bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient Electroluminescence from Type I Quantum Confined Structure Utilizing Organic Dye Materials
Authors: Ohmori Yutaka , Sawatani Takumi , Ando Kazumichi , Yosino Katsumi
Published: May 2011

Improvement of electroluminescence (EL) efficiency by utilizing quantum confined structure, so-called type I superlattice, has been discussed. Superlattice structures, which consist of 8-hydroxyquinoline aluminum (Alq3) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), and of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) and Alq3, and of (1,10-phenanthroline)-tris -(4,4,4-trifluoro -1-(2-thienyl)-butane-1,3-dionate) europium (III) (Eu(TTA )3phen) and (N,N'-disalicylidene-1,6-hexanediaminate) zinc (II) (1AZM -Hex) are studied. As a result, strong EL emission is observed in the type I superlattice structures. The mechanism of enhancement is discussed using energy band structure.
Novel Conjugated Polymers Containing Ferrocene
Authors: Lee Jin-Kyu , Cho Sung In
Published: May 2011

Conjugated inorganic/organic hybrid polymers, poly(phenylene vinylene ferrocenyl vinylene), was prepared by condensation polymerization of bisphosphonate reagent and ferrocenedialdehyde. Conjugated polymers having long alkyl side chains is very soluble in various organic solvents and thin polymer films can be easily produced by spin-coating technique. UV-Vis., NMR, cyclicvoltammetry, and GPC analysis were used to characterize the properties of conjugated polymers, and the averaged molecular weight was in the range of 7,000~25,000 (vs. PS standard). Electrical conductivity measurement of this processible conjugated polymer either in powder or in thin solid film showed very low conductivity probably due to the slow chain-to-chain hopping process. Third order nonlinear optical property of the conjugated polymers was measured as high as ϰ(3) = 1.24×10−8 esu in spin-coated thin film.
Tetraphenylmethane-Based 1,3,4-Oxadiazole as Electron Transporting Materials in Organic Light-Emitting Devices
Authors: Chen Chin-Ti , Lin Tzu-Yao J. , Yeh Hsiu-Chih , Jan Li-Hsin , Balasubramaniam Easwaramoorthy , Tao Yu-Tai
Published: May 2011

A series of tetrahedral tetramers of 2,5-diphenyl substituted 1,3,4-oxadiazole compounds were synthesized and characterized for electron-transporting layer (ETL) in organic light-emitting diode (OLED). The multiple-branch design of the oxadiazole tetramers intends to increase the melting temperature and to generate glass phase of the low molar mass derivative such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). We observed temperatures of the glass phase transition for the oxadiazole tetramer with appropriate peripheral substituents, indicative of amorphous characteristics of the molecule in spite of highly symmetrical molecular framework. The luminescence-current-voltage characteristics of multilayer OLED devices containing the oxadiazole tetramer or PBD as ETL were examined to evaluate the efficiency of our multiple-branch molecular design.
Relationship Between Spectroscopic and Structural Properties of Poly(meta/para Phenylene)
Authors: Dridi Cherif. , Davenas Joël. , Touhami Ahmed. , Ouada Hafedh. Ben , Mâaref Hassen. , André Jean-Jacques.
Published: May 2011

We have used electron paramagnetic resonance (EPR) spectroscopy for investigating the properties of spins, such as those carried by polarons which carry both spin and charge in an electrosynthesized poly (meta/para phenylene) PMPP.Indeed, the study of their mobility provides an insight into the charge transport properties of the conjugated polymer in a microscopic scale.Moreover, we report a correlation between thin film morphology, chainlength and optical gap.Particularly, we show a blue shift upon decreasing chainlength. Furthermore, we have observed a blue shift of the energy band gap with the decrease of the surface grain size deduced from atomic force microscopy (AFM) analyses. This result has been explained in terms of quantum confinement.
New Electron Acceptor for the Control of Crystal Structures and the Generation of High Optical Nonlinearities
Authors: Pu L. S. , Nishikata Y.
Published: May 2011

Cyclobutenedione (CD) as a new electron acceptor for second order nonlinear optical materials is reported. After syntheses and evaluation of new materials containing CD, it is observed that CD is not only a strong electron acceptor to enhance second order molecular hyperpolarizability (β), but also the first substituent to control the molecular orientation in crystals. Compared with nitro (NO2) subsutitent, CD is shown to be advantageous in higher molecular absorption coefficient (ε), shorter λcut-off and easy introduction of chirality with hydrogen bonds into organic molecules. These advantages are useful to produce higher β values and second order nonlinear optical coefficients (dIJK) than nitro analogue, by controlling the molecular orientation in bulk crystals. In particular, CD substituted with chiral 1-amino-2-propanol is shown by x-ray crystallographic analyses to have a function to control molecular orientation one dimensionally in a mono-molecular plate of crystals with space group P1. By oriented gas model, very large d-values including off-diagonals were obtained. From the analysis of the Maker fringe pattern, the coefficient d11 of DAD ((-)-1-(4-dimethyl aminophenyl)-2-(2-hydroxypropylamino)cyclobutene-3,4-dione) was measured to be 200±40 pm/V.
Influence of the Chemical Structure on the Luminescence Properties of Organic Dye Molecules
Authors: Zojer Egbert , Rant Ulrich , Buchacher Petra , Müllner Ruth , Stelzer Franz , Wudl Fred , Schulte Niels , Schlüter Arnulf-Dieter , Leising Günther , Brédas Jean-Luc
Published: May 2011

