bluuebunny/crossref_metadata_2025_split huggingface dataset:
Leaching of Actinides from the French LWR Reference Glass
Authors: Fillet S. , Nogues J L. , Vernaz E. , Jacquet-Francillon N. 
Published: March 2011

AbstractThe French LWR reference glass was spiked successively with 237Np, 239Pu, 238Pu and 241Am to study the specific leaching behavior of each actinide, as part of a larqer program investigating the effects of a decay in this glass. This paper describes the preparation of the α doped glasses and presents the initial leaching results for neptunium, plutonium and americium.Glass samples were leached for up to six months at 90°C under static conditions. Weight loss measurements were performed, and the leachate was analyzed by ICP for the inactive elements, and by a spectrometry for the actinides. The results provide a basis for comparing the retention capability of the glass for each actinide, and the alterability of the bulk glass.Finally, a comparison between glass specimens doped with 239Pu and with 238Pu, having the same chemical composition but very different specific activities, allows the effects of radiolysis on leaching to be estimated.
Effects of Rocks and Backfill Materials on Waste Glass Leaching
Authors: Ishiguro K. , Sasaki N. , Kashihara H. , Yamamoto M. 
Published: March 2011

AbstractExtensive studies have been made on the interactions between a waste glass and repository materials under static conditions. One of the PNC reference glasses was leached in the solution prepared from water in contact with crushed granite, tuff, diabase and backfill materials such as bentonite and zeolite. The leachant solutions except for some bentonite solutions reduced the glass leach rate compared with that measured in distilled water. The extent of the reduction was a function of silicon concentration in solution. The bentonite solutions enhanced the glass dissolution rate by a factor of 2 to 3 at low bentonite/water ratios but the effect was found to be less important at high bentonite/water ratios and in the long-term experiment. Addition of granite and zeolite to the bentonite solutions decreased the leach rate below the value measured in distilled water.
Influence of Higher Waste Loading on Crystallization of Titanosilicate Glass-Ceramics
Authors: Hayward P. J. , Vance E. R. , Cann C.D. , George I. M. 
Published: March 2011

AbstractSphene (CaTiSio5 ) is obtained as the main crystalline phase in Na2O-A12O3-CaO-TiO2-SiO2 glass-ceramics containing up to ∼ 15 wt% of simulated nuclear fuel recycle waste, by maintaining the precursor glass at ∼ 1050°C for sufficient time to allow nucleation and crystal growth. The implications for production of an engineering-scale waste form are discussed.
Source Term for the Activity Release from a Repository for Spent LWR Fuel
Authors: Wuertz Ruediger , Ellinger M. 
Published: March 2011

AbstractIn order to provide basic data for the calculation of the dose burden from a repository for spent LWR fuel in a salt dome, a formula is given for determining activity release into the surrounding salt brine under accident conditions. The main characteristic of this source term is a time-independent, instantaneous release of part of the activity and mobilization of another part at a continuous and temperature dependant rate, using nuclide-specific leach rates. Changes in leach rates resulting from reduction of the waste surface during mobilization and precipitation are taken into account. The model also takes into account axial and radial activity distribution in the fuel rods.
Evaluation of the Localised Corrosion of Carbon Steel Overpacks for Nuclear Waste Disposal in Granite Environments
Authors: Marsh G. P. , Taylor K. J. , Bland I. D. , Westcott C. , Tasker P. W. , Sharland S. M. 
Published: March 2011

AbstractThe application of carbon steel corrosion allowance containers for the long term encapsulation of HLW or spent fuel requires data on the likely rates of corrosion attack so that the metal thickness needed to prevent penetration can be estimated. This paper describes a joint mathematical modelling and experimental approach to the evaluation of the rate of localised corrosion.
Modelling Radionuclide Speciation and Solubility Limits in The Near-Field of a Deep Repository
Authors: Wanner Hans 
Published: March 2011

