bluuebunny/crossref_metadata_2025 huggingface dataset:
Obsidian Hydration Dating - Field, Laboratory, and Modeling Results
Authors: McGrail B. P. , Pederson L. R. , Strachan D. M. , Ewing R. C. , Cordell L. S.
Published: March 2011

Hydration rind thicknesses found on obsidian artifacts provide one means of estimating the age of an archaeological site. The model used in the method usually assumes a diffusion-controlled reaction of the glass with water. However, results using this model are not always in agreement with other dating methods. Observations of secondary mineral formation on glasses in contact with water vapor suggests that other rate-controlling mechanisms may be operative. In this paper, we apply the glass dissolution code GLASSOL, coupled with the geochemical code PHREEQE to model the reaction of Glass Mountain obsidian in water. The results show the importance of accounting for the effects of solution chemistry on the time-dependence of the hydration reaction.
Oxidation and Protection of Fiberglass-Epoxy Composite Masts for Photovoltaic Arrays in the Low Earth Orbital Environment
Authors: Rutledge Sharon K. , Paulsen Phillip E. , Brady Joyce A. , Ciancone Michael L.
Published: March 2011

Fiberglass-epoxy composites have been considered for use as structural members for the mast of the Space Station solar array panel. The low Earth orbital environment in which Space Station is to operate is composed mainly of atomic oxygen, which has been shown to cause erosion of many organic materials and some metals. Ground based testing in a plasma asher was performed in order to determine the extent of degradation of fiberglass-epoxy composites when exposed to a simulated atomic oxygen environment. During exposure, the epoxy at the surface of the composite was oxidized, exposing individual glass fibers which could easily be removed. Several methods of protecting the composite were evaluated in an atomic oxygen environment and with thermal cycling and flexing: The protection techniques evaluated to date include an aluminum braid covering, an indium-tin eutectic and a silicone based paint. The open aluminum braid offered little protection while the CV-1144 coating offered some initial protection against atomic oxygen. The In-Sn eutectic coating provided initial protection against atomic oxygen, but appears to develop cracks which accelerate degradation by atomic oxygen when flexed. Coatings such as the In-Sn eutectic may provide adequate protection by containing the glass fibers even though mass loss still occurs.
Potential for Diboride Reinforcement of Oxide Matrix Composites
Authors: Vedula K. , Abada A. , Williams W. S.
Published: March 2011

Particulate composites of TiB2 in ZrO2, Y2O3 and Al2O3 have been prepared by vacuum hot pressing. Specimens were tested in oxyacetylene flames at 1650 to 2050°C; in vacuum at 1600°C and by induction heating in air at 1400 to 1600°C in order to evaluate the chemical compatability between the diboride/oxide combinations, as well as the effectiveness of the oxides as diffusion barriers. Results indicate that the large vapor ressure of B2O3 formed at the diboride/oxide interfaces presents serious problems under all the conditions tested.
Selective Corrosion Resistance of Chromium Implanted Cu-37w%Zn Alloy
Authors: Hirvonen J-P. , Toivanen R.O. , Lindroos V.K.
Published: March 2011

Selective corrosion resistance of the chromium implanted brass as well as vacancy formation were investigated. Dealloying was observed to create excess vacancies. Chromium and boron and many other potentially beneficial alloying elements like C, N, Si, P, V, Co, Ni, Cu, Ge, As, Y, Nb, Pd, Ag, Sn, Sb, have a repulsive interaction with vacancies and they could increase the dezincification resistance in alpha brass but not in beta brass. Boron implanted brass was found to be more resistant to selective corrosion than the chromium implanted brass.
MBE Regrowth of AlGaAs on Ion Etched GaAs/AlGaAs Microstructures
Authors: Harbison J. P. , Scherer A. , Hwang D. M. , Nazar L. , Beebe E. D.
Published: March 2011

The combination of an ion beam assisted etching (IBAE) system and a Molecular Beam Epitaxy (MBE) growth chamber integrally connected in the same set of ultrahigh vacuum (UHV) chambers has allowed us to etch patterns defined by a strontium fluoride mask down into the underlying semiconductor wafer, and regrow monocrystalline material around these patterned structures entirely in situ. Scanning electron microscopy (SEM) analysis of the regrown structures reveals very directional deposition of the overgrown material. Cross-sectional transmission electron microscopy (TEM) reveals a smooth interface and vertical sidewalls at the boundary between the etched surfaces and the overgrowth. Material deposited on the sidewalls is shown to be monocrystalline, while that deposited over the mask is polycrystalline. The SrF2 mask material, previously shown to be an excellent IBAE mask for extremely fine nanostructures, is also shown to be compatible with the high temperatures need for overgrowth, and regrowth around structures as small as ˜200 nm in size has been demonstrated.
The Influence of Arsenic Flux in the Defect Structure of MBE Deposited GaAs and Ga1−xAlxAs
Authors: Hatzopoulos Z. , Kiriakidis G. , Georgacilas A. , Roditis N. , Christou A.
Published: March 2011

The dependence of the density of defects on the pressure ratio PAs/PGa and on the substrate temperature has been studied on a series of GaAs and GaAlAs samples prepared by MBE. Samples have also been desorbed prior to the MBE deposition by UV laser and the density of defects have been compared with the density of defects obtained in samples where thermal desorption occured. Optimum pressure ratios PAs/GPa and growth temperatures have been found for both GaAs and GaAlAs for minimum defect density. It is shown that insitu laser desorption, prior to MBE deposition is a feasible technique for attaining MBE structures with a low defect density, thus simplifying the substrate preparation process.
Anisotropic Ion Beam Assisted Etching of Optical Structures in GaAs and InP
Authors: Scherer A. , Gaag B. P. Van Der , Kash K. , Craighead H. G. , Grabbe P.
Published: March 2011

