bluuebunny/crossref_metadata_2025 huggingface dataset:
Real-Time Feedback Control of Thermal CL2 Etching of GaAs Based on In-Situ Spectroscopic Ellipsometry
Authors: Parent T. , Heitz R. , Chen P. , Madhukar A.
Published: April 2011

In-situ, real-time, spectroscopic ellipsometry (SE) is utilized to study thermal chlorine etching of GaAs in an all ultra-high-vacuum interconnected growth and etching system. In the low temperature (between ˜40°C and ˜120°C) range, the etch rate is found to exhibit an Arrhenius dependence on substrate temperature with an activation energy of 11.6Kcal/mole and to be proportional to essentially the square root of the chlorine pressure. An SE feedback based real-time etch process control algorithm is developed and successfully implemented on the basis of the above noted input - output relation derived from the experimental data base.
Nano-Scale Viscoelastic Properties of Polymer Materials
Authors: Asif S. A. Syed , Pethica J. B.
Published: April 2011

The AC force modulation technique in nano indentation has been extended to study the dynamic viscoelastic properties of polymer materials. The frequency and temperature dependent loss and storage modulus, the time-temperature superposition, the mechanical relaxation and the activation energy for the relaxation process can all be directly measured from nano scale contact. The results obtained for PMMA and Polyisoprene are in good agreement with the reported literature results obtained from conventional dynamic testing. The technique is likely to be of particular value for polymer thin films.
Aging Effects on the Durability of Tantalum Nitride Films
Authors: Moody N. R. , Medlin D. , Boehme D. , Norwood D.
Published: April 2011

In this study, nanoindentation and nanoscratch testing were used to determine the effects of annealing and long term aging on the properties and fracture resistance of thin tantalum nitride resistor films on aluminum nitride substrates. These films were sputter-deposited to a thickness of 440 nm. Some films were left in the as-deposited condition while others were annealed or annealed and then aged. X-ray diffraction revealed that sputter deposition created high compressive residual stresses in the as-deposited films which were partially relieved by annealing. Subsequent aging of the annealed films had no effect on residual stress levels. Nanoindentation showed that mechanical properties were unchanged after annealing and after annealing and aging. However, nanoscratch testing showed that annealing markedly reduced the susceptibility to catastrophic failure with no further changes discernible after aging.
Curves of Elasto-Plastic Deformation of Thin Coatings Obtained in Depth-Sensing Indentation Experiments
Authors: Dub S. N.
Published: April 2011

A method to obtain curves of elasto-plastic deformation of materials in depth-sensing indentation tests is proposed. Elasto-plastic deformation curves of thin films and brittle materials have been received at room temperature using this method.
Quantitative Measurement of the Effect of Annealing on the Adhesion of Thin Copper Films Using Superlayers
Authors: Kriese M. D. , Moody N. R. , Gerberich W. W.
Published: April 2011

Nanoindentation at loads from 100 to 750 mN was used to measure the interfacial adhesion energy of sputtered copper thin-films, for which the release of elastic strain energy drives delamination. The as-sputtered films were of four thicknesses, nominally 225 nm, 400 rn, 600 nm and 1000 nm, and were deposited onto Si/SiO2 wafers; one wafer of each two-wafer run was annealed at 600°C for 2 hrs in a nitrogen atmosphere. Subsequently, a nominally 700 nm thick sputtered superlayer of tungsten was deposited over all wafers. The tungsten overlayer was used to promote delamination at the copper-SiO2 interface. The energies for fracture ranged from 1 to 80 J/m2, increasing with increased indentation depth, and a trend of higher adhesion energy for annealed films. The large values of adhesion energy with respect to the thermodynamic work of adhesion are attributed primarily to plasticity and/or void nucleation within the copper film, which appears to be strongly influenced by the constraint of an overlayer.
Fatigue Strength Of Thin Films By Means Of Impact Tester
Authors: Lugscheider E. , Knotek O. , Wolff Christian , Bärwulf Stephan
Published: April 2011

Machine parts like rolling bearings or gears are stressed during operation in a changing mechanical strain. This causes wear by impacts and wear by rolling which is marked by the so called surface ruin. The appearance of surface fatigue is based upon structural transformation, cracking and cracking-growth processes and ends with the separation of debris particles caused by the above mentioned permanent changing strain /1/. The final stage, which is equivalent to the component failure, is the so called ‘pitting’ on the technical surface, which is characteristically named ‘surface fatigue’.

The impact tester is used for detailed research about failure mechanisms of thin films. Statements about the adherence of hard material coatings under dynamic compressive stress can be made using this test method, due to the possibility to simulate some effects of rolling strain. Therefore a hard metal ball strikes with a frequency of up to 50 Hz onto the surface. The altitude stress can be varied to get a detailed evaluation of fatigue strength under reversal strain.

