bluuebunny/crossref_metadata_2025 huggingface dataset:
New Structures of Preceramic Polysilazanes Synthesized by Transition Metal Catalysis
Authors: Blum Yigal D. , Schwartz Kenneth B. , Crawford Edward J. , Hamlin Richard D.
Published: March 2011

Further capability of silazane dehydrocoupling polymerization catalyzed by ruthenium carbonyl (20–200 ppm) is demonstrated in a series of reactions. Ammonia and monomethylamine are used as reactants to bridge oligomers and polymers containing Si-H bonds to provide higher molecular weight polymers with higher latent reactivity and to increase the ceramic yields and the nitrogen-to-carbon ratio in the final ceramic compositions. New types of tractable polymers containing cyclomers having [MeSiHNH] units with molecular weights over 2000 d are formed. Various polymeric properties (e.g., viscosities, softening and melting points) and ceramic yields up to 80–85 wt% are obtained by controlling the catalytic reaction conditions.
Studies of the Hydrolysis and Polymerization of Silicon Alkoxides in Basic Alcohol Solutions
Authors: Bogush G. H. , Dickstein G. L. , Lee P. , K.C.  , Zukoski C. F.
Published: March 2011

We report here an experimental technqiue based on changes in reaction medium volume which we have used to observe the kinetics of hydolysis and polymerization of TEOS in aqueous ethanol solutions containing NH3. Our results show that there are three distinct reaction regions. By combining these results with determinations of change in reaction medium conductivity and average particle size, we are able to link the short and long time regions to TEOS hydrolysis and particle growth respectively. The intermediate reaction time region is not associated with hydrolysis, loss of ionic species due to condensation or to particle growth.
Silicon Carbide Via the Hydrolysis-Condensation Process of Dimethyldiethoxysilane/Tetraethoxysilane Copolymers.
Authors: Chen K. C. , Thorne K. J. , Chemseddine A. , Babonneau Florence , Mackenzie J. D.
Published: March 2011

Transparent monolithic pieces of gel have been prepared from the hydrolysis of a mixture of dimethyldiethoxysilane (DEDMS) and tetraethoxysilane (TEOS). The characterization of this gel has been done by infrared and shows that a copolymerization between the two precursors has occurred during the hydrolysis-condensation process. Pyrolysis of this gel lead to the formation of β-SiC at 1550°C. The characterization of the pyrolysing process has been investigated. The Si-CH3 bonds are broken during the heat treatment, leading to a mixture of silica and carbon. The formation of β-SiC is therefore due to a carbothermal reduction of this silica matrix.
Physical and Structural Evolution of Sol-Gel Derived TiO2-SiO2 Glasses
Authors: CHENG Yeu-Chyi , Hench Larry L.
Published: March 2011

A method for producing large TiO2-SiO2 gel-glass monoliths using the sol-gel method has been developed. The gel-glasses are prepared by a pre-hydrolysis method using tetramethylorthosilicate and titanium isopropoxide as precursors. The microhardness, specific surface area and pore radius of the gel-glasses do not change significantly below 600°C. Above 600°C, these properties increase rapidly with densification temperature. At lower TiO2concentration, the glasses obtained by heating to 900°C for 15 hours were not crystallized, while for 15 wt % TiO2 glass, anatase precipitated.
Luminescent Oxide Gels
Authors: Newsham Mark D. , Cerreta Michael K. , Berglund Kris A. , Nocera Daniel G.
Published: March 2011

Luminescent oxide gels were prepared by hydrolysis of silicon alkoxides in solutions containing the luminescent hexanuclear molybdenum cluster Mo6Cl12. The resulting gel exhibited emission and lifetime behavior characteristic of Mo6Cl12 thereby indicating that the excited-state properties of the metal cluster species are not significantly perturbed by the gel environment.
Preparation of YBa2Cu3O7-δ Superconductor by Sol-Gel Method and Fiber Drawing
Authors: Kozuka H. , Umeda T. , Jin J. S. , Sakka S.
Published: March 2011

Superconducting YBa2Cu3O7-δ, ceramic pieces and fibers were prepared through a sol-gel route from ametal acetate aqueous solution of controlled pH. Concentrating the starting solution by evaporating the solvent provided a transparent viscous sol, from which gel fibers could be drawn. Further concentrating of the viscous solution led to formation of gel pieces. Conversion of gel fibers and pieces to superconductors were investigated in terms of precipitating crystalline species and electrical conductivities.
Formation and Characterization of Inorganic Membranes from Zeolite-Silica Microcomposites
Authors: Bein Thomas , Brown Kelly , Enzel Patricia , Jeffrey Brinker C.
Published: March 2011

Small crystals of zeolites (500–1000 nm) with two- and three-dimensional channel systems (faujasite and ZSM-5 structures) were embedded in amorphous thin films derived from TEOS hydrolyzed in alcoholic solution. Scanning electron microscopy studies show that the zeolites can be quite evenly dispersed in the membrane, resulting in single layers of zeolite crystals protruding out of the amorphous matrix. In situ FT-IR studies with a series of probe molecules revealed that in most membranes the zeolites were 100% accessible from the gas phase. The membranes excluded molecules which are larger than the pore openings of the zeolite embedded in the composite.
Chemical Durability of Sio2-Tio2-Zro2, Glass Films Made from Alkoxide Solutions
Authors: Beier W. , Frischat G. H.
Published: March 2011

Water, ethanol, and hydrochloric acid containing solutions of silicon ethoxide, titanium butoxide, and zirconium pro-poxide have been developed which show a constant viscosity for some days. The influence of formamide additions on the viscosity behavior was studied too.