Ion beam assisted etching (IBAE) was used to define submicron structures into GaAs/AlGaAs and InP/InGaAsP heterostructures. Etch rates in excess of I pm/minute were obtained after optimization of the etching process, allowing the fabrication of optoelectronic structures which require smooth, vertical sidewalls and depths of several microns. By altering the gas flow and the ion beam parameters, the same technique was used to pattern electron beam-written structures with lateral dimensions of less than 30 nm and aspect ratios in excess of 5:1 in GaAs.
Hydrogenation of GaAs and Application to Device processing
Authors: Pan N. , Feng M. S. , Jackson G. S. , Bose S. S. , Guido L. J. , Holonyak N. , Stillman G. E.
Published: March 2011

Exposure of GaAs and AlGaAs to a hydrogen plasma has been shown to result in a significant change in the electrical and optical properties. The changes are related to the electrical deactivation of the deep and shallow impurities by hydrogenation. Spectroscopic and electrical measurements have shown that Si donors and C acceptors in high purity GaAs can be passivated by hydrogenation. Hydrogenation of p-type GaAs and AlGaAs has resulted in highly resistive material. SiO2 was found to be a suitable mask for the hydrogenation process. Single and multiple stripe geometry lasers have been fabricated by properly masking the laser structure. The lasers produced using the hydrogenation process have low threshold currents and are capable of cw room temperature operation.
A High Depth Resolution Backside Secondary Ion Mass Spectrometry Technique Used for Studying Metal/Gaas Contacts
Authors: Palmstrøm C. J. , Schwarz S. A. , Marshall E. D. , Yablonovitch E. , Harbison J. P. , Schwartz C. L. , Florez L. , Gmitter T. J. , Wang L. C. , Lau S. S.
Published: March 2011

Understanding metal/semiconductor contacts is important for the fabrication of device structures. To date most studies have been aimed at understanding the metallurgical or the electrical properties. Directly measuring the impurity concentrations immediately beneath a contact rather than inferring it from electrical measurements has up until now been difficult. This paper describes a backside SIMS technique which not only demonstrates the ability of measuring doping concentrations close to a metal/semiconductor contact but also is capable of measuring the consumption of semiconductor material during a metal/semiconductor reaction. The sample preparation technique can be used to enable backside profiling using other profiling techniques such as Auger and x-ray photoelectron spectroscopy depth profiling, Rutherford backscattering, and backside electrical evaluation. The Ge/Pd/GaAs solid phase ohmic contact is used to demonstrate the technique.
Silicon Induced Mixing of AlGaAs Superlattices – Behavior and Mechanisms
Authors: Schwarz S. A. , Venkatesan T. , Mei P.
Published: March 2011

Mixing (or interdiffusion) of AlGaAs superlattice layers is greatly accelerated in the presence of Si doping. We have employed secondary ion mass spectrometry (SIMS) to monitor the depth dependence of the Al diffusion coefficient as well as the Si diffusion profile. Our results reveal unusually complex dependences on implantation and annealing conditions. To isolate the effects of chemistry and lattice damage, several structures were grown by molecular beam epitaxy (MBE) containing plateaus of Si concentration. The doping dependence and activation energy of Al diffusion were then evaluated in as-grown samples and in samples damaged by MeV Ga ion bombardment. To further elucidate the process, samples containing single or multiple implants of various dopants and impurities were examined. Microscopic and electrical characterizations were also performed. Al diffusion was found to be strongly inhibited by lattice damage and by very high Si doping levels. The Al diffusion coefficient has a high power law dependence on Si concentration while its activation energy is relatively unaffected by doping or lattice damage. A wide range of experimental and theoretical mixing studies are surveyed. Mixing models invoking Si pairs, divacancies, Fermi level arguments, and other mechanisms are critically assessed.
Te Induced AlAs/GaAs Superlattice Mixing
Authors: Mel P. , Schwarz S. A. , Venkatesan T. , Schwartz C. L. , Colas E.
Published: March 2011

Te enhanced mixing of AlAs/GaAs superlattice has been observed by secondary ion mass spectrometry. The superlattice sample was grown by organometallic chemical vapor deposition and doped with Te at concentrations of 2×1017 to 5×1018 cm−.3 In the temperature range from 700 to 1000 C, a single activation energy for the Al diffusion of 2.9 eV was observed. Furthermore, it has been found that the relationship between the Al diffusion coefficient and Te concentration is linear. Comparisons have been made between Si and Te induced superlattice mixing.
Corrosion of Radioactive, Crushed Waste Glass
Authors: Björner Inga-Kari , Christensen H. , Hermansson H. P. , Tsukamoto M , Werme L
Published: March 2011