In this contribution we compare experimental investigations (of photoluminescence, absorption and modulation spectroscopy) for a number of novel dye molecules to quantum-chemical simulations. The investigated materials contain phenylene-, phenylenevinylene-, naphthylene- and anthrylene units linked either by saturated or non saturated bonds. In the first part of the paper we give a short overview of the principal optical properties of the investigated molecules including a discussion of exciton localization effects. The latter can be accomplished by studying the geometry modifications in the excited state relative to the ground state. To do so, we couple the Austin Model 1 (AM1) approach to a multi-electron configuration interaction technique (MECI). The optical spectra are subsequently obtained from the Intermediate Neglect of Differential Overlap (INDO) Hamiltonian combined with a Single Configuration Interaction (SCI) approach. In the main section of this contribution we show the results of singlet exciton lifetime measurements performed with a modulation technique. An excellent agreement was found between the experimental data and quantum-chemical simulations for the transition dipole moments
Infrared Photospectroelectrochemistry of Germanium/Pedot/Electrolyte Interfaces
Authors: Neugebauer Helmut , Yohannes Teketel , Sariciftci N. Serdar
Published: May 2011

Difference infrared spectra between illumination and dark of a polyethylenedioxythiophene (PEDOT) covered germanium electrode in contact with the electrolyte solution and under applied potential are shown. The spectra show a different behavior at different redox (doping) states of the polymer. The photoinduced formation of positive charge carriers was found by illumination of the neutral (undoped) form, wheras no significant spectral changes occur in the oxidized (p-doped) and reduced (n-doped) form of PEDOT.
Electrochemically- and Photo-Induced IR Absorption of Low Band-Gap Polydithienothiophenes: A Comparative Study
Authors: Cravino A. , Neugebauer H. , Sariciftci Niyazi S. , Catellani M. , Luzzati S.
Published: May 2011

Poly(dithieno[3,4-b:3',4'-d]thiophene) (pDTT1), poly(dithieno[3,4-b:3',2'-d]thiophene (pDTT2) and poly(dithieno[3,4-b:2',3'-d]thiophene) (pDTT3) are low band-gap polymers that undergo both p- (oxidation) and n- (reduction) type electrochemical reversible doping in organic electrolytes. In this work we report on the in-situ IR spectroscopic characterization of both doping types using attenuated total reflection (ATR) FTIR spectroelectrochemistry. Thin polymer films were prepared on Ge reflection elements by electrosynthesis. During electrochemical potential cycling experiments in a spectroelectrochemical cell, the evolution of infrared active vibrational (IRAV) modes, correlated with the generation of charge within the polymer chain, was studied. In addition to electrochemical doping, the polymers exhibit also charged excitations by photodoping. FTIR spectra recorded by illumination/dark cycles show photoinduced IRAV bands which are similar to those found for the electrochemically p-doped materials. The infrared spectroscopic results are compared with Raman spectra of the neutral polymers. The relationship between vibrational properties and structure of the polymers is discussed in terms of different contribution of the φ-electrons within the repeating units to the electronic structure of the conjugated backbone.
Second Order Nonlinear Optical Films by Alternating Polyelectrolyte Deposition on Hydrophilic and Hydrophobic Substrates
Authors: Roberts M. Joseph , Herman Warren N.
Published: May 2011

Alternating polyelectrolyte deposition (APD) is a room temperature process that can be used to produce noncentrosymmetric ordered films of nonlinear optical polymers (NLOP). In this study, second-order NLOP APD films of a stilbazolium-substituted polyepichlorohydrin, poly (diallyldimethylammonium chloride), and polyacrylic acid were prepared by alternately dipping a substrate into aqueous solutions of each polymer. Evidence for uniform layer to layer deposition includes a linear increase of UV-Visible absorbance, thickness measurements, and quadratic increase of second harmonic generated light intensity as a function of film thickness. Films have been uniformly deposited up to 0.1 micrometer thick. The surface morphology, roughness, and film thickness have been characterized by Tapping Mode Atomic Force Microscopy (TM AFM ). Work is in progress to deposit thicker films of the same quality and to improve NLO figures of merit.
Low Halfwave Voltage Electrooptic Polymer Modulator Technology
Authors: Shi Yongqiang , Lin Weiping , Olson David J. , Bechtel James H.
Published: May 2011

The recent development in nonlinear optical polymer materials and device fabrication technologies has resulted in a significantly reduced halfwave voltage for high-speed optical communications. In this paper, optical push-pull and active cladding approaches are discussed for low halfwave voltage electrooptic polymer modulator design and fabrication. Based on these new designs, experimental polymer modulators were fabricated and a halfwave voltage-interaction length product of 2.2 V-cm was achieved using optical push-pull and a highly active electrooptic polymer system.
Design and Synthesis of New Acceptor Molecules for Photo-Induced Electron Transfer Reverse Saturable Absorption
Authors: Bader M. , Moser J. , Li H. , Tarter S. , Spangler C.
Published: May 2011

