bluuebunny/crossref_metadata_2025 huggingface dataset:
The Agreement of Poly-5,5'-(4,4'-Dinonyl-2,2'Bithiazole) Spectral Signatures to those of Corresponding Oligomers
Authors: Blanda Wendy M. , Francis Anthony H. , Curtis M. David
Published: May 2011

Study of the electronic spectra of conjugated oligomers can provide a useful approach to obtain an analysis of the often complicated spectra of their corresponding polymers. One advantage of studying oligomers is that there is often a well defined conformational morphology and one may eliminate or reduce the spectral consequences of a distribution of conjugation lengths. In the present work, electronic spectra of some oligomers of poly-5,5'-(4,4'-dinonyl-2,2'bithiazole) were studied, both in solution and in the solid state, and the results compared with spectra of the polymer. For solution data, the plot of molar extinction coefficient vs. the number of double bonds is found to be linear, as is the Kuhn plot. This is consistent with quantum-chemical molecular modeling calculations, and closely resembles the behavior of other conjugated oligomers, such as polythiophenes and polyenes. However, the solid state spectra exhibit a large red shift in both absorption and emission. These and other results suggest the presence of strong intermolecular interactions in the solid state that significantly modify the magnitude of the homo-lumo gap of the oligothiazoles and their polymers. By comparing oligothiazoles in solution to thin film results, polymer behavior is explored.
Poly(Binaphthalenevinylene-alt-Phenylenevinylene) Derivatives: Novel Luminescent Polymers for Light-Emitting Devices
Authors: Zheng Lixin , Jiang Xuezhong , Liu Michelle S. , Jen Alex K-Y.
Published: May 2011

Novel conjugated light-emitting polymers were synthesized via a Wittig-Horner condensation reaction between a binaphthyl dicarbaldehyde and a series of electron-rich or electron-deficient aryl diphosphonates. After comparing these materials with the model compound, 4c, it was revealed that the introduction of a twisted, non-coplanar binaphthyl structure provided an effective approach for tailoring the spectral characteristics of the polymers and improving their solubility and thermal stability (glass transition temperature, Tg, 200°C). Furthermore, the band structures of the polymers could be fine-tuned by changing the electronic properties of the bridging aromatic units. The electroluninescence (EL) and device characteristics were also reported in this paper.
Synthesis and Optical Properties of Phthalonitrile Oligomers
Authors: Tsai ZoHong , Sandman Daniel J.
Published: May 2011

Phthalonitrile and its derivatives react with Tin(II) reagents to give intensely colored linear oligomers. Structures are proposed for the oligomers based on elemental analysis, infrared, 1H and 13C spectra, and mass spectra. Stannous chloride has two kinds of properties, reducing reagent and Lewis acid. Tin(II) alkoxide initiates phthalonitrile oligomeriaztion when excess alkoxide is present. The mass spectrum indicates a chain length of at least a hexamer. In semi-empirical AM1 calculations, the helical conformation of a pentamer is indicated to be more stable than a linear conformation. The position of the electronic spectral maximum can be controlled by different kinds of reaction conditions and solution absorption and emission spectra were recorded.
Side Chain Influence on Main Chain Orientation of PPV-Type Oligomers
Authors: Müllner Ruth , Noirez Laurence , Zojer Egbert , Stelzer Franz , Leising Günther
Published: May 2011

Oligo (p-phenylene vinylene)s OPV were synthesized having cyanobiphenyloxy-groups bonded to the vinylene double bonds via alkylene spacers. A Pd(0)-reaction was used to synthesize the oligomers starting with the dibromo-substituted benzene and the alkenyloxy-biphenyl-nitrile. The orientation of the mesogens by a magnetic field and their influence on the orientation of the main chain was investigated by means of neutron diffraction ND. Data on the photophysics of the oligomers were gained using several spectroscopic methods such as UV/VIS, polarized optical microscopy POM, SEC, 1H-NMR, FT-IR.
Frequency Dependent Dielectric Permittivity Studies in Emeraldine Base and Weakly Doped Polyaniline and its Deriviatives
Authors: Pintoa Nicholas J. , Sinha Ghanshyam P. , Aliev Fouad M.
Published: May 2011

We report on a study of the complex dielectric permittivity in polyaniline (PAN), poly-o-toluidine (POT) and poly-o-ethylaniline (OPEA) in the undoped and weakly doped state in the frequency range 1 mHz upto 1 MHz. The doping concentration defined as y=[C1-]/[N] was chosen so that 0 ≤ y ≤ 0.07. OPEA with y=0.50 was also investigated. The objective of this work was to investigate the contribution of the mobile charge defects (polarons and bipolarons) on the conductivity and dielectric relaxation at such low doping levels. The three samples were chosen so as to compare the effects of introducing larger interchain disorder while maintaining a similar conduction mechanism. In all samples studied we observe the presence of a dielectric relaxation mechanism and the relaxation times depend on the doping level and disorder. The presence of a larger number of polarons as the doping level is increased leads to multiple paths for the system to relax leading to progressively non Debye like relaxation process. The results are interpreted in terms of creation and annihilation of polarons and bipolarons and their subsequent diffusion.
Luminescence Properties and Energy Transfer Processes in Fluorescent and Phosphorescent Tris(Phenylquinoxaline)
Authors: Blumstengel Sylke , Colabella Elio , Tubino Riccardo , Jandke M. , Strohriegl P.
Published: May 2011