Glass slides have been dip coated in the solutions, dried in ethanol containing atmosphere, and baked at 300 ° C. Multilayered films were obtained by repeating this procedure. After a final baking at 500 ° C, crack-free transparent SiO2-TiO2-ZrO2 glassy films have been obtained. Compared to the substrate, the films of thicknesses below 500 nm were very stable against hot NaOH solution. The stability of the coatings was analyzed by detection of the remaining TiO2 and ZrO2 in the films after the attack. This was done by a x-ray fluorescence (XFA) technique.
Synthesis and Characterization of Vanadium Oxide Gels from Alkoxy-Vanadate Precursors
Authors: Sanchez C. , Nabavi M. , Taulelle F.
Published: March 2011

Vanadium oxide gels are synthesized through vanadium oxo-alkoxide hydrolysis condensation processes. Different precursors and hydrolysis conditions lead to different sorts of gels. V0(0Amt)3hydrolyzed with a large excess of water results in red jammy gels with a layered structure. They exhibit electronic and ionic behavior comparable to vanadium pentoxide gels from inorganic precursors. Hydrolysis of VO(OPrn)3in an alcoholic medium, leads to orange transparent monolithic gels. They have a highly branched polymeric structure. Controlled hydrolysis of vanadium oxo-alkoxide precursors has the further advantage of giving good adherent thin films.
Maya Blue: How the Mayas Could Have Made the Pigment
Authors: Torres Luis M.
Published: March 2011

For over 50 years Maya Blue has been an unsolved problem in the manufacture of ancient pigments. It can be reproduced with several procedures using palygorskite, indigo and heat; however we do not know how the Mayans made this pigment. Interpretation of ethnohistoric data allows us to deduce that Prehispanic, and even Spanish Colonial, procedures for manufacturing indigo may produce Maya blue if clay is added during the process.

We present ethnohistoric and archaeological evidence to support this hypothesis and following the proposed procedures, Maya Blue is reproduced in the laboratory. Microscopic examination and chemical microscopy are applied to the synthetic Maya Blue to characterize and compare it with original Mayan samples.
Thermoanalytical Investigations on Terracotta Warriors of the Qin Dynasty
Authors: Wiedemann Hans G. , Boller Andreas , Bayer Gerhard
Published: March 2011

Ancient Chinese ceramics is usually related or equated with the terms pottery and porcelain. In fact the manufacture of porcelain in ancient China is one of the most important chapters in the history of ceramics. Porcelain products were developed gradually from stoneware over a time span of nearly a thousand years. The typical white and translucent porcelain that we know as China was probably first made in the ninth century.
Linear Free Energy Relationships in Glass Corrosion
Authors: Abrajano Teofilo A. , Bates John K. , Bohlke J. K.
Published: March 2011

Various theoretical models that have been proposed to correlate glass durability to their composition for a wide variety of silicate, borosilicate, and aluminosilicate glasses are examined. Comparisons are made between the predictions of these models and those of an empirical formulation extracted from existing data in the present work. The empirical approach provides independent confirmation of the relative accuracy of the silica release rate predictions of the different theoretical models in static leaching systems. Extensions of the empirical approach used in this work are discussed.
Dielectric Heating Sensitizers for Processing of Polymers
Authors: Thorsrud Agmund K.
Published: March 2011

Microwave heating has for years been successfully used for some polymer applications, especially in preheating or continous vulcanization of rubber and also for crosslinking of thermosets. It may therefore seem surprising to find how little woork has been reported on the use of dielectric heating of thermoplastic resins. Certainly a major reason is that very few thermoplastics have dielectric properties making them respond to high frequency electromagnetic fields, or their response is inadequate for practical applications.

Many processes could benefit from the many advantages of dielectric heating if the most suitable polymer could be made to absorb such energy. Therefore a study was undertaken to find additives which in small amounts could render virtually all polymers, especially the thermoplastic ones, responsive to microwave or radio frequency electromagnetic energy without significantly changing processing and physical properties.

A series of such sensitizers was developed. Some of these are now commercially available as white, fine particle size, freeflowing powders and others are colorless liquids. Their use will depend on polymer type and application, but their common objective is to substantially increase the material's loss factor.

Selected tests with difficult to process ultrahigh molecular weight polyethylene (UHWPE) and polyphenylene sulfide (PPS) proved that the sensitizers in low concentration will allow dielectric heating of unresponsive polymers with potential for important advantages in cost and quality.
The Place of Microwave and Radiofrequency Applications in Industrial Processes
Authors: Alami Richard
Published: March 2011

The presentation deals with Hydro-Québec implementation in the industrial sectors with special emphasis on microwave amd radiofrequency applications.
Microwave Equipment Considerations for High Temperature Studies in Ceramics
Authors: Yonnone Martin
Published: March 2011

The utilization of microwave energy as a source for the heating of ceramic materials is not a recent discovery. Notably, Von Hippel(1) and others including Tinga(2) investigated the microwave heating of ceramic materials in the 50's and 60's. Today, many microwave scientists and engineers are working on the complexities associated with the rapid heating exhibited by ceramic samples in the microwave field.
Interactions of Silicate Glasses with Aqueous Environments Under Conditions of Prolonged Contact and Flow
Authors: Barkatt A A. , Saad E. E. , Adiga R. B. , Sousanpour W. , Barkatt A L. , Feng X. , O'keefe J. A. , Alterescu S.
Published: March 2011

