bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiply Scattered and Diffusing Ultrasound: Applications, Experiments, Theory
Authors: Weaver Richard L
Published: March 2011

The study of ultrasonic waves in random media in a strong multiple scattering limit is becoming increasingly relevant to applied techniques of nondestructive characterization of material microstructures. This paper reviews the state of that art within the context of engineering applications and also reviews the evidence for the Anderson Localization of ultrasound.

While ultrasound has long been employed as a nondestructive probe of material microstructure, it has usually been the rapidly attenuated coherent wave, and in particular, its speed and attenuation, which has been scrutinized for that purpose. The theory of such waves is discussed here. However, recent experiments and theory are increasingly addressing the diffuse speckle wave field. This small but growing body of work is also reviewed.

While there has been much work recently on optical and microwave realizations for the study of the Anderson localization of classical waves, there has been little such investigation with sound waves. Recent work demonstrating the Anderson Localization of Ultrasound in two dimensions may be the first such for any classical waves in dimension greater than one.
Korringa-Kohn-Rostoker Electronic Structure Method for Space-Filling Cell Potentials
Authors: Gonis A. , Butler W. H. , Zhang X.-G.
Published: March 2011

The multiple scattering theory (MST) method of Korringa, and of Kohn and Rostoker for determining the electronic structure of solids, originally developed in connection with potentials bounded by noa-overlapping spheres (Muffin-tin (MT) potentials), is generalized to the case of space-filling potential cells of arbitrary shape through the use of a variational formalism. This generalized version of MST retains the separability of structure and potential characteristic of the application of MST to MT potentials. However, in contrast to the MT case, different forms of MST exhibit different convergence rates for the energy and the wave function. Numerical results are presented which illustrate the differing convergence rates of the variational and nonvariatonal forms of MST for space-filling potentials.
A Full-Potential Kkr Green's Function Method for Impurities in Metals
Authors: Dederichs P.H. , Drittler B. , Zeller R.
Published: March 2011

We have developed a full-potential extension of the KKR Green's function method for impurities. The crystal potential is split into a sum of non-overlapping, cellular potentials. The solution for the individual anisotropic potentials is constructed by an iteration procedure starting from the solution for the isotropic potential. We discuss some technical details of the method and its efficiency in applications to impurities in metals. As examples we choose: i) calculations of local moments and Friedel oscillations in metals, ii) calculations of vacancy formation energies, iii) calculations of forces based on the Hellmann-Feynman theorem. For these applications we discuss the importance of the inclusion of full-potentials in comparison to atomic-sphere potentials.
The Green Function Cellular Method and Its Relation to Multiple Scattering Theory
Authors: Butler W. H. , Zhang X.-G , Gonis A.
Published: March 2011

We investigate techniques for solving the wave equation which are based on the idea of obtaining exact local solutions within each potential cell, which are then joined to form a global solution. We derive full potential multiple scattering theory (MST) from the Lippmann-Schwinger equation and show that it as well as a closely related cellular method are techniques of this type. This cellular method appears to have all of the advantages of MST and the added advantage of having a secular matrix with only nearest neighbor interactions. Since this cellular method is easily linearized one can rigorously reduce electronic structure calculations to the problem of solving a nearest neighbor tight-binding problem.
Self-Consistent-Field Kkr-Cpa Calculations in the Atomic-Sphere Approximations
Authors: Singh Priabhakar P. , Gonis A. , Fontaine Didier De
Published: March 2011

We present a formulation of the Korringa-Kohn-Rostoker coherent potential approximation (KKPt-CPA) for the treatment of substitutionally disordered alloys within the KKR atomic-sphere approximation (ASA). This KKR-ASA-CPA represents the first step toward the implementation of a full cell potential CPA, and combines the accuracy of the KKR-CPA method with the flexibility of treating complex crystal structures. The accuracy of this approach has been tested by comparing the self-consistent-field (SCF) KKR-ASA-CPA calculations of Cu-Pd alloys with experimental results and previous SCF-KKR-CPA calculations.
First Principles Calculation of Residual Resistivity
Authors: Nicholson D. M. , Brown R. H. , Butler W. H. , Yang H. , Swihart J. W. , Allen P. B. , Mehta A. , Schwartz L. M.
Published: March 2011

The list of physical properties which are important in the design of materials and which are routinely calculated from first principles within the local density approximation to density functional theory is continually growing. In this paper we discuss the application of multiple scattering theory to the calculation of the residual resistivity of disordered alloys. Progress has been made on two fronts. First, the coherent potential approximation for the resistivity, which sums to all orders a limited set of multiple scattering diagrams, has given resistivities in agreement with experiment for alloys where the site occupation is roughly random. Second, the linearized KKR was used to evaluate the Kubo formula for several large configurations of atoms and obtain the resistivity with all multiple scattering paths included. This method is not limited to random alloys, but can be applied to short range ordered and amorphous alloys provided the resistivity is high enough to limit the mean free path to a single unit cell.
Calculations of Spin-Wave Energy Gap in Transition Metals
Authors: Antropov V.P. , Liechtenstein A.I.
Published: March 2011