Selected hard material coatings were analized after testing with the described method applying an impact force of 300 N, 500 N and 700 N. In the framework of this presentation MSIP (Magnetron-Sputter-lon-Plating) coatings on titanium- and chromium basis were used. The fatigue defects and the results of this study will be discussed depending on structure and morphology of thin films.
Grain Impingement and Intrinsic Stresses in CVD Diamond
Authors: Nijhawan S. , Rankin J. , Walden B. L , Sheldon B. W.
Published: April 2011

Intrinsic stresses in polycrystalline CVD diamond films have been related to restructuring at grain boundaries. It is speculated that reducing the interfacial energy induces an elastic tensile strain. There appears to be a correlation between the evolution of macroscopic stresses in the entire sample and localized, non-homogeneous stresses in the microstructure based on Raman Spectroscopy and x-ray diffraction pole figures. A multistep processing sequence developed previously can help reduce these stresses substantially, by using an intermediate annealing step when the diamond grains are partially coalesced. Our results suggest that small changes in the film microstructure due to annealing can reduce both homogeneous and non-homogeneous stresses.
Annealing Effects On The Microstructure Of Electrodeposited Cu/Ag Multilayered Nanocomposites
Authors: Kong Dan , Zhai Qing , Ebrahimi Fereshteh
Published: April 2011

TEM was used to investigate the annealing effects on the microstructure of two electrodeposited Cu/Ag multilayered nanocomposites with bi-layer thickness values of 110nm and 330nm, respectively, as well as electrodeposited pure copper. It was found that silver layers limited the lateral growth of columnar copper grains and possibly acted as sites for nucleation of new copper grains in the as-deposited composites. The refinement of copper grains in this condition is one reason for the much higher strength of these materials in comparison to pure copper. Annealing at 100 °C did not change the microstructure significantly. After annealing at 150 °C, recrystallization occurred in all samples. The degree of recrystallization was dependent on the extent of internal stresses. Recrystallization was complete in the 110nm bi-layer thick composite, which had the highest internal stresses owning to its large Cu/Ag interfacial area. The recrystallization and growth of copper grains can be one reason for the drastic drop of the composites yield strength after annealing at 150°C
Structure And Mechanical Properties Of Reactive Sputter Deposited Tin/Tan Multilayered Films
Authors: Soe W.-H. , Kitagaki T. , Ueda H. , Shima N. , Otsuka M. , Yamamoto R.
Published: April 2011

TiN/TaN multilayers were grown by reactive magnetron sputtering on WC-Co sintered hard alloy and MgO(100) single crystal substrates. Multilayer structure and composition modulation amplitudes were studied using x-ray diffraction method. Hardness and elastic modulus were mea- sured by nanoindentation tester. For bilayer thickness (Λ) larger than 80 A˚, hardness are lower than rule-of-mixtures value of individual single layers, and increased rapidly with decreasing Λ, peaking at hardness values ≈33% higher than that at A=43 Å. As a result of analysis the inclination of applied load for indenter displacement on P-h curve (ΔP/Δh), this paper exhibits that the en- hancement of the resistance to dislocation motion and elastic anomaly due to coherency strains are responsible for the hardness change.
Evaluation of Residual Stresses in Thin Films by Means of Micro-Raman Spectroscopy
Authors: Mizuhara Kazuyuki , Takahashi Shinichi , Kurokawa Jyunichi , Morita Noboru , Yoshida Yoshitaro
Published: April 2011

The effects of temperatures on the stress evaluation of boron doped silicon in solid and film forms are investigated. Several techniques, such as fluid cooling to eliminate the temperature raise and/or simultaneous observation of Stokes and anti Stokes peaks to compensate the temperature effects, are applied. The advantages and disadvantages of each method and the abilities and limits of these techniques are discussed.
On The Measurement Of Residual Stress In Thin Films
Authors: Zhao Z. B. , Hershberger J. , Yalisove S. M. , Bilello J. C.
Published: April 2011

This work reports a comparative study on three curvature based techniques for stress measurement in thin films, including double crystal diffraction topography (DCDT), profilometry, and laser scanning technique (LST). These techniques measure different physical quantities. In the former case, the curvature of crystal lattice planes is assessed while in the latter two cases, the curvature of physical surface of a sample is measured. The current experiments use these three techniques to determine the quantities of interest for a variety of films deposited on Si (100) wafers. In general, profilometry and LST produce similar results on surface curvature. For specimens where the residual stresses produces large curvatures of both types (lattice curvature and surface curvature), the results by DCDT and LST agree fairly well. When small to moderate curvatures are present, the two methods deviate to varying degrees on absolute curvatures. Nevertheless, DCDT and LST generally yield similar results on differential curvatures, i.e., the stress induced curvature differentials. When proper consideration is taken for the inherent limits of each technique, both DCDT and LST can be used as valid procedures for stress measurement in thin film-substrate systems.
Determination Of Temperature Dependent Unstressed Lattice Spacings In Crystalline Thin Films On Substrates
Authors: Cornella G. , Lee S. , Kraft O. , Nix W. D. , Bravman J. C.
Published: April 2011

X-ray strain analysis via Generalized Focusing Diffractometry (GFD) [1], and the concurrent need for accurate values of the unstrained lattice parameter, are discussed. A new method for determining the unstrained lattice parameter without knowledge of the elastic constants of the sample material is described. Stress measurements at varying temperatures, and extraction of the coefficient of thermal expansion from these measurements, are demonstrated for aluminum and gold films.
Residual Stress Generation During Constrained Sintering Of Layered Ceramic Thin Film Structures
Authors: Busso E. P. , Travis R. P. , Chandra L.
Published: April 2011