Studies of the corrosion process of silicate and boro-silicate glasses under a broad range of contact times, surface-to-volume ratios and leachant compositions indicate that dissolution of such glasses in aqueous media can be interpreted in terms of activity of dissolving amorphous silica. This activity is modified by the presence of elements such as Al, Mg and Fe. The effects of these elements, when initially present in the glass or in the leachant, and, in general, the effects of glass composition on the course of the corrosion process can be viewed in terms of the formation of a surface layer on the leached glass. The type, composition and structure of this layer, which are determined by glass composition, control the dissolution behavior of the glass.
Revised Eh-pH Diagrams (25 C, One Bar) for Uranium and Transuranic Elements: Application to Radioactive Waste Studies
Authors: Brookins D. G.
Published: March 2011

Eh-pH diagrams are useful for comparing the probable geochemical behavior of many elements including U and the transuranics Np, Pu, Am. Revised Eh-pH diagrams have been constructed for U, Np, Pu and Am at 25 C, 1 bar conditions. These diagrams, based on new and revised thermodynamic data, include aqueous and solid species in the generic system M-C-O-H. The species M(OH)− is considered herein, although it's existence has not been verified.

Aqueous U(VI) species are dominated by below pH 5 and by carbonate complexes at higher pH. U(IV) species include important fields of UO2, and U(OH)4. If Si is present, USiO4 may be important. U3O8, occurs between the U(IV) and U(VI) species.

Np(IV) solid species are problematic. NpO2 covers a wide range of Eh-pH, but its precursors, NpO. (OH)2 and Np(OH)4 cover more restrictive Eh-pH ranges with more important. This increases potential for radionuclide migration. Np(V, VI) carbonate complexes are important only at high Eh.

Pu(IV) species are dominated by PuO2, but Pu(OH)4 does not occupy as much Eh-pH space, being replaced in large part by . With carbonate present, Pu(III) species also replace part of the Pu(OH)4 field, and Pu2 (CO3)3 becomes important. Pu(VI) carbonate complexess occur only at high Eh.

Am(III) species dominate Eh-pH space in the system Am-C-O-H, with Am2 (CO3)3 a major phase. Under carbonate-poor conditions, Am(OH) 3 is important. AmO2 occurs at high Eh, pH, and at high Eh and very high pH.

The importance of the M(OH)4 precursors to MO2 species is the enhanced possibility of radionuclide migration from buried spent fuel rods, even under reducing condtions.
Induced Obsidian Hydration Experiments: An Investigation in Relative Dating
Authors: Tremaine Kim J. , Fredrickson David A.
Published: March 2011

Induced obsidian hydration experiments have been conducted over the last six months at Sonoma State University. Our initial focus has been to assess the influence of experimental conditions on hydration development within a thermally controlled pressure reaction vessel. Although an ultimate goal is to calculate source-specific rates for local obsidians, given current uncertainties regarding the ability to reliably express hydration widths as calendar years, a more immediate goal is to develop a means to compare hydration rim measurements of samples from one obsidian source relative to another so that archaeological assemblages containing obsidians from two or more sources can be placed into a time series. Induced hydration experiments are expected to provide data that illustrate the relationship between hydration measurements of different obsidians with temporal equivalency. Results and implications of initial experiments are discussed.
Chemical Interactions in Ceramic and Carbon-Carbon Composites
Authors: Luthra Krishan L.
Published: March 2011

The useful lives of many ceramic composites are influenced, if not controlled, by chemical interactions between various constituents and the gas environment. Thermochemical calculations are extremely valuable in evaluating these concerns. Examples of many possible concerns are presented. The usefulness of a thermochemical approach is demonstrated by a somewhat detailed discussion of the oxidation protection of carbon-carbon composites. This includes discussion of the various possible rate limiting steps and the detrimental effects of CO gas formed as a result of carbon oxidation.
Effects of Rapid Thermal Processing on SiO2/GaAs Interfaces
Authors: Tokuda Yutaka , Katayama Masayuki , Ando Nobuo , Kitagawa Akio , Usami Akira , Inoue Yajiro , Takematsu Hideo , Wada Takao
Published: March 2011

Effects of rapid thermal processing (RTP) on SiO2/GaAs interfaces have been investigated with Auger electron spectroscopy and X-ray photoelectron spectroscopy. SiO2 films of 100, 175, 200 and 1250 nm thickness have been deposited on liquid encapsulated Czochralski-grown (100) n-type GaAs wafers by the RF sputtering method. RTP has been performed at 800°C for 6 s. For comparison, conventional furnace processing (CFP) has also been performed at 800°C for 20 min for 200-nm-thick SiO2/GaAs. The Ga is observed on the outer SiO2 surface for RTP samples as well as CFP samples. This indicates that the outdiffusion of Ga occurs after only 6 s at 800°C even through 1250-nm-thick SiO2 films. The depth profile of Ga reveals the pile-up of Ga on the outer SiO2 surface for both RTP and CFP samples. The amount of Ga on the outer surface gradually increases in the thickness range 1250 to 175 nm. The As is also observed on the outer surface. The amount of Ga and As on the outer surface rapidly increases at 100 nm thickness. Electron traps in RTP samples have been studied with deep-level transient spectroscopy. Different electron traps are produced in GaAs by RTP between 100-nm- and 200-nm-thick SiO2/GaAs. It is thought that the production of different traps by RTP is related to the amount of Ga and As loss through SiO2 films from GaAs.
He+ Implanted Stripe Optical Waveguides in LiNbo3
Authors: Weiss B. L. , Reed G. T.
Published: March 2011