Analytical expressions for the total energy derivative with respect to the magnetic moment rotations have been derived in the relativistic local-spin density functional approach and multiple scattering theory. The spin-wave stiffness constant as well as the gap in the spin-wave spectrum due to relativistic anisotropy effects is calculated in KKR-ASA approximation for bcc Fe. This is compared with other theoretical calculations and available experimental data.
Fully Relativistic Layer-KKR Green Function Theory and Its Application to Spin-Polarized Photoemission
Authors: Tamura Eiiti
Published: March 2011

A fully relativistic layer-KKR formalism is developed for calculating the single-particle Green function in atomic layers parallel to crystalline surfaces of magnetic and nonmagnetic materials. Its application to spin-polarized photoemission is also discussed.
Can Polar Interface Energies be Calculated by Means of Supercells?
Authors: Lambrecht W. R. L. , Amador C. , Segall B.
Published: March 2011

Two problems associated with the calculation of polar interface energies in semiconductors or insulators are discussed: (1) the stoichiometry of the associated interface region, and (2) the impossibility of constructing a supercell with two equivalent interfaces in certain cases. An approach for calculating the energy of a single interface is introduced. It utilizes local quantities obtained from supercell calcualtions and the electrostatic energy of the isolated single interface. Results are presented for GaAs inversion domain boundaries and NaCl antiphase boundaries. The problem associated with charge transfer between two different interfaces is discussed.
Electronic Structure of Planar Faults and Point Defects in High Temperature Intermetallics
Authors: Maclaren J.M. , Woodward C.
Published: March 2011

First principles electronic structure calculations, using the layer Korringa-Kohn-Rostoker method, are reported for isolated planar faults in TiAl. The calculated fault energies are discussed in the context of suggested superdislocation separation reactions. The influence of dilute impurities on fault energies are treated using the coherent potentialapproximation. Using this approach, the variation of fault energies in TiAl resulting from stoichiometry changes and from the addition of Mn axe calculated, and compared to recent experimental data.
Lie Group Calculation of the Green Function of Disordered Systems
Authors: Brouder Christian
Published: March 2011

Within the framework of the muffin-tin multiple-scattering theory, the scattering path operators are given by the inverse of a matrix consisting of atomic t-matrices and a structural matrix. The influence of the displacement of an atomic centre on the structural matrix can be described analytically using Lie group techniques. From this analytical expression and the standard perturbation expansion of the Lippmann-Schwinger equation, it is possible to write the Green function of a disordered system as a series of terms whichare averages over configurations. These averages can be calculated analytically from themoments of the interatomic distances. Special terms of this series are then summed up toinfinity using Dyson equation. This formalism is computationally very effective to calculate electronic properties of systems with thermal or structural disorder. In this paper, the theoretical basis of this approach is briefly described and the convergence properties of the expansions are investigated.
Observation of Elastic Wave Localization
Authors: Ye Ling , Cody George , Zhou Minyao , Sheng Ping , Norris Andrew
Published: March 2011

Spatial localization of bending waves was observed on a steel plate (72"X72"X1") decorated with lucite blocks (3.5"X3.5"X3") arranged in either a periodic or a random array. The exponential decay length of the localized modes is as short as 12 cm at 2.8 kHz, and increases with frequency as (f0 - f)-1, where f0 = 3.5 kHz is a quasi-mobility edge. The experimental data and finiteelement calculations suggest that the observed localization ofbending waves is due to the strong resonant scattering of bending waves by the shear modes of lucite/steel system. The generic nature of this localization phenomenon suggests its potential use as a attenuation mechanism for bending waves.
Photoemission of CO/CU(100). Non-Relativistic Spin- and Angle-Resolved Normal Emission
Authors: Schneeweiss R. , König U. , Redinge J. , Weinberger P. , Schneider C. M. , Kirschner J.
Published: March 2011

The Co/Cu(100) system is the first system known where the contributions to the spin polarisation of spin-orbit coupling and the ferromagnetic overlayer were clearly distinguished experimentally. In order to get a first understanding of the photoemission data non-relativistic spin-polarized photoemission calculations are performed for one and two overlayers of Co on Cu(100).
The Application of Scattering Theory to the Evaluation of Correlation Functions
Authors: Winter H. , Szotek Z. , Temmerman W.M.
Published: March 2011

We describe a formalism dedicated to the realistic evaluation of correlation functions in solids and give an account of its success and its limitations by discussing various applications.
The Wave Function in Multiple Scattering Theory
Authors: Butler W. H. , Zhang X. -G.
Published: March 2011

The wave function in Multiple Scattering Theory (MST) is a locally exact solution to the Schrödinger equation for any ℓ truncation (ℓmax), except at the the muffin-tin boundaries (or cell boundaries in a full cell calculation) where it and its derivative generally have discontinuities. These discontinuities vanish only in the limit ℓmax → ∞. Furthermore, the MST wave function as usually calculated is not correctly normalized which means the density of states calculated from the Green function does not agree with that calculated from the Lloyd formula. Here we obtain an alternative wave function from the usual MST secular equation which is smooth and continuous everywhere and which is correctly normalized.
Dielectric Permittivities at X-Band Frequencies of Conductive Fibers Aligned in Polymer Matrices
Authors: Ho Yung-Shou , Lodge J. , Schoen P. E.
Published: March 2011