This work investigates the sintering kinetics and residual stresses which develop in thin layered ceramic structures when sintered on a rigid substrate. A continuum constitutive framework to model the evolution of the microstructure and stresses in the sintering layers under non-isothermal conditions is presented. The sintering model is used to investigate the constrained sintering behaviour of layered ceramic structures used in solid oxide fuel cells (SOFC). Samples of a 50 μm thick SOFC film were screen-printed on a fully dense yttriastabilised zirconia substrate and then sintered at temperatures ranging from 1100°C to 1300°C. Measured values of relative density and average grain size are compared with model predictions. A correlation between residual stresses extracted from curvature measurements and analytical predictions revealed these stresses to have been mostly relieved during the subsequent cooling by microcrack formation.
Computer Simulation of Stress Distribution in Amorphous SiO2 Thin Films
Authors: Kogure Y. , Doyama M.
Published: April 2011

A molecular dynamics simulation of amorphous SiO2 thin films has been made to investigate the structure and internal stress. The atomic configuration of the amorphous structure is investigated through the radial distribution function and the distribution of Si-O-Si bond angles. Distribution of internal stress through the specimen is evaluated from the volume and the shape of the SiO4 tetrahedron, which is the elementally unit of amorphous SiO2.
Interface Stress and an Apparent Negative Poisson's Ratio in Ag/Ni Multilayers
Authors: Schweitz K. O. , Geisler H. , Chevallier J. , Bøttiger J. , Feidenhans'l R.
Published: April 2011

By use of dc-magnetron sputtering, (111) textured Ag/Ni multilayered thin films were deposited with nominal bilayer repeat lengths ranging from 2 nm to 250 nm. Bulk and interface stresses were obtained from X-ray diffraction and measurements of substrate curvatures. Both in-plane and out-of-plane expansions were observed in the Ni layers, and a compressive interface stress of −2.24±0.21 J/m2 was found. This is in agreement with a previously published result of the interface stress in Ag/Ni thin films which had, as opposed to the present multilayers, a high level of total stress.
Stress Evolution In Sputtered Fcc Metal Multilayers
Authors: Ramaswamy Vidya , Nix William D. , Clemens Bruce M.
Published: April 2011

During growth of Cu/Pd multilayers the apparent stress in the Cu layers changes from compressive to tensile during the growth of a single Cu layer. The apparent stress in the Pd layers is initially either tensile or compressive depending on the thickness of the underlying Cu layer. It has been speculated that this stress behaviour may be either a result of island growth of Cu on Pd or alloying at the Cu/Pd interface[I]. We have observed that the stress behavior is similar in Cu/Pd and Pd/Pt multilayers and continue to study these systems to better understand the origins of stress in metal multilayers. Stress evolution during growth is monitored by in-situ substrate curvature measurement using a multiple parallel laser beam technique. High angle superlattice spectra for the multilayers are found from symmetric x-ray diffraction scans in order to determine crystallographic texture. Information about interfacial disorder and alloying in the layers is obtained from simulation of the superlattice diffraction patterns. Stress behaviour is correlated with possible modes of growth of the layers, and with atomic peening and coherency effects.
Mechanical testing and microstructural characterisation of TiN thin films
Authors: Karimi A. , Shojaei O. R. , Martin J. L.
Published: April 2011

Mechanical properties of titanium nitride (TiNx) thin films have been investigated using the bulge test and the depth sensing nanoindentation measurements. The bulge test was performed on the square free standing membranes made by means of standard micromachining of silicon wafers, while the nanoindentation was conducted on the films adhered to their supporting substrate. Thin layeres of titanium nitride (t = 300 – 1000 nm) were deposited in a r. f. magnetron sputtering system on the Si(100) wafers containing a layer of low stress LPCVD silicon nitride (SiNy). The bulge test was first conducted on the silicon nitride film to determine its proper residual stress and Young's modulus. Then, the composite membrane made of TiNx together with underlying silicon nitride was bulged and the related load-displacement variation was measured. Finally, using a simple rule of mixture formula the elastic mechanical properties of TiNx coatings were calculated. Both the Young's modulus and residual stress showed increasing values with negative bias voltage and nitrogen to titanium ratio, but the substrate temperature between 50–570°C was found less significant as compared to the other parameters. Nanoindentation data extracted from dynamically loading-unloading of TiN films converged to the bulge test measurements for compact coatings, but diverged from the bulge test data for porous coatings. Scanning electron microscopy observation of the cross sectioned specimens showed that TiN films first grow by formation of the nanocrystallites of size mostly between 10 – 15 nm. These nanocrystallites give rise to the columnar morphology beyond a thickness of 50–100 nm. The columns change their aspect with deposition parameters, but remain nearly perpendicular to the film surface. Relationship between microstructural evolution of columns and mechanical properties of coatings are discussed in terms of deposition parameters.
A New Technique For Visualizing The Displacement Field Of Indentations: The Case Of A Soft Film On A Hard Substrate
Authors: Vlassak Joost J. , Tsui T. Y. , Nix W. D.
Published: April 2011