We have studied the photophysical properties and energy transfer processes in tris(phenylquinoxalines ) (TPQ). TPQs emit blue fluorescence with a maximum at 2.9 eV as well as green phosphorescence at 2.2 eV. When doped with a phosphorescent dye efficient energy transfer takes place from the excited singlet and triplet state of the TPQ host to the guest molecules. The mechanism of energy transfer can be understood in the frame of Förster's theory of dipole-dipole interaction. Besides the interesting photophysical properties, TPQs are also very efficient electron transport materials. Red light-emitting diodes utilizing doped TPQ as emitter and electron transport layer have been prepared and electroluminescence properties investigated.
The Internal Field Distribution in Light Emitting Electrochemical Cells and Light Emitting Diodes: A Comparative Study
Authors: Moderegger Erik , Wenzl Franz P. , Tasch Stefan , Leising Günther
Published: May 2011

We determined the internal electric field distribution in light emitting electro-chemical cells (LECs) and light emitting diodes (LEDs) based on methyl substituted poly(paraphenylen) (mLPPP) by performing electroabsorption measurements as a function of an external bias voltage. Based on these results we outline the working principle of both types of devices. In the case of the LEC we observed an abrupt increase in the EA signal above a threshold voltage of about 2V which we attributed to junction formation due to in-situ electrochemical doping. For single layer LEDs we found the behavior expected for metal/insulator/metal/structures, i.e. the electric field drops linearly over the bulk polymer and no space-charge regions were observed.

These findings are important for improving the performance of organic electroluminescent devices.
Excited State Electronic Interactions in Oligothiophenes with Novel Supramolecular Structure
Authors: Tubino R. , Borghesi A. , Sassella A. , Botta C. , Porzio W. , Sala F. Della , Carlo A. Di , Lugli P.
Published: May 2011

Molecular beam deposition of quaterthiophene oligomer on a single crystal of potassium acid phtalate yields thin films exhibiting a novel supramolecular organisation which has been determined by a combined study of X-ray diffraction and polarized optical transmission measurements. In this structure consisting of stacks of tilted H aggregates, a commensurate ratio between the KAP substrate and the overgrown oligothiophene layer (quasi-epitaxial growth) is attained. The samples are optically extremely anisotropic, with the projection of the molecular axis on the substrate surface perfectly aligned along the b crystallographic axis. Using these novel structural data, the optical properties are interpreted within the framework of the transition density approach.
New Aspects of Organic Electric Materials in Calamitic Liquid Crystalline Photoconductors
Authors: Maeda Hiroki , Funahashi Masahiro , Hanna Jun-Ichi
Published: May 2011

Calamitic liquid crystalline photoconductors such as 2-(4'-octylphenyl)-6-butyloxynaphthalene (8-PNP-O4) and 2-(4'-octylphenyl)-6-dodecyloxynaphthalene (8-PNP-O12) exhibit fast ambipolar carrier transport in all the smectic mesophases up to 1.0 × 10−2 cm2/Vs. The structural defects of liquid crystals, i.e. domain boundaries and disclinations in domains, are electrically inactive and cause neither shallow nor deep defect states due to their fluid nature. It is illustrated that the carrier transport does not suffer from these structural defects in polydomain, by examining transient photo-currents in very thick liquid crystalline layers over 100μm. With an insight that this allowance of the polydomain structure and the fluidity of liquid crystalline photoconductors provides us new aspects in terms of electric property and application, e.g. multi-gap processing, the position detect sensor is demonstrated in a wedge cell filled of 8-PNP-O12, referring the position sensitive transit time of photo-induced transient current.

The present result indicates that the photoconductive liquid crystalline material is available for multi-gap structured devices.
Electrical and Electrochemical Properties of Nanocomposite Thin Films Formed by Exchange-Precipitation Route from Nanocrystals and Organic Cross-Linkers
Authors: Leibowitz Frank L. , Zheng Wenxia , Maye Mathew M. , Ly Nam K. , Zhong Chuan-Jian
Published: May 2011

The structural, electrical and electrochemical properties of nanoparticle thin films derived by a one-step exchange-crosslinking-precipitation route were characterized by microscopic, spectroscopic and electrochemical techniques. Thiolate-encapsulated gold nanocrystals of 2-nm and 5-nm core sizes and alkyldithiol crosslinkers were studied as a model system. The mixing of the two components in solutions allowed sequential exchanging, crosslinking and precipitation of dithiol-crosslinked nanocrystal thin films. The films were specularly reflecting and electronically continuous, and have potential applications in catalysis and molecular recognition.
Photoemission Study of Metal-Deposited p-Sexiphenyl Film
Authors: Ito E. , Koch N. , Oji H. , Ishii H. , Leising G. , Seki K.
Published: May 2011

Metal deposition on a p-sexiphenyl (6P) film was studied by ultraviolet photoelectron spectroscopy (UPS), metastable atom electron spectroscopy (MAES), and X-ray photoelectron spectroscopy (XPS). The deposited metals were Au, Mg, and several alkali metals (K, Na, Rb, and Cs). No chemical reaction between 6P and Au or Mg was observed in the measured spectra, while additional gap states appeared in the UPS and MAES spectra by deposition of the alkali metals. The diffusion of Au and Mg atoms into the 6P film was observed in the MAES spectra. We found the trend of the vacuum level shift is different between the systems of the 6P on the Au and its reversed systems (Au on the 6P film), suggesting the different formation of the interface depending on the deposition sequence.
In Situ Attenuated Total Reflection FTIR Spectroelectrochemistry Of Polybenzimidazobenzophenanthroline (BBL)
Authors: Yohannes Teketel , Neugebauer H. , Sariciftci Niyazi S. , Yi S. , Jenekhe Samson A.
Published: May 2011