With the advent of efficient and relatively inexpensive pulsed and CW laser systems for both civilian and military applications, the need for adequate eye and sensor protection is becoming increasingly important. While it is possible to filter out harmful wavelengths if the laser frequency is known, the proliferation of frequency agile laser sources underscores the need for “smart” passive materials that can sense the incident wavelength and provide protection. There has been considerable progress made in recent years in the design of optical power limiting (OPL) materials that can function by a variety of mechanisms, most of which derive their limiting behavior from some type of nonlinear absorption process. The most well-studied of these processes involve excited state absorption in which the absorption cross-sections of the photo-generated transient species are much greater than the original S0 to S1 transition. In this presentation we will discuss the efficacy of charge transfer species for optical limiting, and the need for more and better electron acceptor species.
Interfacial Design of Silicon/Polypyrrole Junctions
Authors: Kim Namyong Y. , Vermeir Inge E. , Laibinis Paul E.
Published: May 2011

Hydrogen-terminated silicon surfaces exposing a molecular film of covalently grafted pyrrole units were formed by a solution-phase reaction using the organolithium reagent 5-(N-pyrrolyl)pentyllithium. Electrochemical polymerization of pyrrole onto native hydrogen-terminated silicon surfaces and these chemically modified supports produced silicon/polypyrrole junctions that showed diode-like characteristics, with those formed on the latter substrate exhibiting higher current densities and better ideality factors. The presence of the grafted pyrrole films on silicon provided a better electrochemical control over the polymerization process and yielded smoother polypyrrole films than on the native hydrogen-terminated silicon supports. Impedance measurements revealed that the electrical improvements to the silicon/polypyrrole junctions were a consequence of incorporating sites on the silicon surface for direct contact between the conducting polymer and the semiconductor, as the barrier height of the junction appeared to be unaffected by the chemical modification.
A Route to Stable Interfaces Between Dissimilarly Doped Conjugated Polymers
Authors: Zhou Xin , Langsdorf Brandi , Lonergan Mark C.
Published: May 2011

A route to kinetically stable interfaces between dissimilarly doped conjugated polymers is proposed. The route relies on the use of internally compensated conjugated polymers to kinetically control interfacial redox chemistry. As a demonstration of the feasibility of the proposed route, the enhanced stability of an interface between an oxidatively doped, internally compensated poly(acetylene) and an undoped poly(acetylene) is reported.
Vibronic Structure of PTCDA Stacks: Monomer-Dimer Equilibrium
Authors: Soos Zoltán G. , Hennessy Margaret H. , Bulovic Vladimir
Published: May 2011

Solution spectra of perylenetetracarboxylic dianhydride (PTCDA) show an equilibrium between monomers and dimers, with fluorescence exclusively from monomers and absorption from both. The dimer absorption follows closely the spectrum of PTCDA stacks in crystalline films, which indicate strong coupling to a molecular vibration and mixing of Frenkel and charge-transfer excitons. The same model accounts for solution spectra.
Photoexcitations in Oligothiophenes: The Role of Conformation Mobility and Intermolecular Interactions.
Authors: Botta Chiara , Destri Silvia , Porzio William , Bongiovanni Gianni , Mura Andrea , Loi Maria A. , Garnier Francis , Tubino Riccardo
Published: May 2011

The optical properties of substituted and unsubstituted oligothiophenes are analysed with respect to their supramolecular organization in the solid state. The spectra typical of the isolated molecules are obtained by reducing the intermolecular interactions by both lateral chain substitution and by inclusion in a host organic crystal. The photophysical properties of the weakly interacting oligothiophenes are strongly influenced by their backbone conformation and conformational mobility. Oligomers included in the channels of a guest crystal show fast torsional relaxation processes during the photoexcitation. Powders of β-substituted oligomers display optical properties dependent on the conformation of their particular chain packing arrangement.
Photonic Properties of Dendrons and Dendrimers Incorporating Bis-(Diphenylphosphino)Diphenylpolyenes
Authors: Madrigal L. , Kuhl K. , Spangler C.
Published: May 2011

Substituent effects are quite important in fine tuning the photonic properties of conjugated molecules. In designing new chromophores, electron-donating or withdrawing substituents affect the electron distribution in the conjugation sequence, and previous studies to establish structure- property relationships have noted that when second row elements replace first row elements in the structure (e.g. S for O in donor groups), large enhancements of both the second and third order optical nonlinearity are observed. However, along with the observed enhancement of the nonlinearity, a red-shift in the absorption spectra occurs, often with peak broadening and tailing. This absorptivity-nonlinearity trade-off has been a constant concern in proposing organic materials for electro-optic device applications. In this presentation we will review our recent activity in designing new chromophores wherein P replaces N in donor groups and dendrimer building blocks, and the consequences and opportunities resulting from the observed large blue shifts in the spectra.
Photovoltaic Effect in Multilayer Organic Systems
Authors: Meinhardt G. , Moderegger E. , Schröder R. , Winter G. , Hanack M. , Quante H. , Geerts Y. , Müllen K. , Tillmann H. , Hörhold H.-H. , Leising G.
Published: May 2011

