bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic-scale Analysis of Laser MBE Growth of Oxide Thin Films by in situ Rheed and Caiciss
Authors: Yoshimoto M. , Ohnishi T. , Lee G-H. , Sasaki K. , Maruta H. , Koinuma H.
Published: April 2011

Atomic-scale growth analysis of oxide thin films was performed by in situ reflection high energy electron diffraction (RHEED) and coaxial impact collision ion scattering spectroscopy (CAICISS) combined with Laser MBE. On single crystal substrates with atomically flat terrace and step structures, the two-dimensional nucleation followed by molecular layer-by-layer growth was verified by in situ monitoring of RHEED intensity oscillations, as well as ex situ atomic force microscopy (AFM) observation, for the growth of BaTiO3, Al2O3 and BaO thin films. The epitaxial BaTiO3 films grown on SrTiO3(100) and c-axis oriented Bi2Sr2CaCu2Ox (Bi2212) superconducting films were subjected to in situ CAICISS measurements in order to examine the topmost surface structure. The key factors to develop oxide lattice engineering are discussed with respect to not only in situ monitoring of the growth process using RHEED but also the atomic regulation of the substrate surface by AFM and ion scattering spectroscopy. The present work also demonstrates the advanced oxide thin film processing based on the laser MBE to control the growth and surface of films on an atomic scale.
Rheed Monitoring of Rotating Samples During Largearea Homogeneous Deposition of Oxides
Authors: Matijasevic V. C. , Lu Z. , Dessonneck K. Von , Taylor C. , Barlett D.
Published: April 2011

We have successfully implemented RHEED monitoring of growth of complex oxides in a reactive evaporation process with substrate rotation and an oxygen environment. A rotating substrate heater is used with a partial enclosure kept at a 10 mTorr oxygen pressure. This heater allows for simultaneous and uniform deposition of multiple 2-inch wafers. The RHEED beam diffracts from samples as they pass through the high-vacuum zone of the heater. A CCD camera is used for RHEED data acquisition and image capture is synchronized to sample position. In order to achieve good quality diffracted images, rotation of the sample is required to be less than 1 degree for the duration of data capture. With our relatively inexpensive setup images can be acquired for sample rotation speeds up to 1500 RPM. We use this RHEED diagnostic system for study of in-situ growth of high-temperature superconducting thin films.
In Situ Monitoring of Anodic Oxide Growth on SI (001) by Interface Second-Harmonic Generation
Authors: Janz S. , Bardwell J. A.
Published: April 2011

Optical second-harmonic (SH) generation is used to monitor the anodic growth of oxide on a (001) Si surface. The measured SH intensity is dominated by the nonlinear optical response of the space charge region in the Si just below the Si/oxide interface. The interface SH technique can detect the onset of H desorption, identify the flat band potential, and probe the evolution of space charge within the growing oxide layer.
Infrared Emission Spectra of Indium Phosphide at Elevated Temperatures
Authors: Rogne H. , Timans P. J. , Ahmed H.
Published: April 2011

Process monitoring and control during semiconductor device fabrication frequently relies on good knowledge of the optical properties of the substrate wafer and the surface coatings. However, these optical data are often unavailable, and as a consequence errors arise in pyrometric temperature measurements, as well as in thermal modelling of heating cycles. In this study, isothermal electron beam heating has been combined with in situ optical measurements to record thermal emission spectra of undoped InP specimens from 347 to 478°C, at wavelengths between I and 9 μm. The absorption coefficient was deduced from the emission spectra and reveals information about the temperature dependence of the infrared absorption mechanisms in InP.
Fem Simulation of Micro-Rotating-Structures and Their Applications in Measurement of Residual Stresses in Thin Films
Authors: Zhang Xin , Zhang Tong-Yi , Zohar Yitshak
Published: April 2011

FEM simulation of micro-rotating-structures was performed for local measurement of residual stresses in thin films. A sensitivity factor is introduced, studied and tabulated from the simulation results. The residual stress can be evaluated from the rotating deflection, the lengths of rotating and fixed beams, and the sensitivity factor. The micro-structure technique was applied to measure residual stresses in both silicon nitride and polysilicon thin films, before and after rapid thermal annealing (RTA), and further confirmed by wafer curvature method. Residual stresses in polysilicon films at different RTA stages were also characterized by micro-Raman spectroscopy (MRS). The experimental results indicate that micro-rotating-structures indeed have the ability to measure spatially and locally residual stresses in MEMS thin films with appropriate sensitivities.
Nanoindentation and Nanowear Studies of Thin Carbon Coatings
Authors: Kulkarni Ashok V. , Wyrobek Jerzy T. , Qiant Zhenghong , Siverstent John M. , Judyt Jack
Published: April 2011