AbstractIn the safety analysis recently reported for a potential Swiss high-level waste repository, radionuclide speciation and solubility limits are calculated for expected granitic groundwater conditions. With the objective of deriving a more realistic description of radionuclide release from the near-field, an investigation has been initiated to quantitatively specify the chemistry of the near-field. In the Swiss case, the main components of the near-field are the glass waste-matrix, a thick cast steel canister horizontally stored in a drift, and a backfill of highly compacted bentonite.Based on available experimental data, an ion-exchange model for sodium, potassium, magnesium, and calcium has been developed, in order to simulate the reaction of sodium bentonite backfill with groundwater. The model assumes equilibrium with calcite as long as sufficient carbonates remain in the bentonite, as well as quartz saturation. The application of this model to the reference groundwater used in ‘Project Gewaehr 85’ results in a significant rise in pH (by up to 3 units) as well as a marked increase in the carbonate concentration.Neptunium and plutonium speciation and solubility limits are calculated for the reference groundwater chemistry gradually altered to that of saturated bentonite water and back again by a water exchange cycle model. The solubility limits estimated in this way generally turn out to be higher for the bentonite water than for the reference groundwater, mainly due to carbonate complexation of the actinide components AnO2+ and AnO22+. Uncertainties are particularly large for neptunium solubility due to its strong Eh dependence in bentonite water.
The Chemical Environment in Cement Matrices
Authors: Angus M. J. , Glasser F. P. 
Published: March 2011

AbstractGeneral progress in modelling the behaviour of cement matrices and their interactions with wastes is reviewed in terms of appropriate model-ling concepts and their formulation in terms of parameters Which are susceptible to evaluation. The redox behaviour, particularly of slag-cement blends is shown to differ sharply from that of Portland cement matrices. Experimental methods of measuring Eh and poising capacities are described and the composition of pore fluids determined. Slag cements contain appreciable soluble Sn− species as well as S2O32− and SO42−
Near-Field Thermal Analysis of the Nuclear Waste Disposal Vault
Authors: Radhakrishna H. S. , Lau K-C. , Crawford A. M. 
Published: March 2011

AbstractThis paper describes an experimental and theoretical analysis of the near-field thermal performance of a backfilled disposal vault in which the waste containers are emplaced in boreholes and surrounded by a bentonite-sand buffer. Effects of heat and moisture diffusion on the thermal performance of clay-based buffer and backfills were studied by means of laboratory scale experiments. The bentonite-sand buffer exhibited cracking due to desiccation. The impact of such cracking on the perforamnce of buffer as an engineered barrier is being investigated.An integrated finite difference computer code ‘TRUCHAM’ was written to analyze the transient heat and moisture flow regime in a disposal vault and was validated by a scale model heater experiment. It is hoped that with proper characterization of the material properties ‘TRUCHAM’ can be employed as a useful tool in assessing the thermal response of the prototype disposal vault. Further work is needed to integrate the effects of heat and moisture on the shrinkage and expansion of clay-based buffer and backfills.
NMR-Studies of Pore Water in Bentonite/Water/Electrolyte
Authors: Carlsson Torbjörn 
Published: March 2011

AbstractThe properties of water saturated bentonite systems are highly dependent on the pore water chemistry, water content and temperature. In this study relative changes in the physical state of pore water are studied by means of the nuclear magnetic resonance technique (NMR). It is found that the relative water mobility increases with increasing water content and/or increasing temperature, while an increase in the electrolyte content lowers the water mobility.
Transport of Radionuclides in Inhomogeneous Crystalline Rocks
Authors: Hadermann Joerg , Roesel Fritz , Mccombie Charles 
Published: March 2011

AbstractIn Switzerland high-level radioactive wastes are planned to be disposed of in deep-lying crystalline formations. The modelling approach for geospheric transport in the framework of a HLW safety assessment is described. The processes taken into account are advection and dispersion in water conducting veins or fractures. Out of these, nuclides may diffuse into a spatially limited zone of altered rock. Sorption of nuclides on the rock is taken into account. Diffusion out of fractures and sorption in the adjacent altered rock may often be represented by an effective surface sorption on the fracture walls. For transport of the 237-Np nuclide chain we present a sensitivity analysis. The performance of the geologic barrier depends most critically on the extent of the altered zones.
Sorption of Some Fission Products and Actinides in Concrete Systems
Authors: Höglund S. , Eliasson L. , Allard B. , Andersson K. , Torstenfelt B. 
Published: March 2011