The organic materials presented here, e.g. cyano-ether-PPV, different bisarylamidine-perylenes and conventional as well as substituted forms of phthalocyanines exhibit the advantages of low processing costs and the simplicity of tuning their optical properties. Hence they are promising candidates to be used in large area photovoltaic applications. The investigated cells consist of one or two organic layers sandwiched between electrodes of indium tin oxide (ITO) and aluminum. The experimental techniques of electroabsorption(EA)- spectroscopy, photocurrent-action spectroscopy and current voltage characterization were used to gain further insight into the process of charge generation, charge separation and transport of the charged species to the electrodes. To enhance the quantum efficiencies of the photovoltaic cells, combinations of organic materials with electron-accepting and electron- donating properties in multilayer devices were investigated. We chose the organic materials copper-phthalocyanine and a bisarylamidineperylene whose HOMO and LUMO level alignment should favor a charge transfer process in order to increase the photocurrent(PC) responsivity by enhanced exciton dissociation. Additionally, one of the two layers of a double layer device was blended with small amounts of the material constituting the second layer to further increase charge carrier generation by extending the dissociation zone.
Influence of Colloids in Experimental Solubility Studies of Ni in Natural and Synthetic Aqueous Media
Authors: Vuorinen Ulla , Carlsson Torbjörn , Kekki Tommi
Published: May 2011

The estimation of nickel solubility values for performance assessment is impaired by the lack of experimentally verified solubility values in conditions relevant to actual nuclear waste disposal sites. For this reason, experimental nickel solubility studies were conducted in conditions relevant to a possible Finnish disposal site, Olkiluoto. Using an initial nickel concentration of 10−3 M, nickel solubility was approached from over-saturation in three aqueous media – natural fresh groundwater, synthetic saline groundwater, and cement-conditioned groundwater with added ferrous iron and sulfide. In addition to the nickel solubility values, nickel association with the particle and colloidal phases was measured. Almost 100%of the initial nickel was found associated with the separated particle phase in the natural groundwater and the cement-conditioned groundwater, and in only the natural groundwater about 0.04%or 0.4%with the separated colloidal fraction depending on the initially added amount of ferrous iron and sulfide. In the synthetic saline groundwater, all the nickel was found in the soluble fraction except for a minor fraction sorbed onto the walls of the sample bottle. Colloid-bound nickel did not have any practical influence on the solubility values obtained. The inverse behavior of Ni solubility and sorption in the natural groundwater compared to that in the other two aqueous phases studied was suspected to be caused by the unidentified yellow color of the groundwater for which indications of both possible organic and inorganic nature was obtained. Based on the measured results, the presence of sulfide and ferrous iron would decrease the amount of mobile nickel, both soluble and colloidal, in non-saline natural and cement-conditioned groundwater, whereas in saline groundwater nickel remains in the mobile phases.
Insights to Repository Performance through Study of a Nuclear Test Site
Authors: Smith D.K. , Kersting A.B. , Thompson J.L. , Finnegan D.L.
Published: May 2011

Underground nuclear test sites offer an unprecedented opportunity to evaluate processes relevant to high-level waste repository performance in the absence of engineered barriers. Radionuclide migration programs at the Nevada Test Site represent a twenty-five year systematic investigation of the diverse radiologic source terms residual from weapons testing and the evolution of the hydrologic source term which comprises those radionuclides dissolved in or otherwise available for transport by groundwater. The Nevada Test Site shares actinide source terms, correlative geology, an identical tectonic setting, similar climate, and a thick unsaturated zone with the adjacent potential Yucca Mountain high-level waste repository and provides a natural laboratory to assess long-term radionuclide transport in the near field. Analog studies may ultimately help validate predictions of radionuclide transport from the potential Yucca Mountain repository.
Surface Conductivity and Diffusion Models - Comparison and Evaluation -
Authors: Ohlsson Y. , Arnerdal K. , Neretnieks I.
Published: May 2011

The interest for studying the mobility of near surface cat-ions in rock and clay pores has increased during the last 3-4 years. Several researchers have worked experimentally with liquid phase diffusion experiments and with electrical conductivity measurements, and on developing models describing the phenomenon. Our own measurements have shown that surface mobility can contribute substantially to ionic transport in crystalline rock. Some recently proposed models for surface mobility are discussed.

Part of the problem in comparing different surface transport models lies within the different definitions of what the diffuse layer and the Stern layer really comprise. There are also differences in what is actually considered to be adsorbed ions and what part of these ions that can be considered mobile. We attempt to reconcile some of the different approaches by describing some very simplified concepts upon which all the models are based. This permits us to discuss the different views within one framework. Experimental results interpreted using the various models are discussed in the context of the simplified framework.
Use of Multi-Dimensional Sorption Data-Sets to Constrain Models of Radionuclide-Solid Interactions
Authors: Payne T. E. , Waite T. D. , Lumpkin G.R.
Published: May 2011

In order to adequately constrain surface complexation models for radionuclide sorption, large ‘multi-dimensional’ data-sets, showing the dependence of sorption on numerous experimental parameters, are required. This paper describes how large sorption databases were used to develop surface complexation models of U(VI) uptake on kaolinite and ferrihydrite. It is shown that the shape of U uptake curves as a function of pH and total U (εU) can be used to distinguish between U adsorption and the precipitation of amorphous uranyl hydroxide. The U sorption data-set obtained in this work also includes the effects of several complexing ligands, including phosphate. The dependence of U uptake on these variables can be used to assess the formation of various types of surface complexes (including ternary surface complexes) and the possibility of precipitation reactions. Adsorption experiments with different sorbing materials were also useful in developing models for U sorption and for excluding some possible surface and precipitation reactions. This study shows how combining multi-dimensional sorption databases with advanced spectroscopic or microscopic techniques (such as EXAFS or AEM) can lead to improved models of interactions at mineral-water interfaces.
Migration of Cs-137 and Co-60 in the Australian Arid Zone
Authors: Payne T.E. , Harries J.R. , Itakura T.
Published: May 2011