Composites have been formed of Cycom, nickel-coated graphite fibers, aligned at concentrations of up to 6 weight percent in polymer matrices. Dielectric constants up to approximately 70 have been measured for these samples at x band frequencies. The results have been compared with a single non-interacting particle theory.
Statistical Mechanics of Phase Transitions with a Hierarchy of Structures
Authors: Berker A. Nihat , Caflisch Robert G. , Kardar Mehran
Published: March 2011

Rescaling (renormalization-group) [1] and restructuring [2] transformations are used in the statistical mechanics of systems with different complexities at different length scales, starting with the microscopic scale. These transformations are effected by a partial trace of the partition function, yielding effective coupling constants that incorporate the free energy contribution of the structures and length scales that are summed out of the problem. An example of this approach is a quantitative treatment [3] of the phase diagram of krypton adsorbed onto graphite. At the smallest length scales, adatom adsorption (first and second layer) and vibrations at adsorption sites are considered. At the next scale, sublattice formation and vacancy occurrence on the hexagonal graphite surface are considered. At a larger scale, heavy and superheavy domain wall formation, wall crossings and annihilations (dislocations) [4] are considered. This problem is treated by a sequence of 5 different transformations. Starting with the microscopic potentials, phase diagrams are obtained in temperature versus pressure or coverage, featuring disordered, commensurate and incommensurate solid phases, in good agreement with experiments [5]. The mechanism for reentrant phase transitions is divulged. Such solutions can be considered approximate treatments of physical systems or, alternatively, exact solutions of “hierarchical models” [6]. This “realizability” on hierarchical lattices insures the robustness of the approximation.
Orientation in Biomimetic Polymer-Mineral Composites
Authors: Burdon Jeremy , Calvert Paul
Published: March 2011

Mechanisms for the production of oriented precipitates are reviewed in the context of the orientation in mineralized biological tissues. Organic crystals have been oriented in polymer matrices by crystallization in a temperature gradient and by crystallization within a drawn crystalline polymer. Elongated oxide particles can be formed in a polymer by drawing of a material which contains phase-separated droplets of alkoxide, followed by hydrolysis of the alkoxide. Highly elongated rod-like or disc-like particles can be formed. Alternatively drawn films of a polymer blend can be swollen with alkoxide and hydrolysed to produce elongated chains of particles.
Hierarchial Structure and Physical Properties of Natural Cellulosic Fibers
Authors: Rebenfeld Ludwig
Published: March 2011

Natural cellulosic fibers have in common the fact that cellulose is the key polymeric component in the structure, although the chemical composition varies widely depending on the specific source of the fibers. Cellulose is a long-chain linear condensation polymer of β-D-glucose with three free hydroxyl groups on each monomeric unit, resulting in strong inter- and intramolecular hydrogen bonds. Because of the hydrogen bond network, and also due to restricted rotation around the polymeric 1,4- β-linkage, cellulose is a rigid and stiff chain with a Tg well above the chemical decomposition temperature.

Despite the high Tg native cellulose is invariably highly crystalline as a result of the biosynthetic process. In naturally occurring cellulosic fibers, the cellulose crystallites are aggregated into fibrils which constitute the underlying building blocks of the fiber. In cotton, the fibrils are laid down during the development or growth of the fiber in the form of concentric layers. The fibrils are disposed at an angle of 23° with respect to the fiber axis and thus they describe a helical pattern. The sense of the helix reverses frequently along the length of the fiber. This morphology is unique to cotton; other cellulosic fibers such as ramie and jute have similar fibrillar structures, but fibrillar angles in the 5 to 10 degree range, with no reversals. Wood fibers, on the other hand, are structurally more heterogeneous and may be considered as composites.
Conductive Composite Fibers with a Rigid-Rod Matrix
Authors: Beltsios Konstantinos , Carr S. H.
Published: March 2011

Conductive composite fibers are prepared by dry-jet wet-spinning of a strong-acid solution of rod-like polymers and phthalocyanine(Pc) compounds. A model yielding a hierarchical structure for a pure rigid-rod fiber is described first. The inclusion of NiPc in the spinning dope leads upon coagulation to isolated NiPc domains that are predicted to correspond to body centered cells (exhibiting various degrees of disorder). The observed dependence of fiber conductivity of composition is explained in terms of tunneling and percolation processes.
Electronic Mechanisms of Excitation of Rare-Earth Luminescence in Silicon
Authors: Yassievich I. N.
Published: March 2011

Two ways of electronic excitation for f-electron system of rare-earth ions in silicon are considered: impact excitation and Auger excitation. The probabilities of these processes are calculated.
Fabrication of Luminescent Porous Silicon with Stain Etches and Evidence that Luminescence Originates in Amorphous Layers
Authors: Fathauer R. W. , George T. , Ksendzov A. , lin T. L. , Pike W. T. , Vasquez R. P. , Wu Z.-C.
Published: March 2011

Stain films on Si wafers produced in solutions of HF:HNO3:H2O have been studied for over 30 years [1], and have been suggested [1] to be similar in nature to the anodically-etched porous Si films first demonstrated by Uhlir [2]. More recently, it was shown that stain films produced by etching Si in solutions of NaNO2 in HF and CrO3 in HF were similar in structure to porous Si films produced by anodic etching [3]. In fact, in the etching of Si by HF:HNO3:H3O solutions, the oxidation reaction chemistry is recognized to be the same as that of anodic oxidation, with points on the Si surface behaving randomly as localized anodes and cathodes [4]
Raman and Optical Characterization of Porous Silicon
Authors: Harvey J. F. , Shen H. , Lux R. A. , Dutita M. , Pamulapati J. , Tsu R.
Published: March 2011