AbstractThe sorption of some actinides (Th, U, Np, Pu and Am) and fission products (I, Cs) was measured on two types of Standard Portland cements as well as on samples from old (70 years) hydro power dam constructions using a batch technique. Pore water compositions were analysed, and artificial pore water solutions were used as aqueous phases in the experiments. Measurements were also performed on five other concrete types (not reported in detail in this paper) to illustrate the effects of the cement matrix composition on the sorption behaviour of the radionuclides.The sorption of actinides in the trivalent (americium), tetravalent (thorium) pentavalent (neptunium) and hexavalent (uranium) states was high in all the studied concrete systems.Generally, the sorption of cesium was low due to the low exchange capacity of the cement and the high concentration of competing cations in the pore waters.The sorption of iodine was much higher than in most silicate minerals of geologic origin.The differences between the various concrete systems were generally minor in terms of their sorbing capacities.
Formation and Transport of Americium Pseudocolloids in Aqueous Systems
Authors: Olofsson U. , Bengtsson M. , Allard B. 
Published: March 2011

AbstractThe sorption of americium on colloidal quartz and montmorillonite has been studied using a batch technique. Americium appeared to be distributed between all available surfaces in the system (particles and vessel walls). Distribution coefficients, defined as the ratio of the amount of americium per mass of colloidal matter and the concentration in the solution phase, were estimated to be of the same order of magnitude as obtained in measurements on crushed material of much larger particle sizes.In the presence of sorbents (alumina or granite) the removal of americium from the solution was enhanced, either due to the desorption of the americium from the particle phase and resorption on all available surfaces (sorbent plus vessel wall) or the sorption of the whole colloidal aggregates on the sorbent.No break-through of americium was observed in column experiments (with alumina or granite packing) after the injection of americium pseudocolloids (quartz or montmorillonite) followed by elution with large volumes of aqueous phase (up to 880 column volumes). However, a minor fraction of the americium passed through the column without significant retention, especially under conditions with high flow rate (short hold-up time in the column).
Transient Diffusional Release from Waste Packages in a Repository in Basalt
Authors: Bensky M. S. , Oliver D. L. 
Published: March 2011

AbstractAnalyses of diffusional release of several typical radionuclides in spent fuel from waste packages emplaced in a repository in basalt were conducted to assess the effects of system characteristics and boundary conditions on computed release rates. Radionuclide releases, including spatial and temporal variations that may be present, represent the source term for transport in the geohydrologic setting and are therefore critical to the assessment of repository acceptability.Two mathematical approaches were utilized to determine radionuclide release rate versus time characteristics; (1) an analytical solution for one-deimensional diffusion based upon a Dirichlet (constant-concentration) boundary at the waste form surface; and (2) a finite-element numerical solution based upon a Neumann (zero-flux boundary at the waste form surface. The latter method is suitable for radionuclides such as 129I, whose total inventory in spent fuel could be quickly depleted from the waste form and dissolved in the pore spaces of the packing material surrounding the waste form and which, therefore, cannot be adequately represented by a constant concentration at the waste form (i.e., container) surface.The analysis revealed several system characteristics that are not intuitively obvious. For example, strong sorption in the near-field host rock behaves like a strong mass sink and can yield calculated transient release rates exceeding allowable limits. Similarly, a short half-life effectively removes the radionuclide from the host rock, which induces a steep concentration gradient at the host rock/packing interface and thereby increases the diffusional release rate at that boundary.Typical results for 79Se and 129I are presented to illustrate these effects. The effects of perturbations to key assumptions are shown to indicate the importance of (1) formulating models that accurately represent the physical system and (2) interpreting analytical results carefully to ensure understanding of the capability of the system.
Phase Diagram of Laser Induced Melt Morphologies On Silicon
Authors: Preston John S. , Sipe John E. , Driel Henry M. Van 
Published: March 2011

