bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation of Voids in Thin-Film Interconnects Through Crystallographic Slip
Authors: Shen Y.-L.
Published: April 2011

A two-dimensional void nucleation model in thin-film metal interconnects is proposed. The model is based on the evolution of stress and deformation fields obtained from numerical modeling. Interface flaws between the metal and the surrounding dielectric are assumed to exist. A unique pattern of shear stress resolved on the slip systems of the metal is found. A model of dislocation slip is constructed in accord with the evolution of the shear mode. The mechanism of crystallographic slip is such that lateral thinning of the metal line at the debond region, together with the slip steps produced at the edges of debond lead to a net transport of atoms away from the interface defect, and a physical void is thus formed.
A Novel Method to Measure Poisson's Ratio of Thin Films
Authors: Ziebart V. , Paul O. , Münch U. , Baltes H.
Published: April 2011

We report a novel method to measure Poisson's ratio v of compressively prestressed thin films. The method exploits a v-dependent mechanical instability transition of buckled long rectangular membranes under differential pressure. This allows to determine v with high accuracy, using a physical model of the plate instability. The method was used to extract v = 0.253±0.017 from 0.704±0.003 μim thick PECVD silicon nitride films.
Creation and Motion of Edge Dislocations in Copper Single Crystals
Authors: Masaodoyama  , Kogure Yoshiaki , Nozaki Tadatoshi
Published: April 2011

Dislocations were created near the center of the surface (110) of copper small crystals whose surfaces are (111), (111), (110), (110), (112), and (112) by use of n-body atom potentials and molecular dynamics. At first, a Heidenreich-Shockley partial dislocation was created. As the partial dislocation proceeds, the partial dislocation and the surface was connected with a stacking fault until the next Heidenreich-Shockley partial dislocation was created at the surface.Just before the creation of a partial dislocation the stress was the highest. For larger crystals, forming a step on (110) plane was not enough and a shear was necessary to move dislocations.
Internal Mechanical Stresses and Conductivity Mechanisms of p-n-InAsPSb/InAs-Heterostructures
Authors: Sidorov V. G. , Sokolov V. I. , Sidorov D. V.
Published: April 2011

Influence of internal mechanical stresses (IMS) and dislocations on conductivity mechanisms and reliability of light emitting diode (LED) and laser InAsPSb/InAs double heterostructures has been investigated. It was shown that the presence of lattice mismatch of layers at p-n-heteroboundaries changes LED conductivity mechanisms the same way as longterm working challenges by current. It was determined that LED degradation has barrier character and is followed by appearance and growth of tunnel current components with power dependence of current from voltage. Reliability and external quantum efficiency decrease with growth of lattice mismatch.
The Mechanical Response of Thin Film Substrates Subject to Ultrasonic Joining
Authors: Krzanowski J. E. , Razon E. , Hmiel A. F.
Published: April 2011

The ultrasonic wire bonding process is widely used for making interconnections between IC chips and package lead frames, yet the relationships between the wire/substrate materials properties and the bond formation processes are not yet well understood. In this study, we have conducted experiments to understand the mechanical response in thin film substrates subject to ultrasonic wire bonding. Atomic force microscopy (AFM) has been used to examine the morphology of thin film surfaces before and after bonding. Al wires were bonded to thin films of Cu, Cu-Ni and Ag, after which the aluminum wire was removed by etching. AFM examination of the Cu and Cu-Ni bonded surfaces revealed the extent of surface smoothing increased with bonding power level. However, at power levels typically employed in practice almost no morphological surface changes were observed, indicating surface smoothing is not required to obtain good bonds. TEM and SEM cross-sections were also used to examine Al wedge bonds and Au ball bonds to Al films on Si. A wide variety of features were observed, including surface smoothing, microcracking and void formation.
A Comparative Study of Residual Stresses in Single and Multilayer Composite Diamond Coatings
Authors: Jagannadham K. , Watkins T. R.
Published: April 2011

Residual stresses in four types of diamond films deposited by hot filament chemical vapor deposition on molybdenum substrate, three types on tungsten carbide or silicon nitride substrate are measured. Residual stresses are determined by X-ray method and Raman spectroscopy. The results from both these techniques are compared and conclusions are made on the mechanisms of adhesion of diamond films to the different substrates.
Surface and Interface Strains Studied by X-Ray Diffraction
Authors: Akimoto Koichi. , Emoto Takashi , Ichimiya Ayahiko
Published: April 2011

We have developed a technique of X-ray diffraction in order to measure strain fields near semiconductor surface and interface. The diffraction geometry is using the extremely asymmetric Bragg-case bulk reflection of a small incident angle to the surface and a large angle exiting from the surface. The incident angle of the X-rays is set near critical angle of total reflection by tuning X-ray energy of synchrotron radiation at the Photon Factory, Japan. For thermally grown-silicon oxide/Si(100) interface, the X-ray intensity of the silicon substrate 311 reflection has been measured. From comparison of the full width at half maxima (FWHM) of X-ray rocking curves of various thickness of silicon oxides, it has been revealed that silicon substrate lattice is highly strained in the thin ( less than about 5 nm) silicon oxide/silicon system. In order to know the original silicon surface strain, we have also performed the same kind measurements in the ultra-high vacuum chamber. A clean Si(l 11) 7×7 surface gives sharper X-ray diffraction peak than that of the native oxide/Si(l 11) system. From these measurements, it is concluded that the thin silicon oxide film itself gives strong strain fields to the silicon substrates, which may be the reason of the existence of the structural transition layer at the silicon oxide/Si interface.
Correlation Between The Mechanical Stress And Microstructure In Reactive Bias Magnetron Sputtered Silicon Nitride Films
Authors: Kim Joo Han , Lee Won Sang , Chunga Ki Woong
Published: April 2011