Raman spectra from electrochemically etched porous silicon are correlated with photoluminescence (PL) data from the same spots of the sample. This correlation is consistent with optical properties of quantum confinement. The dielectric constant determined from angle resolved ellipsometry gives values far below that of bulk silicon. This reduction is due to the combined effects of voids as well as quantum confinement. The PL spectrum shows a weak high energy peak around 2.8eV in addition to the strong broad peak at 1.5 to 1.9eV. The temperature dependence of PL resembles that of bound excitons such as Si:S, having a thermal dissociation energy of 100 meV near room temperature. The radiation life time changes from tens of microseconds near room temperature to a few milliseconds at liquid helium temperatures. The rapid increase in lifetime and decrease in PL intensity at low temperatures indicates that phonons are probably involved.
Visible Electroluminescence of Porous Silicon Devices with a Solid State Contact
Authors: Richter A. , Lang W. , Steiner P. , Kozlowski F. , Sandmaier H.
Published: March 2011

The photoluminescence and electroluminescence of light emitting porous silicon (LEPOS) is described. The porous silicon is made by anodic dissolution of silicon in HF with an applied electrical current and illumination with visible light. Photoluminescence is observed using ultraviolet light, visible electroluminescence is achieved by applying a voltage to a solid state contact on top of the porous layer. The luminescence, the structure and the composition of the LEPOS are studied.
Composition and Morphology of Luminescent Porous Si
Authors: Petrova-Koch V. , Kux A. , Müller F. , Muschik T. , Koch F. , Lehmann V.
Published: March 2011

Using thermal effusion of H together with a weighing of the remaining Si we determine the composition of luminescing porous Si. From studies of the IR vibration spectrum and its change with effusion we. argue that the H of freshly prepared microporous Si is bound in the dihydride form SiH2. We thus obtain a surface to volume ratio and a characterisicic linear dimension of the porous surface layer. The paper concludes with some observations on photo- and electroluminescence.
Sims Analysis of the Contamination of Porous Silicon by Ambient Air
Authors: Canham L T , Blackmore G W
Published: March 2011

Microporous silicon layers contain an enormous surface area (> 500 m2 cm−3) that influences their structural, optical and electrical properties. When freshly etched the pore wall surface can be extremely clean and composed primarily of hydrogen and fluorine. Extended storage in ambient air however will convert this clean hydride surface into that of a contaminated native oxide.

Using dynamic SIMS profiling we demonstrate here that slow oxidation at room temperature by ambient air is accompanied by impregnation with atmospheric boron and sulphur but that levels of calcium and sodium for example, remain exceedingly low. We conclude that the pore wall surface is very efficiently protected from particulate - related airborne species but is susceptible to contamination from small molecules present in the atmosphere at trace levels.
Raman Scattering in Electrochemically Prepared Porous Silicon
Authors: Wu Y. -J. , Zhao X. -S. , Persans P. D.
Published: March 2011

Porous silicon of various porosity has been prepared by electrochemical etching of silicon with different doping levels. Room temperature photoluminescence in the visible range is observed from the powder scraped from the top layer of the etched samples. In this paper we use Raman scattering to characterize the source of the high efficiency photoluminescence. We have also studied microcrystalline silicon prepared by thermal annealing of hydrogenated amorphous silicon/amorphous silicon oxide multilayers.
The Structure of Porous Silicon Revealed by Electron Microscopy
Authors: Cullis A. G. , Canham L. T. , Dosser O. D.
Published: March 2011

This detailed electron microscope study of porous silicon compares the different structures of macro-, meso- and microporous material. Mesoporous silicon of high porosity (∼-80%) exhibits efficient red photoluminescence at room temperature. Transmission electron microscopy provides strong direct evidence that this visible luminescence arises from dramatic carrier confinement in quantum-size, crystalline silicon structures. Images of undulating, interconnected ‘quantum wires’ of widths <3nm are shown.
Piezoresistance and Quantum Confinement in Microcrystalline Silicon
Authors: Foresi J. S. , Moustakas T. D.
Published: March 2011

We report piezoresistance studies in microcrystalline silicon films produced by reactive sputtering from a silicon target in an atmosphere of hydrogen and argon. The microcrystalline silicon films are two phase materials consisting of 50-100Å diameter silicon crystallites embedded in an amorphous Si-Hx matrix. The conductivity of the films was found to decrease significantly when the films were put under compression. Conductivity decreases of up to 100% were observed; this large conductivity changes with strain indicate that microcrystalline silicon is ideally suited for highly sensitive strain gauge applications. The results can be qualitatively accounted for in a model which assumes quantum confinement of carriers in 50Å diameter silicon crystallites separated by tunnelable amorphous Si-Hx barriers.
Current–Voltage Characteristics of Porous Silicon Made from A P/N Junction Structure
Authors: Hsu Y. J. , Samanta L. K. , Wang K. C. , Chen P. C. , Hwang H. L.
Published: March 2011