Thin film magnetic disks and head-sliders require protective overcoats, usually some form of carbon, to guard the magnetic elements against corrosion and wear and to provide long interface durability. The mechanical properties of these coatings are important for assessing their tribological performance. In this paper we present the results of nanomechanical properties of amorphous carbon (a-C) and nitrogenated carbon (CN) films deposited on Si(100). a-C and CN films were deposited on silicon by Facing Target Sputtering (FTS) technique. The elemental composition and bond characterization of a-C and CN films have been determined by X-ray Photoelectron spectroscopy (XPS). Nanoindentation experiments were performed using Hysitron Triboscope® in the load range of 10–200 μN, using a sharp 90° 3-sided pyramidal diamond tip ( 50 ± 10 nm radius). Hardness and Young's modulus of elasticity were determined from the load-displacement data. Nanowear studies were performed on the 10 and 20 nm a-C and CN films to determine the critical load. Below the critical load no significant wear is observed. Above the critical load however, the wear increases sharply. Abrasive wear seems to be the cause of the sharp increase in wear depth in case of a-C film. From the above observation, CN films exhibit excellent mechanical properties owing to its superior hardness property.
Advanced Bulge Test System
Authors: Keiner H. , Preissig F. J. von , Zeng H. , Nejhad M. N. G. , Kim E. S.
Published: April 2011

The bulge test is an established method of measuring the residual stress and elastic stiffness of thin-film materials. We present an advanced experimental bulge-testing system that provides advantages in speed, accuracy, and flexibility. Key innovations include the use of a Laser Doppler Displacement Meter to measure deflection, an actuated air-cylinder mechanism to vary pressure, and sophisticated computer handling of data acquisition and analysis. A test case demonstrates that repeatability of results is extremely good.
Optimization of Blend Toughness by Simultaneous Measurement of Heat and Work of Deformation
Authors: Agarwal N. , Farris R. J.
Published: April 2011

The technique of differential gas pressure calorimtery is used to simultaneously measure heat and work of isothermal deformation of acrylic based latex blend coatings. These coatings comprise of phase separated hard and soft components resulting in a combination of stiffness and toughness. An overall energy balance approach is adopted to study the partition of energy between the two phases in their respective energy-dissipating and energy-absorbing mechanisms. The toughness is maximized by a simultaneous maximization of heat dissipation and energy absorption; a fact often overlooked in the design of commercial rubber toughened systems that focus almost entirely on increasing the energy absorbing capacity of the glassy matrix. It is observed that maximizing both the energy absorption as well as dissipation can result in much higher toughness without a large sacrifice in stiffness.
Mechanical Properties Of Ferro-Electric Composite Thin Films
Authors: Fountzoulas C. G. , Sengupta S.
Published: April 2011

Ferro-electric (BSTO) films of 1 μm nominal thickness were deposited on single crystals of sapphire at substrate temperatures varying from 30 °C to 700 °C. Optical analysis showed that the thin films were amorphous up to 500 °C, while at 700 °C they were polycrystalline. The microstructure of the thin films was columnar at all substrate temperatures. The film microhardness increased with increasing substrate temperature. While the cohesion failure load of the films remained fairly constant, the adhesion failure load increased with increasing substrate temperature.
Picosecond Ultrasonics Studies of the Effect of Ion Implantation on InterfAcial Bonding Between a thin Film and a Substrate
Authors: Tas G. , Loomis J. J. , Maris H. J. , Bailes A. A. , Seiberling L. E.
Published: April 2011

We have used picosecond ultrasonics to study the effects of ion irradiation on the interfacial bonding between gold films and a silicon substrate. Acoustic vibrations are excited in the metal film when a picosecond light pulse is absorbed. The rate at which these vibrations damp out via sound transmission across the interface into the substrate gives a measure of the adhesion of the film to the substrate. The films were irradiated with 2.5 MeV helium ions with doses between 7×1014 and 8×1016 ions cm-2. The adhesion, as measured by the rate of acoustic damping, was found to be significantly improved by the ion irradiation.
Two-Dimensional Distribution of the Residual Stress in MBE-Grown InGaAs/GaAs Strained Layer Superlattices
Authors: lizuka K. , Watanabe H. , Komatsu M. , Suzuki T.
Published: April 2011

Distribution of the residual stress in InGaAs/GaAs strained layer superlattices (SLSs) has been investigated by the micro-focus photoluminescence (PL) method and PL topography. Dark lines parallel or perpendicular to [011] direction were observed in the samples by PL topography. The density of dark lines was decreased as the thickness of In0.1Ga0.9As layers increased. Such dark lines were observed even in a sample whose thickness was thinner than critical value. These dark areas corresponded to the regions where the peak wavelength of PL spectrum was shifted to longer side because of tensile stress. These results were explained well by our proposed model. That is, tensile stress acts the top of mountainous regions of wrinkles which were formed by compressive stress caused by the difference of the lattice constant between InGaAs and GaAs.
Stress Controlled Magneto-Mechanical Instability In Terfenol-D Thin Films
Authors: Su Quanmin , Wen Y. , Wuttig Manfred
Published: April 2011

The magneto-mechanical properties of Terfenol-D thin films deposited on Si substrates were studied by magnetic and mechanical measurements of film/substrate composite cantilevers. The AE effect and mechanical damping of the film were measured simultaneously. The stress in the film was controlled by annealing and deposition at different temperatures as well by the selection of the substrate material below the recrystallization temperature and determined to vary from -500 MPa, compression, in as deposited films to +480MPa, tension, in annealed films. This paper highlights the magneto-mechanical response of tensioned 1 m nanocrystalline Terfenol-D films on 50 Pim Si substrates display a pronounced damping maximum at a magnetic field of about 1.5kOe oriented perpendicular to the plane of the film. The phenomenon is critically dependent on the orientation of the magnetic field and is the result of a magneto-mechanical instability in the Terfenol film.
Energy Storage And Recovery In Thin Metal Films On Substrates
Authors: Baker Shefford P , Keller Rose-Marie , Arzt Eduard
Published: April 2011