The corrosion experiments of crushed, radioactive waste glass at Studsvik within phase V of the JSS Project are described. The experiments were performed with high S/V ratios (1100 and 4000 m−1) which resulted in silica saturation already after the shortest reaction time studied (91 d).Thee long term leach rate of the soluble elements is about 10−3 g.m d−1, both in the presence and absence of bentonite. In the presence of bentonite + magnetite the leach rate is higher, about 0.007 g.m1.d−2. The release rate to the solution of Cs is one order of magnitude lower and that of Pu-238 + Am-241 three orders of magnitude lower than the release rate of the soluble elements Mo and B. Most of the Pu-238 and Am-241 fraction, found in the solution, is present as colloids.
Thermal and Radiation Effects in the Range of the Glass Transition Temperature Tg
Authors: Malow G.
Published: March 2011

Licencing procedures for the disposal of vitrified HLW require that there should be no unforeseen changes in the product properties prior to and after emplacement of the waste. Such changes could occur upon deliberate or accidental self-heating of the glass up to or even beyond the glass transformation temperature, Tg, over extended periods of time. Hence, an evaluation of the consequences of excessively high temperatures in the waste form is necessary.
Cooling and Cracking of Technical HLW Glass Products: Experimental and Numerical Studies
Authors: Kienzler Bernhard
Published: March 2011

Various cooling procedures have been applied to canisters filled with inactive simulated HLW glass and the measured temperature distributions have been compared with numerically computed data. Stress computations of the cooling process were carried out with a finite element method. Only those volume elements having temperatures below the transformation temperature Tg were assumed to contribute thermoelastically to the developing stresses. Model calculations were extended to include real HLW glass canisters with inherent thermal power. The development of stress as a function of variations of heat flow conditions and of the radioactive decay was studied.
Investigation of the Redox Behavior of Technetium in Borosilicate Glass Melts by Voltammetry
Authors: Freude E. , Lutze W. , Rüssel C. , Schaeffer H. A.
Published: March 2011

Technetium is a potentially hazardous radionuclide in the waste vitrification process as its oxides are volatile. Electrochemical measurements, i.e. potentiometry and voltammetry are applied to investigate the redox reactions of Tc in the glass melt. Re is studied for comparison. Under normal oxidizing conditions Tc is in the -T-state, and substancial losses of Tc occur as a result of compound volatility. Reducing conditions lead to the formation of TcO2, which precipitates from the melt. Stronger reducing conditions lead to the formation of metallic Tc
Product Models for the Vitrification of West Valley High-Level Wastes
Authors: Pegg I. L. , Saad E. E. , Feng X. , Adiga R. B. , Freeborn W. P. , Macedo P. B.
Published: March 2011

Property models have been developed for the major properties that need to be controlled in the production of borosilicate glasses for West Valley high-level nuclear waste immobilization. The chemical durability is the most important parameter for product performance, while melt viscosity is the most critical parameter in assuring the processability of the glass. Simple models for these properties are described that are based on data from numerous glasses which were prepared with compositions in the region around the West Valley reference glass. A scheme for optimization of the target glass and for predicting the acceptability of glasses resulting from natural process variations is illustrated. This involves integration of the product models with a process model that was described previously. This approach has guided the present placement of the West Valley reference glass.
Fabrication and Leach Testing of Synroc Containing Actinides and Fission Products
Authors: Reeve K. D. , Levins D. M. , Seatonberry B. W. , Ryan R. K. , Hart K. P. , Stevens G. T.
Published: March 2011

Synroc containing mixed fission products and four actinides (237Np, 239Pu, 241Am and 244Cm) was fabricated by hot pressing on a 75 g-scale in separate hot-cell and glove-box facilities. Samples were physically characterised by density, which ranged from 98.2 to 99.1% of theoretical, by scanning electron microscopy (SEM) and by the cc-track etch technique to determine the distribution of actinide elements.

The chemical durability of specimens prepared from the hot-pressed Synroc was determined in 460 leach tests carried out under static conditions at 70°C. Release of 137Cs dominated the fission-product source term while 237Np was the most leachable actinide element. Short-term release is dominated by the initial spilce from Cs and other readily soluble species at grain boundaries and in non-equilibrium phases. Long-term release is probably controlled by matrix solubility. A phenomenological model is developed which accounts for both short- and long-term release.
Mechanisms of Actinide Isotope Leaching from Monazite
Authors: Eyal Yehuda , Olander Donald R.
Published: March 2011

The remarkable geological stability of the actinide-containing rare-earth orthophosphate mineral monazite has led to consideration of synthetic analogs of this material as the wasteform for high-level nuclear wastes (1). Monazite is resistant to metamictization in spite of the alpha radiation from decaying actinides to which it has been subjected during its lifetime. This material is also very insoluble in most groundwaters. Consequently, dissolution of the mineral and leaching of its constituent actinides are very small. However, leaching experiments on natural monazite specimens, presented here, show that radioactive decay and radiation damage produce significant differences in the release rates of several isotopes into aqueous solutions. Within the duration of the present experiments, 6.3 to 6.8 years, these effects are particularly prominent in the nuclides in the decay chain of 232-Th. This series includes the alpha-recoil 228-Ra atom (a 5.8-year fT emitter formed directly by 232-Th decay), and its daughter 228-Th (a 1.9-year a emitter, produced by 3 decay). The present experiments exhibit preferential release into solution of 228-Th relative to 232-Th by a factor of 1.3 to 21. This highly enhanced 228-Th release is explained by four different isotope incongruency effects that operate during leaching. One mechanism involves the preferential etching of alpha-recoil tracks. The three other mechanisms depend upon the behaviour of 228-Ra. In particular, dissolution-released, recoil-released and diffusion-released 228-Ra atoms (the latter process is applicable to a high-temperature anneal) are observed to remain with the solid as an insoluble precipitate, possibly loosely attached to the mineral surface. Subsequent decay of this released insoluble 228-Ra immediately leads to the formation of readily dissolved 226-Th. The phenomena may be quite general, so potential wasteforms should be examined for these isotope fractionation effects in order to insure satisfactory prediction of the long-term leaching of actinides from the material.
Mechanism of Heavy Element Retention in Hydrated Layers Formed on Leached Silicate Glasses
Authors: Petit J.-C. , Dran J.-C. , Trotignon L. , Casabonne J.-M. , Paccagnella A. , Della Mea G.
Published: March 2011