In this paper the fabrication process and characteristics of waveguides produced by He+ implantation in Y-cut X- and Z-propagating LiNbO3 are presented It is shown that low propagation losses, down to 1dB cm−1 at λ = 633μm can be obtained for TM modes only in Y-cut X-propagation samples whilst Y-cut Z propagating samples support both TE and TM modes with relatively low losses.
Stable Solid-Phase Ohmic Contacts to n-GaAs with Diffusion Barriers
Authors: Kolawa E. , Nieh C. W. , Flick W. , Molarius J. , Nicolet M-A.
Published: March 2011

Contacts to GaAs substrates with n-type epilayers formed by GaAs/Ni/Ge/WN/Au, GaAs/Ni/Ge/Ni/WN/Au and GaAs/Ge/ Ni/WN/Au systems were investigated. Ohmic contacts in these systems were formed by a solid-phase reaction between Ni/Ge and GaAs. Interfacial reaction and electrical properties of these contacts are characterized by backscattering spectrometry, transmission electron microscopy and contact resistivity measurements. Resistivities in the 10−δ Ω cm range are achieved.
Ion Implanted Strip Optical Waveguides in GaAs/GaAl as MQW Material
Authors: Weiss B. L. , Wismayer A. C.
Published: March 2011

This paper is the first report of the use of Si+ implantation into GaAs/GaAlAs MQW material to form optical waveguides operating at a wavelength of 1.15μm. Lateral confinement is achieved by mixing of the MQW material which is produced by the implantation of Si+ and subsequent annealing at 750°C. The properties of these waveguides are compared with those of chemically etched rib waveguides and are shown to have reasonably low losses.
Static Leaching of Actinides and Fission Products from Fully Radioactive Waste Glass of Hllw Generated in Tokai Reprocessing Plant
Authors: Miyahara K. , Ashida T. , Yusa Y. , Sasaki N. , Tsunoda N.
Published: March 2011

Fully radioactive waste glass of HLLW generated in Tokai Reprocessing Plant was produced by using a small Joule-heated ceramic melter at the Chemical Processing Facility (CPF), Tokai Works, PNC, Japan. Static leach tests using the glass were carried out in doubly distilled water for a period of up to three months at 30°C and 90 °C. Gamma spectrometry was performed to measure 134Cs, 137Cs and 60Co in the leachates. After the chemical separation of Cs isotopes in the leachates, it was newly possible to measure 125Sb, 144Ce, 154Eu and 155Eu. Alpha spectrometry was performed to measure 239Pu+240Pu, 241Am and 244Cm in the leachates. Adsorption of the actinides on the wall of the leach vessel was recognized in all cases. Leaching behavior of the measured radionuclides were evaluated by considering mass balance of the radionuclides which were leached.
Correlation of Laboratory and Stripa Field Leaching Studies
Authors: Zoitos B. K. , Clark D. E. , Lodding A. R. , Wicks G. G.
Published: March 2011

A variety of surface sensitive techniques has been used to assess surface layers formed on SRL 165 waste glass specimens from the Stripa burial study and from a laboratory study designed to simulate conditions of the Stripa environment. The laboratory study included static and slow flow tests carried out for periods up to 6 and 24 months, respectively. Comparisons of leached layers formed in the two studies are based upon secondary ion mass spectrometry (SIMS), Fourier transform infrared reflection spectroscopy (FTIRRS), and scanning electron microscopy-electron microprobe (SEM-EMP) analysis.

Results demonstrate that surface layers having similar trends in elemental profiles were developed in both lab and field tests. It was also found that both sets of samples showed similar changes in FTIRR spectra. One significant difference between the lab and field samples was that surface alteration, as indicated by changes in FTIRR spectra and leached layer thickness (from SIMS), occurred more rapidly in the lab tests.
Long Term Crystallization Behavior of Glasses at Temperatures T < Tg
Authors: Stalios A. D. , De Batist R. , Van Iseghem P.
Published: March 2011

Boulos et al. [1], derived a mathematical expression predicting the minimum time needed for a glassy system to experience fractional crystallization, not exceeding a few volume percent at temperatures lower than the glass transition temperature, T. The range of applicability of this expression is extended to include crystallization processes governed by either homogeneous or heterogeneous nucleation and by diffusion controlled one-, two-, and three-dimensional crystal growth. This study demonstrates that the Boulos et al. expression is fairly independent of the nucleation, growth habit and dimensionality of the crystallization process. Moreover, the inherent theoretical as well as experimental limitations of the technique are reviewed and discussed.