Dislocation segments which extend through the thickness of a film can move through the film only if dislocation line length is deposited or removed at the film/substrate and film/passivation (if any) interfaces. The dislocation density and, therefore, the energy stored in the film increase during plastic deformation. The reverse process, that is, the reduction of strain energy in the film by the reduction of dislocation line length, is here suggested to be the origin of a number of unexplained features of experimentally obtained stress-temperature curves, including very low (or even “negative”) yield stresses in compression, tensile-compressive flow stress asymmetries, increasing strength with increasing temperature upon heating, and a very strong Bauschinger-like effect which has been seen in thin Cu films. The results of stress-temperature measurements of passivated Cu thin films on silicon substrates are presented.
Microstructural Effects on the Hardness, Elastic Modulus and Fracture Toughness of CVD Diamond
Authors: Kant A. , Drory M. D. , Moody N. R. , MoberlyChan W. J. , Ager J. W. , Ritchie R. O.
Published: April 2011

The hardness, elastic modulus, and fracture toughness of chemical vapor deposited (CVD) polycrystalline diamond have been investigated on several thick (∼100 μm) free-standing films with regard to the grain size, impurity content and failure mechanisms. Micro-hardness measurements using Vickers indentation, in conjunction with Young's modulus measurement techniques such as nano-indentation, were employed to estimate the indentation fracture toughness. The toughness of CVD diamond was increased through the addition of non-diamond carbon, which promoted intergranular fracture and enhanced the toughness by grain bridging.
Nanoindentation of Atomically Modified Surfaces
Authors: Corcoran Sean G. , Brankovic Stanko R. , Dimitrov Nikolay , Sieradzki Karl
Published: April 2011

Nanoindentation studies on metal and semiconducting surfaces often display excursions in the load-displacement curves. These displacement excursions have been attributed to phase transitions, oxide breakthrough, surface contamination effects, and dislocation nucleation under the indenter tip. We have shown recently that displacement excursions were present for nanoindentation on single crystal Au (111), (110) and (100), and were attributed to dislocation nucleation since all other phenomena were ruled out. We present our recent results that have been aimed at understanding the effects of surface modification at the nanoscale on dislocation nucleation. The effects of modifying the Au surface with electrochemically deposited metal monolayers (Pb and Ag), with an electrochemically deposited oxide monolayer and an electrochemically reconstructed surface will be presented. Hardness differences as great as a factor of 3 have been observed for these surfaces. These experiments are unique in that they were carried out under electrochemical control where strict control of the surface cleanliness can be maintained.
Further Developments of the Reductive Capacity Model for Spent Fuel Stability: Application to Minor Radionuclides
Authors: Bruno J. , Cera E. , Duro L. , Spahiu K. , Eriksen T. , Eklund U-B. , Werme L.O.
Published: April 2011

A reductive capacity (RDC) kinetic model previously developed for the radiolitically induced oxidative dissolution of the spent fuel matrix has been applied to critical minor radionuclides present in spent fuel [1]. The model has been tested in front of experimental results from spent fuel corrosion obtained within the SKB programme. The experimental procedure is detailed in a previous publication [2]. The RDC model considers
Predicting the Performance of a Site Closure System Through Engineering Risk Assessment
Authors: Garrard G. F. G. , Lany P. Von , Powrie W. , Humphreys P. N. , Pinner A. V.
Published: April 2011

Since 1959 British Nuclear Fuels pie (BNFL) have operated a disposal site for solid low level radioactive wastes (LLW) at Drigg, approximately 6 kilometres south of Sellafield in West Cumbria. Prior to 1988 the disposal method involved the excavation of a series of parallel trenches across the site which were back filled with LLW and covered with an interim, water resistant cap. Since 1988 the disposal method has changed and waste is now compacted and placed into steel isofreight containers into which a highly fluid cement based grout is added prior to the containers being disposed of in a series of open concrete lined vaults. It is proposed that, when full, each vault will also be capped. The change in disposal method has extended the life of the site and final closure is therefore not anticipated until about the middle of the next century.
Crystal Chemistry of Natural Zirconolite: Implications for High-Level Waste Incorporation in Synroc
Authors: Gierpé Reto , Williams C. Terry , Lumpkin Gregory R.
Published: April 2011

Zirconolite, ideally CaZrTi2O7, is a relatively rare mineral crystallizing at different geological conditions and in a wide range of generally SiO2-poor rock types. Synthetic zirconolite is one of two major actinide (ACT) host phases in SYNROC, a very promising option for the disposal of high-level nuclear waste (HLW). The available samples of naturally occurring zirconolite cover an extensive range in ACT content, age and host rock type, and thus offer an ideal opportunity to study the relationships between alpha-decay doses, radiation damage, and geochemical alteration processes [1]. In this paper, we present results obtained from a statistical study of nearly 300 chemical analyses of natural zirconolite [2].
Volkonskoite From a Natural Analogue of a Cementitious Repository
Authors: Khoury H.N.
Published: April 2011

Many repository designs-particularly those for low- and intermediate-level waste-involve use of very large quantities of cementitious materials. The interaction of such materials with groundwater results in a hyperalkaline leachate which will contain any radionuclides dissolved from the waste. The interaction of such leachate with surrounding rocks and the mobility of radionuclides in this complex system has to be considered in repository safety assessment. The very slow kinetics of many of the reactions involved, however, greatly limit the applicability of conventional laboratory studies.