The influence of ion bombardment on the mechanical stress and microstructure of sputtered silicon nitride (SiNx) films has been systematically investigated. Applied substrate bias voltage was used to control the bombardment energy in a radio frequency (rf) reactive magnetron sputtering system. The resultant films were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), Rutherford backscattering spectrometry (RBS), stress and chemical etch rate measurements. As the bias voltage was increased, the internal stress in SiNx films became increasingly compressive and reached a value of about 18.3 × 109 dyne/cm2 at higher bias voltages. These correlated well with the transition of the film microstructure from a porous microcolumnar structure containing large void to the more densely packed one. The obtained results can be explained in terms of atomic peening by energetic particles, leading to densification of the microstructure. It was also found that the amount of argon incorporated in the film is increased with increasing bias voltage, whereas the oxygen content is decreased. The lowest etch rate in buffered HF solution, approximately 1.2 Å/sec, was observed with the application of a substrate bias of -50 V.
Stress Evolution and Notch Formation During Polysilicon Gate Electrode Etching
Authors: Vyvoda Michael A. , Graves David B.
Published: April 2011

We have developed a numerical simulation based on the boundary element method that models thermal contraction-induced stresses within semiconductor microstructures, and the effects of these stresses on surface evolution. The test case we have studied is that of polysilicon gate etch during over-etching in a plasma environment. We assume a local etch rate proportional to the normal component of the surface strain energy density gradient caused by the differential thermal contraction of polysilicon substrate and underlying silicon dioxide film. This leads to the prediction of stress-enhanced etching in the area near the polysilicon / gate oxide interface, where large stresses develop during cooling from deposition temperature to room temperature. It is proposed that stress-enhanced etching of this nature may be partially responsible for a common type of deleterious feature observed experimentally during gate electrode patterning known as “notching”.
Comparison Of Aln Films Synthesized By Pulsed Laser Ablation And Magnetron Sputtering Techniques
Authors: Jagannadham K. , Sharma A. K. , Wei Q. , Kalyanraman R. , Narayan J.
Published: April 2011

A comparative study is reported on the aluminum nitride (AIN) films on Si (111) substrate deposited by pulsed laser deposition and reactive magnetron sputtering. The structure, bonding characteristics, relative impurity levels, and wear resistance have been investigated to compare these films. We have used the techniques such as high resolution transmission electron microscopy, Raman spectroscopy, fourier transform infra-red spectroscopy, secondary ion mass spectrometry, and crater grinding method for wear test, to delineate differences between these AIN films.
Micromechanical Properties of Silicate Glass Films on Sapphire Substrates
Authors: Zagrebelny Andrey V. , Carter C. Barry
Published: April 2011

The deformation of thin layers of glass on crystalline materials has been examined using newly developed experimental methods for nanomechanical testing. Continuous films of anorthite (CaAl2Si2O8), celsian (BaAl2Si2O8), and monticellite (CaMgSiO4) were deposited onto A12O3 surfaces by pulsed-laser deposition (PLD). Mechanical properties such as Young's modulus and hardness were probed with a high-resolution depth-sensing indentation instrument. Nanomechanical testing, combined with AFM in-situ imaging of the deformed regions, allowed force-displacement measurements and imaging of the same regions of the specimen before and immediately after indentation. Emphasis has been placed on examining how changes in the glass composition, residual stress introduced into the films, effect of film's heat-treatment, and the effect of substrate crystallographic orientation will affect the mechanical properties of silicate-glass films.
3D Discrete Dislocation Models Of Thin-Film Plasticity
Authors: Hartmaier A. , Fivel M. C. , Canova G. R. , Gumbsch P.
Published: April 2011

Three-dimensional simulation schemes for discrete dislocation dynamics (DDD) have been used successfully to investigate plasticity of bulk materials. The adaptation of these DDD schemes to a description of thin-film plasticity requires detailed modeling of the interfaces and surfaces of the film. One possible method is to compensate for the normal stresses that a dislocation distribution exerts on a surface by appropriate point loads. This traction-compensation method is extended to a free standing film (two opposing surfaces). The extension to a thin film on a substrate is possible.
High Temperature Tensile Behavior Of Free-Standing Gold Films
Authors: Emery R. , Simons C. , Mazin B. , Povirk G. L.
Published: April 2011

A method for tensile testing thin films at elevated temperatures is presented. Freestanding tensile specimens were prepared by evaporating 2.1 μm of gold onto a patterned oxidized silicon wafer. Tensile tests were performed at various temperatures up to 600°C. The ultimate tensile strengths of the films decreased as temperature increased, and ductility increased with increasing temperature. Films tested at high temperatures (≥ 400 °C) exhibited significant strain rate-dependence, while films tested at low temperatures (≤ 200 °C) were found to be virtually rate-independent. At higher temperatures and strain rates, stress-enhanced grain growth was observed.
Dislocation-Based Models of Stress-Strain Behavior in Multilayered Thin Films†
Authors: Anderson Peter M. , Kreidler Eric R.
Published: April 2011