ABSTRACTDuring cw laser induced melting, over a large range of intensities, silicon films phase separate into patterns of coexisting solid and molten regions. We have identified several distinct and reproduceable morphologies of this inhomogeneous coexistence region ranging from random lamellae (“amorphous”) structures to periodically ordered (“crystalline”) strips. The type of morphology formed is a function of laser intensity and spot size and these parameters can be viewed as constituting the two axes for a steady state “phase diagram” of the structures. “Phase transitions” between these structures occur for small changes of the experimental parameters with the fraction of liquid being an order parameter.
Oscillatory Morphological Instabilities During Rapid Solidification A The Role of Diffusion In The Solid
Authors: Bansal Atul , Bose Arijit 
Published: March 2011

ABSTRACTRecent results by Coriell and Sekerka [J. Crystal Growth, 61, 499(1983)] on the oscillatory instability of a planar rapidly solidifying binary melt are extended to include diffusion in the solid phase. Under assumptions equivalent to those made by Coriell and Sekerka, it is shown that no matter how small the diffusion coefficient is in the solid, the system is stable to all oscillatory and non-oscillatory disturbance modes if the modified constitutional supercooling criterion is satisfied and if the nonriequilibrium segregation coefficient is zero. Thus, a range of the non-equilibrium segregation parameter exists where these results allow the possibility of instability, whereas Coriell and Sekerka predict that the system will be stable.System stability is increased for both oscillatory and non-oscillatory modes. It is necessary for the diffusivity ratio Ds/D1 to be nearly 0.1 before oscillatory modes are affected. Both the critical wavelength of the disturbance as well as the oscillation frequency are reduced slightly from the case where diffusion in the solid is ignored.
Pulsed Laser Melting of Graphite
Authors: Braunstein G. , Steinbeck J. , Dresselhaus M. S. , Dresselhaus G. , Elman B. S. , Venkatesan T. , Wilkens B. , Jacobson D. C. 
Published: March 2011

ABSTRACTExperimental evidence for laser melting of graphite, by irradiation with 30ns pulses from a ruby laser, is presented. RBS-channeling analysis, Raman scattering and TEM measurements reveal that the surface of graphite melts at a threshold energy density of about 0.6 J/cm2. For laser pulse energy densities above 0.6 J/cm2, the melt front penetration depth increases nearly linearly with increasing energy density. An intense emission of carbon particles during and after irradiation is observed. The thickness of the carbon layer removed in this process also increases nearly linearly with increasing pulse fluence. A dramatic redistribution of ion implanted impurities is also observed. Furthermore, the crystalline structure of the resolidified material is shown to depend on the energy density of the laser pulse. In order to explain these phenomena, a model for laser melting of graphite at high temperatures to form liquid carbon has been developed in which a free electron gas approximation is used to describe the properties of liquid carbon. The model is solved numerically to give the time and depth dependences of the temperature as a function of the laser pulse energy density. Very good agreement is found between the observed melt depth dependence on laser pulse energy density, as determined by RBS-channeling, and the model calculations. The redistribution of ion implanted impurities and the modification of the crystalline structure, caused by the pulsed laser irradiation, are also consistent with the model and permit the determination, for the first time, of interfacial segregation coefficients for impurities in liquid carbon. The model also predicts that liquid carbon at low pressure (p < 1 kbar) has metallic properties.
Nanosecond Time Resolved Reflectivity Measurements At The Surface of Pulsed Laser Irradiated Graphite
Authors: Venkatesan T. , Steinbeck J. , Braunstein G. , Dresselhaus M. S. , Dresselhaus G. , Jacobson D. C. , Elman B. S. 
Published: March 2011

ABSTRACTTime resolved reflectivity measurements at the surface of pulsed laser irradiated graphite are found to be complicated by the evolution of carbon atoms from the surface which attenuates the probe beam. The evolution of the species occurs concomitant with the observation of the melt on a time scale of <2 nsec. Further, the emitted species have velocities of:≤ 2 x 105 cm/s. The experimental results suggest the formation of large clusters at the molten surface though more experiments are required to clearly distinguish the effect of clusters from those due to the formation of a randomly reflecting plasma.
Nucleation of Allotropic Phases During Pulsed Laser Annealing of Manganese
Authors: Perepezko J. H. , Follstaedt D. M. , Peercy P. S. 
Published: March 2011

