of North America, and Atlantic Ocean sediments from the Southern Nares Abyssal Plain and the Great Meteor East region. Results show extremely small effective diffusion coefficients with values less than 10−14 m2s−1 for plutonium, americium, curium, thorium, and tin. Radionuclides with high diffusion coefficients of approximately 10−10 m2s− include the anionic species pertechnetate, TcO4−, iodide, I−, and selenite, SO3−2. Uranyl(VI) and neptunyl(V) ions which are stable in solution, have diffusion coefficients around 10−12m2s−1. The diffusion behavior of most radionuclides is similar in the oxygenated Pacific sediments and in the anoxic sediments from the Atlantic. An exception is neptunium, which is immobilized by Great Meteor East sedi-ment, but has high mobility in Southern Nares Abyssal Plain sediment. Under stagnant conditions a 30 m thick sediment layer forms an effective geologic barrier isolating radionuclides in a subseabed repository from the biosphere.
Heat Induced Fracturing of Rock in an Existing Uniaxial Stress Field
Authors: Mathis J. I. , Stehpansson O. , Bjarnason B. , Hakami H. , Herdocia A. , Mattila U. , Singh U. 
Published: March 2011

AbstractThe thermal fracturing of rock has been the object of several research projects, notably for initial rock breakage in mining [4] as well as crushing [6] In addition, the process has been studied carefully in regards to the storage of radioactive waste underground where rock fracturing could lead to a loss of radioactivity confinement. The Stripa Project, a project concerning large scale testing of procedures for underground storage of nuclear waste, probably has dealt most thoroughly with this subject by theoretical studies and in-situ heater testing in an attempt to describe the thermal failure process in rock [13]This project was designed to test the agreement between theoretical and actual rock fracture times of a rock block, loaded with a physical as well as a thermal load. Laboratory testing consisted of physically loading center-drilled cubes of rock, 0.3 m on a side, uniaxially from 0 to 25 MPa. These were then thermally loaded with a nominal 3.7 kW (factory rating) cylindrical heater until failure occurred. This time to failure was recorded for comparison with a direct mathematical and a finite element solution. For both cases, calculations were performed at specific time-steps and an estimated failure time calculated from the compiled results.
Time-Resolved X-Ray Absorption of An Amorphous Si Foil During Pulsed Laser Irradiation
Authors: Murakami Kouichi , Gerritsen Hans C. , Brug Hedser Van , Bijkerk Fred , Saris Frans W. , Wiel Marnix J. Van Der 
Published: March 2011

ABSTRACTWe report time-resolved X-ray absorption and extended X-ray absorption fine structure (EXAFS) measurements on amorphous silicon under nanosecond pulsed-laser irradiation. Each measurement was performed with one laser shot in the X-ray energy range from 90 to 300 eV. An X-ray absorption spectrum for induced liquid Si (liq*Si) was first observed above an energy density of 0.17 J/cm2. It differs significantly from the spectrum for amorphous Si and characteristically shows the disappearance of the Si-L(II,III) edge structure at around 100 eV. This phenomenon is interpreted in terms of a significant reduction in the 3s-like character of the unfilled part of the conduction band of liq*Si compared to that of amorphous Si. This is the first direct evidence that liq*Si has a metallic-like electronic structure. Timeresolved EXAFS results are also discussed briefly.
Direct Imaging of “Explosively” Propagating Buried Molten Layers In Amorphous Silicon Using Optical, Tem And Ion Backscattering Measurements
Authors: Lowndes D. H. , Jellison G. E. , Pennycook S. J. , Withrow S. P. , Mashburn D. N. , Wood R. F. 
Published: March 2011

ABSTRACTThe behavior of pulsed laser-induced “explosively” propagating buried molten layers (BL) in ion implantation-amorphized silicon has been studied in a time- and spatially-resolved way, using nanosecond time-resolved reflectivity measurements, “Z-contrast” scanning transmission electron microscope (STEM) imaging of implanted Cu ions transported by the BL, and helium ion backscattering measurements. Infrared (1152 nm) reflectivity measurements allow the initial formation and subsequent motion of the BL to be followed continuously in time. The BL velocity is found to be a function of both its depth below the surface and of the incident KrF laser energy density (El); a maximum velocity of about 14 m/s is observed, implying an undercoolingvelocity relationship of about 14 K/(m/s). Z-contrast STEM measurements show that the final BL thickness is less than 15 nm. Time-resolved optical, TEM and ion backscattering measurements of the final BL depth, as a function of E1, are also found to be in excellent agreement with one another.