Elementary dislocation arrays are applied to multilayered thin films to predict the critical stress required to propagate dislocation loops within individual layers and to study the tendency for deformation to be uniform or localized. The analyses suggest that shearing normal to layers is a mechanically unstable, softening process while stretching parallel to layers produces substantial hardening. Further, films with smaller layer thickness, h, require larger plastic strains to initiate pile-up modes of slip. Although the initial stress required to propagate an isolated loop within a single layer scales as ln(h)/h, there is a minimum h below which the critical stress is predicted to depend only on the resistance of the interface to dislocation transmission.
Structure Determination of B4C and SiC Thin Films Via Synchrotron High-Resolution Diffraction
Authors: Hershberger J. , Kustas F. , Rek Z. U. , Yalisove S. M. , Bilello J. C.
Published: April 2011

Thin films of B4C and SiC deposited by magnetron sputtering as components of multilayers have the potential to provide significant property improvements over current wear resistant coating technology. B4C and SiC have previously been found to be amorphous and possibly nanocrystalline under the deposition conditions used. This study reports results of synchrotron x-ray scattering experiments providing information on the degree of crystallinity, strain, average density, and coordination number in 2000 Å films of these compounds on Si substrates. Radial distribution functions from B4C and SiC thin films were obtained and used to model the structure. Strain results are compared with Double Crystal x-ray Diffraction Topography (DCDT) results as a means for establishing a standard strain state.
Practical Limitations to Indentation Testing of Thin Films
Authors: Schneider J. A. , McCarty K. F. , Heffelfinger J. R. , Moody N. R.
Published: April 2011

A method that is becoming increasingly common for measuring the mechanical behavior of thin films is low-load indentation testing. However, there can be complications in interpreting the results as many factors can affect hardness and moduli measurements such as surface roughness and determination of the indentation contact area. To further our understanding, the mechanical properties of thin (50 nm) films of AlN on sapphire substrates were evaluated using a scanning force microscopy (SFM) based pico-indentation device to allow imaging of the surface and indentations. Our primary emphasis was the types of problems or limitations involved in testing very thin, as deposited films in which properties are desired over indentation depths less than 50 nm.
Safety Analysis for the Loviisa Low- and Intermediate-Level Radioactive Waste Repository
Authors: Eurajoki T. , Outa S. , Routamo T.
Published: April 2011

The Loviisa low and intermediate level radioactive waste repository is located in southern Finland, at Loviisa NPP site on Hästholmen island, where two VVER-440 reactor units are operated by Imatran Voima Oy (IVO). The repository is excavated in the bedrock, 110 meters below the sea level.
A Mechanistically-Based Model for Spallings Releases at the Waste Isolation Pilot Plant
Authors: Hansen F.D. , Knowles M.K. , Thompson T.W.
Published: April 2011

The Waste Isolation Pilot Plant (WIPP) is an underground facility operated by the US Department of Energy (DOE) for permanent disposal of transuranic waste. The compliance of the WIPP to the US Environmental Protection Agency regulations, as assessed by the performance assessment process, is demonstrated by comparison of potential releases to the regulatory limits. In the Compliance Certification Application the potential for solids release to the surface exists only for “disturbed” scenarios, whereby the repository is intersected by an exploratory borehole at some time during the regulatory period of 10,000 years. Releases for this scenario are dominated by three mechanisms associated with the hypothetical scenario. These mechanisms are “cuttings”; the removal of solid materials by the action of drilling, “cavings”; the removal of solids by erosion by the circulating mud, and “spallings”; the removal of solids by a gas-driven blow-out.
Wellenberg, Switzerland: Controls on Groundwater Flow and Solute Transport Derived From Hydrochemical Observations
Authors: Waber H. N. , Pearson F. J. , Scholtis A.
Published: April 2011

The Wellenberg area, central Switzerland, is under investigation for a potential low and intermediate level radioactive waste repository. The host rock, the Palfris marl, is bounded on the north by Cretaceous limestone units of the Drusberg nappe and is underlain by a sequence of Tertiary to Jurassic sediments (limestones, marls) of the Wissberg-Firrenband-Equivalent. Chemical and isotopic data on groundwaters and rocks show that three essentially independent groundwater flow regimes occur in the area: (1) groundwaters of the Palfris marl, (2) groundwaters of the limestone units of the Drusberg nappe, and (3) groundwaters of the Wissberg-Firrenband Equivalent.
Report on Workshop on Cementitious Barriers
Authors: Glasser F.
Published: April 2011

During the course of the title Symposium, six informal presentations were made. Structured discussion of research needs identified a priority list which is presented here.
Modeling of Glass Dissolution and Transport With the Code SUGAR
Authors: Small J.S. , Trivedi D.P. , Abraitisti P.K.
Published: April 2011