We have developed a new technique for visualizing displacement fields of indentations in thin films. In this technique, the indented film consists of alternating layers of two different materials. One of the materials serves as a marker for visualizing the plastic flow induced by the indentation. Focused Ion Beam (FIB) milling is used to cross-section the indentation, revealing the deformed layers. This technique can be used to study how the presence of the substrate affects the plastic displacement field around the indentation. The technique is applied to a multilayered film of aluminum and titanium nitride on a silicon substrate. The titanium nitride layers are much thinner than the aluminum layers and serve the function of marker. Pile-up of the film material around the indenter and the effect of the hard substrate are easily revealed and a mechanism for pile-up is suggested. The technique also shows that the grain structure in the deformed zone around the indentation is altered profoundly.
Problems of Radioactive Sodium Removal and Disposal From Decommissioning LMFR Equipment
Authors: Shtynda Yu. Ye. , Polyakov V. I.
Published: April 2011

Preparing for safe disposal of the LMFR primary circuit equipment and sodium reprocessing for storage and burial with minimum volume of radioactive wastes resulted in testing of radionuclide sorption trapping, distillation and rinsing with water under vacuum used for safe sodium removal and decontamination of equipment.
Molecular-Dynamics Simulation of Displacement Cascades in Zircon (ZrSiO4)
Authors: Crocombette J-P. , Ghaleb D.
Published: April 2011

Zircon (ZrSiO4) is of great interest for the nuclear industry as it is one of the new crystalline waste form considered for the disposal of actinides, for example weapons' plutonium in USA. In this study the effects of displacement cascade due to α-decay has been modelled from an atomistic point of view by molecular dynamics simulation using Born-Mayer-Huggins empirical potential. The numerical values of the parameters of this potential have been fitted on structural equilibrium properties of the crystal and on atomic arrangements.

Displacement cascades are reproduced by accelerating one of the atoms of the cell, thus modelling the effect of the α-decay recoil nucleus. Kinetic energies up to 2 keV have been introduced. The unfolding of the cascades and the final structures have been studied in detail. The centre of the displacement cascade exhibits an amorphous zone where the zircon structure is completely lost. It contains an assembly of distorted SiO4 tetrahedra and disordered zirconium polyhedra. The zirconium ions (originally surrounded by 8 oxygen atoms) exhibit a decrease in their coordination number to 7 or 6 in agreement with what is observed for zirconium ions in amorphous zircon, zirconia or glasses. The size of the amorphous zone and the number of atoms displaced have been estimated for different recoil energies.

The energy stored during the cascade has been calculated. It exhibits an overall good agreement with the available experimental data at complete amorphization.

The existence of an amorphous track in our calculated cascades shows that the correct model for the amorphisation process should take into account the existence of a direct impact amorphous zone.
Uncertainties on Future States of Radioactive Waste Disposal Systems - Interest and Sketch of a Methodology
Authors: Badie O.M. , Santucci P. , Horowitz E , Bruyere F. , Giaume Ph.
Published: April 2011

High level waste repositorie facilities are complex systems : the parameters, processes, their interactions and the relationships between the system and its environment are numerous. Lack of knowledge and variability of parameters in the field we are studying and the time periods we require to consider, generate uncertainty which may be hard to evaluate and may affect sensitive factors (ex: human intrusion).
Laboratory Examination of Microbial Effects Upon Redox in a Geological Disposal Site for Radioactive Waste
Authors: Bateman K. , West J. , Aoki K. , Yoshida H. , Coombs P. , Gillespie M. R. , Henney P. , Reeder S. , Milodowski A. E.
Published: April 2011

The laboratory experiments described here, were aimed at examining the interaction of microbes with mineralogical surfaces involved with groundwater flow. These experiments were designed to study simple systems and were aimed at identifying relevant reactions both chemical and biological. They contained groundwater with either sulphate reducing bacteria (SRB), iron reducing bacteria (IRB) or a mixture of both, together with control experiments without bacteria. The results of the chemical analyses of fluid phases showed evidence for dissolution of primary minerals. Microbial analysis showed both SRB and IRB appeared to be active albeit for a limited period due to exhaustion of nutrient and energy supplies. SRB seem to have a greater effect on groundwater chemistry than IRB with sulphide being produced. However, when the two types of bacteria are mixed together, the IRB appear to dominate the system. Further work is underway to give detailed mineralogical analysis of the solids in order to better understand the influence of microbial interaction on the redox reactions.
Production, Accumulation, and Transport of Helium in the Subsurface - Possibilities and Limits for Groundwater Dating
Authors: Lehmann B.E. , Loosli H.H. , Purtschert R. , Lippmann J. , Osenbruick K. , Rübel A. , Sonntag C. , Tolstikhin I. , Tokarev I. , Vetrin V. , Scholtis A.
Published: April 2011