Fourier transform infrared (FTIR) spectroscopy is a powerful method to determine the doping induced structural changes and electronic band structure modifications of conjugated polymer films. Here, we report in situ attenuated total reflection (ATR) FTIR spectroelectrochemical results of reduction reactions (n-doping) of the conjugated ladder polymer polybenzimidazophenanthroline, BBL. The ATR-FTIR spectra are recorded in situ during continuous potential cycling of a BBL coated germanium reflection element in a three electrode spectroelectrochemical cell. The spectra and the structural changes during the reduction (n-doping) of the polymer film at different electrode potentials are presented. In contrast to most of the other conjugated polymers, this polymer shows four reversible redox reactions during n-doping, corresponding to various forms of BBL with different conductivities.
Realization of Polymeric Electro-Optic Modulators with Less Than One Volt Drive Voltage Requirement
Authors: Zhang Cheng , Lee Michael , Winklemann Adam , Northcroft Heidi , Lindsey Christopher , Jen Alex K. Y. , Londergan Timothy , Steier William H. , Dalton Larry R.
Published: May 2011

The roles played by spatially anisotropic intermolecular electrostatic interactions, chromophore shape, host dielectric constant, and poling field strength in defining maximum achievable electro-optic activity for electrically poled chromophore/polymer materials are investigated by equilibrium and Monte-Carlo quantum statistical mechanical calculations. Even simple Hamiltonians reproduce critical qualitative features such as the existence of a maximum in plots of electro-optic activity versus chromophore number density in a polymer matrix. Comparison of theoretical results for various methods provides a useful check on the validity of approximations employed with individual methods. The most significant conclusion to derive from a comparison of experimental and theoretical results is the dependence of maximum achievable electro-optic activity upon chromophore shape. Theoretical calculations suggest a new paradigm for the design of optimum electro-optic chromophores; realization of the desired shapes may be facilitated by dendritic synthetic approaches. In the presence of intermolecular electrostatic interactions, the dependence of electro-optic activity upon material dielectric permittivity and electric poling field strength is more complex than in the absence of such interactions. Of particularly, interest are conditions that lead to second order phase transitions to lattices containing centrically (antiferroelectricallly) ordered chromophore domains. Such phase transitions can lead to further complications in the attempted preparation of device quality materials but can be effectively avoided by utilization of theoretically derived phase diagrams.
High Performance Side-Chain Polyquinolines and Perfluorocyclobutane-Containing Thermoset Polymers for Electro-Optic Applications
Authors: Ma Hong , Wu Jianyao , Herguth Petra , Chen Baoquan , Purohit Ajay , Jen Alex K.-Y.
Published: May 2011

A modular approach for making second-order nonlinear optical (NLO) side-chain aromatic polyquinolines has been developed. The synthesis provides a method for readily incorporating NLO chromophores into the pendent phenyl moieties of parent polyquinolines at the final stage via the Mitsunobu reaction. The method produces polyquinolines with a wide range of polymer backbones and offers great flexibility in the selection of NLO chromophores. These side-chain NLO polyquinolines demonstrate high electro-optic (E-O) activities (up to 35 pm/V at 830 nm and 22 pm/V at 1300 nm) and excellent tradeoffs among thermal, optical, and electrical properties.

Most recently, a series of novel second-order NLO thermoset polymers containing silicon-perfluorocyclobutane (PFCB) has also been synthesized. This was accomplished via the crosslinking reaction between the di(trifluorovinylether)-containing NLO chromophores and the tris(trifluorovinylether) monomer in solid state at 180-250 °C. The radical-mediated, stepwise cycloaddition reaction offers great tolerance to very sensitive functional groups such as tricyanovinyl acceptor. A variety of NLO chromophores could be easily incorporated into these thermoset polymers compared to the modular approach. Preliminary results have indicated these polymers to possess excellent processability, low optical loss, and a combination of highly desirable thermal, nonlinear optical, and mechanical properties.
Tuning of Redox Behavior and Fluorescence of Cyano-containing Oligophenylenevinylenes
Authors: Liu Michelle S. , Jiang Xuezhong , Jen Alex K-Y.
Published: May 2011

A series of cyano-containing distyrylbenzenes which have the electron-withdrawing groups functionalized on the central phenylene ring were synthesized via the Wittig-Horner reaction. Electrochemical study showed that the electron-affinity of these molecules increased with the increasing strength of electron-accepting groups. 1,4-Bis(4'- t-Butylstyryl)-2,5-bis(dicyanovinyl)benzene (6) possessed a low LUMO energy level at -4.01 eV, which provided a better match to the work function of Al cathode. Compared to the cyano-terephthalylidene (2), introducing cyano groups on the aromatic ring (3) instead of on the vinylene linkage provided better stabilization to the radical anions. The emission colors spanning green, yellow, orange, red could be achieved by changing the electron-accepting strength of oligophenylenevinylenes (3-6). Energy gap reductions were caused by a stronger decrease of the LUMO energies than the HOMO energies. These results provided new insights for the design of suitable polymers with much improved electron affinities facilitating electron injection from higher work function metal electrodes.
A Polyaniline Coating Material for Inhibiting Corrosion in Marine Environment
Authors: Lin Yuan , Yang Sze C. , Clark Robert , Brown Richard
Published: May 2011

