bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTBy 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

ABSTRACTDuring 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

ABSTRACTMechanical 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

ABSTRACTWe 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

ABSTRACTPreparing 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

ABSTRACTZircon (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

ABSTRACTHigh 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

ABSTRACTThe 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

ABSTRACTNatural 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.
Accumulation History of Uranium in Boulders - New Support for Postglacial Matrix Diffusion
Authors: Rasilainen Kari , Suksi Juhani , Lindberg Antero 
Published: April 2011

Extended AbstractGeological 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 fuelThe 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

ABSTRACTThis 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

ABSTRACTDose-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

ABSTRACTMost 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

ABSTRACTSorption 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

ABSTRACTProduction 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

ABSTRACTThis 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

ABSTRACTUnderstanding 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.