Natural rocks are radioactive. They contain e.g. uranium and thorium and their daughter products in very small quantities and emit alpha-particles at well-defined rates. Neutralized alpha-particles are helium atoms and therefore natural rocks produce helium. The production rates are easy to calculate if the U and Th concentrations are known. In a closed system helium will accumulate with time; a measured helium concentration represents a certain accumulation time.
SANTA-SORB: Modeling High pH Plume-Host Rock Interactions
Authors: McKiel D. , Neall F.B. , Mihara M.
Published: April 2011

Many UIILW and TRU waste disposal concepts use cement and concrete both as construction materials and providers of favourable near-field chemical conditioning. However, what is gained in the near field may be lost in the geosphere if interaction between high pH water leaving the repository and the host rock results in detrimental perturbations of the far field properties. Hence, assessing the influence of this interaction on the transport of radionuclides in the geosphere is an important factor in safety assessment.
Retardation Mechanism of Uranium Migration at Koongarra, Australia
Authors: Ohnuki Toshihiko , Murakami Takashi , Isobe Hiroshi
Published: April 2011

The migration of radionuclides through rocks is one of the important paths to estimate the impact of radioactive waste disposal on the environment. Because some amount of the radionuclides is sorbed on the minerals of rocks during the migration, Kd model is considered to be used to estimate the radionuclide migration. However, long-term applicability of Kd model is not known.
Accumulation History of Uranium in Boulders - New Support for Postglacial Matrix Diffusion
Authors: Rasilainen Kari , Suksi Juhani , Lindberg Antero
Published: April 2011

Extended Abstract

Geological formations are being considered as host media for nuclear waste disposal. The occurrence of natural U in rocks provides a possibility to test the radionuclide migration models used in safety studies of the disposal over comparable time periods. Here we study U accumulation into boulders as a process analogue for matrix diffusion; the boulders were found in glacial till in Hämeenlinna, southern Finland. Based on the glacial history of the site, matrix diffusion simulations, and independent U-series disequilibria (USD) dating, the U accumulation was interpreted to originate from the end stage of the latest glaciation, i.e. the system age is about 10 000 years1,2. The known time scale offers a rare opportunity for quantitative model testing; normally the time scale is difficult to determine for a single process in a natural analogue.

The U accumulation was earlier1,2 interpreted to be due to matrix diffusion and sorption. The postulated accumulation history consists of short in-diffusion and out-diffusion stages, as well as a longer chain decay stage. The in-diffusion was caused by U-rich waters discharging on the boulders at the end stage of the glaciation. The subsequent partial out-diffusion represents the period the boulders were temporarily submerged in the Yoldia sea during the early stage of the Baltic Sea. The final isolated radioactive chain decay stage began when the boulders, and their surroundings, rose above the sea level due to land uplift.

In this paper we report the first radiochemical results of a new larger boulder from the same area as the one studied earlier1; qualitatively, also the U distribution appears to be the same. Due to the larger dimensions, we can sample the inner zone of the boulder which matrix diffusion can not have reached within the postulated time, i.e. the state of the boulder before the U accumulation. The large amount of sample material containing almost only the recently accumulated U provides an opportunity to experimentally approach the kinetics of U fixation in situ. Understanding the long-term U fixation is essential in natural analogue studies, because the matrix diffusion model only has fast reversible adsorption (based on Kd) as the fixation process. Attempts to separate and quantify sorbed U in natural analogues have been reported elsewhere3.
Preliminary Safety Studies for Conventional Spent Fuel, MOX, and Vitrified High-Level Waste
Authors: Schneider J.W. , Zuidema P. , Smith P.A. , Gribi P. , Hugi M. , Niemeyer M.
Published: April 2011

This paper discusses the results of post-closure safety studies for two different waste streams that, according to current Swiss waste-management concepts, may be co-disposed in a single deep geological repository. The waste streams are:

• directly disposed spent UO2 and mixed-oxide (MOX) fuel

• vitrified high-level waste from the reprocessing of spent fuel

The inventories are based on a consideration of the anticipated arisings from nuclear power generation in Switzerland. A part (at least) of these arisings will be reprocessed, with the resultant vitrified high-level waste and long-lived intermediate-level waste returned to Switzerland. The Swiss electricity utilities have placed contracts with BNFL (UK) and COGEMA (France) for the reprocessing of about one third of the total arisings of spent fuel from nuclear power generation, assuming an electricity production scenario of 120 GWa(e). The decision as to whether to reprocess the remainder is currently left open, implying that up to two thirds of the arisings could be in the form of unreprocessed spent fuel for direct disposal. For the purposes of the present study, however, it is assumed that the arisings from the full 120 GWa scenario will be either directly disposed or reprocessed.
Leaching Behavior of Zirconolite-Rich Synroc Used to Immobilize High-Fired Plutonium Oxide
Authors: Hart K. P. , Vance E. R. , Stewart M. W. A. , Weir J. , Carter M. L. , Hambley M. , Brownscombe A. , Day R. A. , Leung S. , Ball C. J. , Ebbinghaus B. , Gray L. , Kan T.
Published: April 2011