SUGAR (Simplified Understading of Glass And environment Reactions) is a one dimensional (lD) reactive transport code which sequentially couples dissolved chemical species transport and sorption with, chemical speciation, mineral precipitation and kinetic controlled glass dissolution. SUGAR also has the capability to model radioactive decay and steel corrosion. This paper describes the computer model and presents results of model testing against experimental data. The capabilities of the model are demonstrated by a preliminary investigation of the geochemical evolution of glass in crystalline rock formations.
Further Studies of Synroc Immobilization of HLW Sludges and Tc for Hanford Tank Waste Remediation
Authors: Vance E.R. , Hart K.P. , Carter M.L. , Hambley M.J. , Day R.A. , Begg B.D.
Published: April 2011

Synroc/glass composites were designed for simulated Hanford HLW sludges containing U (the current “All-Blend” formulation). The composite contained ∼ 50 wt% of simulated HLW (oxide equivalent), to which ∼ 6, 10, 10, and 24 wt% of CaO, Al2O3, TiO2 and SiO2 were added, and melted under an argon atmosphere at 1350°C. The phase assemblage consisted of zirconolite, perovskite, spinel, nepheline, whitlockite and glass as major phases. Seven-day PCT tests yielded values of < 0. 1 g/m2 for all elements studied. The PCT results were tolerant to changes of ∼ 20% of the inventories of the additives, and to variations in redox conditions.

Technetium separated out during decontamination of liquid Hanford wastes can be incorporated as metal in hot-pressed Synroc prepared under reducing conditions, and its leach resistance is good (∼ 10∼3 g/m2/day at 70°C), and can be improved by alloying with iron group metals. With a choice of “neutral” (P(O2) ∼ 10−4 atm., near the Ni/NiO buffer) hot-pressing conditions, Tc can also be incorporated as Tc4+, substituting for Ti4+ in the ceramic phases, and in this form, it should be highly leach resistant also.
High-Level Nuclear Waste Management: How Physics Can Help
Authors: Salvatores M. , Zaetita A.
Published: April 2011

The potential value of Partitioning/Transmutation (P/T) strategies for high-level nuclear waste management has been investigated (one would be tempted so say “periodically”) since 1970. The basic physics phenomena are well understood, and scenarios for the fuel cycle can be imagined. However, the criteria to judge the impact of P/T are matter for discussion (and controversy). Moreover the relation to disciplines other than reactor physics can be significant (e.g. innovative fuels and Actinide chemistry).

A number of key issues are revisited here and will be discussed in some detail.
Large-Scale Model Testing of a Concrete Silo EBS for Low- and Intermediate-Level Waste Disposal
Authors: Konishi K. , Ukaji K. , Fujiwara A. , Endo T. , Tsuji Y.
Published: April 2011

This study focuses on demonstrating the feasibility of constructing a large reinforced concrete silo for the disposal of low- and intermediate-level radioactive waste. In a large-scale model test, the results of temperature (from heat of hydration) and thermal stress analyses were confirmed, as was the practicality of countermeasures to prevent thermal cracking. After one year, the average permeability of the model silo was estimated to be below 1×10−11m/s.
Scientific Progress Toward Meeting R&D Needs: Autobahns and Wanderwegs
Authors: Hadermann J. , Berner U. , Pearson F.J.
Published: April 2011

This paper summarises the last talk given at the conference. Its contents were prepared during the first four days of the symposium with the goal of comparing the R+D needs as specified by three invited lectures with the actual scientific work as given in oral and poster contributions by symposium participants. We first present some general conclusions and then address specific aspects of the individual sessions. Finally, the main conclusions from the six workshops are given.
Ionic Transport in Compacted Bentonite: Preliminary Equilibrium Results
Authors: Lehikoinen J. , Muurinen A. , Olin M.
Published: April 2011

An attempt is made to decompose some quantities, most commonly integrated over the chemical composition, the structure of the pore network and the time scale, into their differential counterparts. Into this category typically fall, say, the apparent diffusivities of ionic species. To serve this objective, a two-dimensional unsteady molecular-level electrokinetic transport model for ionic species in bentonite clays will be developed. The model incorporates additional features to the conventional Gouy-Chapman (GC) theory: ionic hydration, dielectric saturation, and the volume exclusion of ions. The governing equations for the flow of electrolyte solution through the pores are solved by an iterative numerical scheme to relate the characteristics of the flow to the characteristics of the pores and to the composition of the external solution in contact with the clay. The pore geometry of the clay is modelled as an array of non-interconnected tortuous channels with no parallel or serial-type non-uniformities along the pathway. This roughly corresponds to the picture of clay particles of infinite extent aligned in parallel and spaced apart by a constant distance. The model aims to simulate and interpret equilibrium and transport experiments for bentonite clays containing different types of background electrolytes at various compactions. Specifically, emphasis is placed on quantifying the extent of co-ion exclusion and understanding the postulated surface diffusion mechanism on the basis of the well-established electric double-layer (EDL) theory. This contribution presents and discusses some preliminary results, based on the modified Boltzmann statistics, for the equilibrating part of the model.
Geochemical Modeling of the Interaction of HLW Glass With Boom Clay Media
Authors: Lolivier Ph. , Lemmens K. , Iseghem P. Van
Published: April 2011