We have investigated the relationship between hydrated layer formation during aqueous corrosion of silicates and retention of heavy elements (Fe, REE, actinides). Our approach is based on the comparison of the dissolution behaviour of silicate glasses, silicate minerals implanted with increasing doses of lead ions (1×E+12 to 1×E+15 ions/cm2), sorption experiments on silica surfaces and direct precipitation of hydrosilicates. The characterization of reacted surfaces was performed by combining Rutherford backscattering spectrometry (RBS) for profiling heavy elements with Resonant Nuclear Reaction Analysis (RNRA) for hydrogen profilimetry. The accumulation of these elements does not necessarily imply a selective dissolution and can be explained by the “precipitation” of hydroxides or hydrosilicates.
Surface Analysis of UO2 Leached in Mineral Water Studied by X-Ray Photoelectron Spectroscopy
Authors: Lahalle M. P. , Krupa J. C. , Guillaumont R. , Genet M. , Allen G. C. , Holmes N. R.
Published: March 2011

X-rays photoelectron spectroscopy (XPS) analysis has been carried out on uranium dioxide single crystals placed in both deionised or mineral water at 60 °C and 90 °C for a few months. The surface layer on the sample immersed in mineral water at 90 °C was sufficiently thick to mask the presence of uranium in the recorded XPS spectrum. Depth profiling experiments showed that the deposit was ∼ 100 nm in thickness and revealed the formation of a mixed magnesium-uranium oxide region between the bulk UO2 and the outer magnesium- rich layer. Analysis of the aqueous medium following immersion of the UO2 samples showed that the concentration of uranium released to the mineral water was 10 to 100 times lower than that in deionised water.
Leaching of Cesium from a Cement Matrix
Authors: Torstenfelt B. , Hedin G.
Published: March 2011

The leaching rate of cesium has been studied in cement. The solidification matrix was a standard Portland cement with increased sulphate resisting properties mixed with 300 kg/m3 or 350 kg/m3 powdered ion exchange resins, and with or without 5 weight-% zeolite added to the grout. The leaching rates from an ordinary cement matrix and a cement matrix mixed with zeolite were measured to be (1.3 to 2.6)×10–7 kg/m2s and (1.6 to 2.1)×10−8 kg/m2s, respectively. From the leaching data the apparent diffusivity of cesium in an ordinary cement matrix with a waste load of 300–350 kg/m3 powdered ion exchange resins was measured to be (0.6 to 1.3)×10−10 m2/s, and in a cement matrix mixed with 5 weight-% zeolite and the same waste load, the diffusivity was measured to be (0.8 to 1.0)×10−12m2/s.
Non Destructive Waste form and Package Characterization by Computerized Tomography
Authors: Illerhaus B. , Goebbels J. , Kettschau A. , Reimers P.
Published: March 2011

Transmission computerized tomography (TCT) was used for nondestructive characterization of nuclear waste packages (HLW, ILW). Ready conditioned waste packages may be tested to reveal density fluctuations, cracks, fluids etc. Emission computerized tomography (ECT) combined with TCT gives the activity distribution corrected for density variations within the waste packages.
Package Characterization by Laboratory Leaching and Diffusion Experiments using Radionuclides
Authors: Das H. A.
Published: March 2011

The leaching of solid inorganic waste from loaded concrete or cement by Incoming water can be described in terms of a “steady-state” outward diffusion of the saturated solution, formed inside the pores. The derived equations permit the prediction of long-term leaching behaviour. Radiotracer experiments enahle the determination of the parameters involved.
Characterization of Bituminous, Intermediate-Level Waste Products
Authors: Kopajtic Z. , Laske D. , Linder H. P. , Mohos M. , Nellen M. , Zwicky H. U.
Published: March 2011

The influence of γ-irradiation on the properties of two types of bituminous reprocessing waste has been studied. Standard test methods were adapted for use with radioactive samples. Measurements of penetration, gas generation, thermal stability and leaching of irradiated and non-irradiated samples have been compared.
Safety Analysis and Comparison of Toxicities for the Disposal of Radioactive Waste of Negligible Heat Generation Including Transuranic Elements
Authors: Berg H. P. , Ehrlich D. , Thomauske B.
Published: March 2011

Requirements on radioactive waste of negligible heat generation with respect to transuranic elements, derived from the safety analysis of the operational phase of the Konrad repository, are described and resulting activity limitations are discussed. For assessing the long term safety, the calculation of individual doses in connection with the very slow water movements and, additionally, toxicity comparisons to other waste and to the natural toxicity at the site are discussed. Some information is given on the procedure of taking into account the activity limitations in an optimal way when planning emplacement campaigns.
Performance Assessment with Realistic Data for a Hypothetical High-Level Waste Repository in A Salt Dome
Authors: Hirsekorn R.-P. , Storck R.
Published: March 2011

In the frame of the European R&D program on “Management and Storage of Radioactive Waste” assessments for HLW repositories in different geological formations have been performed with realistic data. Part of this action was the discussion of altered evolution scenarios for a repository in a salt dome.