The marbles travertines of Maqarin-Daba-Siwaqa sites of North and Central Jordan can serve as natural analogues of a cementitious repository. A similar hyperalkaline environment is still found in some of these areas, controlled by dissolution of natural portlandite and calcium silica hydroxide (CSH) mineral phases. The high pH groundwaters interact with the surrounding limestones and marls offering a close analogy of the situation likely to occur if a repository were constructed in a sedimentary site. The high pH seepages precipitate travertines as a result of the uptake of atmospheric CO2.

The sites offer a good chance to investigate the interactions of the high pH water with rocks containing diagenetic enrichments in safety-relevant trace elements (Zn, Cr, U, Se, Ni, Sn, etc.). For example, the unusual smectite (volkonskoite) and other phases (similar to hydrated cement products) precipitated from the mobile alkaline water may act as sinks for such trace elements. Such studies can be used to qualitatively confirm the expected low mobility of important elements in this system. Coupled with hydrochemical studies, the geochemical models used to support performance assessment can be tested (validated).
Problems With the Spallings Model in the Compliance Certification Application of the Waste Isolation Pilot Plant
Authors: Lee William W.-L.
Published: April 2011

This paper questions the spallings model in the performance assessment supporting the compliance certification application (CCA) of the Waste Isolation Pilot Plant (WIPP). Spallings release is one of the dominant release pathways.
Age Structure of Groundwaters Determined by Isotope Methods
Authors: Loosli H.H. , Lehmann B.E. , Mattle N. , Scholtis A. , Heidinger M. , Eichinger L.
Published: April 2011

For the calibration of flow models, isotope methods play an important role. It is possible to deduce time information from radionuclides and therefore information about groundwater ages or flow velocities. Usually a flow system has not one single age (which is also called piston flow age) but an age distribution. In addition, groundwater may be a mixture of different components. For waste disposal investigations it is especially important to know if a small fast flowing water component is admixed. Therefore, one isotope method alone does not allow to answer all questions and a combination of isotope methods is advantageous. The results of such isotope combinations are presented. Possible isotopes are 3H, 85Kr (in combination also with Freon measurements) for a young component; 39Ar allows dating up to about 1000 years and 14C (together with δ13C and carbonate chemistry) reaches back to about 35‘000 years. Qualitative time indicators for very old waters are 4He, 40Ar/36Ar ratios, stable isotopes δ2H and δ8O and special chemical concentrations. In the first part of the poster the input functions of some isotope methods are given for the last decades. A combination is especially successful if the input functions have a totally different shape and therefore the isotope ratio a strong time dependence. In the second part, two to four examples of a successful combination of isotope methods are given. Main area is the Wellenberg site of the NAGRA investigations. Various combinations are demonstrated with time ranges from a few decades to palaeowaters. The conclusions illustrate the possibilities and limits of isotope combinations.
Description of Performance Allocation: A Case Study at Yucca Mountain
Authors: Vallikat Vinod , Sevougian S. David , McNeish Jerry A.
Published: April 2011

A methodology was developed to determine the effectiveness of different components/barriers in isolating waste from the accessible environment for the potential nuclear waste repository at Yucca Mountain, Nevada [1]. Quantifying the performance offered by different barriers aids in prioritizing the testing and analysis activities aimed at resolving uncertainty in processes and parameters of greatest significance to long-term performance. If a substantial fraction of the overall performance of a repository system may be attributed to the performance of a particular barrier, then it is prudent to devote the necessary resources toward enhancing the confidence in our predictive ability regarding that barrier (through more in-depth characterization and testing).
Local Structure of Simplified Waste Glass: Complementarity of XAS and MD Calculations
Authors: Galoisy L , Delaye J.M. , Ghaleb D. , Calas G. , Grand M. Le , Morin G. , Ramos A. , Pacaud F.
Published: April 2011

X-ray Absorption Spectroscopy (XAS) together with x-ray diffraction methods were used in inactive analogues of the French nuclear waste glass to analyze Pd-Te precipitates and the peculiarity of the sites occupied by some structural probe elements such as Mo, Zn, Zr and Si in the glassy part of the material. The influence of the precipitates on the structure of the glassy matrix around these structural probes was investigated by comparing noble metal bearing compositions together with noble metal free glasses.

