bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comparative Case Study of the U.S.-Philippines Alliance in the 1990s and the U.S.-South Korea Alliance between 1998 and 2008
Authors: Park Jae-Jeok
Published: May 2011

This article compares the discontinuation of the U.S.-Philippines alliance between 1992 and 1999 with the continuation of the U.S.-South Korea alliance between 1998 and 2008. Whether either country reconciled with the U.S. to accommodate the latter's core military strategy was a primary determining factor of the different outcomes.
The Left Front's 2009 Lok Sabha Poll Debacle in West Bengal, India
Authors: Chakrabarty Bidyut
Published: May 2011

This paper demonstrates that the Left Front is no longer unassailable in West Bengal, after three decades of rule. It identifies the specific reasons for the Left Front electoral debacle in the 2009 Lok Sabha elections. The paper also argues that the Left Front is caught between the contrasting imperatives of adapting to changing socioeconomic conditions in liberalizing India, while concurrently attempting to remain true to its traditional communist ideology and support base in a globalized world.
Sino-Vietnamese Relations in the Early Twenty-first Century
Authors: Cheng Joseph Y. S.
Published: May 2011

Sino-Vietnamese relations since the mid-1980s represent an interesting case for studying how economic considerations can transform two conflicting states into peaceful accommodation in an asymmetrical bilateral relationship. The Chinese leadership's pursuit of a peaceful international environment for economic development has been followed by its Vietnamese counterpart.
Plasmonics: Electromagnetic Energy Transfer and Switching in Nanoparticle Chain-Arrays Below the Diffraction Limit
Authors: Brongersma Mark L. , Hartman John W. , Atwater Harry H.
Published: May 2011

A model is given for the transport of electromagnetic energy through structures that consist of chains of closely spaced metal nanoparticles. This transport relies on the near-field electrodynamic interaction between metal particles that sets up coupled plasmon modes. The model predicts that the propagation is coherent and the group velocities can exceed typical saturation velocities of electrons in semiconductors (≈ 105 m/s). Furthermore, it is shown that in these structures propagation of energy around sharp corners (bending radius << the wavelength of visible light) is possible at high efficiency. This efficiency is a strong function of the frequency and polarization direction of the plasmon mode. The operation of a plasmon switch is modeled, in which plasmon waves can be switched or modulated. Finally, suggestions are given for the choice of metal particle and host material.
Artificial Atoms of Silicon
Authors: Holmes Justin D. , Ziegler Kirk J. , Johnston Keith P. , Doty R. Chris , Korgel Brian A.
Published: May 2011

Size-monodisperse, stable 15 Å diameter silicon nanocrystals were synthesized in significant quantities using supercritical octanol as a capping ligand. The silicon nanocrystals exhibit an indirect band gap with discrete electronic transitions in the absorbance and photoluminescence excitation (PLE) spectra. The octanol-capped clusters show efficient blue band-edge photoemission with a luminescence quantum yield of 23 % at room temperature.
From Langmuir-Blodgett Films to Electroluminescent Devices with an Amphiphilic Phenyl-Ethynylene Oligomer
Authors: Arias-Marin E. , Arnault J.C. , Maillou T. , Guillon D. , Moigne J. Le , Geffroy B. , Lorin A. , Nunzi J.M. , Rosilio A.
Published: May 2011

New rigid rods amphiphilic molecules based on phenyl ethynylenes oligomers with hydrophilic side chains were synthesized by step by step method. The two most interesting products, the pentamer and the heptamer are enough amphiphilic to give stable Langmuir films that are able to be deposited as LB film on substrates as hydro-philic glass, ITO or hydrophilic silicon. A good transfer ratio of 1 is observed only by lifting, which suggests a Z type deposited film. A multilayer deposition can be carried out to 36 layers. The well structured films of 3.7 nm thick which are observed by X ray reflectivity suggest a rearragement in Y–type bilayer. By AFM, the observed irregular surface with steps of 3.7 and 1.8 nm high or multiples is coherent with a self-rearrangement of the single deposited layer to a double layer during the drying phase. The heptamer and pentamer show large stokes-shifts with a high photoluminescence emission peak at 516 and 504 nm respectively. LED properties were demonstrated using the ITO/oligoPY/ LiF-Al sandwich yielding photon emission at 516 nm for the heptamer. The electroluminescent device yields in the range of 10−3%. The demonstration of electroluminescence in a LB film of molecules aligned parallel to the substrate is very interesting because it confirms the possibility to tailor conduction and emission properties of the devices using a layer by layer deposition technique.
Photo-Induced Properties of Liquid Crystal Molecules on Alternately Assembled Charged Azobenzene Dyes and Polyelectrolyte Films Using Attenuated Total Reflection Method
Authors: Baba Akira , Kato Takashi , Ishikawa Jun , Kaneko Futao , Shinbo Kazunari , Kato Keizo , Advincula Rigoberto
Published: May 2011

In this report, we describe the photo-induced in-plane alignment of nematic liquid crystal (LC) molecules, 5CB, in a hybrid cell with alternate self-assembled films of low-molecular weight azobenzene dye and polyelectrolyte on gold electrodes using the attenuated total reflection (ATR) measurement method. The molecular self-assembly process was also investigated by the ATR method. Reflectivities due to excitations of the surface plasmon polariton (SPP) were observed in the ATR properties of the LC cell. In-plane switching of the LC molecules adjacent to the aligning layer was evaluated from the ATR curves after irradiation of linearly polarized visible light to the LC cell. The sensitivity of the ATR method gives information on the alignment, tilt angle, and extent of LC reorientation in the bulk. Thus, the importance of using the molecular self-assembly processes of individual polyion-dye pairs for fabrication of new photo-aligning layers is emphasized.
Characterization of Polymer Light Emitting Diodes Fabricated by Ionically Self-Assembled Monolayer Technique
Authors: Marciu D. , Miller M. B. , Heflin J. R. , Murray M. A. , Ritter A. L. , Neyman P. J. , Graupner W. , Wang H. , Gibson H. W. , Davis R. M.
Published: May 2011