For the considered HLW repository a combined altered evolution scenario with brine intrusion via the main anhydrite vein and brine intrusion from undetected brine pockets has been considered. For this scenario limited intrusions of brine at very early times are assumed, which inundate boreholes and parts of the repository. Radionuclides are leached out of the waste forms and contaminate the brine. At later times brine intrusion via the main anhydrite is assumed to take place. Under certain conditions contact between both amounts of brine is possible, and contaminated brine reaches the overburden. Here, the radionuclides are swept away with the groundwater flow.

Decisive for the transport of radionuclides from the repository to the geosphere are several interacting effects (e.g. convergence, permeability, pressure) which determine the movement of brine through the drifts and seal-ings. For the parameters involved in the modelling of physical and chemical effects as realistic data as available (best estimate) were used. Local sensitivity studies show that with the best estimate values for some parameters the combined intrusion scenario is just at the transition point between release and no release.

Results are obtained showing time histories for the decrease of the voids in the repository, release rates for relevant nuclides injected into the overburden, and for dose rates. Dependences on the model parameters are discussed and most relevant parameters are identified.
Application of the Monte Carlo Method in the Performance Assessment of a Hypothetical HLW Repository in Salt
Authors: Nies Alexander
Published: March 2011

Recent advances in complementing the capabilities of our safety assessment code development allow for an explicit investigation of the consequences of parameter uncertainties by Monte Carlo simulation of the disposal system. The implemented methods aire described and applied to impact assessment of a brine intrusion scenario on a high level waste repository in a salt dome. Results display the strong effect of parameter uncertainties on the analysis results. With help of several sensitivity estimators input parameters are ranked according to their influence on output uncertainty.
Source-Term Comparison Using the Arest and Syvac-Vault Models: Effects of Decay-Chain In-Growth and Precipitation
Authors: Apted M. J. , Engel D. W. , Garisto N. C. , Leneveu D. M.
Published: March 2011

A series of calculations of radionuclide release was performed with the AREST and SYVAC-Vault models (SVM) in order to assess concurrance. Specifically, the effects of precipitation and decay chain in-growth on the predicted release of nuclides from waste packages containing spent nuclear fuel were compared between each code. The results for maximum release rates generally agreed within a factor of 10. The differences in results can be explained based on the differences in geometry and boundary conditions between the two codes. Both codes showed nearly identical enhancement factors in release rates of uranium-series nuclides (U-238, U-234, Th-230, Ra-226) arising from the effect of decay-chain in-growth. Calculated enhancement factors in release rates for precipitation of a new uranium-bearing solid within the waste package were also in good agreement between AREST and SVM.
In Situ Migration Experiments in the Boom Clay at Mol ; Experimental Method and Preliminary Results
Authors: Put M. , Monsecour M. , Fonteyne A. , Yoshida H. , De Regge P.
Published: March 2011

A first generation of underground migration experiments is described, consisting of labelled clay cores emplaced in boreholes drilled in the Boom clay formation. The boreholes are sealed by natural convergence of the clay and porewater percolates through the labelled clay cores which are consolidated in situ. After monitoring of the radioactive tracers in the percolating porewater, the experiment is retrieved from the borehole and the tracer profile is measured in the clay cores. With the exception of accelerated porewater flow, due to the existence of a high hydraulic head around the underground gallery, the experimental conditions are close to those expected in the far-field of a closed repository for radioactive waste. The main advantage of this approach is the availability of real porewater during relatively long-term experiments. Results are reported for the experiments performed with europium and strontium tracers.
Chemical Evolution of Water and Brines in Contact with Different Zechstein Salt Formations
Authors: Herbert H.-J. , Sander W.
Published: March 2011

The paper gives a quantitative description of the chemical reactions, the dissolution and precipitation processes which take place when water or brines come into contact with the main mineral assemblages of the German Zechstein salt formation, rock salt with Ca-sulfates, and the potash beds hartsalz and carnallitite. The results of two large scale in situ dissolution tests are presented. These results have been successfully reproduced by computer modelling using the geochemical code EQ3/6.
Near-Field Geochemistry of Vitrified HLW in a Sedimentary Host Rock
Authors: Mckinley Ian G. , Bradbury Mike
Published: March 2011

The Project Gewähr 1985 (PG'85) safety analysis considered the practicality of HLW disposal in the crystalline bedrock of Northern Switzerland. More recently, an alternative disposal option in the argillaceous sediments overlying the crystalline basement has been examined. This paper examines some aspects of the performance of the near-field engineered barriers in an argillaceous environment, with specific comparison to the PG'85 crystalline case. Two phenomena are considered in particular detail: oxidation of the host rock during the operational phase and the related failure mode of the steel tunnel liner.
Formation and Evolution of Alteration Layers on Borosilicate and Basalt Glasses: Initial Stage
Authors: Murakami T. , Banba T. , Jercinovic M. J. , Ewing R. C.
Published: March 2011