The conventional molecular ion doped polyaniline undergoes dedoping in sea water because the sea water, with pH = 8, induces deprotontation of polyaniline. In this article we report polyaniline complexes that remain conductive in sea water. These complexes are useful for corrosion protection of metals in marine environment and for chromate replacement coatings. The reason for the pH stability of these polyaniline complexes was discussed. The polymeric complexes of polyaniline were used as an additive in an epoxy primer coating on AL7075-T6 without surface pre-treatment of the metal. Corrosion tests show that these polymeric complexes of polyaniline are effective for improving the corrosion inhibition in seawater for aluminum alloys.
Building Confidence in Radionuclide Transport Models for Fractured Rock: The Nagra/JNC Radionuclide Retardation Programme
Authors: Ota K. , Alexander W.R. , Smith P.A. , Möri A. , Frieg B. , Frick U. , Umeki H. , Amano K. , Cowper M.M. , Berry J.A.
Published: May 2011

The joint Nagra/JNC Radionuclide Retardation Programme has now been ongoing for 15 years with the main aim of direct testing of radionuclide transport models in as realistic a manner as possible. A large programme of field, laboratory and natural analogue studies has been carried out at the Grimsel Test Site in the central Swiss Alps and the Kamaishi In Situ Test Site in north-east Japan. The understanding and modelling of both the processes and the structures influencing radionuclide transport/retardation in fractured host rocks have matured as has the experimental technology, which has contributed to develop confidence in the applicability of the underlying research models in a repository performance assessment. In this paper, the successes and set-backs of this programme are discussed as is the general approach to the thorough testing of the process models and of model assumptions. In addition, a set of key findings is presented, involving discussions on the enhancement of confidence through the program.
On the Hydrolysis of Tetravalent Metal Ions
Authors: Ekberg C. , Brown P. , Comarmond J. , Albinsson Y.
Published: May 2011

The stability constants of the hydroxide complexes of zirconium(IV) and uranium(IV) have been measured at 15, 25 and 35°C [in 1.0 mol dm−3 (Na, H)ClO4] using potentiometry. For zirconium(IV), the results indicate the presence of Zr(OH)3+ and the polymeric species Zr3(OH)48+ and Zr4(OH)88+ whereas the results for uranium(IV) indicate the presence of U(OH)3+ and the polymeric species U4(OH)124+. The hydrolysis of both metal ions was studied at three temperatures allowing the determination of ΔH° and ΔS° of reaction for each species. The results were compared with previous results determined for thorium(IV) under the same experimental conditions to ascertain whether thorium should be used as an analogue for other tetravalent metal ions in safety assessment studies of nuclear repositories.
Categorization of Cement Hydrates by Radionuclide Sorption Mechanism
Authors: Noshita K. , Nishi T. , Yoshida T. , Fujihara H. , Saito N. , Tanaka S.
Published: May 2011

A categorization of cement components was attempted from the viewpoints of their chemical constituents and sorption behaviors. In this study, we assumed that the cement components are categorized into four groups, calcium silicate compounds, hydroxides, calcium aluminate compounds, and others. The sorption behaviors were compared among the four groups by batch sorption experiments carried out for 12 kinds of cement components using the radionuclides cesium, iodine, inorganic carbon, and nickel as different chemical species. The characteristic sorption trends were obtained in each group. We found that the sorption mechanism is closely related to the chemical constituents and surface species. Categorization of these cement of components will contribute to the understanding of sorption mechanisms.
Sorption Behavior of Radium and Actinium on Soils
Authors: Sakamoto Yoshiaki , Takebe Shinichi , Ogawa Hiromichi , Muraoka Susumu , Ishii Tomoaki , Inagawa Satoshi , Gunji Yasuyoshi
Published: May 2011

Distribution coefficients of 226Ra and 227Ac on soils and tuff have been obtained by a batch method. The distribution coefficients of Ra on loam, two kinds of sand and tuff were 28m3/kg, 0.45m3/kg, 0.19m3/kg and 1.9m3/kg, respectively. A linear relationship between the distribution coefficients of Ra on each soil and Cation Exchange Capacity(CEC) of each soil was obtained to suggest cation exchange sorption reaction of Ra2+ on soil surface. Sorption-migration behavior of Ra in sand column has been studied. Most of Ra remained in the column after passing of 5,000 pore volume of the column, showing several times the distribution coefficients of Ra than that by the batch method. The distribution coefficients of 227Ac on the soil samples were in the range from 1m3/kg to 10m3/kg.
Diffusion and Adsorption in Porous Silica Considered as a Reference Material for Crystalline Rock
Authors: Aalto Hannu , Lehikoinen Jarmo , Muurinen Arto , Valkiainen Matti
Published: May 2011

In the present study, well-characterized mesoporous silica was used as a reference material for crystalline rock. Saturation-leaching and through-diffusion tracer experiments were systematically carried out to determine the adsorption capacity factors and apparent and effective diffusivities for the radioactive tracers 3H, 22Na and 36Cl. The ionic strength of the supporting NaCl electrolyte, in equilibrium with atmospheric air, was either 0.002 M or 0.1 M. The apparent diffusivities derived from saturation-leaching experiments reveal that equilibrium adsorption on a negatively charged silica surface does not act to retard the mass transfer of sodium ions. The steady-state diffusion results are found to demonstrate the increasing break-through for sodium with decreasing ionic strength of the background electrolyte in comparison to 3H. These observations are consistent with the picture of chloride ion exclusion and of the diffuse double layer surface-excess for sodium ions being transported in the direction of the macroscopic concentration gradient. Furthermore, they are shown to be at odds with the widely adopted macroscopic pore diffusion model, which neglects the mobility of the counter-ion surface- excess.
Long-Term Behavior of Bituminized Waste: Modelling of Auto-Irradiation and Leaching
Authors: Chaix P. , Camaro S. , Simondi B. , Vistoli P.P. , Blanc V.
Published: May 2011

During interim storage, the main evolution factor of the bituminized wastes is radiolysis under auto-irradiation, while in deep disposal conditions, after radioactive decrease, site resaturation with water, and container corrosion, the main factor of evolution is leaching by water.