Ionically self-assembled monolayer (ISAM) films are a recently developed class of materials that allows detailed structural and thickness control at the sub-nanometer level combined with ease of manufacturing and low cost. The ISAM fabrication method simply involves the dipping of a charged substrate alternately into polycationic and polyanionic aqueous solutions at room temperatures. Importantly, the ISAM technique yields exceptionally homogeneous, large area films with excellent control of total film thickness. We describe detailed studies of ISAM light emitting diodes incorporating poly(para-phenylene vinylene) (PPV) as the light emitting polymer. The individual thickness of each monolayer and the interpenetration of adjacent layers can be precisely controlled through the parameters of the electrolyte solutions. The effects of the pH and ionic strength of the immersion solutions, the total film thickness, and the PPV thermal conversion parameters on the photoluminescence and electroluminescence yields have been systematically studied. The ISAM process also allows the advantage of depositing well-defined thicknesses of separate polymers at the indium tin oxide and the aluminum electrode interfaces.
Investigation of Photoinduced Charge Transfer in Composites of a Novel Precursor PPV Polymer and Fullerenes
Authors: Brabec Christoph J. , Cravino Antonio , Zerza Gerald , Padinger Franz , Sariciftci N. Serdar , Kiebooms Raphael , Vanderzande Dirk , Hummelen Jan C.
Published: May 2011

Homogenous blends of a processable methanofullerene, [6,6]-Phenyl C61 - butyric acid methyl ester (PCBM), with poly (p-phenylene vinylene) (PPV) made from a novel nonionic precursor route were investigated by optical spectroscopy and by photocurrent measurements. The conversion process of the precursor polymer to the PPV in the blends with PCBM was monitored by IR absorption. In composites of PPV/PCBM strong quenching of the PPV luminescence was observed. LESR (light induced electron spin resonance) and PIA (photoinduced absorption) studies confirmed the occurrence of photoinduced electron transfer from the PPV to PCBM. Photovoltaic devices made from PPV/PCBM blends showed monochromatic power conversion efficiencies of app. 0.3%. The spectral photocurrent was observed to follow the absorption profile of the PPV.
Highly Ordered Crystalline Thin Film Bilayers of Para-Hexaphenyl and C60 Grown by Hot Wall Epitaxy
Authors: Sitter Helmut , Matt Gebhard , Andreev Andrei Yu. , Brabec Christoph J. , Badt Dirk , Neugebauer Helmut , Sariciftci Niyazi S.
Published: May 2011

This work focuses on single - and bilayers of para - hexaphenyl (PHP) and C60 grown by Hot Wall Epitaxy. A detailed study of the growth process was performed on glass, ITO and (001)- oriented cleaved mica substrates. The ordering of the layers was investigated by X-ray diffraction, showing clear diffraction peaks for layers grown on mica. The PHP layers grown on mica show high optical anisotropy (dichroic ratios up to 14 in emission) according to the polarization dependent photoluminescence experiments. The highly ordered structure is also reflected in the surface morphology of the layer as observed by atomic force microscopy. The epitaxial growth on mica is mirrored by the main alignment of the surface structure to the orientation of the mica substrate.
Synthesis and Characterization of New Polyaryleneethynylenes based on 3-Hexyl Multisubstituted Oligothiophene Blocks
Authors: Destri Silvia , Porzio William , Khotina Irina A. , Botta Chiara , Consonni Roberto
Published: May 2011

A series of new regioregular polyaryleneethynylene obtained by condensation of 3-hexyl multisubstituted oligothiophene derivatives with benzene and anthracene compounds were prepared. A complete NMR characterization of the starting monomers and model compounds lead to a deep investigation of the corresponding macromolecules. Both small and large molecules were optically characterized, the former, particularly when containing anthracene, moieties display noticeable photoluminescence quantum yield. In the polymers the photoluminescence quantum yield is lower than that of the starting molecules when anthracene is present, while the polymers containing benzene are more luminescent.
Luminescence Dynamics of Alq3-Based Multilayer Structures in Terms of HOMO and LUMO Energy Discontinuity
Authors: Fujita Shizuo , Nakazawa Tadahiro , Asano Mitsuru , Fujita Shigeo
Published: May 2011

Optical properties of organic multilayer structures with type-I and type-II energy lineups with respect to the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels were investigated and compared. The fast energy transfer followed by carrier confinement in the material with lower HOMO-LUMO energy difference was proved for the structures with type-I energy lineup, while the tendency of separation of excited states, i.e., electrons and holes generated in the excited molecules, was demonstrated for those with type-II. These results indicate that the luminescence dynamics of organic multilayer structures are well discussed in terms of HOMO and LUMO energy lineups similarly to valence and conduction band energies in inorganic semiconductors.
Synthesis and Application of Chiral Conjugated Polymers and Dendrimers
Authors: Pu Lin
Published: May 2011

1,1'-Binaphthyl-based chiral polymers and dendrimers have been synthesized and their potential applications have been explored. These materials have shown a variety of interesting properties such as electroluminescence, optical nonlinearity, enantioselective catalysis and chiral sensing.
Applications of Organic and Inorganic Optical Thin Films in Telecommunications
Authors: Lipscomb G. F. , Lam J. , Stiller M. , Schroeter P.
Published: May 2011