A geochemical model has been developed to describe the interactions of the main elements released from the COGEMA R7T7 SON68 glass with the Boom Clay environment and predict the formation of secondary phases which may influence the glass corrosion. It is based on two submodels: a model describing the interaction between the clay and its porewater, and a model for glass corrosion in groundwater. According to the calculations, no secondary minerals are predicted to precipitate when glass dissolves in the Boom Clay. The oncentrations of the main elements released from the glass are controlled by stable phases present in the Boom Clay (a.o. Si, Al) or by cation exchange reactions (e.g. Na). The concentration of silica in solution can be maintained below the glass silicon solubility limit. Therefore, the Boom Clay can suppress the saturation of silica, explaining the enhancing effect of Boom Clay on glass corrosion. The influence of the presence of clay on the other components of the glass is also discussed.
The Influence of Thermal Gradients on the Long-Term Evolution of the Near-Field Environment of High-Level Nuclear Wastes Disposal
Authors: Poinssot C. , Toulhoat P. , Goffé B.
Published: April 2011

The initial stage of some HLW disposal systems will be characterised by a large thermal pulse in the near-field environment, due to the heat of the radioactivity decay. This will lead to the development of a transient spatial thermal gradient between the hot canister and the cold geological medium, which could significantly affect the composition and the elemental distribution within the near-field environment. A coupled experimental and modelling work is presented in order to determine the influence of a thermal gradient on water-rock interaction processes. First experiments with a simulated nuclear glass evidenced mass transfer processes leading to chemical differentiation in the solid phases between the hot and the cold end of the system. The relevance of these experimental results to the case of a HLW disposal is strongly supported by in-situ experiments at Stripa, in which a realistic EBS under thermal gradient developed exactly the same mass transfers.

In order to understand the driving force of these processes, we tried to model simplified experiments by using a mixing cell geochemical model built upon the geochemical code EQ3/EQ6. The discrepancies between modelling and experiments indicate the existence of coupled processes involving irreversible precipitation.

Finally, thermal gradients were applied in nuclear glass-clay interaction experiments to enhance elemental migrations. The main results are: (i) a re-crystallisation of the initial clay toward a more silicic one through incorporation of elements released by the glass, (ii) a strong influence of clay chemistry on the nuclear glass secondary phases.
Corrosion of Ti99.8-Pd Under Gamma Irradiation in MgC12-Rich Brine
Authors: Smailos E. , Schild D. , Gompper K.
Published: April 2011

The combined influence of gamma radiation (10 Gy/h) and high temperature (150 °C) on the corrosion of the promising HLW container material Ti99.8-Pd was investigated in an MgCl2-rich brine, and the corrosion surface films formed were characterized by XPS. For comparison, specimens without irradiation were also examined.

Under the test conditions used, the alloy Ti99.8-Pd is resistant to local corrosion and its general corrosion is negligible low. The thin corrosion films formed on the surface of unirradiated specimens and in the crevices of specimens exposed to radiation consist of TiO2. However, outside the crevices of irradiated specimens, a surface layer consisting of Mg (main component of the brine) and Si (impurity in the brine) oxide is built up over the TiO2 layer. Comparable TiO2 layer thicknesses (30 - 65 nm, depending on the experimental conditions) are found for unirradiated and irradiated laboratory specimens. The TiO2 layer formed on the in-situ corrosion specimens (33 nm / 5.3 years) is thinner than that of the laboratory specimens (58 nm / 191 days) indicating less aggressive conditions in the field experiments. In view of these results, the alloy Ti99.8-Pd continues to be considered as a strong candidate container material and will be further investigated.
Flow Versus Transport Property: Stochastic Approach for Estimation of Its Effective Values in Heterogeneous Media
Authors: Ando K. , Vomvoris S.
Published: April 2011

Flow and transport in a fractured rock is often conceptualized as flow between parallel plates and/or flow in tubes. For simple conceptual models, such as parallel plates or tube, it has been shown theoretically that the increase in effective porosity for transport is proportional to the variability (roughness) of the fracture aperture or tube radius. This paper focus on a tube model and estimates transport properties which are consistent with the estimated measured hydraulic properties from well tests in deep boreholes.
A Modest Proposal: A Robust, Cost-Effective Design for High-Level Waste Packages
Authors: Apted M.J.
Published: April 2011

An alternative waste-package design for the geological disposal of high-level waste (HLW) glass is presented. In conventional designs, a massive buffer of compacted bentonite is placed around a thick-walled, mild-steel overpack; in the revised design, a much thinner buffer is placed within a thin-walled, mild-steel overpack. This simple expedient eliminates certain performance concerns in existing waste-package designs, while not necessitating the study of any new materials. This integrated waste package (IWP) design has comparable release-rate performance as current package designs for HLW. In addition, the 1WP design requires far-less rock excavation, permits significantly higher temperatures for longer periods, leads to a 20-50% reduction in repository area, and is more cost efficient than previous designs.
Scenario Analysis and Conceptual Model Development Using FANFARE
Authors: Kelly M , Billington D.E.
Published: April 2011

A computer programme (FANFARE) for facilitating scenario analysis and conceptual model development is discussed. FANFARE implements a systematic methodology, based on the use of Directed Diagrams, that makes the assessment of comprehensiveness of FEPs and scenarios a tractable problem. Coupled with its ability to store a traceable audit trail of judgments and decisions, this makes FANFARE a useful tool for carrying out FEP analysis, scenario analysis and conceptual model development for performance assessments of radiological disposal facilities. It can also be applied to other systems that require consideration of the underlying phenomena to determine system performance.
Site Characterization Strategy and Its Role in Post Closure Performance Assessment
Authors: Littleboy A.K. , Degnan P.J. , Mcleod R.S. , Norris S.
Published: April 2011

Calculations of risk or dose from the groundwater flow pathway are a central part of the assessment of post closure performance for a deep repository system for radioactive waste. These calculations need to be supported by a knowledge of the various components of the disposal system. Site characterisation provides a site specific geological database which can be used to build, test and refine numerical models of the geosphere and, to some extent, the biosphere components of the disposal system in order to evaluate its future evolution.