An experimentally altered (1–14 days, deionized water, 90°C), synthetic borosilicate glass and naturally altered (104 years, fresh water, 0–100°C), basalt glass were characterized by analytical electron microscopy to evaluate the development of alteration layers. Layers formed on borosilicate glass are initially amorphous. With increasing age, nontronite, chlorite, septechlorite, and/or stilpnomelane appear to precipitate and grow within the amorphous matrix and on the surface of the layer. Crystals are enriched in Fe, Co, and Ni, and depleted in Si relative to the surrounding amorphous matrix. Alteration layers on basalt glass are texturally and mineralogically similar to layers formed on borosilicate glass, but the degree of crystallinity is less.
Water Uptake and Swelling Pressure in a Bentonite-Based Backfill
Authors: Kahr G. , Bucher F. , Mayor P. A.
Published: March 2011

The partial specific enthalpy and the partial specific entropy for the water uptake of two bentonites was investigated by means of the water vapor adsorption-desorption isotherms and the heat of immersion with liquid water. From these experiments, and as confirmed by X-ray measurements, it is evident that the interlayer water shows a high degree of order. Calculations of the swelling pressure from the adsorption isotherms show good agreement with measured swelling pressures.

The uptake of liquid water by the compacted bentonites under conditions of restrained swelling can be described as a non-steady state diffusion with constant surface concentration. The water uptake of two bentonites in their natural sodium and calcium forms has been investigated. The measurements were carried out in a swelling pressure apparatus with water supply from one or both sides, and in a device modelling the repository conditions with radial water supply. In this modelling experiment, the water uptake was measured and the enclosed air determined. In addition, the swelling pressure was observed and compared to earlier test results.
Modelling the Behaviour of Organic Degradation Products
Authors: Cross J. E. , Ewart F. T. , Greenfield B. F.
Published: March 2011

Results are presented from recent studies at Harwell which show that the degradation products which are formed when certain organic waste materials are exposed to the alkaline conditions typical of a cementitious environment, can enhance the solubility of plutonium, even at pH values as high as 12, by significant factors. Characterisation of the degradation products has been undertaken but the solubility enhancement does not appear to be related to the concentration of any of the major organic species that have been identified in the solutions. While it has not been possible to identify by analysis the organic ligand responsible for the increased solubility of plutonium, the behaviour of D-Saccharic acid does approach the behaviour of the degradation products. The PHREEQE code has been used to simulate the solubility of plutonium in the presence of D-Saccharic acid and other model degradation products, in order to explain the solubility enhancement. The extrapolation of the experimental conditions to the repository is the major objective, but in this work the ability of a model to predict the behaviour of plutonium over a range of experimental conditions has been tested.
Diffusion of Plutonium(IV) in Dense Bentonite-Based Materials
Authors: Sharma H. D. , Oscarson D. W.
Published: March 2011

Diffusion coefficients were measured (Dm) for Pu(IV) in dense mixtures of bentonite and sand (soil) saturated with a synthetic groundwater solution (SGW) at a pH of 8 and at 25°C. The Dm values were approximately 10-14 m2/s. The clay content of the soil, in the range of 10 to 50%, did not have a significant effect on Dm. The Dm values were also compared with diffusion coefficients calculated (Dc) from a model based on a distribution coefficient. Fair agreement between Dm and Dc for Pu(IV) was found for the soils and SGW examined here. It is unlikelv. however, that the model will accurately estimate Dm for Pu, which has a complex solution and sorption chemistry, over a wide range of conditions.
Chemical Corrosion of Cogema Glass R7T7 in High Saline Brines - Part II
Authors: Lutze W. , Müller R. , Montserrat W.
Published: March 2011

The kinetic results of corrosion experiments of glass R7T7 in brine 2 (high Mg and Ca concentrations) and brine 3 (high Na, low Ca concentrations) in this study are similar to those reported for the corrosion in brine 1 (high Mg concentration, no Ca) in [1]. Further support is lent to the idea that corrosion can be described, by a transient process that depends on the Si concentration in solution (prior to arriving at steady state Si concentration) and another one where this dependence vanishes or becomes small (after constant Si concentration is reached). This is analogous to what is known about corrosion of glass R7T7 and of other glasses in deionized water [4].
Uranium Transport in Topopah Spring Tuff: An Ion-Microscope Investigation
Authors: McKeegan K. D. , Phinney D. , Oversby V. M. , Buchholtzten Brink M. , Smith D. K.
Published: March 2011

We investigated the effect of different methods of surface preparation on ion-microscope profiles of uranium concentration (added to the sample by diffusion from an aqueous solution) vs depth in a welded, devitrified, tuffaceous rock from Yucca Mountain. The concentration profiles were used to study transport of uranium in the tuff. Four wafers of rock were prepared from primary drill core material and finished by polishing with increasingly finer abrasive material. Final polishes were made with 400 grit SiC, 600 grit SiC, 0.3μm alumina, and 0.05μm alumina. The polished tuff wafers were exposed for eight hours to a solution of groundwater doped with 2 ppm 235-U. The wafers were then examined by SEM and the ion microscope was used to measure the lateral and depth distributions of 235-U and other isotopes in the wafer. No systematic correlation of the measured 235-U concentration- vs-depth profiles with the degree of surface finish was observed, indicating that the polishing does not affect the measurable transport of U in the tuff. A zone of enhanced 235-U concentration was observed in the upper few microns, which we attribute to sorption onto surfaces of exposed pores. Concentrations of 235-U were elevated above background to depths > 15μm, indicating that rapid transport paths exist. When the uranium distribution near the surface of the wafer was modelled by an error function, an upper limit for a slower transport path was defined by an apparent diffusion coefficient of approximately 10−3 cm3/s.
Validation of the SKBU1 Uranium Thermodynamic Data Base for its use in Geochemical Calculations with EQ3/6
Authors: Bruno Jordi , Puigdomenech Ignasi
Published: March 2011