The demands of exponentially growing Internet traffic, coupled with the advent of Dense Wavelength Division Multiplexing (DWDM) fiber optic systems to meet those demands, have triggered a revolution in the telecommunications industry. In the three short years of deployment, DWDM performance has accelerated dramatically. Channel counts have grown from 4 to 80, with 170 announced, and channel spacings have shrunk from 400 GHz to 50 GHz. Practical systems that put 1 TeraBit/sec. of information on a fiber are now on the horizon. This dramatic increase has been built upon, and has driven, improvements in fiber optic component technology, which has in turn driven improvements in photonic materials. The next generation of systems for the “all optical network” will require higher performance components coupled with dramatically lower costs. One approach to achieve significantly lower costs per function is to employ Planar Lightwave Circuits (PLC) to integrate multiple optical functions on a single substrate leading to a single package. In this way multiple components can be fabricated and interconnected at once, significantly reducing both the manufacturing and the packaging/assembly costs. The manufacture of PLCs, however, places demanding requirements on materials, design and fabrication processes. Parameters such as index of refraction, absorption and birefringence must be tightly controlled. PLCs have been made using inorganic crystals, such as Lithium Niobate, oxide glasses or polymers on silicon substrates and semi-conductor materials, such as Indium Phosphide (InP). All except InP are commercially available. In this paper we give an overview of the applications of PLCs in DWDM fiber optic transmission systems and discuss how material's requirements flow down from end-use requirements. The specific example of the use of polymer based thermo-optic switches for reconfigurable Optical Add/Drop Multiplexer (OADM) applications is discussed.
Requirements on Organic Electro-Optic Devices for Aerospace Applications
Authors: Anderson W. W. , Ermer S. P. , Eck T. E. Van , Girton D. G. , Taylor R. E.
Published: May 2011

Terrestrial digital photonic technology development will not satisfy all of the aerospace requirements since RF links are often required. Organic electro-optic devices are readily adaptable to RF functions into the 100 GHz and above frequency range. In addition to lossless links, they can be utilized for RF signal processing functions such as mixing, efficient harmonic generation and filtering. Devices can be densely packed with negligible cross talk.

In addition to the well known survivability requirements for space born applications (lifetime, reliability, thermal, shock, vibration and radiation hardness), issues of weight and power become dominant. Organic devices based on thin film technologies have an obvious potential advantage with respect to weight. However, integration with other optical and/or electronic components needs to be considered since connectors often dominated size and weight. Performance (when translated back into the electronic domain) scales as the optical power and device sensitivity squared. Thus, advances in device sensitivity can be nullified by increases in optical loss.
Experimental Study and Modeling of the Radium Sorption onto Goethite
Authors: Bassot Sylvain , Mallet Caroline , Stammose Denise
Published: May 2011

Iron oxyhydroxides play a significant role in radium behavior in uranium mill tailings. Although they are present at trace level (less than 1% in mass), iron oxyhydroxides are responsible of the retention of significant amounts of radium in these residues. A part of these oxyhydroxides is present as amorphous or ill-crystallized forms, the other part corresponds to crystalline iron oxyhydroxides like goethite.

In this paper, we present data concerning radium sorption on a well-characterized goethite (α-FeOOH). Batch experiments have been performed and the influence of different parameters such as contact time, pH and electrolyte concentration of the solution has been examined. The sorption equilibrium was obtained after a contact time of 1 hour. In sodium perchlorate medium, the amount of sorbed radium reaches a maximum for pH higher than 8 and no significant influence of sodium concentration was observed. However, the calcium concentration greatly influences the radium sorption: the greater the calcium concentration, the less radium is sorbed. The kinetics of the radium desorption are slower than those of sorption: more than 30% of radium remains sorbed on goethite after 1 week of contact time.

Using the characteristics of the goethite surface (total number of sites, intrinsic acidity constants, intrinsic constants of calcium), modelling of the experimental data with inner sphere complexes gave satisfactory results. Two surface species involving radium can be formed (SORa+ and SORaOH). These sorption constants determined allow prediction of the radium sorption onto goethite in the chemical conditions of uranium mill tailings.
Pretreat: A Graphical User Interface-Based Spreadsheet Model for Hanford Tank Waste Pretreatment Processes
Authors: Yang Lietai , Pabalan Roberto , Jain Vijay
Published: May 2011

A spreadsheet model, PRETREAT, was developed for mass-balance calculations of pretreatment processes proposed for the immobilization of Hanford nuclear wastes. In PRETREAT, a graphical user interface is implemented for convenient navigation through the large number of worksheets used in the model, for data input, modification of process parameters, and viewing model results. PRETREAT can be used to estimate radionuclide and chemical species concentrations in the waste streams at each stage of the pretreatment flowsheet, and to help in assessments of potential radiological, chemical, and criticality hazards and in identification of mitigation strategies. The model can also be used to evaluate the sensitivity of model results to uncertainties in model parameters such as decontamination or separation factors.
Studies of sorption of Th and Np on UO2 and TiO2
Authors: Albinsson Yngve , Nilsson Hans , Jakobsson Anna-Maria
Published: May 2011

When designing an underground repository for spent nuclear fuel it is important to know if and to what extent Np and Pu are reduced. At the moment only Np has been studied, but further investigations with Pu are planned.