The calculation for evaluating this minimum time limit has been applied for an alkali ferrisilicate alpha-waste reference glass. It is found that, for this system, a barely observable crystallized volume fraction (less than 5 % vol) will be reached at 25°C only after storage for more than 10 years. This time period is certainly beyond the times to be considered for evaluations of geological disposal. In addition some preliminary calculations of the minimum time limit for two types of borosilicate high level waste glass forms (HLW) are presented. These indicate safe time limits of the order of 10–100 years at 450°C, suggesting that crystallization effects cannot be ignored if the assumptions made in the calculations are valid.
Thermochemical Comparison of the Systems Re-O and Tc-O
Authors: Migge H.
Published: March 2011

Technetium is a hazardous fission product with a long half-life. In vitrification of nuclear waste, technetium tends to be lost substantially by evaporation [1], and the formation of gaseous Tc oxides is assumed to be the reason. Reliable thermochemical treatment of the problem is difficult, since data on the Tc-O system are surprisingly scarce [2]. Therefore, the system Re-O is treated for comparison. Key thermodynamic data for the condensed rhenium oxides exist [3,4,5] as well as measurements on the sublimation and the evaporation of the oxides [6–11]. Consistency of the different data is investigated by assessing the sublimation data of solid Re2O7, using them to calculate other sublimation equilibria and to compare the results with published measurements. Then a predominance area diagram is constructed and discussed with respect to the pressures of the gaseous oxides and their dependence on the temperature, oxygen partial pressure, and condensed oxide phase present. Predominance area diagrams of the Tc-O system are calculated and critically discussed. Owing to the small amout of available data, the possible existence of solid TcO3 is discussed. Comparison with the system Re-O is used to clarify, where further investigations need to be done.
Leaching Studies of Synroc Crystalline Ceramic Waste Forms
Authors: Solomaha A. G. , Matzkeb Hj.
Published: March 2011

The leaching performance of pressureless sintered SYNROC crystalline ceramic waste forms containing simulated high-level radioactive waste has been evaluated under different leach conditions, i.e. in deionized water and in a simulated brine (Q-brine) at different leach temperatures. The leach solutions were analyzed using inductively coupled plasma and atomic absorption spectrometry (ICPS and AAS) to determine the concentrations of the simulated waste elements and the matrix components released into the leachants. The leach rates of Ba and Ca were in the range of 0.1 to 0.02 g/(m2.d) after one week of leaching in deionized water at 150 °C. No significant difference in the leach behaviour of SYNROC was observed in distilled water and in simulated brine. The leached surfaces of SYNROC were characterized using Rutherford backscattering spectrometry (RBS), secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM) and elastic recoil detection analysis (ERDA). RBS and SIMS analyses revealed the existence of near-surface layers enriched in Ti and depleted in Ba and Ca. Elastic recoil detection analysis showed the existance of hydrated surface layers on the leached SYNROC which were much thinner than those observed in parallel work with borosilicate waste glasses. Radiation damage produced by ion implantation increased the otherwise very-small leach rates of SYNROC. At high damage levels, SYNROC was shown to become amorphous (metamict).
Alpha-Decay Damage and Annealing Effects in Natural Pyrochlores: Analogues for Long-Term Radiation Damage Effects in Actinide, Pyrochlore, Structure Types
Authors: Lumpkin G. R. , Ewing R. C.
Published: March 2011

Cubic pyrochlore structure types, A2-mB2O6(O, OH, F) i-n*pH2O, and their derivatives (e.g., monoclinic zirconolite) are important actinide-bearing phases in polyphase, ceramic waste forms (e.g., SYNROC). These waste form phases may typically accumulate alpha-decay doses of 1025 alpha-events/m3 in 1, 000 years or 1026alpha-events/m3 in one million years (i.e., for SYNROC with 20 wt. % HLW). Natural pyrochlores have calculated doses ranging from 1024 to 1027 alpha-events/m3 (= 0.02 to 50 dpa) which have accumulated over ten to a thousand million years. Actinide doping experiments typically reach doses of 1025 alpha-events/m3over periods of several years. Detailed x-ray diffraction analysis of natural samples reveals that the alpha-decay dose at which there is an initial loss of crystallinity (i.e., transition from crystalline to the aperiodic, metamict state as a result of alpha-decay damage) increases as a function of the geologic age of the sample. The increase in the calculated alpha-decay dose which is associated with a specific degree of damage (e.g., loss of x-ray diffraction intensity) is attributed to annealing of isolated alpha-recoil tracks back to the original, crystalline structure. Based on a model of gradual track fading, the alpha-recoil tracks in natural pyrochlores have mean lives on the order of 108 years. In contrast, minerals which remain crystalline (e.g., uraninite, UO2) despite doses of over 1027 alpha-events/m3 have mean alpha-recoil track lives of approximately 104 years. This demonstrates that the microstructure of alpha-decay damaged materials depends not only on the total alpha-event dose, but also on the annealing kinetics of alpha-recoil track fading. Therefore, the prediction of the long-term performance and final state of crystalline phases in ceramic nuclear waste forms requires the determination of alpha-recoil damage annealing as a function of time and temperature.
Leaching of Whole, Defected Used Candu™ Fuel Elements in Saline Solutions Under Argon Pressure
Authors: Stroes-Gascoyne S. , Johnson L. H. , Tait J. C. , Sellinger D. M.
Published: March 2011

In the context of the Canadian Nuclear Fuel Waste Management Program, experiments were performed in which whole, intentionally defected used CANDU™ fuel elements were exposed to deoxygenated saline solutions at 100°C for 484 days. Results suggest that both 90Sr and 99Tc are preferentially released from grain boundaries and that 85Kr release is a good measure of the extent of grain-boundary dissolution. Severe grain-boundary attack in particular areas of the fuel is also evident from scanning electron microscope observations. It is hypothesized that such localized attack is related to fuel porosity. Because of its poor corrosion performance in saline solutions, the Zircaloy sheath cannot be considered as a radionuclide release barrier.
Leaching of Used Candu™ Fuel in the Presence of Clay, Titanium and Granite Rock
Authors: Tait John C. , Stroes-Gascoyne Simcha , Porth Robert J. , Wood Don , Heimann Robert B.
Published: March 2011