Batch adsorption experiments with Cs-137 and Co-60 were undertaken using representative samples of geologic materials from the arid region that has been selected for an Australian low-level waste repository. The results indicate that the pH is the main factor affecting the adsorption of Co-60 but has little influence on the sorption of Cs-137. The ionic strength affects Cs sorption, with a decrease in Kd associated with higher ionic strength. Selective sorption sites on mica and illite control uptake of trace Cs, whereas the high total site availability of smectite is significant when the total Cs is higher (1 mmol/L). The effects of mineralogy on Cs sorption which were observed for these complex materials confirmed previous results reported for pure minerals.
The Solubility of Metallic Selenium under Anoxic Conditions
Authors: Iida Yoshihisa , Yamaguchi Tetsuji , Nakayama Shinichi , Nakajima Tomoko , Sakamoto Yoshiaki
Published: May 2011

The solubility of metallic selenium was measured in a mixture of 0.1M-NaCl and 0.05M-N2H4under anoxic conditions (O2 < 1 ppm) by both oversaturation and undersaturation methods. Equilibrium was attained in 40 days. The aqueous selenium species identified were HSe at pH between 5 and 8, and Se42at pH between 10 and 13, by UV-Vis absorption spectrometry. The solid phase was identified as Se (cr) by X-ray diffraction. The equilibrium constants of

Se(cr) + H+ + 2e- = HSe- logK0 = -6.5±0.5 and

4Se(cr) + 2e- = Se42- logK0 = -16.8±0.5

were determined. The standard molar free energy of formation of HSe- and Se42-was determined to be (37.1±2.9) and (95.9±2.9) kJ/mol, respectively.
Isolation and Microscopic Characterization of Nuclear Fuel Particles from Two Contaminated Soils of Chernobyl
Authors: Noureddine Ahamdach , Denise Stammose
Published: May 2011

Nuclear fuel particles were separated, from two different Chernobyl contaminated soils, by sedimentation in bromoform. Their physico-chemical characteristics were studied by scanning electron microscopy. The two soils show the same types of fuel particles: one part of these particles contains U and O and the other part contains U, Zr and O. The structure and the surface morphology of the studied particles are variable and are characteristic of the conditions of their formation. The source term is thus heterogeneous. This heterogeneity has direct consequences on the dissolution of the fuel particles and should be taken into account in mathematical models.
Tritium and Iodide Diffusion through Opalinus Clay
Authors: Llano A. Yllera de , Sainz-Ezquerra M. Mingarro , Gutiérrez M. García
Published: May 2011

The International Mont Terri Project [1, 2] started in 1995 under the patronage of the Swiss National Hydrological and Geological Survey (SNHGS), and has the authorization of the République et Canton du Jura. The underground rock laboratory is located at the northwestern part of Switzerland (Canton Jura), in and beside the reconnaissance gallery of the Mont Terri motorway tunnel, one of the several tunnels of the A16 “Transjurane” motorway. The depth of overburden above the rock laboratory is approximately 300 meters.

The project is aimed to investigate the geological, hydrogeological, geochemical and rock mechanical properties of the Opalinus Clay for assessing the feasibility and safety of a repository for radioactive waste placed in this type of host rock. One of the issues under study is radionuclide migration by diffusion through clays. As a part of this investigation, an interlaboratory comparison on small-scale diffusion experiments was carried out by three research laboratories: AEA Technology (UK), SCK·CEN (Belgium) and CIEMAT (Spain). The radionuclides investigated were tritium and iodine. This paper concerns to the methodological approach and results of the experiments undertaken by CIEMAT.

The effective diffusion coefficients were measured for tritiated water and iodine (as I-), resulting larger for tritium [(1.7±0.4)×10−11 m2/s] than for iodide [(2.7±0.3)×10−12 m2/s]. The porosity available for diffusion was calculated by using the time-lag method, but some results seemed unrealistic and showed a large variability. In general, tritium exhibited higher values of porosity than iodide (17 to 26% and 12 to 17%, respectively), which were consistent with the anion exclusion affecting the distribution of iodide into the clay pores.
Electrical Conductivity and Structural Properties of Cesium Iron Phosphate Glasses: A Potential Host for Vitrifying Nuclear Waste
Authors: Mogus-Milankovic  , Furic K. , Day D. E.
Published: May 2011