Np in the pentavalent state and Th in the tetravalent state (234Th, about 10−9 M) have been used to study the sorption onto TiO2 (no reduction is expected) and onto UO2 with different atmospheres (air, nitrogen and nitrogen and hydrogen at 5 MPa pressure), and with different Np- concentrations (about 10−12M, 239Np and 10−6 M,237Np).

Th is sorbed to a high extent at pH>3 on both TiO2 and UO2. The sorption increases 3 orders of magnitude over one pH-unit when log Ka (the distribution coefficient with respect to surface area) is plotted against pH.

The Np sorption on TiO2 is independent of the Np concentration and shows a slope of one when pH is plotted against log Ka. The higher sorption of Np onto UO2 compared with TiO2 indicates that Np is partially reduced even when it is in contact with air. No large differences can be observed for Np between the nitrogen and hydrogen-atmosphere, indicating that the absence of oxygen is the important factor for the reduction. The different Np concentrations had no great impact on the reduction/sorption on UO2.
Evidence of Heterogeneous Matrix Diffusion in Fractured Crystalline Rock in Laboratory Migration Experiments
Authors: Xu Shulan , Wörman Anders
Published: May 2011

The geostatistics of the main properties of transport in crystalline rock at Äspö Hard Rock Laboratory, Sweden have been determined experimentally, using a large number of samples, as a basis for the analysis of the effect of the uncertainty in rock heterogeneity on radionuclide migration in a single fracture. The auto-covariance functions were estimated for the porosity, effective diffusivity and adsorption characteristics, such as partition coefficient, kdand adsorption kinetics. The one-dimensional analytical solutions for the mean values of the temporal moments of the residence time probability density function (PDF) were derived by using the spectral method. The solutions were applied to the evaluation of migration experiments on granitic drill cores from the Äspö Hard Rock Laboratory. Fractures were created in drill cores by sawing and tritium was used as a non-sorbing tracer in several experiments in each drill core. By systematically varying the flow velocity, u, we could verify the non-linear influence of 1/u on the variance of the residence time PDF according to the theory. The effect of the uncertainty in the heterogeneous rock properties on the solute transport observed in the migration experiments corresponds fairly well to the theoretical effect using the auto-covariance functions.
Experimental Study of Nickel Solubility in Sulfidic Groundwater under Anoxic Conditions
Authors: Carlsson T. , Vuorinen U. , Kekki T. , Aalto H.
Published: May 2011

This paper presents the results from an experimental study of the nickel solubility in sulfidic groundwater under anoxic conditions. The waters used were natural groundwater from Olkiluoto and synthetic saline groundwater, to which sulfide had been added. Two sulfide concentrations, 3.1.10−6 M and 9.4.10−5 M, were used. The possible influence of ferrous iron on the nickel concentration was also studied by adding small amounts of iron chloride, which yielded ferrous iron concentrations of 1.8.10−5 M or less.

The initial nickel concentrations in the water samples were 1.0.10−6 M and 1.0.10−3 M. The nickel concentrations were determined using 63Ni and liquid scintillation counting. The duration of the experiments was 177 days.

The results for the waters differed markedly. The nickel concentration in the natural groundwater decreased in all samples to roughly 10% of the initial value.

The nickel concentration in the synthetic groundwater was found to decrease in those samples having initial sulfide and nickel concentrations of 9.4.10−5 M and 1.0.10−6 M, respectively. The nickel concentration was in this case reduced to about 1% of its initial value. For the other synthetic groundwater samples, the nickel concentration remained at its original initial level.

The variation of the ferrous iron concentration did not have any observable effect on the measured nickel concentrations.
Development of Zirconolite-based Glass-Ceramics for the Conditioning of Actinides
Authors: Loiseau P. , Caurant D. , Baffier N. , Mazerolles L. , Fillet C.
Published: May 2011

Zirconolite (CaZrTi2O7) based glass-ceramics designed for the specific immobilization of plutonium wastes or minor actinides (Np, Am, Cm) from high level radioactive wastes were investigated. To reach an efficient double containment, actinides must be preferentially located in the crystalline phase, which is homogeneously dispersed in a calcium aluminosilicate residual glass. Several heat treatments (between 950° and 1350°C) of a parent glass belonging to the SiO2-Al2O3-CaO system and containing TiO2 and ZrO2 were performed to prepare glass-ceramics. Trivalent minor actinides were simulated introducing Nd2O3 in the glass composition. Electron microscopy, X-ray diffraction (XRD) and thermal analysis have shown that devitrification processes in the bulk and on glass surface are different. They lead to the crystallization of zirconolite in the bulk and to a mixture of titanite (CaTiSiO5) and anorthite (CaAl2Si2O8) near the surface. For heat treatment temperatures greater than or equal to 1250°C, baddeleyite (m-ZrO2) crystals form at the expense of zirconolite in the bulk of glass-ceramics. XRD indicates that the order in zirconolite Ca/Zr planes increases with heating temperature. At the same time, extended defects density decreases.
Gadolinium Borosilicate Glass-Bonded Gd-Silicate Apatite: A Glass-Ceramic Nuclear Waste Form for Actinides
Authors: Zhao Donggao , Li Liyu , Davis L.L. , Weber W.J. , Ewing R.C.
Published: May 2011