Dissolution experiments have been performed at 95 or 100°C on used fuel in the presence of various components of a disposal system: granite rock, clay (Na-montmorillonite, illite), container (titanium), and two groundwaters with different ionic strengths (0.0015, 0.28). The results showed that Cs and Sr release to solution is highest in the high-ionic-strength groundwater and that clay type is less important in determining short-term release from the fuel. It also appears that after an initial release period lasting about 10 to 20 days, radionuclide release from the fuel to solution slows considerably. Cs was found to sorb more effectively than Sr on illite and montmoril-lonite, while Sr sorbed more effectively than Cs on the granite.
Localized Corrosion and Stress Corrosion Cracking of Candidate Materials for High-Level Radioactive Waste Disposal Containers in U.S.: A Critical Literature Review
Authors: Farmer Joseph C. , Daniel McCright R.
Published: March 2011

Three iron-based to nickel-based austenitic alloys and three copper-based alloys are being considered in the United States of America as candidate materials for the fabrication of high-level radioactive waste containers. The austenitic alloys are Types 304L and 316L stainless steels as well as the high-nickel material Alloy 825. The copper-based alloys are CDA 102 (oxygen-free copper), CDA 613 (Cu-7A1), and CDA 715 (Cu-3ONi). Waste in the forms of spent fuel assemblies from reactors and borosilicate glass will be sent to a proposed repository at Yucca Mountain, Nevada. The decay of radionuclides will result in the generation of substantial heat and in gamma radiation.
The Long-Term Prediction of Corrosion of Stainless Steel Nuclear Waste Canisters
Authors: Sharland S. M. , Newton C. J.
Published: March 2011

In this paper, we describe the preliminary stages of the development of a mathematical model of the evolution of the solution chemistry within a corroding crevice on passive stainless steel. It is based on a formulation by Oldfield and Sutton [1], but models the physical and chemical processes which determine the crevice solution in a more rigorous manner. The model will eventually be used to assess whether a ‘critical solution composition’, which results in the depassivation of the crevice and the onset of localised corrosion, is attainable for a range of repository conditions, steel types and canister designs etc. We also describe experiments that provide input data in the form of passive currents for this model. Preliminary sensitivity tests with the model have indicated a need for accurate thermodynamic data for the chemical equilibria constants (particularly those for the chromium reactions). These tests also suggest that there are certain critical relationships between various parameters in the system (such as crevice dimensions, the composition of solution outside the crevice and the passive current) that mark different behaviour in the evolution of the solution composition. Further experiments will be performed, as part of this work, both to validate the predictions of the model and to determine whether the predicted compositions of the crevice solutions are sufficiently aggressive to initiate crevice corrosion.
Corrosion Induced Hydrogen Evolution on High Level Waste Overpack Materials in Synthetic Groundwaters and Chloride Solutions
Authors: Simpson J. P. , Schenk R.
Published: March 2011

Hydrogen evolution from anoxic corrosion of cast steel overpacks in high-level waste repositories is an important issue for design if, as has been estimated, the hydrogen is prevented from escaping by diffusion by a low permeability compacted bentonite backfill.

Evaluation of the corrosion results showed three basic types of corrosion behaviour: general corrosion with oxide layer formation, unstable corrosion behaviour with pitting or macro-element formation and stable passive behaviour.

Cast steel containers under Swiss repository conditions are expected to suffer general corrosion with oxide layer formation. This behaviour gives the highest long term corrosion rates (2–5 μm/a) without local attack, above the 0.03–0.8 μm/a tolerated for hydrogen escape by diffusion but below the 20 μm/a assumed for overpack design.
Calculation of the Radiolytic Gas Production in Cemented Waste
Authors: Offermann P.
Published: March 2011

Hydrogen production by radiolysis of water in cement waste forms has to be limited due to safety requirements. Specific generation rates (g-values) are derived from data obtained in laboratory scale experiments and measurements on 200 1 drums containing real waste. To interpret the data model calculations are carried out including those for PH, dose rate, nitrate concentration and diffusion. An OH depleting reaction is added to the radiolytical reaction mechanism of water to model the hydrogen production rate observed for γ-irradiated cement.
Degradation and Material Transport for Thin Plates of Cement Pastes
Authors: Nilsson Karen , Brodersen K.
Published: March 2011

A ‘thin-plate’ technique, which is well suited for laboratory studies on cements, has been used in equilibrium experiments aimed at studying material transport between concretes of different composition. The extent of material transport is small, but there appear to be a movement of calcium towards thin plates containing excess silica fume, where supposedly the pozzolanic reaction takes place, an aspect which can be of interest for crack-healing of cements. A model concerned with crack healing of cement is discussed. Preliminary data have been obtained in a study where thin plates have been employed to investigate the effect of leaching on the microstructure of cements using the technique of Small Angle Neutron Scattering (SANS).
Physical Properties and Leachability of MLW Stream Containing Cr, Ni and Cd Immobilized in a Cement Matrix
Authors: Zamorani E. , Sheikh I. A. , Della Rossa M. , Serrini G.
Published: March 2011

Cement samples containing variable amounts of Cr(III) or Ni(II) or Cd(II) as chloride admixtures present in a MLW stream from reprocessing of spent fuel were prepared under established procedure. Due to the high pH generated in the cement clinker hydration, respective metal hydroxides are formed and improve the physical characteristics of the cement matrix. An increase in the value of the compressive strength was observed when about 7% of the above elements were blended in cement. The increase depends on the nature of the element in the sequence Cr >Ni >Cd.