A validation of the SKBUl uranium thermodynamic data base is performed. Experimental solubilities for schoepite, rutherfordite, UO2(am) and UO2(c) determined in a wide range of pH, PCO2, carbonate concentration and temperature are compared to calculated ones by using EQ3NR.
Complexation of Europium(III) with Carbonate Ions in Groundwater
Authors: Chatt A. , Rao R. R.
Published: March 2011

The equilibrium extraction behavior of Eu(III) studied in chloroform solutions containing l-nitroso-2-naphthol (HA), either alone or combined with 2, 2'-dipyridyl, 1, 10-phenanthroline (phen), or trioctylphosphine oxide (TOPO) shows that the metal ion is extracted as either EuA, EuA3.2, 2'-dipyridyl, EuA3·phen, or EuA3·2TOPO, respectively. The synergic effect of phen or TOPO on the extraction of Eu(III) with l-nitroso-2-naphthol is more pronounced over that of 2, 2'-dipyridyl. The carbonate complexation of Eu(III) has been studied in 1.0 M ionic strength solutions at pH 8.0–9.0 and 25 °C using the synergic extraction system of 1-nitrşso-2-naphthol and pheo. The following complexes have been identified: EuCO34, Eu(CO3)2-, Eu(CO3)33-, and Eu(CO3)45- the results suggest that the first two species predominate at carbonate concentrations and pH similar to those found in most groundwaters. The formation constants of these species have been calculated at zero ionic strength using both SIT and ion pairing models.
The Importance of Variables and Parameters in Radiolytic Chemical Kinetics Modeling
Authors: Piepho M. G. , Turner P. J. , Reimus P. W.
Published: March 2011

Radiolysis may significantly affect the long-term performance of nuclear waste packages in a geologic repository. Radiolysis of available moisture and air in an unsaturated or saturated environment will create transient species that can significantly change the pH and/or Eh of the available moisture. These changes can influence rates of containment corrosion, waste form dissolution, and radionuclide solubilities and transport.

Many of the pertinent radiochemical reactions are not completely understood, and most of the associated rate constants are poorly characterized. To help identify the important radiochemical reactions, rate constants, species, and environmental conditions, an importance theory code, SWATS (Sensitivity With Adjoint Theory-Sparse version)-LOOPCHEM, has been developed for the radiolytic chemical kinetics model in the radiolysis code LOOPCHEM. The LOOPCHEM code calculates the concentrations of various species in a radiolytic field over time. The SWATS-LOOPCHEM code efficiently calculates: 1) the importance (relative to a defined response of interest) of each species concentration over time, 2) the sensitivity of each parameter of interest, and 3) the importance of each equation in the radiolysis model. The calculated results will be used to guide future experimental and modeling work for determining the importance of radiolysis on waste package performance. A demonstration (the importance of selected concentrations and the sensitivities of selected parameters) of the SWATS-LOOPCHEM code is provided for illustrative purposes, and no attempt is made at this time to interpret the results for waste package performance assessment purposes.
A Uranium Geochemical Study at the Natural Analogue Site of Needle's Eye. SW Scotland
Authors: Roberts P. D. , Ball T. K. , Hooker P. J. , Milodowski A. E.
Published: March 2011

A detailed study is being carried out at the Needle's Eye locality, on the Solway Firth, into the movement and fixation of U and its daughter isotopes. The site contains pitchblende veins, some of which have acted as a source of soluble uranium flowing into and through estuarine silts laid down in the last 2000 years or so. A section through these has provided samples for detailed analysis by X-ray fluorescence and neutron activation techniques. High resolution gamma spectrometry has contributed information on the distributions and disequilibria between uranium and its daughters. These data have been combined with analyses from groundwaters to produce a geochemical model of the origins of the U radioisotope distributions and transport mechanisms. There are thought to be two main inputs of dissolved U(VI) into this system; the surface flow of groundwater from the exposures of the mineralisation in the cliff, and upward flow from the bedrock below. The fixation of U in the sediments is controlled by the presence of organic matter in the upper humic layers, and by an iron oxy-hydroxide sorption reaction in the deeper silts at about 110cm. This concentration of U in the silt is divorced from the sub U-234 daughters. In contrast. Th is coherently associated with its daughters within detrital resistate phases. This study is a prelude to a more rigorous modelling investigation in collaboration with the Ecole des Mines de Paris.
Modeling of the Mixing of Cement Pope Water and Groundwater Using the Phreeqe Code
Authors: Ijundén Irene , Andersson Karin
Published: March 2011

The equilibria between cement solids and pore water as well as between groundwater and rock/fracture filling minerals have been modeled, using the PHREEQE geochemical code. Additions of mineral phases to the original PHREEQE data base have been necessary for both systems. Comparisons of the predicted saturation state of the different waters with fracture filling mineralogy determined in the same area was performed.

When a satisfactory modeling of the separate cement and rock systems was achieved, a modeling of the mixing of the two waters was performed. The state of saturation with respect to the minerals considered in the initial calculations as well as to potential “new” minerals was evaluated.