This study reports on the use of zirconolite-rich Synroc to demonstrate the safe immobilisation of ‘high-fired’ Pu02. The zirconolite-rich Synroc used in this study was prepared by adding 13 wt% Pu with equimolar amounts of Gd and Hf, relative to Pu, as neutron absorbers. The incorporation of the Pu and neutron absorbers has been studied microstructurally as well as by longer-term leach testing. This work has shown that the sintered ceramic can immobilise 13 wt% of Pu with almost complete incorporation of the Pu (≃ 98%) into the zirconolite phase. Durability studies have shown that under a wide range of leaching conditions there is no major separation of the Pu and neutron absorbers, with the majority of these elements either remaining in the matrix or leaching at low (< 10−4 g m−2 d−1) and comparable rates from the waste form.
The Crystalline-Amorphous Transformation in Natural Zirconolite: Evidence for Long-Term Annealing
Authors: Lumpkin Gregory R. , Smith Katherine L. , Blackford Mark G. , Gieré Reto , Williams C. Terry
Published: April 2011

Dose-age relationships have been determined by analytical and transmission electron microscopy (AEM and TEM) for the onset dose and critical amorphization dose of a suite of natural zirconolites. Together with a preliminary investigation of the thermal histories of the zirconolite-bearing rocks, the results indicate that valid estimates of D0 (intercept dose at t = 0) and K (annealing rate constant) are obtained and that the host rocks experienced temperatures on the order of 100-200 °C averaged over time. The natural samples are therefore best suited as radiation damage analogues for waste forms stored under deep borehole conditions where temperatures of 100-450 °C are expected. Our results indicate that the critical amorphization (or saturation) dose of zirconolite will increase by a factor of approximately 2 or more as a result of storage at elevated temperature. The effect of long-term annealing on the critical amorphization dose is only important for times in excess of 107-108 years due to the low annealing rate constant of 10−9/yr.
SIMFUEL and UO2 Solubility and Leaching Behavior Under Anoxic Conditions
Authors: Quiñones J. , Garcia-Serrano J. , Serrano J.A. , Díaz-Arocas P. , Almazan J.L.R.
Published: April 2011

Most of performance assessment models for spent fuel repository safety consider radiolysis-self-oxidation to describe fuel matrix release. Nevertheless, due to radioactive decay, the matrix dissolution process under reducing conditions would be controlled by the solubility limit of the steady U solid phase. In this work, leaching behaviour under anoxic and reducing conditions of spent fuel unirradiated chemical analogues (natural U02 and SIMFUEL) in simulated groundwater is studied.

The trial procedure was performed taking into account the possibility that the uranium oxide to be leachated had an initial outer layer with an oxidation state higher than the matrix. This oxidised layer would produce an overestimation on U concentration in solution for the solid studied. In order to avoid this effect, a complete replacement of the leaching solutions was carried out after several days of experimentation. After this initial experimental step, the steady state concentrations obtained in all tests were more than one order of magnitude lower than before. Uranium concentrations found in reducing and anoxic experiments for both U02 and SIMFUEL tests were very close. This fact is attributed to similarity in environmental conditions (pH, Eh, etc.). From that, it can be assured that steady state concentration obtained is independent of solid leached (UO2 or SIMFUEL). In order to assess which is the solid phase that could control the solubility of U, the experimental concentration obtained was compared with results from geochemical code EQ3/6. According with the theoretical calculations U4O9 would be the controlling pure phase formed in whole experimental tests described in this work. Comparisons with bibliography data from leaching experiments of spent nuclear fuel were made as well.
Cation and Anion Sorption Capability of Organophilic Bentonite
Authors: Bors J. , Dultz St. , Riebe B.
Published: April 2011

Sorption experiments were performed with iodide, cesium and strontium ions on MX-80 Wyoming-bentonite treated with hexadecylpyridinium (HDPy+) in amounts equivalent to 0.2 - 4.0 times the cation exchange capacity (CEC) using125I-134Cs+and85Sr2+as tracers. In HDPy-bentonite, iodide exhibited increasing adsorption, while cesium and strontium ions showed decreasing adsorption with increasing organophilicity. It was also found that the Cs+affinity to original and HDPy-bentonite was considerably higher than that of Sr2+ions. HDPy+uptake in increasing concentrations resulted in a pronounced expansion of the basal spacings (d002reflex at 2.78 nm) and in a change of the negative particle surface charge to positive values.
Coprecipitation of Radionuclides During Cement Degradation: A Preliminary Modeling Study for the Swiss L/ILW Repository
Authors: Curti E.
Published: April 2011

Production of carbonate minerals will be a dominant alteration reaction during cement degradation in the near-field of the L/ILW repository planned at Wellenberg (Switzerland). Very large amounts of calcite are predicted to precipitate as a result of (a) the interaction between bicarbonate-rich ground water and cement phases and (b) the in-situ degradation of organic waste components in the repository.

A preliminary model was developed to estimate to which extent coprecipitation with calcite could reduce radionuclide concentrations in solution. Since the main objective was only to determine the order of magnitude of this effect, a very simple, closed-system model was considered to be sufficient. The model assumes instantaneous dissolution of the entire radionuclide inventory in the water-saturated pore space of the repository caverns and simultaneous reversible sorption on the cement. Coprecipitation of radionuclides with calcite and residual solution concentrations are calculated assuming in-situ precipitation of a given amount of calcite and using nuclide-specific partition coefficients.