The leach tests confirm the formation of insoluble hydroxide presenting a low concentration in the leachate corresponding to 0.05, 0.004 and 0.052 mg.L−1 for Cr, Ni and Cd, respectively. On the other hand, the hydro-lyzed chloride ions seem to react with calcium with consequent increased degradation of the cement matrix.
Freshwater Alteration of Basaltic Glass, Hanauma Bay, Oahu, Hawaii: A Natural Analogue for the Alteration of Borosilicate Glass in Fresh Water
Authors: Cowan Rachel , Ewing Rodney C.
Published: March 2011

Alteration (fresh water) products (palagonite and zeolites) of a 12, 000–28, 000 year old basaltic glass from Hanauma Bay, Hawaii, were examined by electron microprobe analysis, scanning electron microscopy, and X-ray diffraction analysis. The palagonite, 0 to 300 microns thick, is depleted in Si, Al, Ca, Na, and K and enriched in Ti and Fe. Ca-rich zeolites are associated with palagonite that is slightly more depleted in Ca; all samples contain zeolites and low Al-palagonite. The rate of palagonitization (0.002–0.005 volume percent/year) is less than the experimentally predicted rate for basalt glasses due to the episodic presence of the percolating groundwater. The Si/AI ratio of the zeolites decreases with increasing pH of the groundwater as it passes through the vertical section. Zeolite paragenesis is (first to last): analcime (NaAlSi2O 6·H2O), phillipsite [(1/2 Ca, Na, K)(Al3Si5O16).6H2O], chabazite (CaAl2SiO16.6H2O).
Performance Assessment of a High-Level-Waste Repository in Clay
Authors: Marivoet Jan L. , Volckaert Geert , Bonne Arnold A.
Published: March 2011

Performance assessment studies have been undertaken on the geological disposal of high-level waste in a clay layer in the framework of the CEC project PAGIS. The methodology applied consists of two consecutive steps : a scenario and a consequence analysis. The scenario analysis has indicated that scenarios of normal evolution, of human intrusion, of climatic change, of secondary glaciation effects and of faulting should be evaluated. For the consequence analysis as well deterministic “best estimate” as stochastic calculations, including uncertainty, risk and sensitivity analyses, have been elaborated.

The calculations performed show that most radionuclides decay to negligible levels within the first fewjneters of the clay barrier. Just a few radionuclides, 99Tc, 135Cs and 237Np with its daughter nuclides 233U and 229Th can eventually reach the biosphere. The maximum dose rates arising from the geological disposal of HLW, as evaluated by the “best-estimate” approach are about 10−11 Sv/y for river pathways. If the sinking of a water well into the 150 m deep aquifer layer in the vicinity of the repository is considered together with a climatic change, the maximum calculated dose rate rises to a value of 3×10−7 Sv/y. The maximum dose rates evaluated by stochastic calculations are about one order of magnitude higher due to the considerable uncertainties in the model parameters. In the case of the Boom clay the estimated consequences of a fault scenario are of the same order of magnitude as the results obtained for the normal evolution scenario. The maximum risk is estimated from the results obtained through stochastic calculations to be about 5×10−8 per year. The sensitivity analysis has shown that the effective thickness of the clay layer, the retention factors of Tc, Cs and Np, and the Darcy velocity in the aquifer are parameters which strongly influence the calculated dose rates.
Alteration of Basaltic Glass in Iceland as a Natural Analogue for Nuclear Waste Glasses: Geochemical Modelling with DISSOL
Authors: Crovisier J. L. , Advocat T. , Petit J. C. , Fritz B.
Published: March 2011

The long term geochemical consequences of basaltic glass dissolution in fresh water at 0°C have been calculated with the computer code DISSOL. The clay minerals were represented by an ideal solid solution model (CISSFIT) able to describe variations in chemical composition of a clay phase in response to variations of the solution chemistry. The predicted mineral phases were iron hydroxides followed by kaolinite, TOT clays, chabazite and cli-noptilolite. These results are in reasonably good agreement with experimental results and observations of altered subglacial hyaloclastites from Iceland. The formation of secondary products are mainly controlled by thermodynamic constraints. Kinetic effects, such as diffusion in the near glass surface are not important.
The Brine Migration Test - A Nuclear Waste Repository Simulation Experiment at the Asse Salt Mine - Federal Republic of Germany
Authors: Rothfuchs T. , Wieczorek K. , Mcnulty E. G. , Gupta S. K. , Clark D.
Published: March 2011

A joint US/FRG nuclear waste repository simulation experiment was performed at the Asse Salt Mine in the Federal Republic of Germany (FRG). The High Level Waste (HLW) disposal in boreholes was simulated by the simultaneous emplacement of electrical heaters and cobalt-60 sources at four individual test sites located in a special underground test room at the 800 m-level.