The main mineral phases that are predicted to be supersaturated when mixing the waters are in the initial stage calcite, hydroxyapatite, chlorite, and laumontite.
A Method for Determining the Oxidation State of Uranium at Concentration as Low AS 1010M
Authors: Hussonnois M. , Guillaumont R. , Brillard L. , Fattahi M.
Published: March 2011

This paper describes the development and testing of a chemical procedure for determining the tetravalent and hexava-lent states of uranium in aqueous media at concentration as low as 10−10M. Results show the U(IV) stability towards fast modifications of the pH of the solution with oxygen free hydrochloric acid. Some results on the oxidation kinetic of the uranium tetravalent state versus the HCl and uranium concentrations as well as the Fe(III) content are presented.
Ion Beam Deposition of Diamond-Like Coatings
Authors: Greenwald Anton C. , Hirvonen James K. , Jaggi Narendra K.
Published: March 2011

Mass analyzed and non-mass analyzed carbon ion beams were used to deposit coatings on polished silicon wafers. Extremely, hard dense coatings that are structurally similar to i-carbon as determined by Ramon spectroscopy were achieved with high current beams of methane and argon. Residual contaminants of oxygen and nitrogen were minimized.
Diffusion in Irradiated AgZn Alloys using Defect-Concentration Dependent Migration Energies
Authors: Andreadis T. D. , Rosen M. , Eridon J. M.
Published: March 2011

Concentration dependent migration and reaction migration energies, calculated with the molecular dynamics code DYNAMD using Embedded Atom Method Potentials, were inserted into the appropriate diffusion and rate coefficients. The time and space evolution of the concentration of interstitials, vacancies, Zn impurity, interstitial-inpurity, aid vacancy-impurity complexes was calculated for an irradiated AgZn alloy in the framework of the approach presented in Johnson and Lam. A significant effect on defect segregation and profiles was found.
Control of Metal Film Properties by Ion Assisted Deposition
Authors: Roy Ronnen A. , Yee Dennis S. , Cuomo Jerome J.
Published: March 2011

Ion-assisted deposition allows for independent control of ion energy, ion flux, and adatom flux incident on the growing film. We describe herein general trends in property and structure modification of thin film metals using this
technique.
Amorphous and Metastable Phase Formation in Systems with Positive Heats of Mixing using High-Rate Sputter Deposition
Authors: Rizzo H. F. , Echeverria A. , Massalski T. B. , Baxi H.
Published: March 2011

The triode sputtering technique and a “split-target” arrangement were used to produce metastable crystalline and amorphous phases in the Cu-W, Mo-Cu, Ag-Fe, Ag-Cu, Pu-Ta and Pu-V systems. These systems all exhibit liquid and solid immiscibility and have positive heats of mixing and atomic radii that differ by at least 10%. The sputtered coatings, whose thickness varied between 25 and 200 microns, were formed at deposition rates between 35 and 200 Å/s. They were characterized using x-ray diffraction, TEM, microprobe, microhardness, and DSC techniques. The observed amorphous and metastable solid solution phases are discussed in terms of predicated heats of formation for these phases using Miedema's thermodynamic approximations [1] that include chemical, elastic, and structural contributions. Differences in compositional ranges observed by high rate sputter deposition compared to other vapor deposition techniques (e.g., coevaporation) appeared to arise as a result of processes that occur during deposition or immediately following deposition.
Composition- and Temperature-Dependence of Ion Mixing in Amorphous Si/Ge Artificial Multilayers
Authors: Park B. , Spaepen F. , Poate J. M. , Priolo F. , Jacobson D. C.
Published: March 2011

Amorphous Si/Ge artificial multilayers with a repeat length of around 60A have been partially mixed with 1.5 MeV Ar+ ions at temperatures in the range 77–673K. The change in the intensity of the first X-ray diffraction peak resulting from the composition modulation is used to determine the mixing lengths. The diffusive component of the square of the mixing length, at a given dose, is independent of the dose rate and has an Arrhenius-type temperature dependence, with activation enthalpies between 0.19 and 0.22 eV, depending on the average composition.
Ge Heteroepitaxy on (100) Si Substrates by Ion Assisted Deposition
Authors: Holesinger T. G. , Heim D. J. , Lakin K. M. , Shanks H. R.
Published: March 2011

Ge films have been grown by ion-assisted deposition on Si(100) substrates. Initial studies were conducted to determine the growth and morphology of Ge using a modified crucible arrangement and ionization chamber. It was observed that a narrow substrate temperature range existed for the deposition of smooth Ge films without ion assistance. Ionization and acceleration appear to induce additional damage to the film without improving crystalline quality.
Phase Stability of Ni2Al3under Electron Irradiation
Authors: Kenik E. A. , Nastasi M.
Published: March 2011

In-situ electron irradiations at 200, 300, and 1000 keV have been performed on Ni2Al3at 100 and 300 K. At low doses, the Ni2Al3partially disorders to a B2 structure with a lattice parameter of 0.284 nm, close to that extrapolated for β-NiAl at 60 at.% Al, the Ni2Al3composition. The electron dose required to disorder the Ni2Al3decreased with increasing accelerating voltage and possibly with decreasing temperature. At high doses, precipitation of aluminum from the B2 matrix occurs, along with radiation-induced sputtering and radiation-induced segregation. Lattice parameter changes for the B2 structure observed during irradiation are explained in terms of the compositional dependence of the lattice parameter of β-NiAl. The B2 structure remains stable to a dose of 6 × 1028electrons/m2, with no amorphization detected.