A Gd-rich crystalline phase precipitated in a sodium gadolinium alumino-borosilicate glass during synthesis. The glass has a chemical composition of 45.4-31.1 wt% Gd2O3, 28.8-34.0 wt% SiO2, 10.8-14.0 wt% Na2O, 4.3-5.9 wt% Al2O3, and 10.8-14.9 wt% B2O3. Backscattered electron images revealed that the crystals are hexagonal, elongated, acicular, prismatic, skeletal or dendritic, tens of μm in size, some reaching 200 μm in length. Electron microprobe analysis confirmed that the crystals are chemically homogeneous and have a formula of NaGd9(SiO4)6O2 with minor B substitution for Si. The X-ray diffraction pattern of this phase is similar to that of lithium gadolinium silicate apatite. Thus, this hexagonal phase is a rare earth silicate with the apatite structure. We suggest that this Gd-silicate apatite in a Gd-borosilicate glass is a potential glass-ceramic nuclear waste form for actinide disposition. Am, Cm and other actinides can easily occupy the Gd-sites. The potential advantages of this glass-ceramic waste form include: 1) both the glass and apatite can be used to immobilize actinides, 2) silicate apatite is thermodynamically more stable than the glass, 3) borosilicate glass-bonded Gd-silicate apatite is easily fabricated, and 4) the Gd is an effective neutron absorber.
Apparent Solubility Limit of Nuclear Glass
Authors: Vernaz Étienne , Gin Stéphane
Published: May 2011

Most nuclear glass alteration models are based on a first-order kinetic law of the general type r = r0 (1–Csi/C*) or r = r0 (1–Q/K). It is generally assumed that the establishment of quasi steady-state concentrations in solution corresponds to an intrinsic glass solubility limit that may be expressed either in terms of the dissolved silicon concentration C* or as an ion activity product at saturation K. Experimental research over the last five years in France has shown that the quasi steady-state concentrations observed in solution do not correspond to a thermodynamic solubility limit with respect to the glass. This assertion is supported by a large body of experimental evidence that is discussed in this paper. The signification of the C* parameter is therefore reconsidered, and its implications on long-term behavior modeling are discussed.
Structural Effect of Pu Substitutions on the Zr-Site in Zirconolite
Authors: Begg B.D. , Day R.A. , Brownscombe A.
Published: May 2011

As the level of Pu4+ substituted on the Zr-site in CaZr1-xPuxTi2O7 zirconolite increased, from x=0.1 to 0.6, a series of structural transitions occurred from zirconolite-2M to zirconolite-4M and subsequently from zirconolite-4M to pyrochlore. The solid-solution limit for Pu4+ substituted on the Zr-site in zirconolite-2M was ~ 0.15 formula units. Zirconolite-4M was only stable over a narrow compositional range, centered about CaZr0.59Pu0.41Ti2O7, whilst the pyrochlore structure was stabilized with CaZr0.4Pu0.6Ti2O7 stoichiometry. The stability of the zirconolite polytypes is therefore sensitive to the average effective ionic size of the ions occupying the seven-coordinated Zr-site. The reduction in Pu from Pu4+ to Pu3+ destabilized the zirconolite-4M, producing a mixture of perovskite and possibly zirconolite-3T. The CaZr0.4Pu0.6Ti2O7 pyrochlore was also predominantly transformed to perovskite as a result of this reduction of Pu.
Durability of Zirconolite in Hydrothermal Fluids: Implications for Nuclear Waste Disposal
Authors: Gieré R. , Malmström J. , Reusser E. , Lumpkin G.R. , Düggelin M. , Mathys D. , Guggenheim R. , Günther D.
Published: May 2011

Synthetic zirconolite (CaZrTi2O7) doped with rare earth elements (REEs) and Hf has been subjected to corrosion tests in a closed system at elevated temperature and pressure in fluids with various compositions. Together with previous studies, the results indicate only a very weak corrosion below 250°C at a pressure of 50 MPa. Above that temperature and up to 500°C zirconolite suffers from relatively rapid corrosion and, depending on the fluid composition, it may be covered by various secondary phases. Above 500°C in Na-rich fluids, zirconolite is replaced by perovskiteand calzirtite (nominally CaTiO3 and Ca2r5Ti2O16, respectively), but theREEs and Hf (acting as actinide analogues and/or neutron absorbers) are almost quantitatively incorporated into the secondary phases. The breakdown of zirconolite and its replacement by other phases in the laboratory tests are comparable to reactions observed in natural systems. Additional experiments with U-doped zirconolite revealed differences in the behavior of the used actinide analogues (Nd, Ce, Gd)and U during corrosion. The results of this study, together with observations on natural samples, strongly support the use of zirconolite-based ceramic waste forms for actinide-rich wastes.
Effects of Cesium, Iodine and Strontium Ion Implantation on the Microstructure of Cubic Zirconia
Authors: Wang L.M. , Zhu S. , Wang S.X. , Ewing R.C.
Published: May 2011

Cesium, iodine and strontium ions have been implanted into yttria-stabilized cubic zirconia (YSZ) to determine the effects of fission product incorporation in YSZ that is considered as an inert nuclear fuel matrix. The ion implantation was conducted at room temperature to 1 × 1021ions/m2 for each ion with ion energies ranging from 70 to 400 keV. The peak displacement damage level and the peak ion concentration in YSZ reached 205-330 dpa and 11-26 at%, respectively. The microstructure of the implanted YSZ was studied by in situ and cross-sectional transmission electron microscopy. In the iodine and strontium implanted samples, a damaged layer with a high density of defect clusters was observed, while in the cesium implanted specimen, the damaged layer is amorphous. Nanocrystalline precipitates were observed in the strontium implanted specimen after annealing at 1000°C. The results are discussedin terms of the ionic size, mobility and the solubility of the implanted species in YSZ.
The Influence of Chemical Composition of Liquid Radioactive Waste on the Evaporation Process
Authors: Poluektov P.P. , Soukhanov L.P. , Zhicharev M.I.
Published: May 2011