We have made studies on the TRANSVERSE transport properties of the porous Si made from a novel P/N junction structure. The structures of porous Si were examined for various electrochemical etching conditions and they were correlated with the electrical data. The junciton was fabricated by shallow diffusion, with porous Si formed perpendicular to the junction and between two indium ohmic contacts. This structure confines currents to the direction parallel to the surface. Distinct feature on I–V curves have been observed, including sudden rise of currents and the existence of negative differential resistances (NDR). The characteristics appeared stable and depended on the polarity of bias. Suggestions are made that the porous Si could be composed of microcrystals, and feasibility of carrier transport through quantum boxes responsible for the electrical behaviors are discussed.
Backfill Modification Using Geochemical Principles to Optimize High Level Nuclear Waste Isolation in a Geological Repository
Authors: Langmuir Donald , Apted Michael J.
Published: March 2011

The clay backfill that will surround a buried high level nuclear waste package in most national repository programs, could be modified to play a greater role as a barrier to radionuclide (RN) releases. The RN steady state release (Mb) rate from a clay backfill to adjacent rock is directly proportional to backfill porosity (ε), RN diffusion rate In the backfill (Ds), and RN solubility at the waste form surface (C*), and Inversely proportional to RN half-life (λ) and RN retardation coefficient (R) in the backfill [1]. We propose ways to reduce ε, Ds and C* and Increase R for important radionuclides, mostly through the addition of reactive minerals to the backfill. Silica, calcite and anhydrite may be added to precipitate and clog porosity. Increased backfill compaction similarly reducesε, Ds and Mb for all the RN's. Strongly sorbent phases can be added to selectively adsorb both cationic and anionic RN's (e.g. 1–129). However, adsorption will not Importantly reduce peak release rates of most long-lived RN's. The backfill can be poised at reducing Eh's with mineral additives to lower Ds and so immobilize radioisotopes of NI, Np, Pa, Pu, Se, Tc and U. Minerals of stable or more stable isotopes of Cs, NI, Se, Sn and U can be added to lower Ds values of the RN's and to coprecipitate them in solid solution. Phosphorite-apatites, which are known to have high selectivities for rare earths and RN's, may be added to coprecipitate Am, Np, Pu, Sr, Th and U.
Alumina as a Matrix for Fixation of Fission Products
Authors: Zimmer Erich , Scharf K. , Schmidt S.-O.
Published: March 2011

Fission products and α-emitters from reprocessing plants ( HAW ) are incorporatedinto a ceramic matrix consisting of 90 w/o α-AI2O3 The amount of HAW in the product is 10 w/o. The matrix is produced by a sol-gel technique using a boehmite powder and a SiO2 sol as starting materials. To reduce the sintering temperature seeding with α-AI2O3 particlesis applied. The first step of the process is mixing of the starting materials with the nitric acid containing HAW. This results in the production of a gel. The gel is extruded and subsequently dried at 105ºC. Calcination is carried out in a hydrogen containing atmosphere. Finally, the material is sintered at 1300ºC. During heat treatment only minor volatilization is observed. Even cesium is almost completely retained sinceit forms an aluminosilicate (Cs2O. xSiO2. yAI2O3; feldspar type). The waste product has a total leach rate of 4 * 10-7g * cm-2 d-1 at 97ºC as determined in a Soxhlet apparatus. Under the same conditions, specific leaching rates of radiologically important nuclides, such as cesium and strontium, are approximately 10-6 g * cm-2 d-1. The process has the advantage that commercially available starting materialscan be used. In addition, only a moderate sintering temperature is required and pressingbefore or during sintering is not necessary.
Alternative Synroc Formulations
Authors: Vance E.R. , Smith K.L. , Thorogood G.J. , Begg B.D. , Moricca S.S. , Angel P.J. , Stewart M.W.A. , Blackford M.G. , Ball C.J.
Published: March 2011

Perovskite is the least durable of the resistate minerals comprising Synroc-C and it is desirable to reduce its abundance in Synroc. Kinetic limitations and competition with Csapparently affect the incorporation of Sr into hollandite during hot-pressing at 1200ºC/20 MPa so that ∼ 10% of perovskite (a value below the percolation limit) is probably an optimum target. Zirconolite-rich Synroc formulations have been prepared for actinide-rich wastes. Background XRD and TEM studies have also been performed to study the crystal-chemical behaviour of Nd (a simulant of trivalent actinides) in zirconolite. Either rare-earth compensated perovskite or freudenbergite in Synroc can evidently be used to immobilise Na-bearing HLW.
Actinide Sorption onto Silica in the Presence of Humic Substances: Proposal of Retentionmechanisms
Authors: Labonne N. , Moulin V. , Stammose D.
Published: March 2011