The thermally stimulated current (TSC) and dc conductivity for iron phosphate glasses containing up to 28 mol% Cs2O have been measured in a temperature range from 120 to 400 K. The dc conductivity and activation energy were constant and independent of Cs2O content. With increasing cesium concentration in cesium iron phosphate glasses the slowly moving cesium ions are more tightly bound to the non-bridging oxygen ions and make no measurable contribution to dc conductivity. The dc conduction in these glasses is totally electronic, controlled by electron hopping between iron ions. The ionic conduction is immeasurably small because of the low mobility of the cesium ions. This agreement is reinforced by the excellent chemical durability of the glasses, where the dissolution rate at 90oC changes little with increasing Cs2O content. Raman spectroscopy indicated that the structure of these glasses was composed of predominantly pyrophosphate (P2O7) groups, but the metaphosphate chains (PO3) also existed.
Influence of Platinum-Group Metals on Nuclear Glass Properties: Viscosity, Thermal Stability and Alterability
Authors: Bart F. , Dussossoy J.L. , Fillet C.
Published: May 2011

The fission products resulting from reprocessing of commercial spent fuel are currently vitrified industrially by COGEMA at La Hague. The properties of 21 non-radioactive borosilicate glass samples containing between 4 and 6% of the platinum-group metals (PGM: Pd and Ru) compared with 1.6% in the industrial glass were investigated for chemical composition variations covering the full specification range. After a brief morphological description of the undissolved PGM in the glass, the viscosity variations at temperatures ranging from 1100 to 1200°C are discussed with emphasis on the effects of the particle inclusions on the rheological properties of the glass. Variations in the chemical durability of quenched glass specimens are then discussed. The initial leach rate V0 at 100°C remained near the values obtained for the reference glass. The same tests were repeated on glass heat-treated to obtain maximum crystallization, and the results confirmed that the chemical durability of the glass is practically unaffected by the crystallization observed in this type of glass.
Melted Synthetic Zirconolite-Based Matrices: Effect of Cooling Rate and Heat Treatment on Ceramic Microstructure and Chemical Durability
Authors: Advocat T. , McGlinn P.J. , Fillet C , Leturcq G. , Schuller S. , Bonnetier A. , Hart K.
Published: May 2011

The heat treatment conditions are a key factor in fabricating zirconolite ceramics and glass-ceramics following high-temperature melting. An oxide mixture melted at 1450°C and subsequently heat-treated at 1200°C yielded a glass-ceramic containing crystallized zirconolite–2M. The silica-enriched residual glass represented about 60-70 vol% of the total; the actinide surrogates (Nd, Ce)were equally distributed between the residual glass and the zirconolite crystals. Zirconolite ceramics obtained after melting an oxide mixture at 1600–1700°C consisted of zirconolite, perovskite and rutile. Rapid cooling rates (> 100°#x00B0;··min-1) were obtained by pouring the melt into ingot molds; the resulting zirconolite ceramics were characterized by crystals of zirconolite-2M ranging from 1 to no more than 20 μm. Slow cooling (< 25°C#x00B0;··min-1 produced ceramics with crystals several hundred micrometers long. Despite the microstructural differences, the chemical durability of the zirconolite ceramics was identical. The initial alteration rates r0 were about two orders of magnitude lower than those measured for the residual aluminosilicate glass of the zirconolite glass-ceramics. Moreover, during long-term leach tests at high S/V ratios to obtain advanced degrees of reaction progress, the alteration rates of all the materials diminished by over 3 to 4 orders of magnitude below r0.
Dissolution of Synthetic Brannerite at 90°C
Authors: Zhang Y. , Hart K.P. , Thomas B.S. , Aly Z. , Li H. , Carter M.
Published: May 2011

Brannerite, as a minor phase, exists in the pyrochlore-rich titanate ceramic formulations designed for immobilization of surplus weapons Pu. The dissolution of synthetic brannerite was studied at 90°C using static tests in pH 4 solution, deionized water and Finnsjön synthetic groundwater.

After 140 days the normalized U release rates into a pH 4 solution and deionized water reach similar values, ~10−2 g m−2 d−1, and are about 2 orders of magnitude higher than those in Finnsjön synthetic groundwater. The normalized Ti release rate into Finnsjön synthetic groundwater is about an order of magnitude higher than those in pH 4 solution and deionized water. The dissolution of brannerite is incongruent in the pH 4 solution and deionized water (preferential release of U over Ti), and nearly congruent in Finnsjön synthetic groundwater. SEM observations of the samples after 140 days in pH 4 solution and deionized water revealed minor surface alteration, in the form of a thin surface layer, probably TiO2, as a result of preferential releases of U in both cases.
Emanation Thermal Analysis Study of Brannerite
Authors: Balek V. , Zelenák V. , Málek Z. , Vance E. R. , Subrt J.
Published: May 2011

Radon emanation thermal analysis (ETA) during ”step by step”heating to selected temperatures up to 1200oC in argon and subsequent cooling yielded detailed information on the annealing of radiation damage and macroscopic defects in a natural brannerite. Thermogravimetry showed mass losses in the temperature ranges 230-315, 570-760 and 840-1040oC. Mass spectrometry of the evolvedgases indicated M/Z = 44, i.e. CO2. Crystallization of initially amorphous brannerite was indicated by ETA in the temperature range 900-1020oC, in agreement with the X-ray diffraction results. From the radon diffusion activation energy values determined in ETA, the degree of structural ordering was assessed at different temperatures.
Measured Displacement Energies of Oxygen Ions in Zirconolite and Rutile
Authors: Smith Katherine L. , Cooper Ronald , Colella Michael , Vance Eric R.
Published: May 2011