In order to resolve the issues of rock mass/waste package interaction the temperature field, brine migration into the heater boreholes, borehole gas pressure and composition, and rock mass stresses and displacements were monitored during the test. In order to validate computer code predictions the acquired data were compared to calculational results. Corrosion specimens remained in the heater boreholes during the course of the experiment and were afterwards examined.
A Channeling Experiment to Study Flow and Transport in Natural Fractures
Authors: Abelin Harald , Birgersson Lars , Ågren Thomas , Neretnieks Ivars
Published: March 2011

Model calculations show that channeling may have a detrimental effect on radionuclide transport because fast channels may carry some of the mass of the radionuclides considerably faster than the average flow would and may give this portion considerably less time to decay. Channeling further aggravates the retardation of the sorbing nuclides because less surface area is available for sorption in a channel within a fracture than if the whole fracture is exposed to the flowing water. An ongoing experiment in the Stripa mine aims at studying some aspects of channeling. A special packer of a new design is used. Preliminary results show that there is uneven flow in the fractures which indicates channeling.
Possible Complex Formation of Actinides with Organic Matter and Phosphate in Deep Groundwaters. Speciation Calculations and Data Evaluation
Authors: Aidersson Karin
Published: March 2011

Calculations of solubility and speciation of U, Th, Ip, Pu, and An in a deep groundwater, containing humlc acid and phosphate have been performed, using the PHRBEQB equilibrium code. Where equilibrium data are missing, estimates have been made.

Some of the studied complexes and solid phases may be of importance to the actinide behaviour in deep groundwaters, eg AmPO4(s) and several aqueous phosphate species and also humic acid for trivalent actinides.
Characterisation of Natural Colloids in a Shallow Glacial Aquifer and Their Radionuclide Loading
Authors: Longworth G. , Wilkins M. A. , Ivanovich M.
Published: March 2011

This paper presents the results of a physical, chemical and actinide characterisation of the groundwater in a shallow glacial sand aquifer, in which tracer tests aie currently being conducted by t lu- British Geological Survey (BGS).

Uranium Series disequilibrium measurements have been used to determine the partition of natural actinide activities betueen the particulate, colloid and solution phases of the groundwnters from sevpral geologically dissimilar sites. The activity fractions associated with the colloid phase were found to be (0.1–0.52) for uranium and (1–52) for thorium.

Scanning electron microscopy analysis yielded values of 103−101 particles/litre for the colloid concentration. Mean mobilities for the colloids determined by electrophoresis were in the range -(1–2) × 10−6 m2S−1v−1.
The Influence of Microbial Activity on the Movement of Uranium at Osamu Utsumi Mine, Poços De Caldas, Brazil
Authors: West Julia M , Mckinley Ian G , Vialta Airton
Published: March 2011

The Osamu Utsumi uranium mine, Poços de Caldas, Brazil is a roll front uranium deposit currently under investigation in an international natural analogue project involving Brazil, Sweden, Switzerland, the United Kingdom and the United States. This is a multi-disciplinary study (see the paper at this meeting by Smellie et al (1)), one component of which is an examination of the movement of natural series radionuclides across redox fronts. The processes at such fronts are analogous to those which could occur at radiolytic redox fronts found in the near- or far-field of deep repositories for HLW or spent fuel. Microbiological investigations have been carried out to determine the presence and activity of microbes known to be important in the uranium biogeochemical cycle; to define their importance in the movement of uranium across the redox front and to assess the significance of these observations to relevant safety assessment issues. This paper will summarise the results of these findings.
Colloid Investigations in the ‘Pocos De Caldas” Natural Analogue Project
Authors: Miekeley Norbert , Jesus H. C. , Silveira C.L.P. , Kuechler I. L.
Published: March 2011

Preliminary data are presented on colloids in groundwaters from two radioactive ore deposits (C-09 mine and Morro do Ferro) situated in the Pocos de Caldas plateau in the state of Minas Gerais, Brazil. Ultrafiltration with flat membranes of different nominal MW cutt-off limits (450 nm to 1, 000 dalton) was used to prepare colloid concentrates from 40 to 50 1 water samples. The colloidal retentates as well as the original groundwaters were analysed for relevant ‘major’ and trace element concentrations and for DOC. Distribution characteristics of elements like Si, Fe, Mn, DOC, U, Th and rare earths between colloidal phases and ‘solution’ as result of different groundwater chemistry will be discussed.
Modeling of Nickel Sorption and Speciation in a Natural Sediment-Groundwater System
Authors: Koss Volker
Published: March 2011

The sorption of nickel in 15 natural sediment-groundwater systems from Gor leben has been modeled using a simple surface complexation model. An apparent constant of nickel sorption has been computed taking into account the bulk cation exchange capacity of the sediment, the analytical composition of the groundwater and experimental sorption data obtained from related systems. The method of determining the prevailing surface complex has been described in detail, using changing properties of the natural systems. Competition from natural groundwater components for sorption sites has been taken into account.

The main parameters governing nickel sorption are cation exchange capacity of the sediment, together with ionic strength and pH of the groundwater. The model describes the influence of citrate on sorption and allows one to compare the varying sorption data of similar systems.

Computations were performed using the geochemical code MINEQL.
Investigation into the Solubilities. Sorption and Migration Behaviour of Agl. CsNO3, Na2U2O7. NpO2OH and Pu(OH)4 in Near-Field-Systems
Authors: Marx G. , Keiling Ch.
Published: March 2011

Results are presented from investigations into the solubilities, sorption and migration behaviour of Agi. CsNO3, Na2U2O7. NpO2hOH and Pu(OH)4 in the near-field environment of an ILW repository located in a salt dome. Emphasis is placed on the synthetic complexing organics DBP, TBP, EDTA, citrate and oxalate, which influence the leaching and retardation of the above elements. Leachate data from real ILW forms, obtained from saturated salt solutions, have been compared with the results of the synthetic systems described.