A method is suggested to assess the tolerable salt content of the evaporator bottoms from the data on solubility in salt systems taken as simplified models of liquid radioactive waste (LRW) arising from nuclear power plants (NPP) with boiling reactors. It has been demonstrated that the degree of evaporation may be substantially increased by implementing the process in nitric acid. Equations have been derived that allow the calculation of the minimum needed acidity of the solution to allow maximum evaporation.
Synthesis and Study of 239Pu-Doped Ceramics Based on Zircon, (Zr,Pu)Sio4, and Hafnon, (Hf,Pu)SiO4
Authors: Burakov B.E. , Anderson E.B. , Zamoryanskay M.V. , Yagovkina M.A. , Strykanova E.E. , Nikolaeva E.V.
Published: May 2011

Zircon, ZrSiO4, as well as its Hf-analogue hafnon, HfSiO4, have been proposed for use as durable Pu host phases for the immobilization of weapons grade Pu and other actinides. Four samples of Pu-doped ceramics based on the zircon and hafnon structures were synthesized through sintering in air using precursors containing 5-6 and 10 wt% 239Pu. Synthesized ceramic samples were studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), microprobe method, MCC-1 leach test at 25 and 90°C. Inclusions of separated a PuO2phase in the matrix of zircon-based ceramic and presumably, (Pu,Hf)O2 phase in the hafnon-based ceramic were observed for samples obtained from precursors doped with 10 wt% Pu. No separated Pu-phases in significant amounts were identified in the matrices of both ceramics obtained from the precursors doped with 5-6 wt% Pu. It was found that normalized Pu mass losses (without correction on ceramic porosity) for samples doped with 10 wt% Pu which contain separated inclusions of PuO2 or (Pu,Hf)O2 after 14/28 days were approximately (in g/m2) - for zircon: 0.2/0.2 - at 90°C and 0.03/0.04 - at 25°C and for hafnon: 0.02/0.04 - at 90°C and 0.01/0.01 - at 25°C. The losses of Pu from samples doped with 5-6 wt% are 1-2 order of magnitude less. It was suggested that optimal amount of Pu which could be incorporated by zircon and hafnon lattices does not exceed 7 wt%. An important additional conclusion is that Pu- doped ceramic based on zircon or hafnon can be successfully fabricated excluding hot pressing method.
Durabilities of Pyrochlore-Rich Titanate Ceramics Designed for Immobilization of Surplus Plutonium
Authors: Zhang Y. , Hart K.P. , Blackford M.G. , Thomas B.S. , Aly Z. , Lumpkin G.R. , Stewart M.W. , Mcglinn P.J. , Brownscombe A.
Published: May 2011

The chemical durabilities of two Pu-doped pyrochlore samples were studied by Single-Pass-Flow-Through (SPFT) tests at 70°C. The dissolution of pyrochlore is incongruent with preferential releases of Ca and Gd over Ti, close to stoichiometric releases of U and Ti, and lower releases of Hf and Pu than Ti. Altered pyrochlore and polymorphs of TiO2 (brookite and probably anatase) have been identified on the surface of the leached sample and the principal secondary phase is an unknown polymorph of TiO2 containing Hf and varying amounts of Gd and Pu. These surface alteration phases are consistent with reported studies of natural samples. The releases of U, Gd, Ca and Ti into solution follow linear kinetics, whereas the releases of Pu and Hf exhibit non-linear behavior. The presence of ∼5% PuO2 and trace amounts of glass does not appear to have an effect on the overall durability of the material. Further, the low Pu release rate and the similar kinetics for Pu and Hf releases limit the possibility of nuclear criticality under repository conditions. Overall, this study provides useful information on the lower bounds of durabilities of the materials.
Phase and Chemical Stability of Murataite Containing Uranium, Plutonium and Rare Earths
Authors: Yudintsev S.V. , Stefanovsky S.V. , Nikonov B.S. , Omelianenko B.I.
Published: May 2011

Murataite –a complex actinide (An)- and rare earth element (REE)-bearing oxide with a cubic fluorite-related lattice – is one of the promising host-phases for immobilization of Pu-containing waste. The murataite phase composition corresponds to the empirical formula:A4B2C7O22-x, where the A-sites are occupied by Ca, Mn, REE, and An (U); B sites – by Mn, Ti,Zr, and An (U); and C sites – by Ti, Al, and Fe. The total amount of the actinides (U) and REE (Ce, Gd) in the murataite may exceed 20 wt%. In contrast to the other prospective hosts for actinide waste immobilization (cubic zirconia and pyrochlore), murataite accommodates higher amounts of corrosion products(Al, Fe) along with the actinides. The authors compared murataite-based ceramics having similar compositions and produced by melting in a high-temperature resistance furnace or via inductive melting in a cold crucible. Eight samples of the murataite-based ceramics were produced and investigated in detail. Murataite was found to be the major phase in four of the samples – with a basic composition, in wt%, of: 5.0 Al2O3, 10.0 CaO, 55.0 TiO2, 10.0 MnO, 5.0 Fe2O3, 5.0 ZrO2, and 10.0 UO2. These samples were produced by melting in a resistive furnace and in the cold crucible and included Gd-bearing samples and one Pu-bearing sample. The extra phases were other titanates: (from more to less typical) rutile, pyrochlore, zirconolite, crichtonite, pseudobrookite, and perovskite (in the Pu-doped samples only). Three varieties of the murataite, with 3-, 5-, and 8-fold fluorite-type lattices, were observed. Addition of uranium and rare earth oxides stabilizes pyrochlore as the major phase, whereas addition of zirconia yields zirconolite. Plutonium stabilizes the perovskite-type phase, probably due to the formation of Pu3+. The maximum waste oxide content in the murataite for the elements studied was found to be 10% ZrO2, 12% CeO2, 13% Gd2O3, and 14% UO2. Waste element partitioning among the murataite and all the other phases with similar fluorite-related structure (pyrochlore and zirconolite) was analyzed. The uranium leach rate for the sample with maximum murataite content was measured using a procedure similar to MCC-3. This leach rate was close to10-5 g/(m2*day) in a½-day test and decreased by more than one order of magnitude in 28-day tests. Investigation of the stability of the murataite structure after irradiation byheavy ions is in progress.
The Effect of Hydrogen Peroxide Concentration on the Oxidative Dissolution of Unirradiated Uranium Dioxide
Authors: Pablo J. De , Casas I. , Clarens F. , Aamrani F. El , Rovira M.
Published: May 2011