Optical emission spectra in the 300-700 nm range were collected from zirconolite and rutile specimens irradiated with a 3 μs pulsed electron beam using a Febetron 706 variable energy pulsed electronbeam generator. The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths ~ 100 nm) bands centred around ~400 nm. Over the range 0.2 MeV to 0.6 MeV, the emission intensity per unit dose versus electron beam energy data from the rutile sample showed a single stage dependence on electron beam energy, whereas the zirconolite data suggested a two stage dependence. Rutile has a threshold of 0.23 ½ 0.02 MeV, which gives an Ed value of 39 ½ 4 eV for oxygen. Zirconolite has a threshold of 0.26 ½ 0.02 MeV, which gives an Ed value of 45 ½4 eV for oxygen. These data are discussed in the context of previously measured and calculated Ed values for other oxides.
Influence of Container Base Material (Fe) on SIMFUEL Leaching Behavior
Authors: Quiñones J. , Serrano J.A. , Díaz P.P. , Almazán J.L. Rodríguez , Cobos J. , Esteban J.A. , Martà–nez-Esparza A.
Published: May 2011

The chemical stability of spent fuel will be greatly influenced by the redox potential of the near field. Presence of reductants such as iron is likely to be an important factor to maintain the original integrity of spent fuel. In this work experimental data about the influence of metallic iron (container base material) on SIMFUEL leaching behavior under simulated granite and saline repository conditions is presented. In the presence of iron uranium concentration undergoes a sharp decrease. This is much more noticeable in the experiments performed under initial oxic conditions. The effect of iron on simulated fission products of SIMFUEL is very important for the elements with high redox sensitivity such us molybdenum. On the contrary, strontium remains stable during the entire tests and it seems not be affected by changes in redox potential.
Release of Radionuclides from Spent Fuel Under Repository Conditions: Mathematical Modelling and Preliminary Results
Authors: Cera Esther , Merino Juan , Bruno Jordi
Published: May 2011

In the framework of the Enresa 2000 PA exercise and as a continuation of the developments made during SR 97, we have developed a conceptual and numerical model to calculate the release of radionuclides from spent fuel under repository conditions. The model includes both thermodynamic and kinetic considerations. Hence, although certain radionuclides are solubility controlled, for other radionuclides their release is governed by kinetic processes such as radiolytically promoted oxidative dissolution of the matrix and the associated water turnover inthe gap. The fluxes of selected radionuclides are calculated as an indication of the relative importance of the various processes considered to define source term concentrations in the performance assessment of the spent fuel repository.
A New Approach to the RN Source Term for Spent Nuclear Fuel under Geological Disposal Conditions
Authors: Poinssot Christophe , Jegou Christophe , Toulhoat Pierre , Piron Jean-Paul , Gras Jean-Marie
Published: May 2011

Under the geological disposal conditions, spent fuel (SF) is expected to evolve during the 10,000 years while being maintained isolated from the biosphere before coming in contact with water. Under these circumstances, several driving forces would lead to the progressive intrinsic transformations within the rod which would modify the subsequent release of radionuclides. The major mechanisms are the production of a significant volume of He within the UO2 lattice, the accumulation of irradiation defects due to the low temperature which avoids any annealing, the slow migration of radionuclides (RN) within the system by (i) the α self-irradiation-induced athermal diffusion and (ii) locally the building-up of internal mechanical stresses which could turn the pellets into powder. However, the current RN source terms for SF have never accounted for this evolution as they are based on existing knowledge of the fresh SF. Two major mechanisms were considered, the leaching of the readily available fraction (one which was supposed to be instantly accessible to water), and the release of RN through alteration of the UO2 grains. We are now proposing a new RN source term model based on a microscopic description of the system in order to also take account of the early evolution of the closed system, the amplitude of which increases with the burnup and is greater for MOX fuels.
Mechanical Properties of Oxides Formed by Anaerobic Corrosion of Steel
Authors: Smart N.R. , Bond A.E. , Crossley J.A.A. , Lovegrove P.C. , Werme L.
Published: May 2011

In Sweden, it is proposed that spent nuclear 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, there would be a build up of ferrous corrosion product, which could induce stresses in the outer copper canister. This paper describes an apparatus, the ‘stress cell’, which was designed to measure the expansion caused by the anaerobic corrosion of steel under compressive loads. The apparatus consisted of a stack of steel and copper discs, which were immersed in simulated anoxic groundwater. A system of levers amplified the change in height of the stack, and the displacement was measured using sensitive transducers. Three cells were set up; two contained alternate mild steel and copper discs, and the third, a control cell, consisted of alternate stainless steel and copper discs. A slight contraction of the control cell was observed but no expansion was measured in the mild steel - copper cells.

In parallel, coupons of mild steel and cast iron were corroded in anoxic, artificial groundwater at 50°C and 80°C for several months. The coupons were examined by atomic force microscopy (AFM) to determine the mechanical properties and the structure of the corrosion product films, and X-ray photoelectron spectroscopy (XPS) to identify the chemical composition of the film.
Influence of Oxygen Concentration and Alkalinity on the Hydrogen Gas Generation by Corrosion of Carbon Steel
Authors: Fujiwara A. , Yasutomi I. , Fukudome K. , Tateishi T. , Fujiwara K.
Published: May 2011

A repository for low and intermediate level radioactive wastes will contain a great deal of carbon steel as reinforcement materials and waste containers. These steel components are expected to generate hydrogen gas due to reductive corrosion of carbon steel under repository condition. In this study, we have investigated the influence of the environmental factors such as oxygen concentration and pH in the solution on the rate of the gas generation. This rate was measured with a gas flow type test system under the controlled oxygen concentration, which simulates the redox conditions from initial to final environment in a repository. In addition, the corrosion mechanism was examined through the electrochemical tests.