ABSTRACTManganese has four allotropes with an equilibrium melting point of the high temperature δ-phase at 1517 K and calculated metastable melting points for the ϒ, β and α phases at 1501 K, 1481 K and 1395 K, respectively. Our observations for Mn irradiated with a pulsed laser and supporting estimates of maximum allotropic transition rates indicate that transformations between allotropes are suppressed during heating with ~ 25 ns laser pulses, as well as during subsequent cooling. Upon pulsed heating of β-Mn to the melt threshold, the melt is undercooled 122 K below the δ-Mn melting point. For incident laser pulse energy densities near the melting threshold, resolidification involves regrowth of β-Mn from the substrate. At energy densities well above threshold, the ϒ-Mn phase forms by separate nucleation and growth from the undercooled melt, and is retained upon rapid solidification. From these results and analyses, we conclude that significant melt undercooling, which may exceed 100 K, can occur during pulsed laser melting of metallic crystals and that the resulting crystalline structure is determined by both thermodynamics and nucleation kinetics.
Laser-Material Interactions In Phase Change Optical Recording
Authors: Barton Roger , Rubin Kurt A. 
Published: March 2011

ABSTRACTWe have studied laser induced crystallization and amorphization reactions in tellurium and tellurium alloy thin films, which are of interest for use in optical data storage. The writing characteristics of these films are determined by plotting changes in film reflectivity against the parameters of laser power and pulse width. The laser pulse conditions necessary for film melting, crystallization, and amorphization are identified and then checked against the results of a numerical heat diffusion model. In this way we determine the critical quenching rate for formation of the amorphous phase in pure tellurium (2 × 109 C/sec). Minimum crystallization times are determined and found to increase by orders of magnitude with addition of alloying elements such as germanium or selenium. TEM analysis reveals significant differences in the crystallization mechanisms of different alloy systems.
Au-Cluster Redistribution During Nanosecond Laser-Annealing of Metal/Insulator Matrices
Authors: Pamler W. , Marinero E. E. , Chen M. , Jipson V. B. 
Published: March 2011

ABSTRACTWe report on the growth and redistribution of Au clusters caused by nanosecond laser interaction of Aux(TeO2 )1−x thin films with intense excimer laser radiation. This laser-induced phenomenon is studied in a time-resolved manner using transient reflectivity and transmissivity techniques. Structural and compositional changes are investigated using Rutherford Backscattering, XPS depth profiling, x-ray diffraction and conductivity measurements. Our studies indicate that melting of the binary structure initializes segregation, growth and coalescence of Au crystallites in the amorphous TeO2 matrix.
Temperature Dependent Amorphization of Silicon During Self-Implantation
Authors: Maszara W.P. , Rozgonyi G.A. , Simpson L. , Wortman J.J. 
Published: March 2011

ABSTRACTWe have investigated the damage which results from silicon self-implantation for the range of doses from 2E14 to 1E16 cm−2 for temperatures from 82 to 296 K for 150 and 300 keV implants. Cross-sectional TEM was used to evaluate the nature of the amorphous layer. The experimental results were correlated with computer calculated damage distributions using a Monte Carlo simulation program. The depth of amorphous-crystalline interface(s) was evaluated as a function of dose and temperature. An experimental damage energy density curve was constructed. Using the curve, a critical energy density for amorphization, Ec was calculated for the samples implanted at different temperatures. The energy was found to depend on depth and implant energy, and it increased with temperature. A study of a-c interface morphology shows no dependance on temperature within the range considered. Kinetics of dynamic annealing are discussed in conjunction with the above findings.
Metastable Alloy Formation By Ion Beam Mixing
Authors: Saris F.W. , Westendorp J.F.M. , Vredenberg A. 
Published: March 2011

ABSTRACTIn Ion Beam Mixing new surface alloys are produced by a combination of vacuum deposition and ion irradiation. One may wonder what the advantages are of this combination. Indeed one may ask:- Why not just ion implantation?- Why ion beams instead of laser or electron beams?- Why ion mixing instead of evaporation only?- What phases are formed and what is the stability of ion mixed phases?In an attempt to answer these questions the role of ion beam mixing in modern materials modification will de delineated. Areas of controversy and further development will also be illustrated.