The dissolution rate of unirradiated uranium dioxide was studied in batch experiments as a function of hydrogen peroxide concentration (from 10−5 to 10−3 mol dm−3). Unirradiated UO2(s) was used in order to differentiate surface chemical processes from radiolytic effects. Dissolution rates were determined from both uranium release and hydrogen peroxide consumption. Results showed that H2O2consumption rate was higher than UO2 dissolution rate. This observation may indicate that the overall UO2 oxidative dissolution process would be controlled by the dissolution of the oxidized solid surface. The calculated hydrogen peroxide reaction order was 1 in the H2O2 concentration range from 10−5 to 10−4 mol dm−3, while at higher concentrations no clear dependence was observed.
Congruent and Incongruent Radionuclide Release During Matrix Dissolution of Partly Oxidized High Burnup Spent Fuel
Authors: Loida A. , Grambow B. , Geckeis H.
Published: May 2011

With respect to the assessment of the long-term behavior of the waste form spent fuel it is of high importance to study in particular the UO2 matrix dissolution behavior and the associated release/retention of radionuclides in contact with groundwater. During long term fuel storage, fuel oxidation may not be avoided. Main issue of this work is to identify the impact on the corrosion of partly oxidized fuel of environmental conditions such as (1) the nature of solution contacting the matrix, the (2) presence/absence of CO2, (3) fixed pH values within a range between pH 7- pH 11, and (4) the presence/absence of corroding container material (Fe-powder). Dissolution tests with powdered oxidized spent fuel in various granite waters, and NaCl-brine resulted in matrix dissolution rates in the same order of magnitude for all investigated media (ca.5×10−4/d). The presence of CO2 and fixed pH values (pH 5 – 11) was without a distinct effect. The independence of the dissolution rate of the oxidized fuel matrix upon the nature of solution, pCO2, fixed pH values (5-11) can probably be explained by a masking effect of radiolysis. In presence of Fe powder the matrix dissolution rate was found to be slowed down by a factor of ca. 20, associated with strong retention effects of radionuclides.
On Metal Aggregates in Spent Fuel, Synthesis and Leaching of Mo-Ru-Pd-Rh Alloy
Authors: Cui Daqing , Eriksen Trygve , Eklund Ulla-Britt
Published: May 2011

The results of leaching tests on the synthesised 46%Mo-29%Ru-21%Pd-4%Rh alloy show selective release Mo at both reducing and air saturated conditions. The leach rate increases with rising redox potential (Eh) of leaching solution and temperature, and slightly decreases with leaching time. The electrochemical study indicates that the alloy is more stable than carbon steel against corrosion but less stable than copper and stainless steel. Based on the leach rates of Mo, Ru, Rh, Pd and oxidation potentials of these four metals and Tc0, the leach rates of Tc from alloy aggregates, 40%Mo, 30%Ru, 10%Tc, 15% Pd, 5%Rh in spent fuel at reducing and air saturated conditions are estimated, to be 4.10−9 g.cm−2.day−1 and 4. 10−7 g.cm−2.day−1, respectively.
Release of Radiotoxic Elements from High Burn-Up UO2 and MOX Fuel in a Repository
Authors: Glatz Jean-Paul , Carbol Paul , Cobos-Sabaté Joaquin , Gouder Thomas , Miserque Frédéric , Gimenez Javier , Wegen Detlef
Published: May 2011

In a spent fuel repository the processes that govern the release of radionuclides are dissolution and transport in a possible groundwater flow. The cladding will be the last barrier before the water comes into contact with the fuel, namely with the outer rim of the pellet. Here the heterogeneity of the material due to the irradiation process is responsible for a complex release process. Fission products and minor actinides inventories are considerably higher at the pellet periphery as a result of increased epithermal neutron capture and of migration in the case of the volatile fission products.

The present paper gives a review of experimental activities at the Institute for Transuranium Elements (ITU). Both single effects studies and integral tests are carried out to study the behavior of spent fuel under storage conditions.

Leaching of irradiated UO2 (up to 50 GWd/tU) and MOX (up to 25 GWd/tU) fuel rods with preset cladding defects at 100°C under anoxic or reducing conditions should simulate the realistic case of groundwater coming into contact with a spent nuclear fuel repository. For all main radionuclides the release process can be described considering a two-step dissolution mechanism that includes the initial dissolution of an oxidized layer present on the fuel surface followed by a long-term oxidative matrix dissolution. By means of α-doped (238Pu) UO2 it could be demonstrated, that radiolysis has a significant influence on this dissolution. Especially high initial release rates were found for the volatile cesium and iodine for the reasons mentioned above.