As a result, it has been found that pH in the solution and the oxygen concentration considerably affected the generation rate of hydrogen gas in various way. As to the influence of pH of the solution, it has been found that the gas generation rate increased with the increase of pH between 11.8 and 14. Further, as to the influence of the oxygen concentration, when the oxygen concentration in the blowing nitrogen gas was 2 ppm or more, the gas generation rate increased with the oxygen concentration. This trend was possibly caused by local decrease of pH due to localized corrosion. The gas generation rate was very low when the oxygen concentration was in the passive region. The rate was equal to 0.01 μm/y or less if the corrosion occurs with an equation: 3Fe+4H2O → Fe3O4 + 4H2 ↑ to 0.01 *m imcro;/y (hereafter we call this the equivalent corrosion rate). However the gas generation rate increased when the oxygen concentration was controlled to the extent that sufficient passive film cannot be produced and thus it shifts from passive state to active state.
Study of the Consequences of Secondary Water Radiolysis within and Surrounding a Defective Canister
Authors: Liu Jinsong , Strömberg Bo , Neretnieks Ivars
Published: May 2011

A model has been developed to study the effects of secondary water radiolysis caused by dispersed radionuclides in a bentonite buffer surrounding a copper canister. The secondary radiolysis is the radiolysis caused by radionuclides that have been released from the spent fuel and are present either as solutes in the pore-water, as sorbed species on the surface of other minerals, or as secondary minerals. The canister is assumed to be initially defective with a hole of a few millimeters on its wall. The small hole will considerably restrict the transport of oxidants through the canister wall and the release of radionuclides to the outside of the canister. The dissolution of the spent fuel is assumed to be controlled by chemical kinetics at rates extrapolated from experimental studies. Two cases have been considered with the purpose to illustrate the behaviors of both conservative and non-conservative nuclides. The nuclides that are most relevant are those expected to be the dominant α-emitters in the long-term (e.g. 239Pu, 240Pu, 241Am). In the first case it is assumed that there is no precipitation of secondary minerals of the relevant radionuclides inside the canister. In the second case it is assumed that the radionuclide concentration within the canister is controlled by its respective solubility limit. The radionuclide released to the surrounding buffer is then predicted using a mass balance model. The modelling results show that in both cases, the spent fuel will not be oxidized at a rate significantly faster compared to the case where secondary radiolysis is completely neglected. In the first case, however, a large domain of the near-field can be oxidized due to a much faster depletion of reducing minerals in the buffer, compared to the case where secondary radiolysis is neglected. In the second case, the effects of the secondary water radiolysis will be quite limited.
Coupled Thermo-Hydro-Geochemical Models of Engineered Barrier Systems: The Febex Project
Authors: Samper J. , Juncosa R. , Navarro V. , Delgado J. , Montenegro L. , Vázquez A.
Published: May 2011

FEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository (HLWR). It includes two main experiments: an situ full-scale test performed at Grimsel (GTS) and a mock-up test operating since February 1997 at CIEMAT facilities in Madrid (Spain) [1,2,3]. One of the objectives of FEBEX is the development and testing of conceptual and numerical models for the thermal, hydrodynamic, and geochemical (THG) processes expected to take place in engineered clay barriers. A significant improvement in coupled THG modeling of the clay barrier has been achieved both in terms of a better understanding of THG processes and more sophisticated THG computer codes. The ability of these models to reproduce the observed THG patterns in a wide range of THG conditions enhances the confidence in their prediction capabilities. Numerical THG models of heating and hydration experiments performed on small-scale lab cells provide excellent results for temperatures, water inflow and final water content in the cells [3]. Calculated concentrations at the end of the experiments reproduce most of the patterns of measured data. In general, the fit of concentrations of dissolved species is better than that of exchanged cations. These models were later used to simulate the evolution of the large-scale experiments (in situ and mock-up). Some thermo-hydrodynamic hypotheses and bentonite parameters were slightly revised during TH calibration of the mock-up test. The results of the reference model reproduce simultaneously the observed water inflows and bentonite temperatures and relative humidities. Although the model is highly sensitive to one-at-a-time variations in model parameters, the possibility of parameter combinations leading to similar fits cannot be precluded. The TH model of the “in situ” test is based on the same bentonite TH parameters and assumptions as for the “mock-up” test. Granite parameters were slightly modified during the calibration process in order to reproduce the observed thermal and hydrodynamic evolution. The reference model captures properly relative humidities and temperatures in the bentonite [3]. It also reproduces the observed spatial distribution of water pressures and temperatures in the granite. Once calibrated the TH aspects of the model, predictions of the THG evolution of both tests were performed. Data from the dismantling of the in situ test, which is planned for the summer of 2001, will provide a unique opportunity to test and validate current THG models of the EBS.