The experimental investigation and modelling of radionuclides sorption processes is an essential part of safety analyses of an underground repository of radioactive wastes in geological formations. Physico—chemical phenomena at oxide/solution interfaces have been studied in the case of the system constituted by amorphous silica and americium (III) in the presence of humic substances as organic complexing agents. The retention behaviour of Am(III) onto silica appears dependent on pH, ionic strength and in particular humic concentration. At a ionic strength of 0.1 M, the presence of low concentration of humic acids (1 mg/l) enhances the Am(III) retention in the pH range 3-5.5, whereas at higher pH, its uptake is largely decreased. At lower ionic strength (0.001 M), Am(III) retention on silica is highly lowered, in the pH range 3-7 in the presence of humic acids. Reversibility experiments show the desorption of americium in the absence of humic substances, and also the desorption of the humics on the silica with respect of the pH. The surface complexation model has been applied to our results in the different systems and apparent surface complexation constants have been determined.
Determination of Formation Constants, Solubilities, and Ionic Speciation of Uranium, Plutonium and Thorium in Aqueous and Saturated Salt Solutions for Modelling Safety Aspects of Ilw Repositories
Authors: Bischoff H. , Kramer-Schnabel U. , Esser V. , Xi R.H. , Heppner P.-M. , Marx G.
Published: March 2011

The solubility products of uranyl hydroxide and uranyl carbonate and the formation constants of the complexes present in the solution have been determined at 25ºC and I=0.1 mol dm−3by potentiometry and solubility experiments. The uranyl complexes U02(OH)2'(UO2)2(OH)22+,(UO2)3(OH)5+, UO2CO3', UO2(CO3)22−and UO2(CO3)34−were identified. For the system uranyl-hydroxide the results were verified by analysis of conductance measurements. A similar investigation was carriedout for thorium. Using Pu(IV)-chloride complexes as an example the potential of differential pulse voltarnmetry is demonstrated for the determination of small formation constants.
Recovery and Mutual Separation Process of Noble Metals from Simulated Insoluble Residue of Spent Fuel
Authors: Matsui Tsuneo , Naito Keiji
Published: March 2011

Recent results on the various methods for the recovery and the mutual separation of Mo, Ru, Rh and Pd from the simulated insoluble residue in the reprocessing plant, such as liquid lead and zinc extractions, nitric acid dissolution and preferential oxidative vaporization in various atmospheres by the authors are briefly reviewed. By combining these results, four kinds of processes for the recovery and the mutual separation of Mo, Ru, Rh and Pd (and Tc) i.e. two processes composed of Pb (and Zn) extraction(s) and subsequent nitric acid dissolution, and two processes using vaporization in various oxidizing atmospheres at various temperatures are proposed.
Potential Hazard of Ferrocyanide Salts in High-Level Waste Tanks Within the Hanford Tank Farm
Authors: Agnew S. F. , Eisenhawer S. W. , Davidson R. F. , Sullivan L. H.
Published: March 2011

Over the past few years, there has been an increased awareness of the potential hazard of energetic chemical reactions in high-level radioactive waste tanks at the Hanford tank farm. In particular, a mixture of Na2NiFe(CN)6 with NaNO3 and NaNO2 in several high-level waste tanks has caused concern. The problem of the FeCN tanks is fundamentally one of a potentially unstable mixture of fuel (the CN- moiety) and oxidizer (NO3- or NO2-).

At Los Alamos National Laboratory, we have performed an extensive reanalysis of the safety problems associated with the presence of Na2NiFe(CN)6 mixed with NaNO3/NO2 for a particular tank (104-BY) that contains by far the largest amount of the nickel ferrocyanide salt (∼2E5 mol). Our approach is to use conservative assumptions to bound both the energy density for a potential runaway reaction and the mass that could participate if we assume ignition as the result of bounding radionuclide concentrations. The subsequent progress of the accident is analyzed using an advanced hydrodynamics computer code called MESA to evaluate the loads on the structure and the generation of aerosols. The subsequent doses are shown to be low both on and off the site. The conservatism in the analysis is quite large, and the expected results using more realistic assumptions are discussed.
Effect of Radiation on the Corrosion of Candidate Materials for Nuclear Waste Containers
Authors: Shoesmith D.W. , Ikeda B.M. , King F.
Published: March 2011

The published information on the effect of radiation on the corrosion of potential waste container materials is reviewed. The materials discussed are irons and carbon steels, copper and copper alloys, stainless steels, nickel-based alloys, and titanium alloys. In general, a dose rate of >5 Gy·h-1 is required to accelerate the general corrosion of corrosionallowance materials. The effects of radiation on the localized corrosion of corrosion-resistant materials appear to be contradictory. In some cases, localized corrosion is induced, whereas in others it is inhibited.
Diffusion of Lead from a Perforated Titanium-Shell Lead-Matrix Container
Authors: Mathew P. Mani , Krueger Paul A. , Krause M.
Published: March 2011

This paper describes experiments and analyses conducted to determine the range of apparent diffusion coefficients of lead diffusing from an intentionally perforated lead-matrix titanium-shell container into a compacted 1:1 (by dry mass) silica-sand/sodium-bentonite buffer mixture saturated with Standard Canadian Shield Saline Solution at 363 K. Analysis of the experimental data using a single apparent diffusion coefficient could not explain the findings. A possible explanation of the behaviour is presented here. It uses a 2–D finite-element model with six lead species having six different apparent diffusion coefficients. The model can explain the data satisfactorily. Sixty-three percent of the source concentration consisted of slow-moving species, with an apparent diffusion coefficient of 10-15 m2 /s, whereas the fastest species, with an apparent diffusion coefficient of 10-10 m2 /s, constituted only three percent of the source concentration.
Lifetimes of Titanium and Copper Containers for the Disposal of Used Nuclear Fuel
Authors: Johnson Lawrence H. , Shoesmith D.W. , Ikeda B.M. , King F.
Published: March 2011