Besides the conventional leaching experiments electrochemical techniques are used to investigate for instance the complex corrosion behavior of the heterogeneous MOX fuel materials or the influence of α-radiolysis on spent fuel dissolution.

In the integral tests mentioned above with large S/V values, reprecipitation of U is likely to happen. Therefore special dynamic test are conducted where this reprecipitation is prohibited and true U solubility can be determined.

Thin layer of UO2 and (U,Pu)O2 doped with various fission products and minor actinides are prepared to study the influence of these elements on the matrix dissolution. When Cs is for instance co-deposited, the U oxidation state changes from U4+ to U6+ for the same O2 pressure possibly indicating a stable Cs uranate. This could be an indirect proof of the existence of such a species in irradiated fuel (e.g. at the grain boundaries).
Iodine Immobilization by Sodalite Waste Form
Authors: Nakazawa T. , Kato H. , Okada K. , Ueta S. , Mihara M.
Published: May 2011

Leachabilities and solubilities of the synthesized iodide sodalite and natural (chloride) sodalite were measured by leach test. The iodide sodalite was synthesized in nitrogen gas flow at 800°C for 2 hours. The crystalline structure of the product was certified by XRD analysis. The natural sodalite containing chlorine was obtained at Bancroft, Canada. The several types of solution were used to evaluate the influence of the solubility of sodalite that included the varied pH and the chemical compositions. The solubilities of chloride sodalite were calculated by the thermodynamics data. The solubility measured for the synthesized iodide sodalite was compared with that calculated. The solubility of the synthesized iodide sodalite was approximately 2 x 10-4 mol/L, which shows a good agreement with the calculated one of the natural sodalite.
Mass Transport of Multicomponents Solute in Bentonite Clay
Authors: Ichikawa Y. , Kawamura K. , Nakano M. , Kitayama K. , Saito N. , Kawamura H. , Yamamoto S.
Published: May 2011

A fundamental concept combining a molecular behavior and macro-continuum phenomenon is presented for a multicomponent solute diffusion problem in bentonite clay, which is a key component of the Engineering Barrier System (EBS) of high-level radioactive waste disposal (HLRW). Bentonite is a micro-inhomogeneous material. Properties of the saturated bentonite are characterized by the constituent clay mineral (montmorillonite) and water, namely montmorillonite hydrate. We analyze its molecular behavior by applying a molecular dynamics (MD) simulation to inquire into the physicochemical properties such as diffusivity of chemical species. For extending the microscopic characteristics of constituent materials to a macroscopic diffusion behavior of the micro-inhomogeneous material we apply a homogenization analysis (HA).
Ash and Soil Conditioning Using Exothermic Metallic Compositions
Authors: Karlina O.K. , Varlackova G.A. , Ojovan M.I. , Tivansky V.M. , Klimov V.L. , Pavlova G.Yu. , Dmitriev S.A.
Published: May 2011

A thermochemical approach to conditioning ash residue that involves the use of exothermic metallic compositions (EMC) has been previously reported. EMC intermixed with ash residue at the appropriate ratios can sustain a glass forming reaction wave that produces monolith glass-like blocks. Herein, the thermochemical conditioning process is extended for conditioning contaminated clay soils. The results are reported for a study of the conditioning process and product materials to determine the optimal processing parameters and to characterize the product materials.
The National Radioactive Waste Repository Project
Authors: Perkins C. , Harris J. , Veitch S. , Kellett J.
Published: May 2011

In 1992, the Commonwealth Government supported by States and Territories commenced an Australia-wide search for a site for a suitable site for a national radioactive waste repository for Australia's small inventory of low level and short-lived intermediate level waste. In 1998, the central-north region of South Australia was chosen as the preferred area in which to undertake detailed site investigations as it had the largest area of potential suitability compared to relevant technical and social criteria. Public consultation has been conducted both nationally and in the region.

Site investigations are currently in their final phase, and it is expected that a preferred site will be identified before the end of 2000. Environmental assessment and licensing processes will then commence, and the repository may be constructed in 2002.
SR 97: Spent Fuel Alteration/Dissolution and the Influence of Near Field Hydrogen
Authors: Spahiu Kastriot , Sellin Patrik
Published: May 2011

A discussion of the evaluation of the source term in the SR 97 safety assessment of a deep repository for spent nuclear fuel is presented. Since the majority of the radionuclides are embedded in the uranium dioxide fuel matrix, they will be released only after the alteration/dissolution of the matrix. Therefore a description of the process of alteration/dissolution of the spent fuel matrix is needed in a safety assessment.

Under normal repository conditions, i.e. reducing environment and neutral to alkaline pH, uranium dioxide has a very low solubility in water. If solubility is assumed to be the limiting factor, the dissolution of the fuel matrix will proceed very slowly due to the low water exchange in the defective canister. On this basis, a solubility-limited model for the release of the radionuclides from the fuel may be formulated.

The reducing conditions can be upset by the radioactivity of the spent fuel, which generates oxidizing products through water radiolysis. This causes the oxidative alteration/dissolution of the UO2(s) matrix. A model for fuel matrix conversion resulting from radiolytic oxidative dissolution is discussed, as well as parameter variations and the associated uncertainties.

In a repository the spent fuel will come in contact with groundwater after the copper canister has breached. Large amounts of hydrogen are then produced through the anoxic corrosion of the cast iron insert. Recent data on spent fuel leaching in presence of repository relevant hydrogen pressures and the implications on the actual and future spent fuel dissolution modeling will also be discussed.