This paper presents two models, designed to describe respectively radiolytic gas evacuation, and bituminized waste alteration under leaching.

The first model is based on the integration of simple descriptions of gas production by radiolysis, gas diffusive transport, bubble nucleation and ripening, and bubble transport under buoyancy and viscosity.

The second model is based on simple descriptions of water adsorption and solubilization at the surface, water diffusion into the matrix, water uptake by the most soluble salts, salt grain swelling and alteration of matrix waterproofing, diffusive transport of salts out of the waste.
The Effect of Radiolytic Degradation Products of Eurobitum on the Solubility and Sorption of Pu and Am in Boom Clay
Authors: Valcke E. , Sneyers A. , Iseghem P. Van
Published: May 2011

The potential effect of water-soluble organic ligands, originating from the radiolytic degradation of Eurobitum bituminized waste, on the Pu and Am solubility and sorption in Boom Clay, was assessed. Granulated inactive Eurobitum simulate in contact with representative solutions was gamma-irradiated, and the irradiated solutions were thoroughly analyzed (GC-MS, IC, ICP-AES,…). Pu and Am solubility and sorption tests were then performed in pure Real Boom Clay Water (RCW) and in RCW containing 50 mass% of the solution containing the radiolytic degradation products. The relevance of the applied methodology is discussed.
Neodymium Incorporation in Zirconolite-Based Glass-Ceramics
Authors: Loiseau P. , Caurant D. , Baffier N. , Fillet C.
Published: May 2011

The investigations on enhanced reprocessing of nuclear spent fuel, and notably on separating the long-lived minor actinides, such as Am and Cm, from the other fission products have led to the development of highly durable specific matrices such as glass-ceramics for their immobilization. This study deals with the characterization of zirconolite (CaZrTi2O7) based glass-ceramics synthesized by devitrification of an aluminosilicate parent glass. Trivalent actinide ions were simulated by neodymium, which is a paramagnetic local probe. Glass-ceramics with Nd2O3 contents ranging from 0 to 10 weight % were prepared by heat treatment of a parent glass at two different growth temperatures: 1050° and 1200°C. X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and electron spin resonance (ESR) measurements clearly indicate that Nd3+ ions are partly incorporated in zirconolite crystals formed in the bulk of the glass-ceramic samples. The amount of neodymium in the crystalline phase was estimated using ESR results and was found to decrease with increasing either heat treatment temperature or total Nd2O3 content.
Thermochemical Approach on Treating Spent Ion Exchange Resins
Authors: Ojovan M.I. , Klimov V.l. , Petrov G.A. , Dmitriev S.A. , Laurson A.V. , Semenov K.N.
Published: May 2011

A thermochemical approach was suggested for treating and conditioning specific streams of radioactive wastes for example spent ion exchange resins (IER), mixed, organic or chlorine-containing radioactive waste (PVC, etc.). Conventional thermal treatment of such waste encounters serious problems concerning complete destruction of organic molecules and possible emissions of radionuclides, heavy metals and chemically hazardous species. The thermochemical treatment uses powdered metal fuels (PMF) that are specifically formulated for the waste composition and react chemically with the waste components. The composition of the PMF is designed in such a way as to minimize the release of hazardous components and radionuclides in the off gas and to confine the contaminants in the ash residue. The thermochemical procedures allow decomposition of organic matter and capturing hazardous radionuclides and chemical species simultaneously. Previous preliminary work demonstrated the feasibility of applying the thermochemical approach to treatment of spent IER using PMF. Herein, the results are presented of theoretical and experimental studies to define the optimal PMF composition as well as the PMF/waste ratio.
The Effect of Gamma Radiation on the Dissolution of High-Level Waste Glass in Boom Clay
Authors: Lemmens K. , Iseghem P. Van
Published: May 2011

The effect of γ-radiation on the dissolution of candidate high-level waste glasses was investigated in potential disposal environments at 90°C. The media consisted of mixtures of Boom Clay, bentonite clay and cement with clay water. During the experiments the pH of Boom Clay decreased, probably mainly by radiolytical oxidation of pyrite. The addition of bentonite, cement and glass buffered the pH decrease. Under radiation the glass mass losses decreased, whereas the leach rate of soluble elements was not influenced or appeared to increase. This is explained through the radiolytical acidification, and possibly by bubble formation in the glass.
Surface Alteration of Nd-Bearing Zirconolite Following Hydrothermal Treatment
Authors: Zhang Zhaoming , Vance Eric R. , Blackford Mark G.
Published: May 2011