Titanium and copper have been proposed as suitable container materials for disposal of nuclear fuel waste in plutonic rock of the Canadian Shield. Studies of the corrosion of these materials have led to the development of container failure models to predict long-term performance. Crevice corrosion and hydrogen-induced cracking of titanium have been identified as potential failure mechanisms, and these two processes have been studied in detail. Using data from these studies as well as a number of conservative assumptions, titanium container lifetimes of 1200 to 7000 a have been estimated. For copper, general corrosion has been studied in detail in bulk solution and in compacted clay-based buffer material. Results indicate that the copper corrosion rate is likely to be controlled by the rate of transport of copper species away from the container surface. An assessment of copper pitting data suggests that pitting is an extremely improbable failure mechanism. The copper container failure model predicts minimum container lifetimes of 30 000 a. The results demonstrate that long lifetime containment can be provided, should performance assessment studies indicate the need for such an option.
Radionuclide Transport by Groundwater Colloids at the Koongarra Uranium Deposit
Authors: Payne T.E. , Edis R. , Seo T.
Published: March 2011

Groundwater and entrained particles were sampled from several boreholes at the Koongarra uranium deposit in the Northern Territory of Australia. Conventional filtration techniques, hollow fibre ultrafiltration, and stirred-cell ultrafiltration were used to separate dissolved species, large particles (> 1 μm) and colloids (< 1 μm). The colloids and particles included clay minerals, particularly kaolinite, and chlorite, together with fine quartz grains. Iron was present as particle coatings, and in a separate colloidal form. The amount of238U associated with colloids (expressed as a percentage of the total238U which passed through the 1.0 μm filter) ranged up to 6.5%. The corresponding figures for Th were 10-85%. However, the amount of230Th which passed through the 1.0 μm filter was extremely small, and230Th was associated to a much greater extent with larger particles, which are unlikely to be mobile in natural groundwaters. In some fine particle and colloidal fractions, the227Th/230Th activity ratio in the thorium alpha spectrum was unusually high, indicating the presence of substantial quantities of227Ac. This suggested that actinium could be present as a mobile colloid phase. Overall, there was very little colloidal material in these groundwaters, with only iron, uranium, actinium, and thorium showing a significant association with colloids.
Natural Analogue study on the Long-Term Durability of Bentonite –Time-temperature condition and water chemistry on illitization at the Murakami deposit, Japan.–
Authors: G. Kamei , Y. Yusa , N. Sasaki
Published: March 2011

Time-temperature conditions and water chemistry on illitization at the Murakami deposit in central Japan were determined. The extent of the illitization and timetemperature condition estimated were as follows: the duration for conversion from 0 to 80%illite (volumetric ratio) was approximately 3.5Ma in the temperature range from 340 to 100°C. Conversion from 0 to 40% requires approximately 3.0Ma in the temperature range from 240 to 100°C. During 2.0Ma in the temperature range from 160 to 100°C, however, illite was scarcely observed. Water chemistry is estimated from two approaches, namely laboratory experiment and numerical analysis. The former is an interactive experiment between seawater and the tuff of the deposit. The latter is a calculation based on the difference of bulk composition between illitized and non-illitized tuff. The extent of each ionic concentration is inferred to be as follows: K+; 560 to 6400, Mg2+; 800 to 1700, Ca2+; 360 to 2900, Na+; 9400 to 15000 (mg/l).
Settlement of An Embedded Nuclear Waste Container Due to Creep of a Surrounding Geological Barrier
Authors: Selvadurai A.P.S.
Published: March 2011

The paper discusses the influence of creep deformations of either engineered or natural geological barriers on the long term settlement of waste containers located within them. The paper describes, briefly, the potential application of numerical procedures for the estimation of the creep settlement rigid cylindrical containers embedded in engineered and natural geological media.
Fast Model for Calculating Steady State Release of Radionuclides from the Near Field
Authors: Nilson Lennart , Romero Leonardo , Moreno Luis , Neretnieks Ivars
Published: March 2011

A model has been developed which describes the steady state transport of dissolving species of radionuclides from a single canister in a repository for spent nuclear fuel into the passing water in fractures in the surrounding rock. The steady state transport of nuclides is described by a network of transport resistances, coupled together in the same way as an electrical circuit network. With the model a number of calculations are done for various sets of fracture geometry data. The calculations indicate that the resistance network model gives results comparable to those of a complex 3-dimensional numerical model. The present model is very simple and fast.
The Impact of Episodic Nonequilibrium Fracture-Matrix Flow on Repository Performance at the Potential Yucca Mountain Site
Authors: Buscheck Thomas A. , Nitao John J. , Chesnut Dwayne A.
Published: March 2011