In noble metal bearing glasses, Pd is associated to Te as (Pd90Te10) precipitates. Pd K-edge EXAFS shows the presence of Te in the Pd coordination shell and is in accordance with a non-metallic character of the Pd-Te bond. Mo K-edge EXAFS shows that Mo occurs as molybdate groups non connected to the glassy matrix, which may be related to the occasional separation of Mo-rich phases in some compositions. Zr is located in an octahedron with d(Zr-O)=2.08Å 0.01Å whereas Zn is 4-fold coordinated with d(Zn-0)=-1.95 Å± 0.01Å. Beyond this well defined first coordination shell, XAS detects some degree of medium range order which gives insight on the bonding of the site to the polymeric borosilicate network. The interatomic Zn-Si and Zr-Si EXAFS-determined distances agree with a ZnO4and Si04tetrahedra sharing corners geometry and Zr-Si octahedra sharing corner with Si04tetrahedra. A third shell of neighbors around Zr was evidenced in the noble metal bearing glasses and in a four oxide glass, indicating that Zr is an element useful for detecting subtle changes in the local structure of complex borosilicate glasses. Si K XANES shows modifications in the connection between Si04tetrahedra when noble metals are present. To obtain accurate and precise structural interpretations, a direct comparison between EXAFS data and Molecular Dynamic (M.D.) calculations on simplified nuclear glass comprising six oxides has been performed. MD calculations show that the distribution of the Zr-O distances is harmonic in the k-range accessible with EXAFS in glasses.
Vitrification of High-Level Radioactive Waste by Sintering Under Pressure
Authors: Lutze W. , Gong W. , Abdelouas A. , Ewing R. C. , Scales C.
Published: April 2011

Sintered silicate glass waste forms with a continuous glass phase and embedded but not completely dissolved waste particles were prepared by powder technology. We used a typical defense waste compositions, containing 38 wt.% of ZrO2 and prepared sinter glass samples with 30, 35, and 40 wt.% waste loading at 830°C and 27.6 MPa, by hot isostatic pressing. The glass former was amorphous silica powder. Simulated waste was added as calcine. Samples were characterized using scanning and transmission electron microscopy. The results show that extensive sintering took place, particularly with the 40 wt.% samples. Waste components, such as Na2O, CaO, MnO2, La203, Fe2O3, NiO, Cr2O3, and P2O5, dissolved completely in the continuous glass phase. ZrO2 was partly dissolved and occurred as aggregates of tiny baddeleyite crystals. The porosity of the samples was 2-3%, indicating that the optimum sintering conditions have not been met to reach porosities <1%.

Chemical durability tests were carried out with sintered glass with 35 wt.% waste loading in deionized water at 90°C under static conditions, showing that the glass is at least as chemically durable as a borosilicate glass with 31 wt.% melted at 1350°C.
Modeling the Evolution of a Soluble Matrix in Various Environments
Authors: Maillard S. , Iracane D.
Published: April 2011

We model the dissolution of a soluble matrix protected by a diffusion barrier. The dissolution, driven by a first order kinetics law, allows the solute to diffuse in the barrier with sorption and precipitation interactions. The dissolved mass evolution and the lifetime of the wasteform can be expressed in a closed form and as a function of relevant length scales, reflecting the phenomenon controlling the dissolution. Application to a nuclear glass in a clay barrier shows that diffusion in the barrier is the main phenomenon unless precipitation of chalcedony occurs or silicon is very strongly sorbed in the barrier. This requires further experimental investigation of silicon/clay interaction.
Study of Glass-Ceramic Waste Forms
Authors: Stefanovsky S.V. , Ioudintsev S.V. , Nikonov B.S. , Omelianenko B.I. , Lashtchenova T.N.
Published: April 2011

Since the early of the 1990s the method of inductive melting in a cold crucible (IMCC) has been applied at SIA “Radon” for production of various wasteforms, including glasses and Synroc-type ceramics. Sphene-based glass-ceramics composed of glass and crystalline phases were considered as appropriate wasteform for High Level Waste immobilisation. Investigation of two glass-ceramic specimens prepared with the IMCC has been performed using optical microscopy, XRD, SEM/EDS, and TEM methods. The samples produced consist of vitreous and crystalline phases. The vitreous phase consists of two varieties of glass formed by the immiscibility of the initial melt onto two separate liquids. One of the glasses is observed as spherical microinclusions in the matrix glass. The glass of the microspheres are differed from the matrix glass composition by higher contents of Ca, Ti, Ce, Sr, Zr (or Cr), while the matrix glass contains higher amounts of Si, Al, and alkalies. The crystalline phases with sphene- and perrierite-like structures have been also occurred. Their total quantity reaches up to 50 vol.%. The synthetic perrierite has similar unit-cell parameters with its natural mineral analogs with the only exception in two-fold value of c dimension. Zr, Ce, and Sr are incorporated into synthetic sphene and perrierite, while Cs is hosted by the glass phases.
Surface Characterization of Olivine-Rock by X-ray Photoelectron Spectroscopy (XPS). Leaching and U(VI) Sorption Experiments
Authors: Rodrigues E. , Aamrani F.Z. El , Giménez J. , Casas I. , Torrero M.E. , de Pablo J. , Duro L. , Hellmuth K-H.
Published: April 2011

High-FeO olivine-rock from Lovasjäarvi intrusion (SE-Finland) has been suggested as redox-active backfill-additive in deep high level nuclear waste repositories. In this w'ork, surface characterization of olivine-rock by X-Ray Photoelectron Spectroscopy (XPS) has been used in order to assess the behavior of this rock during leaching experiments and sorption properties of redox sensitive radionuclides. Uranium (VI) sorption has also been performed. Olivine leaching experiments at basic pH have shown the abundance of Fe and 0 relative to Si and Mg clearly indicating the precipitation of a Fe(III)-oxide secondary phase, probably amorphous FeOOH. At acid pH, the decrease of Mg/Si and Fe/Si ratios can be attributed to the formation of silicon dioxide on the mineral surface. The deconvolution of the 4f7 2 Uranium peak has shown the reduction of U(VI) to U(IV) onto the olivine surface.
New Approach for Predicting the Long-Term Behavior of Bentonite: The Unified Method of Molecular Dynamics and Homogenization Analysis
Authors: Kawamura K. , Ichikawa Y. , Nakano M. , Kitayama K. , Kawamura H.
Published: April 2011