Site characterisation programmes, and groundwater flow modelling within the performance assessment need to progress in an interactive manner to ensure that both remain focused on the resolution of key uncertainties which impact the overall performance assessment. The data derived from site investigations can be classified in terms of their application within the performance assessment: establishing the framework for numerical models; enabling the parameterisation of numerical models; testing model output; refining models; and demonstrating their credibility. Site characterisation programmes need to be established to provide the appropriate level of information for each of these stages. It is therefore not particularly useful to classify information into the traditional disciplines of geology, hydrogeology and geochemistry.

A key issue for developing a geological and hydrogeological database for performance assessment is determining when sufficient information has been obtained. Primarily, this is dictated by the needs and sensitivities of the performance assessment and any regulatory requirements. However, radioactive waste disposal agencies work in a political environment that is strongly influenced by public perception. In order to progress, any programme must attain a broad measure of credibility and acceptability to other key “stakeholders”.

The paper draws on examples and experiences from the extensive programme of work which has been performed by Nirex to understand the characteristics of a site near Sellafield in Cumbria, and to develop groundwater flow models to support the assessment of the post closure performance of a potential repository located at that site. Uncertainties important in influencing calculated risk within an interim assessment, published as the “Nirex 95 assessment” were used to develop further site-specific investigations. The resulting site characterisation activities generated an enhanced and refined site-specific geological and hydrogeological database for a subsequent assessment - the “Nirex 97 assessment”.
The Wellenberg K-Model: A Geostatistical Description of Hydraulic Conductivity Distribution in the Host Rock for Site Characterization and Performance Assessment Purposes
Authors: Marschall P. , Vomvoris S. , Jaquet O. , Lanyon G.W. , Vinard P.
Published: April 2011

The Wellenberg K-model describes the distribution of the hydraulic conductivity of the host rock at Nagra's proposed site for a LLW/ILW repository. The description takes the form of the expected value of hydraulic conductivity at a location and the uncertainty around this expected value. The development of the K-model is based on geostatistical concepts and, in particular, on kriging and conditional simulation methods. The model is built of cubes with sides of 100 m. Upscaling of the transmissivity profiles at the borehole locations to effective K-values on the 100 m scale is realised by fracture network modelling. The K-model accounts explicitly for the hydraulic conductivities estimated at each borehole. It is consistent with the hydrogeological conceptualization of the host rock and generates realistic hydraulic conductivity distributions with a degree of variability similar to that observed in the data.
Application of Thermodynamic Sorption Models to Distribution Coefficients of Radionuclides in Bentonite
Authors: Ochs M. , Lothenbach B. , Yui M.
Published: April 2011

The application of thermodynamic models to calculateKdvalues for Sr/Ra and Pb on bentonite is demonstrated. The model discussed here can be used to identify relevant sorption processes, as well as other factors that determineKdvalues, such as impurities contained in bentonite or artifacts (precipitation); i.e. it can be used to conduct sensitivity analyses ofKdvalues.Kdvalues can be modeled over a very wide range, indicating that such models may also be used for an evaluation of experimental data, and for predictive purposes where no such data are available.
Modeling the Chemical Evolution of Porewater in the Palfris Marl, Wellenberg, Central Switzerland
Authors: Pearson F. J. , Waber H. N. , Scholtis A.
Published: April 2011

The chemical evolution of groundwater in the Palfris marl at Wellenberg has been simulated using a reactive transport model. The results were tested against the chemical and stable carbon isotopic composition of water samples from exploratory boreholes. Water chemistry is constrained by mineral and cation exchange equilibria. To reproduce measured CO2(tot) and δ3C values requires H+ ion exchange. Matching measured ratios between Cl– and other dissolved constituents constrains the relative amounts of reacting water and rock to porosities between I and 10%. NaHCO3 waters sampled from the Palfris are formed by replacement of the initial Na-Cl water by one to five pore volumes of infiltrating Ca-HCO3 recharge water. To entirely exhaust the exchange capacity of the formation so that Ca-HCO3 water persists requires several hundred to several thousand pore volumes of flow. The agreement between model results and measured water chemistry demonstrates a quantitative understanding of the geochemical processes controlling the chemistry of water naturally present in the Palfris marl. These processes will also determine the behaviour of material that might emanate from a repository. In addition, the modelling provides water flow information of use in testing groundwater flow models.
Seismic Velocity Structure of the EDZ Around Drifts at the Kamaishi and Tono Mines in Japan
Authors: Sato T. , Matsui H. , Kikuchi T. , Sugihara K. , Okubo S.
Published: April 2011