The model calculations show that the solution concentration of several radionuclides (tetravalent and trivalent actinides, Sr and Ni) is likely to decrease by orders of magnitude as a consequence of coprecipitation with large amounts of secondary calcite. Further, radionuclide coprecipitation is found to depend on the extent to which the same radionuclide is sorbed on cement phases. The results confirm that coprecipitation with calcite will be an important process in determining concentration limits for dissolved radionuclides in the Wellenberg repository.
Modeling FEBEX Large-Scale In Situ Test
Authors: Gens A. , Alonso E.E. , Garcia-Molina A. , Huertas F. , Santiago J.L.
Published: April 2011

This paper reports the coupled thermo-hydro-mechanical (THM) analyses of the “in situ” test carried out during the pre-operational stage of the FEBEX project. The determination of parameters has been performed using the results of the characterization stage and other available information. The results of the analyses provide a good understanding of expected test behaviour. This understanding is enhanced by the performance of a quite extensive programme of 1-D sensitivity analyses in which the values of critical parameters are varied. Two dimensional effects are discussed on the basis of the results of 2-D axisymmetric THM analyses carried out using a longitudinal section that provides a better representation of real test geometry.
The FEBEX Project. General Overview
Authors: Huertas F. , Santiago J.L.
Published: April 2011

Understanding the near-field evolution of a deep geological disposal system for HLW is crucial for assessing its long term performance and, therefore, safety. For that reason ENRESA devised the FEBEX Project, a Full Scale Engineered Barriers Experiment in crystalline rock. The project consists of a full-scale “in-situ” heating test, a large-scale laboratory mock-up and supporting materials tests, and modelling.

Even though the object of the project is to contribute to the search for methods of behaviour and of safety analyses for a repository, other subinvestigations have been/are being included. The stated objectives are to demonstrate the procedures of constructing an engineered barrier system (EBS), especially the fabrication, handling, and installation of bentonite blocks (buffer) at an almost industrial scale, to improve and validate the numerical models for thermo-hydro-mechanical behaviour, and to investigate the geochemical processes that are produced in the buffer including canister corrosion, as well as the generation and transport of gas. Since early 1997, with the commencement of the heating phase, both large-scale tests have been fully operative. At this point it can be said that the demonstration objective of constructing the EBS has been successfully achieved. The measured thermal response of the buffer follows the pattern predicted in the preliminary modelling. The saturation rate of the buffer and associated mechanical processes are being continuously monitored.
Simulating Radio Element Release and Water-Rock Interactions During Dissolution of Borosilicate Glass
Authors: Chambers A V , Heath T G , Linklater C M , Thompson A M , Wiggin R M
Published: April 2011

A model has been developed that can simulate in some detail the chemistry of the glass dissolution process. To test the performance of the model, calculations were carried out to predict the dissolution behaviour of a commercial borosilicate glass. The model could reproduce accurately the behaviour of major elements released from the glass, although in the case of silica, ‘sorption’ at the glass surface was required in order to achieve good agreement with experimental data. Secondary reaction products sepiolite, montmorillonite, analcime and goethite were predicted to form. Further calculations were carried out to simulate the release of radioelements (caesium, strontium, uranium, plutonium) from within the dissolving glass. The precipitation of insoluble solids was the only mechanism included in the model to retain the radioelements at the glass surface. For plutonium, there was good agreement between model predictions and available experimental data. For caesium and strontium, the model underestimated the amount of retention at the glass surface and additional retention mechanisms, such as coprecipitation or ion exchange reactions involving newly-formed clay-type minerals at the glass surface must be invoked to explain experimental observation.
Binding Force Between Clay Mineral and Water Molecules by Semiempirical Molecular Orbital Calculation
Authors: Nagasaki S. , Umemura Y. , Todoriki M. , Tanaka S. , Suzuki A.
Published: April 2011

We evaluate the charge distribution on the surface of a model cluster which simulates a 2:1 type clay mineral and the binding forces between the model cluster surface and water molecules with semi-empirical molecular orbital method (MOPAC). It is found that the negative charge is not localized on the oxygen atoms of the model cluster surface. We calculate the binding forces acting on the water molecules in model cluster-water system and compare them with the binding forces of solid and liquid phases of water. We qualitatively discuss the binding force acting on the water molecule directly sorbed on the model cluster surface and the binding force acting on the water molecule which is not sorbed on the model cluster surface.
Transport Phenomena in Smectite Clay Explained by Considering Microstructural Features
Authors: Pusch Roland
Published: April 2011

The microstructure of clays controls their transport properties. This is concluded from comparing microstructural parameter data with the hydraulic conductivity and the ion diffusive transport capacity. Illitic clays contain a number of interacting open voids with a high flow capacity while natural smectite-rich clays are more homogeneous with smaller voids and a lower hydraulic conductivity than illitic clays with the same density. Artificially prepared smectitic clays, like those proposed for embedding canisters with highly radioactive waste, have a higher conductivity than natural clays with the same smectite content because the microstructural homogeneity of the artificial clays is less good.