For predicting the long-term behavior of bentonite, we present a new and unified simulation procedure of Molecular Dynamics Method (MD) and Homogenization Analysis (HA). The MD is applied to establish molecular-scale bentonite properties and the HA is introduced to extrapolate the molecular model to the bulk-scale continuum model.
Evolution of the Porewater Chemistry in Compacted Bentonite
Authors: Muurinen Arto , Lehikoinen Jarmo
Published: April 2011

The evolution of porewater chemistry in bentonite was studied in solution-bentonite interaction experiments under anaerobic conditions at room temperature. The parameters varied were the bentonite density, bentonite-to-water ratio (b/w), ionic strength of the solution, and the composition of bentonite. At the end of the experiment, the equilibrating solution and the porewater squeezed out of the bentonite samples were analysed. This paper presents the preliminary experimental results of these ongoing studies. The evolution of porewater chemistry was determined by the dissolving components initially present in the bentonite together with the ions coming with water from the surroundings. Ion-exchange processes occured between the exchangeable cations of montmorillonite and the cations in the water. The obtained concentrations in the external solution and porewater strongly depended on the b/w used. The concentrations in the squeezed porewaters were clearly lower than in the external waters and decreased with increasing density during squeezing.
Application of Electrochemical Acceleration Test Method to Changes in Cementitious Barrier Performances by Leaching Degradation
Authors: Saito H. , Tajima T. , Fujiwara A. , Tsuji Y.
Published: April 2011

Since cementitious materials used in repositories will be in contact with water, one of the most important tasks is to assess their long-term performance while they are being degraded very slowly by leaching. The authors have proposed an electrochemical acceleration test method and clarified its applicability. In this method, a specimen is placed between two glass vessels containing water. An anode and a cathode connected to a DC power source provide a potential gradient across the specimen. Ca2+ ions in the pore solution move rapidly to the cathode side, and thus hasten cement hydrate dissolution.

In this study, we obtained two types of almost homogeneously degraded specimens by controlling cumulative quantity of dissolved Ca2+ ions. In the first type, there was no Ca(OH)2and the C-S-H phases underwent insignificant alteration, whereas in the second type, degradation of the C-S-H phases occurred.

As a preliminary evaluation of cementitious materials, diffusion coefficients of tritiated water were measured for nondegraded and degraded specimens. Diffusion coefficients were increased by degradation and closely corresponded to changes in porosity.
Experimental Investigation of Passivation Behavior and Corrosion Rate of Carbon Steel in Compacted Bentonite
Authors: Taniguchi N. , Honda A. , Ishikawa H.
Published: April 2011

Carbon steel is one of the candidate materials for overpacks for high-level radioactive waste disposal in Japan. Passivation behavior and corrosion rate of carbon steel were investigated by electrochemical measurements under simulated repository conditions. The results of the anodic polarization measurements showed that carbon steel was hard to passivate in highly compacted bentonite. Therefore, general corrosion seems to be most probable in repository conditions. In order to monitor the in-situ general corrosion rate in compacted bentonite, the AC impedance of carbon steel was measured under aerated conditions. It was confirmed that the corrosion rate in saturated bentonite decreased with time and it was almost the same as that observed in deaerated aqueous conditions. The corrosion rate did not increase in the presence of corrosion products formed by external current supply.
Microstructure of a Slag-Cement Paste Determined by Small-Angle Neutron Scattering
Authors: Aldridge L.P. , Bertram W.K. , Sabine T.M. , Ioffe A
Published: April 2011

Small angle neutron scattering from hydrating cement paste was compared to that from a paste made of a blend of cement and ground granulated blast furnace slag. The scattering measurements were used to determine the average size of the scattering particles during hydration. Their rate of growth was monitored in-situ over the first 40 hours of hydration. There was little difference in the scattering spectra, showing that the scattering particles in paste containing slag blend or cement were of similar size. At the beginning of hydration the particle radii were about 250 nn and after 14 days they had grown to over 600nm.

Estimates of particle sizes are critically dependent on the amount of multiple scattering. Therefore the amount of multiple scattering of the sample must be taken into account before making comparisons between the sizes of particles of different matrices.
Chlorination Reactions Applied to Reprocessing of Aluminum-Uranium Spent Nuclear Fuels
Authors: Bohel A.E. , Nassini H.E. , Bevilacqua A.M. , Pasquevich D.M.
Published: April 2011

An innovative dry method for reprocessing highly enriched Al-U spent fuel is presented. It is based on the use of hot chlorine gas to chemically attack the irradiated fuels, converting aluminum, uranium and fission products into their respective chlorides. Separation of the large amounts of non-radioactive species, basically aluminum and its impurities, can be further accomplished by exploiting the significant differences between relative volatilities of metallic chlorides and also by selectivity of chlorination reactions. The technical feasibility of the method proposed is theoretically demonstrated by performing a case study on the highly enriched Al-U fuels of the RA-3 Argentine research and test reactor.
Numerical Modeling and Column Experiments to Simulate the Alkaline Disturbed Zone Around a Cementitious Radioactive Waste Repository
Authors: Bateman K. , Coombs P. , Noy D. J. , Pearce J. M. , Wetton P. D.
Published: April 2011