The excavation disturbed zone (EDZ) is defined as the rock zone where rock properties and conditions have been changed due to the processes induced by excavation, such as excavation damage, stress redistribution and desaturation. In-situ excavation disturbance experiment has been performed to determine the rock properties and width of the EDZ at the Kamaishi and Tono mines in Japan. Rock mass fails when blasting vibration velocity exceeds limit velocity so that we can estimate excavation damaged zone from vibration measurement. The width of the zone where blasting vibration velocity exceeded the limit velocity is roughly consistent with the width of low seismic velocity layer detected from the seismic refraction survey at both mines.
Self-Radiation-Induced Anisotropic Structure Damage in 244Cm-Doped Orthophosphate LuPO4
Authors: Liu G. K. , Luo J. S. , Li S. T. , Loong C.-K. , Abraham M. M. , Beitz J. V. , Bates J. K. , Boatner L. A.
Published: April 2011

We have conducted a series of experiments using laser spectroscopy and analytic electron microscopy (AEM) to study the microscopic effects of radiation damage in single crystals of LuPO4 doped with 244Cm3+ ions. The crystals (body-centered tetragonal, zircon-type structure) were grown in 1980 using a flux method with an initial 244Cm(t1/2 =18.1 y) concentration of ∼1% by weight. The dimensions of the single crystals of Cm3+:LuPO4 are about 0.5×1.0×4.0 mm3. After 17 years, the crystals are no longer transparent. Dark brown to gray straps along the crystal c-axis are observable under an optical microscope. Macroscopic fractures are not obvious on the natural surfaces of the a- and b-planes. However, due to alpha-particle emission of 244Cm, significant microscopic structural damage, including microscopic cavities, has accumulated in this end member of the xenotime minerals
Conceptual Models for Geochemical Processes in Reactive Transport of Compacted Bentonites
Authors: Delgado Jorge , Samper Javier , Molinero Jorge , Juncosa Ricardo , Juanes Rubén , Carretero Pablo
Published: April 2011

Several agencies in charge of nuclear waste management consider the use of compacted bentonites as engineered barriers for the migration of radionuclides towards the geosphere. The geochemical processes occurring in the clay buffer system are of capital importance for the assessment of a HLW repository performance. Therefore, it is necessary to develop tools able to deal with the complex interactions between water and bentonite, submitted simultaneously to a thermal field and water flow. These tools may be referenced as thermo-hydro-geochemical (THG) modelling codes
Prediction of Solid-Aqueous Equilibria in Cementitious Systems Using Gibbs Energy Minimization: I. Multiphase Aqueous - Ideal Solid Solution Models
Authors: Sinitsyn V.A. , Kulik D.A. , Khodorivsky M.S. , Karpov I.K.
Published: April 2011

Concrete and other cement-based materials are increasingly utilized as major structural components of the disposal facilities for low-level and intermediate-level radioactive waste (LLW/ILW). At the same time. cementitious materials function as engineered barriers against migration of radionuclides and other hazardous compounds [1]. Taking into account the expected operation times of such constructions, the long-term prediction of environmental interactions and stability of concretes is important for the development of reliable facilities for LLW/ILW disposal. Thermodynamic approach has been widely used to promote understanding of chemical phenomena in cementitious systems. Recently, several authors attempted to demonstrate usefulness of computer codes for description of the available experimental data and prediction of cement/water equilibria [1-5]. These calculations were based on the Law-of-Mass Action - Reaction Stoichiometry Algorithm (LMA-RSA), widely applied so far in speciation modeling [6]
Corrosion of Carbon Steel Containers During Open Site Tests of Vitrified Radioactive Waste
Authors: Barinov A.S. , Ojovan M.I. , Ojovan N.V.
Published: April 2011

In the middle of 80-s the Moscow SIA “Radon” initiates a program on long term tests of vitrified intermediate level radioactive waste from nuclear power plants with different types'of reactors and with different composition of waste. Glass blocks were prepared and disposed for tests in experimental shallow ground repository and on open testing area. Borosilicate glass as matrix material is investigated in order to obtain data on real behaviour of glass [1]. The waste glass was poured in carbon steel rectangular containers therefore containers also were subjected to aqueous and atmospheric corrosion. Exposure conditions at testing site are varying depending on season. They can be described only as average parameters with some uncertainties.
Importance of the Alkaline Degradation of Cellulose in Performance Assessment of a Cementitious Radioactive Waste Repository
Authors: Glaus M.A. , Laube A. , Stallone S. , Van Loon L.R.
Published: April 2011

It is the aim of the present poster to show two approaches for assessing the influence of the alkaline degradation of cellulose on the sorption of tri- and tetravalent radionuclides. The two approaches differ in their degree of conservativity, one is a conservative, the other a realistic model case. The result of both examinations is expressed in terms of sorption reduction factors, valid for a situation where cellulose degradation products are influencing the sorption of radionuclides on cement.
Prediction of Solid-Aqueous Equilibria in Cementitious Systems Using Gibbs Energy Minimization: II. Dual Thermodynamic Approach to Estimation of the Nonideality of End-Member Parameters
Authors: Kulik D.A. , Sinitsyn V.A. , Karpov I.K.
Published: April 2011