Static dissolution tests on Nd-bearing zirconolite were conducted in deionized water at 150°C for up to 6 months. Surfaces, both before and after aqueous dissolutions, were examined using X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). Individual submicron-sized crystals wereobserved only on some zirconolite grains after hydrothermal treatment for one week, and were identified as brookite (possibly plus anatase) by Transmission Electron Microscopy (TEM). The number of secondary crystals present on the zirconolite surface was, however, reduced significantly after 6 months of durability testing. The results of electron microscopy studies are consistent with those obtained from XPS in that the average Ca and Ti concentrations of the top surface layer (< 5 nm) decreased slightly with respect to Zr, while the average Al concentration increased after durability testing.
Feasibility Limits in Using Cerium as a Surrogate for Plutonium Incorporation in Zircon, Zirconia and Pyrochlore
Authors: Zamoryanskaya M.V. , Burakov B.E.
Published: May 2011

Cerium is a well-known surrogate element for Pu that is widely used in experiments on the synthesis and study of ceramic waste forms for actinide immobilization. Cathodoluminescence (CL) images and emission spectra from synthetic zircon, (Zr,…)SiO4, cubic zirconia, (Zr,Y,Gd,…)O2 and pyrochlore, Ca(Hf,Gd,…)Ti2O7, individually doped with Ce and Pu were investigated. It was determined that some of the Ce, which was added as Ce4+ in the form of CeO2, was converted to the 3+ valence state during synthesis of zircon-based ceramics by sintering in air and in argon gas. However, Pu-doped zircon synthesized in air under the same conditions does not exhibit the CL emission of Pu3+. Analysis of CL spectra of cubic zirconia doped with Ce as well as Pu suggests that both ions are in the tetra-valent state in these synthetic materials. However, the CL peak of Ce-doped zirconia is almost identical to that of pure zirconia (2.6 eV). The CL peak for Pu-doped zirconia is shifted to 2.4 eV. No CL emission of Ce3+ or Pu3+ was observed in pyrochlore samples. The CL spectra for Ce-and Pu-doped pyrochlore samples were almost identical. We suggest that under oxidizing conditions Ce is good surrogate of Pu for experiments on the synthesis of pyrochlore-based and acceptable enough for zirconia- based ceramics. The use of Ce as Pu surrogate for zircon-based ceramics should be considered as limited.
Effect of Synthesis Conditions on Phase Composition of Pyrochlore-Brannerite Ceramics
Authors: Stefanovsky S.V. , Yudintsev S.V. , Nikonov B.S. , Lapina M.I. , Aloy A.S.
Published: May 2011

Three melted samples of pyrochlore-brannerite-based ceramics produced under different redox conditions were examined. Two of the samples were produced using cold crucible melting at ~1600 C. The third sample was obtained via melting in a microwave oven at 1700-1800 C. All the samples are composed of major pyrochlore and brannerite phases, and minor rutile and UO2-based solid solution or pseudobrookite phases. Pyrochlore-structured phases predominate in all three samples and account for 50-60% of the total bulk. Two pyrochlore varieties – Ca-pyrochlore (predominant) and Ba-pyrochlore have been found in these samples. The latter phase is more stable at high temperatures than the Ba-hollandite present in sintered pyrochlore-rich Synroc-F ceramics. Decomposition of the Ba-hollandite results in rutile formation in the melted samples.
Pyrochlore-Rich Synroc as a Host for Immobilization of Actinides
Authors: Yang Jianwen , Tang Baolong , Luo Shanggeng
Published: May 2011

Six different formulations of pyrochlore-rich synroc waste forms were designed to contain 32-50wt% simulated actinides. Their physical properties were determined. Phase identification was carried out by using X-ray diffractometer (XRD), and backscattered electron image (BEI) in scanning electron microscopy (SEM). Phase microanalyses were carried out using energy dispersive spectrometer (EDS) in SEM. Their durability properties were determined by PCT leach tests, the leachate was analyzed by using inductive coupled plasma mass spectroscopy (ICP/MS) and atomic absorption spectroscopy (AAS).
Aqueous Dissolution of Rb-Bearing Hollandite and Synroc-C at 90°C
Authors: Carter M. L. , Vance E. R. , Lumpkin G. R. , Loi E.
Published: May 2011

Rb-doped Ba-hollandite and synroc-C samples were prepared for aqueous dissolution studies at 90°C in deionized water using MCC-1 protocols. Small amounts of possibly Rb-bearing BaTiO3, hibonite and alumina accompanied the major Rb-doped (0.1 formula units) hollandite phase. The Rb loadings in the synroc samples ranged from 0.89 to 2.67 wt%. Rb leached at <0.2 g/m2/d from hollandite samples and <0.1g/m2d from synroc, with the values decreasing with increasing dissolution time. The variance between the dissolution rates for the different Rb-doped hollandite and synroc samples is discussed, in terms of Rb-bearing minor phases.
Effect of Spent Fuel Burnup and Composition on Alteration of the U(Pu)O2 Matrix
Authors: Jégou C. , Peuget S. , Lucchini J.F. , Corbel C. , Broudic V. , Bart J.M.
Published: May 2011

For a potential performance assessment of direct disposal of spent fuel in a nuclear waste repository, the chemical reactions between the fuel and possible intruding water must be understood and the resulting radionuclide release must be quantified.

Leaching experiments were performed with five spent fuel samples from French power reactors (four UO2 fuel samples with burnup ratings of 22, 37, 47 and 60 GWd·tHM−1 and a MOX fuel sample irradiated to 47 GWd·tHM−1) to determine the release kinetics of the matrix containing most (over 95%) of the radionuclides. The experiments were carried out with granitic groundwater on previously leached sections of clad fuel rods in static mode, in an aerated medium at room temperature (25°C) in a hot cell.