In order to be able to describe the migration of an alkaline plume, coupled chemistry and flow computer models may be employed. A series of laboratory column experiments were conducted to test the capabilities of currently available coupled models to predict product solids and output fluid compositions as a function of time. The predictions did not replicate all the variations of Ca:Si observed during mineralogical analysis, probably due the unavailability of sufficient kinetic and thermodynamic data for the range of calcium silicate hydrates (CSH) phases of interest. However, the predictions do reproduce the variation of Ca:Si ratios with time and distance along the columns. A better understanding of the above processes will lead to greater confidence in predictive modelling of the migration of alkaline plumes away from the cementitious barriers of radioactive waste disposal facilities.
Borosilicate Nuclear Waste Glass Alteration Kinetics: Chemical Inhibition and Affinity Control
Authors: Advocat T. , Chouchan J. L. , Crovisier J. L. , Guy C. , Daux V. , Jegou C. , Gin S. , Vernaz E.
Published: April 2011

The objective of this work was to develop a more representative mathematical formulation of the alteration kinetics of the borosilicate SON68 glass by combining three approaches: (1) Compare extensive prior experimental static leaching results for SON68 glass with the first-order kinetic law in which silica is the predominant element, (2) Assess the exact role of dissolved silica on the alteration rate under conditions near and far from saturation, by means of dynamic leach tests and, (3) Compare the new data with the general kinetic law for silicates in which the reaction affinity, catalysis and inhibition are the three influencing factors.
The Excavation Project in the Grimsel Test Site: In Situ High-Resolution Gamma and Alpha Spectrometry of 60Co, 75Se, 113Sn, 152Eu, 235U, and 237Np/233Pa
Authors: Eikenberg J. , Ruethi M. , Alexander W.R. , Frieg B. , Fierz T.
Published: April 2011

Full excavation of a water-conducting shear zone used for radionuclide migration experiments is part of a comprehensive study to physically determine the sites of in-situ radionuclide retardation. Prior to the excavation, multi-tracer solutions containing strongly sorbing y- and αemitting nuclides were injected into the shear zone and the water extracted was analyzed on-line using in situ, high-resolution y-spectrometry. In addition, water samples were collected to compare quantitatively the on-line data with subsequent laboratory measurements α- and γ- spectrometry) and also to analyze samples with activities below the detection limits of the in-situ analysis. The breakthrough curves indicate that Se had passed through the fracture with a velocity comparable to a conservatively behaving dye (uranine), but very strong retardation of Co. Eu and Sn was observed. The recoveries of these nuclides were found to be in the order of only a few percent when the dipole flow-field was interrupted about one month after radionuclide injection and the fracture was sealed off for excavation. Significant retardation was also obtained for the oxemitters U, Np and Pa. Almost identical breakthrough curves for these actinides were measured, suggesting a similar spatial distribution in the fracture at any given time.
Progress in Physical Rock Matrix Characterization: Structure of the Pore Space
Authors: Sütari-Kauppi M. , Flitsiyan E.S. , Klobes P. , Meyer K. , Hellmuth K-H.
Published: April 2011

Quantitative autoradiography for the investigation of rock matrices has been further developed by use of tritium-labeled polymethylmethacrylate (3H-PMMA), the use of thin sections and image analysis functions allowing correlations of mineralogic-petrographical and analytical or porosity information. The autoradiographic system was studied experimentally and theoretically. The autoradiography could achieve a resolution down to 10 and 20 μm for3H and14C, respectively. Possible candidates for intact, low-porous rock standard materials were studied and the measurement of their transport properties discussed. Porosities and diffusivities measured in rock types dominated by very small pores were depending on the probe molecule used. The effect was most pronounced in flint which gave low porosities for MMA, Hg and He and no diffusivities at all for He.
Crystal Chemistry and Microstructures of Uranyl Phosphates
Authors: Suzuki Y. , Murakami T. , Kogure T. , Isobe H. , Sato T.
Published: April 2011

The crystal chemistry and microstructures of saleeite (Mg(UO2PO4)2•10H2O) and metatorbernite (Cu(UO2PO4)2•8H2O), from Koongarra, Australia and Shinkolobwe, Congo, were examined by X-ray diffraction analysis, infrared spectroscopy (IR), scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis, transmission electron microscopy (TEM) and analytical electron microscopy. The uranyl phosphates consist of uranyl phosphate layers with cations and waters in the interlayers. The IR spectra of saleeite and metatorbernite show the presence of hydroxyls in the interlayers in addition to water molecules. The d002 spacings of the hydrated phases of saleeite and metatorbernite up to 300°C reveal that the uranyl phosphate layers themselves are quite stable in the temperature range although the interlayer water molecules are lost easily. The presence of a mixed phase of saleeite and metatorbernite is confirmed in the micrometer and nanometer scales. However, SEM and TEM examination suggest saleeite and metatorbemite generally grow separately, and rarely form solid solution or interstratification. The results imply that U is retained in uranyl phosphate minerals even when the temperature at around repositories increases, and that saleeite and metatorbernite precipitate independently from solution according to their solubilities even when Mg2+ and Cu2+ coexist in solution.
Modeling of Groundwater Flow at Wellenberg Using Monte Carlo Simulations
Authors: Jaquet O. , Schindler M. , Voborny O. , Vinard P.
Published: April 2011