Prediction of pathways of radionuclides, heavy metals and other harmful components isolated in cementitious matrices is considered critical in geochemical studies related to hazardous waste disposal [1-3]. Hence, rigorous multi-phase multi-aggregate thermodynamic models with appropriate kinetic and metastability constraints can be very helpful in solving this difficult problem. In a companion contribution [4], we demonstrate that usage of the Gibbs energy minimization (GEM) algorithms permits direct calculation of solid solution – aqueous solution (SSAS) equilibria which adequately describe the solubility data. The suggested "core" thermodynamic dataset can be extended and tuned on the basis of solubility, mineralogical and petrographical studies of fresh, aged and doped cements.
Development of Stable a-Si/a-SiGe Tandem Solar Cell Submodules Deposited by a Very High Hydrogen Dilution at Low Temperature
Authors: Shima Masaki , Isomura Masao , Maruyama Eiji , Okamoto Shingo , Haku Hisao , Wakisaka Kenichiro , Kiyama Seiichi , Tsuda Shinya
Published: April 2011

The world's highest stabilized efficiency of 9.5% (light-soaked and measured by the Japan Quality Assurance Organization (JQA)) for an a-Si/a-SiGe superstrate-type solar cell submodule (area: 1200 cm2) has been achieved. This value was obtained by investigating the effects of very-high hydrogen dilution of up to 54:1 (= H2: SiH4) on hydrogenated amorphous silicon germanium (a-SiGe:H) deposition at a low substrate temperature (Ts). It was found that deterioration of the film properties of a-SiGe:H when Ts decreases under low hydrogen dilution conditions can be suppressed by the high hydrogen dilution. This finding probably indicates that the energy provided by hydrogen radicals substitutes for the lost energy caused by the decrease in Ts and that sufficient surface reactions can occur. In addition, results from an estimation of the hydrogen and germanium contents of a-SiGe:H suggest the occurrence of some kinds of structural variations by the high hydrogen dilution. A guideline for optimization of a-SiGe:H films for solar cells can be presented on the basis of the experimental results. The possibility of a-SiGe:H as a narrow gap material for a-Si stacked solar cells in contrast with microcrystalline silicon (μ c-Si:H) will also be discussed from various standpoints. At present, a-SiGe:H is considered to have an advantage over μ1 c-Si:H.
Reaction Processes for Low Temperature (<150°C) Plasma Enhanced Deposition of Hydrogenated Amorphous Silicon Thin Film Transistors on Transparent Plastic Substrates
Authors: Parsons Gregory N. , Yang Chien-Sheng , Klein Tonya M. , Smith Laura
Published: April 2011

This article presents mechanisms for low temperature (<150°C) rf plasma enhanced chemical vapor deposition of silicon and silicon nitride thin films that lead to sufficient electronic quality for thin film transistor (TFT) fabrication and operation. For silicon deposition, hydrogen abstraction and etching, and silicon disproportionation reactions are identified that can lead to optimized hydrogen concentration and bonding environments at <150°C. Nitrogen dilution of SiH4/NH3 mixtures during silicon nitride deposition at low temperatures helps promote N-H bonding, leading to reduced charge trapping. Good quality amorphous silicon TFT's fabricated with a maximum processing temperature of 110°C are demonstrated on flexible transparent plastic substrates. Transistors formed with the same process on glass and plastic show linear mobilities of 0.33 and 0.12 cm2/Vs, respectively, with ION/IOFF ratios > 106.
Stabilized Three Color Piinip Sensor For High Illumination Conditions
Authors: Knipp D. , Stiebig H. , Wagner H.
Published: April 2011

A stabilized three color piinip sensor for high illumination conditions was developed. The spectral response of the novel device shows a maximum at 480nm, 530nm and 630nm changing the applied bias voltage from −0·2V, −2·OV to 2·OV, respectively. Only a slight influence on the device performances is observed after more than 100h light soaking under AM1·5 illumination conditions. This is achieved by employing low temperature deposited a-Si:H with high hydrogen dilution and a microcrystalline silicon layer in the top diode of the sensor. For piinip detector systems with different absorption materials in the top diode the influence of light induced degradation on the spectral response and the dark current is discussed. Furthermore, the transient behavior of the new stabilized detector is presented.
Stepped Gate Polysilicon Thin Film Transistor for Large Area Power Applications
Authors: Aschenbeck J. , Chen Y. , Clough F. , Xu Y. Z. , Narayanan E. M. Sankara , Milne W. I.
Published: April 2011

For the first time, we report a new poly-Si stepped gate Thin Film Transistor (SG TFT) on glass. The Density of States extracted from measured I-V characteristics has been used to evaluate the device performance with a two dimensional device simulator. The results show that the three-terminal SG TFT device has a switching speed comparable to a low voltage structure and the high on-current capability of a metal field plate (MFP) TFT and the potential for comparable breakdown characteristics.
The Tail States as Sensitizing Recombination Centers for Holes Lifetime in a-Si:H
Authors: Lubianiker Y. , Rapaport R. , Balberg I. , Fonseca L. , Weisz S.Z.
Published: April 2011

We have measured the dependence of the holes mobility-lifetime product on temperature under various light intensities in intrinsic a-Si:H. We find that this product exhibits thermal quenching which is accompanied by a superlinear light intensity dependence. Numerical calculations that we have carried out show that these results can be accounted for within the framework of the conventional recombination model. However, to yield such an agreement the capture coefficients for both charge carriers at the tail states must be smaller than the corresponding coefficients for the dangling bonds. Thus the sensitizing nature of the tail states is revealed.