After 1000 or 2000 days of leaching, the Sr/U congruence ratios for all the UO2 fuel samples ranged from 1 to 2; allowing for the experimental uncertainty, strontium can thus be considered as a satisfactory matrix alteration tracer. No significant burnup effect was observed on the alteration of the UO2 fuel matrix. The daily strontium release factor was approximately 1 à 10−7 d−1 for UO2 fuel, and five to six times higher for MOX fuel. Several alteration mechanisms (radiolysis, solubility, precipitation/clogging) are examined to account for the experimental findings.
Long-Term Dissolution Behavior of Spent Fuel in Compacted Bentonite and Synthetic Granitic Groundwater
Authors: Chun K.S. , Kim S.S. , Kang C.H.
Published: May 2011

The long-term dissolution behavior of spent PWR fuel in synthetic granitic groundwater has been investigated since June of 1998 in order to identify the release mechanism of spent fuel in contact with domestic Ca-bentonite, which was compacted as a density of 1.4g/cm3. Several spent fuel specimens were cut to around 3-mm thick, and these specimens were then loaded into each leaching cell. Every half year, one specimen was collected and the bentonite block was sliced into several pieces. The element distribution on the specimen surface was measured by EPMA and an optical microscope, and the gamma activities in the sliced bentonite pieces were measured. All the leachates were sampled and then the gamma and gross alpha activities were measured. By the results, coming from leaching up to about 1.5 years, the fraction of radiocesium released through the compacted bentonite layer from the spent fuel is approximately a hundredth lower than that without the bentonite layer. By the depth profile of the gamma activity on the bentonite, the activity gradually decreased in accordance with more distance from the specimen and the fractional release rates of cesium were nearly the same. On the other hand, the EPMA results indicate that more time and more information is required in order to identify the surface alteration of spent fuel by leaching. This experiment will therefore be continued at least into the year 2006.
Electrochemical Measurements during the Anaerobic Corrosion of Steel
Authors: Smart N.R. , Fennell P.A.H. , Peat R. , Spahiu K. , Werme L.
Published: May 2011

In Sweden, it is proposed that spent fuel should be encapsulated in sealed cylindrical canisters for disposal in a geologic repository. The canisters would consist of a thick ferrous inner container and a copper overpack. If mechanical failure of the copper overpack occurred, allowing water to enter, the ferrous inner container would corrode anaerobically and liberate hydrogen. The rate of hydrogen generation due to the anaerobic corrosion of steel in anoxic groundwater has been measured using barometric cells. The aim of the work presented in this paper was to measure the redox potential, Eh and pH in the presence of anaerobically corroding steel, in a barometric cell. Two specially designed barometric cells were constructed. They were equipped with a silver chloride or calomel reference electrode, a gold Eh electrode, a glass electrode, and a steel electrode. The electrodes were allowed to stabilize in anoxic artificial groundwater and then a mass of pickled steel wire was introduced into the test cell. As the wires were added, the redox potential rapidly became more negative due to the rapid consumption of the residual oxygen. The corrosion potential of the steel was stable and a slow drift in pH was observed. The results are compared with the results of geochemical modelling. Extension of the work to investigate the electrochemical parameters in the presence of dissolved uranium species is discussed.
Evaluation of the Possible Susceptibility of Titanium Grade 7 to Hydrogen Embrittlement in a Geologic Repository Environment
Authors: Greene Charles A. , Henry Alvin J. , Brossia C. Sean , Ahn Tae M.
Published: May 2011

Ti grade 7 has been selected by the U.S. DOE as the current material of choice for the drip shield in the proposed high level waste (HLW) repository design. Due to the addition of Pd, Ti grade 7 exhibits enhanced resistance to hydrogen embrittlement (HE), yet there is relatively little data on HE of this material. Calculations of hydrogen absorption/recombination, solubility, and free energy of hydride formation in Ti and Pd are presented to qualitatively evaluate Keff, the stress intensity factor for crack propagation induced by hydride formation, of Ti grade 7 in relation to other Ti alloys without Pd. Calculations were performed that show concentration of hydrogen in Ti grade 7 may exceed the critical hydrogen concentration, Hc, where the material becomes embrittled, when accelerated passive dissolution of Ti grade 7 in concentrated Cl- and Cl-+F- solutions as the source of hydrogen is considered.
The Influence of Ligands and Precipitates on the Release of Nuclides from the Near Field under Natural Repository Conditions
Authors: Liu L. , Neretnieks I.
Published: May 2011

Once groundwater intrudes into a damaged canister and wets the spent fuel pellets, radiation emitted from the spent nuclear fuel splits nearby water into oxidizing and reducing species. This may lead to an oxidizing condition near the fuel pellets. As a result, uranium oxide that makes up the fuel matrix will become more soluble, and the incorporated radionuclides will be released more rapidly. The dissolution process is, however, a dynamic one that can be influenced by many factors. Of great importance are the radiation power of the fuel matrix, the concentration of ligands near the fuel surface, and the transport resistance of the near field. Consequently, the escape of nuclides from the damaged canister is dominated mainly by the intrusion of ligands, and the precipitation/dissolution of secondary phases within the fuel rods. To investigate the possible effects of ligands and precipitates, a coupled dissolution and transport model, which includes the barrier effect of the Zircaloy claddings, is developed. The application of the model to a SKB-specified reference scenario indicates that by far the largest fraction of the oxidized uranium will reprecipitate within the canister. This may significantly decrease the fuel surface available for oxidation and the water available for radiolysis. Subsequently, much less fuel matrix will be dissolved and much less of the other nuclides will be released. Simulations further identify that carbonate and silicate have the greatest influences on the formation of secondary phases, and on the release of nuclides, under natural repository conditions.
Technology and Equipment Based on Induction Melters with.Cold. Crucible for Reprocessing Active Metal Waste
Authors: Pastushkov V.G. , Molchanov A.V. , Serebryakov V.P. , Smelova T.V. , Shestoperov I.N.
Published: May 2011

The operation and, particularly, the decommissioning of NPPs and radiochemical plants result in substantial arisings of radioactive metal waste (RAMW) having different activity levels (from 5×10−4 to ≍ 40 Ci/kg).