Wellenberg is the proposed candidate site for LLW/ILW repository in Switzerland (Figure 1). The performance assessment of the planned repository calls for a thorough hydrogeological characterization of the site. The spatial distribution of the hydraulic conductivity within the host rock is a key input for the evaluation of the host rock performances. The spatially variable conductivity field is modelled geostatistically in 3 dimensions using a conditional simulation method. In order to account for the possible range of spatial variability, several simulations of the conductivity are generated. The conditional simulation of the conductivity - representing possible versions of the unknown reality - are used as input for numerical modelling. For each simulated conductivity field, the groundwater flow is numerically modelled using finite elements. This Monte Carlo approach allows the propagation of the input uncertainty due to spatial variability of the conductivity onto the predictions delivered by the flow model. With the help of this approach several specified performance criteria - together with their uncertainty - were estimated for the evaluation of storage capabilities of the Wellenberg host rock.
Retention of Neptunium in Uranyl Alteration Phases Formed During Spent Fuel Corrosion
Authors: Buck E. C. , Finch R. J. , Finn P. A. , Bates J. K.
Published: April 2011

Uranyl oxide hydrate phases are known to form during contact of oxide spent nuclear fuel with water under oxidizing conditions; however, less is known about the fate of fission and neutron capture products during this alteration. We describe, for the first time, evidence that neptunium can become incorporated into the uranyl secondary phase, dehydrated schoepite (UO3•0.8H2O). Based on the long-term durability of natural schoepite, the retention of neptunium in this alteration phase may be significant during spent fuel corrosion in an unsaturated geologic repository.
Glass Waste Form Performance for Disposal of the Cesium and Strontium Concentrate Resulting From the Partitioning of HLW
Authors: Aloy A.S. , Iskhakova O.A. , Kol‘tsova T.I. , Trofimenko A.V.
Published: April 2011

The recent advances in HLW partitioning indicate that cesium–137 and strontium–90 can be separated in the form of a pure concentrate. Based on this concentrate the glass RT2–1 containing 4.7 wt.% Cs2O and 2.7 wt.% SrO was selected for more intensive and wider studies to predict long-term performance of this waste form under repository conditions.

Leach tests were made in distilled and mineralized water before and after crystallization at 20, 90 and 130°C.

Fully devitrified glass contained only one crystalline phase corresponding to the pollucite structure.
Advanced Concept of Partitioning for Transmutation Treatment in Improved Geologic Disposal of HLW
Authors: Kitamoto Asashi
Published: April 2011

Geologic disposal scenario combined with multiple-recycle P&B/T (partitioning, and burning and/or transmutation) treatment has some potential merits to complete the current geologic disposal scenario, and is discussed herein based on three plus two criteria for partitioning. The important gain of P&B/T treatment is that an unanticipated uncertainty due to geologic behavior for near and far field of repository can be avoided without verification for super-long period. The number reduction of GSC (glass solidified canister, i.e. waste package)is another important gain of P&T treatment to decrease the cost of geologic disposal, because the number reduction of GSC can save the total cost for the current disposal scenario
The Relative Radiation Resistance of Zirconolite, Pyrochlore, and Perovskite to 1.5 MeV Kr+Ions
Authors: Smith Katherine L. , Zaluzec Nestor J. , Lumpkin Gregory R.
Published: April 2011

Zirconolite (CaZrTi2O7), pyrochlore (vIIIA2VIB2IVx6y) and perovskite (CaTiO3) are candidate phases for the immobilisation of rare earth elements (REEs) and actinides (ACTs) in various high level radioactive waste (HLW) forms [1]. The effect of radiation damage on the structure and consequently on the durability of these phases is important to predictive modelling of their behaviour in the repository environment and risk assessment
The Dependence of the Diffusion Coefficients of 3H and Cs on Grain Size in Compacted Montmorillonite
Authors: Nakajima Mamoru , Kozaki Tamotsu , Kato Hiroyasu , Sato Seichi , Ohashi Hiroshi
Published: April 2011

Compacted bentonite is a candidate buffer material in geological disposal of high-level radioactive waste. The transport of radionuclides in compacted bentonite is dominated by diffusion, because of its very low permeability. In this study, we focused on the grain size of clay mineral, which is considered to be closely related to the formation factor in the pore water diffusion model[1,2]. The apparent diffusion coefficients (Da) of HTO and cesium ions in compacted clays were determined using montmorillonite samples with different grain size and dry density, and the effect of the grain size on diffusion behavior was discussed.
Treatment of Heterogeneous Aspects of Concrete Radiolysis Using the CHEMSIMUL Code
Authors: Bouniol Pascal
Published: April 2011

The durability of concretes under irradiation must be investigated in connection with research on radioactive waste conditioning (matrices, canisters) and disposal (engineered barriers). The weak element of the concrete, the water present in the pores, or in the hydrated compounds, is the source of radiolysis, the chief cause of radiation damage. The emission of associated dihydrogen, or radiolytic breakdown by internal overpressure, are two objective risks for which the many factors involved and the heterogeneous nature of the material make any long-term forecast difficult.