Adequate representation of fracture-matrix interaction during episodic infiltration events is crucial in making valid hydrological predictions of repository performance at Yucca Mountain. Approximations have been applied to represent fracture-matrix flow interaction, including the Equivalent Continuum Model, which assumes capillary equilibrium between fractures and matrix, and the Fracture-Matrix Model, which accounts for nonequilibrium fracture-matrix flow. We analyze the impact of matrix imbibition on episodic nonequilibrium fracture-matrix flow and transport for the eight major hydrostratigraphic units in the unsaturated zone at Yucca Mountain.
The Assessment of the Performance of the Engineered Barriers in a Repository for the Disposal of Low- and Intermediate-Level Radioactive Waste
Authors: Atkinson A. , Harris A.W. , Naish C.C. , Sharland S.M. , Smith A.C.
Published: March 2011

Current plans for the disposal of low- and intermediate-level radioactive waste in the U.K. comprise emplacement of steel or concrete containers of waste in a deep underground repository where they will be surrounded by a cementitious backfill. Research is in progress to assess the effectiveness of steel and concrete as barriers to radionuclide release from the repository. A joint experimental and modelling approach is used. Studies of the transport properties of dissolved radionuclides and gases through concrete, and the ability of the concrete to control the pH in the repository are described. Localised and uniform corrosion of carbon and stainless steels are investigated in the high pH conditions of the repository. The research shows that engineered barriers of concrete and steel can provide useful physical containment in the short term and contribute to chemical containment for hundreds of thousands of years.
A Model for Nearfield Performance Assessment in the Presence of a Permeable Engineered Barrier
Authors: Broc D. , Lamoureux M. , Durin M. , Voinis S. , Raimbault P.
Published: March 2011

One of the options envisaged by ANDRA for some of the engineered barriers in a geological repository in hard rock is the use of a permeable granular material (clay/sand or clay/crushed rock mixtures).

This choice will lead to modification of the flow distribution around the repository borehole and the consequences on the migration behaviour in the near field need to be evaluated.

The aim of this study is to develop a borehole model which describes the release in the borehole from the waste matrix through the engineered barrier. This model can be readily integrated in a near field model of the waste storage area.
Fluid and Solute Transport in a Network of Channels
Authors: Moreno Luis , Neretnieks Ivars
Published: March 2011

A model is proposed to describe flow and transport in fractured rocks. It is based on the concept of a network of channels. This approach is backed by observations in drifts and tunnels that flow in fractured rocks takes place in sparse narrow channels with widths typically less than 10 cm and a channel frequency of one channel per a few square meters to one channel per more than a hundred square meters. Observations in boreholes also indicate that there are large distances, tens to hundreds of meters, between the most conductive sections in boreholes.

For visualization purposes our model is displayed on a rectangular grid. The individual channels are given stochastically selected conductances and volumes. Flowrate calculations have been performed in grids of sizes 20*20*20 channels in most cases but larger grids have also been used. For large standard.deviations in conductances, greater than 1.6 in the log normal distribution (base 10), channeling becomes pronounced with most of the water flowing in a few paths. The effluent patterns and flowrate distributions obtained in the simulations have been compared to three different field measurements in drifts and tunnels. Standard deviations of channels conductances were found to be between 1.6 and 2.4 or more in some cases. Channel lengths were found to vary between 1.2 m and 10.2 m in the different sites. In one site where detailed borehole measurements were available the channel length could be assessed independently and was found to be 1.2 m as compared to the 1.7 m obtained from the drift inflow measurements.

A particle tracking technique was used to simulate solute transport in the network. Nonsorbing as well as sorbing tracer transport can be simulated and by a special technique also tracers which diffuse into the rock matrix can be simulated.

Tracer measurements in one site, Stripa, were used to compare dispersivities. These were found to be large, having Peclet numbers less than 5 both in simulations and the field results. From the Stripa tracer data it was also found that the tracers were taken up into the rock matrix by molecular diffusion. The surface area needed for this uptake was estimated to be between 0.2-20 m2/m3 for different tracers. The wetted surface for the model estimated from flowrate distribution data indicate a wetted surface of 0.2- 0.4 m2/m3.
Tracer Tests in a Small Fracture Zone at Stripa
Authors: Birgersson Lars , Neretnieks Ivars , WidÙn Hans , Ågren Thomas
Published: March 2011

A large scale tracer test has been performed as a part of the Site Characterization and Validation (SCV) Project in the Stripa experimental mine. Tracers were injected in a fracture zone intersecting a newly excavated drift and collected in plastic sheets and sump holes. The experiment gave information on the variability of flow and transport properties in a fracture zone.
The Effect of Microbial Activity on the Near and Far Fields of a Swiss Type b Repository
Authors: West J.M. , Cave M. , Higgo J.J.W. , Milodowski A.E. , Rochelle C.A. , Ross C.A.M.
Published: March 2011

A series of batch laboratory experiments (‘black boxes’) were set up to study the gross effects of microbial activity on repository geochemistry, radionuclide sorption and the integrity of repository and host rock materials in a Swiss type B repository. The observed principal chemical exchanges and precipitations were confirmed by modelling and could be interpreted by excluding microbiological effects. However, mineralogical studies showed steel corrosion to be localised in deep pits with microbiology playing a possible role. Talc was precipitated in all of the cells which lowered ambient pH through removal of OH- causing dissolution of CSH compounds. This has implications for the long term stability of cements. Microbiology influenced far-field radiochemistry experiments in which added microbes increased Cs sorption particularly under anaerobic conditions.