This paper reviews the specific features of the technology and equipment used to melt RAMW in electric arc and induction furnaces with ceramic or cold crucibles. The experimentally determined and calculated data are given on the level to which RAMW is decontaminated from the main radionuclides as well as on the distribution of the latter in the products of melting (ingot, slag, gaseous phase).

Special attention is focused on the process and the facility for the induction-slag melting of RAMW in furnaces equipped with cold crucibles. The work described is under way at SSC RF VNIINM to master the technology of melting simulated high activity level Zr-alloy and stainless steel waste.
Ion Exchange Behavior of the Febex Bentonite: 2. Batch Experiments and Geochemical Modeling
Authors: Delgado J. , Carretero P. , Juncosa R. , Samper J. , Huertas F.J. , De Cisneros C. Jiménez , Caballero E. , Huertas F. , Linares J.
Published: May 2011

Ion exchange experiments have been performed with the FEBEX bentonite. Five grams of dry powder of this clay were put inside dialysis bags, which were located inside PFA reactors filled with 125 ml of water of a given chemical composition (Moody, Grimsel, and bentonitic-granitic type waters). The reactors containing the clay powder/water mixture were heated to different temperatures (from room temperature up to 80°C) along a time span ranging from 1 day to 1 year. Water was renewed according to a prescribed schedule but not the clay, which remained in place for the whole extent of each test. After each water renewal, major cations, silica, total inorganic carbon, and pH were analyzed. At the end of each test, the exchange complex and CEC of the bentonite were measured. These experiments have been modeled with a conveniently modified version of the EQ3/6 software package where ion exchange reactions were formulated as half reactions and added to its database. In general, model results are in fairly good agreement with experimental data, especially in the case of dissolved cations. Computed values of exchanged concentrations also match the measurements, although in some cases they deviate from them. The fact that the numerical results reproduce the observed patterns of exchange tests indicates that the adopted geochemical conceptual model is appropriate. Some features of the geochemical evolution of these tests also take place at the “mock-up” and “in situ” FEBEX tests.
The Effect of Pore Structural Factors on Diffusion in Compacted Sodium Bentonite
Authors: Sato Haruo
Published: May 2011

Four kinds of diffusion experiments; (1) through-diffusion (T-D) experiments for diffusion direction dependency to compacted direction, (2) in-diffusion (I-D) experiments for composition dependency of silica sand in bentonite, (3) I-D experiments for initial bentonite grain size dependency, and (4) I-D experiments for the effect of a single fracture developed in bentonite, were carried out using tritiated water (HTO) to evaluate the effect of pore structural factors on diffusion. For (1), effective diffusivities (De) in Na-bentonites, Kunigel-V1Ŵ and Kunipia-FŴ, were measured for densities of 1.0 and 1.5 Mg.m-3 in the axial and perpendicular directions to compacted one. Although De values in Kunigel-V1Ŵ for both directions were similar over the density, De values for perpendicular direction to compacted one in Kunipia-FŴ were higher than those for the same direction as compacted one. For (2), apparent diffusivities (Da) in Kunigel-V1Ŵ with silica sand were measured for densities of 0.8 to 1.8 Mg.m-3. No significant effect of the mixture of silica sand was found. For (3), Da values for densities of 0.8 to 1.8 Mg.m-3 were measured for a granulated Na-bentonite, OT-9607Ŵ. However, no effect of initial bentonite grain size was found. For (4), Da values in Kunigel-V1Ŵ, in which a single fracture was artificially reproduced and immersed in distilled water, were measured. No effect of the fracture on Da was found. Based on this, it may be said that the composition of smectite in bentonite affects the orientation property of clay particle and also affects diffusion. Furthermore, a penetrated fracture formed in bentonite is restored for a short while and does not affect diffusion.
Experimental Indications of Effects of Surface Deprotonation on Na-Bentonite Porewater Chemistry in a Geological Repository
Authors: Oda C. , Shibata M. , Yui M.
Published: May 2011

Bentonite-water interaction was studied using a simple equilibrium model based on experimental measurements in order to describe bentonite porewater chemistry. Direct pH measurements for highly compacted bentonite and batch-type bentonite-water interaction experiments were performed under anaerobic conditions. In the direct pH measurements, resin particles doped with a pH indicator were sandwiched between a pair of bentonite columns immersed in a test solution. The experimental results showed that the solution compositions in equilibrium with bentonite depended on the bentonite to liquid ratio (B/L) and the initial solution composition. An equilibrium model assuming only fast equilibration processes between the bentonite minerals and the solution could be used to calculate the trends of pH and other ion concentrations with B/L. This study indicates that the surface deprotonation of smectite is a very important factor influencing the porewater chemistry in highly compacted bentonite.