The anion diffusive transport capacity of smectite-rich clays with high density is much lower than that of clays with low density in contrast to the cation diffusive capacity. This is explained by using quantitative microstructural data.
Predictive Numerical Modeling of Artificial Tracers Migration in the Large-Scale Heating and Hydration Experiments of the FEBEX Project
Authors: Samper J. , Delgado J. , Molinero J. , Juncosa R.
Published: April 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. In the FEBEX experiment the bentonite barrier will be subject to heating and hydration during at least three years. One of the novel aspects of FEBEX is the use of artificial tracers, which are intended to provide additional insight into the hydrodynamic and geochemical behavior of the bentonite buffer. Here the results of the numerical prediction of tracers migration are presented. Numerical modeling of the experiments has allowed the identification of the most relevant parameters and will be useful for the design of post-morten analyses.
Determination of the Structure and Porosity of Rock in the Disturbed Zone Around Experimental Full-Scale Deposition Holes Using the 14C-PMMA Method
Authors: Autio J. , Slltari-Kauppi M.
Published: April 2011

In a nuclear waste repository the disturbed rock zone adjacent to the deposition holes of waste canisters is a potential transport pathway of radionuclides. The properties of the disturbed zone may also play an important role in the saturation of the bentonite buffer and in gas release.

Three experimental holes of the size of deposition holes (depth 7.5 m and diameter 1.5 m) in a KBS-3 type repository were bored in hard granitic rock in the Research Tunnel at Olkiluoto. The disturbed rock zone caused by the boring was analyzed including determination of the porosity and structure of the disturbed and intact rock. These were studied in the laboratory using core samples by using the novel 14C-polymethylmethacrylate (14C-PMMA) method. In addition the structure of the disturbed zone was also examined using scanning electron and optical microscopy. A distinct zone of disturbance adjacent to the surface of the deposition holes was found. This disturbed zone was further divided into three separate sub-zones with gradual transition between the zones. It was also observed that the machine and tool factors have effect on the properties of the disturbed zone.
SIMS Analysis of Lead Isotopes in the Primary Ore Body of the Koongarra Deposit, Australia: Behavior of Lead in the Alteration of Uranium Minerals
Authors: Isobe H. , Hidaka H. , Ohnuki T.
Published: April 2011

Lead, the final decay product of uranium, is found in natural uranium ore deposits. The isotope composition of lead in uranium-bearing minerals reflects their age and the migration behavior of lead. Secondary Ion Mass Spectroscopy (SIMS) can be used to analyze the isotopic composition of minerals. SIMS analysis of lead contained in the Koongarra uranium deposit, Australia, revealed that uraninite and uranyl minerals with different chemical composition in the primary ore region have homogeneous lead isotope, from the highest grade area to a uranyl silicate zone at a distance of 6.1m. Uranyl minerals, which have good crystallinity and retain stoichiometric composition, have “old” lead isotope composition identical to that of uraninite. Uranyl minerals keep exchanging lead with ground water in the primary ore region through metamictization and recrystallization by alpha-decay damage. Sulfide minerals just outside the primary ore body contain only radiogenic lead with an isotopic composition different from that of uranium minerals. Lead that migrated from the primary ore body formed sulfide minerals in a specific geological event. Since then, lead produced from uranium decay has been retained in the primary ore body, in spite of recrystallization of uranyl minerals and exchange and homogenization of lead isotopes. Uranium minerals may retain minor elements despite intense alpha-decay dose.
Solubility of Radionuclides in Fresh and Leached Cementitious Systems at 22°C and 50°C
Authors: Ochs M. , Hager D. , Helfer S. , Lothenbach B.
Published: April 2011

The solubility of Ni, Sn, Pb, Eu, and Sr was investigated at 22°C and 50°C in simulated cement porewaters corresponding to fresh cement (‘FPW’, pH 13.2) and cement leached of soluble alkalis, whose porewater chemistry is dominated by equilibrium with portlandite (‘APW’, pH 12.5). Solubility limits were approached from undersaturation, using Ni(OH)2(c), SnO2(c) (cassiterite), PbO(red), and Eu(OH)3(c) as solids. For Sr, no solubility experiments were carried out since the cement contains enough Sr to reach equilibrium with strontianite and celestite. Solubilities generally increase with increasing pH and temperature. The measured solubility of Pb ranges from about 4× 10−3 to 1×1O−2M and is within thermodynamically predicted values. The measured solubility of Ni is <O.5-1.3×10−7M in APW and about 3-4×10−7M in FPW, which is lower than predicted by most thermodynamic data. The measured solubility of Eu ranges from <6.6×10−10M in APW to 1.8-2.7×10−9M in FPW, which agrees well with thermodynamic calculations. The solubility of cassiterite is low, with dissolved Sn concentrations ranging from 3.5× 10−8M in APW to 3.3× 10−6M in FPW. Thermodynamic calculations predict much higher solubilities, presumably for less crystalline phases. However, oversaturation measurements in APW reproduced the solubility limits obtained by undersaturation within a factor of two. To our knowledge, no relevant thermodynamic data are available.