bluuebunny/crossref_metadata_2025_split huggingface dataset:
Np-Incorporation Into K-boltwoodite
Authors: Shuller Lindsay C. , Ewing Rodney C. , Becker Udo 
Published: April 2011

AbstractNp-237 (τ1/2 = 2.1 million years) is a potentially important contributor to the total dose for a geologic repository under oxidizing conditions. Further, the Np5+-complexes are mobile aqueous species. Several processes may limit the transport of Np, as well as other actinides: i) the precipitation of Np-solids, ii) the incorporation of Np into secondary uranium phases, and iii) the sorption and reduction of Np-complexes on Fe-oxide surfaces. This study utilizes quantum-mechanical calculations to determine the most energetically favorable Np5+-incorporation mechanisms into uranyl phases, where Np5+-substitution for U6+ requires a charge-balancing mechanism, such as the addition of H+ into the structure. Experimental results suggest that uranyl structures with charged interlayer cations have a greater affinity for Np5+ than uranyl structures without interlayer cations. Therefore, the uranyl silicate phase boltwoodite (KUO2(SiO3OH)(H2O)1.5) is selected for this computational investigation. The charge-balancing mechanisms considered to occur with substitution include: i) addition of H+, ii) substitution of Ca2+ for K+, and iii) substitution of P5+ for Si4+. While the incorporation energy results (1-3 eV)are higher than energies expected based on current experimental studies, solid-solution calculations are used to estimate the limit of Np incorporation for the P5+ substitution mechanism (10 ppm at ̃100°C). The electronic structure of the boltwoodite structure provides insight into the electron density that may be involved in the incorporation of Np into the structure.
Uranium(VI) Uptake by Synthetic Calcium Silicate Hydrates
Authors: Tits J. , Fujita T. , Tsukamoto M. , Wieland E. 
Published: April 2011

AbstractThe immobilization of U(VI) by C-S-H phases under conditions relevant for the cementitious near field of a repository for radioactive waste has been investigated. C-S-H phases have been synthesized using two different procedures: the “direct reaction” method and the “solution reaction” method.The stabilities of alkaline solutions of U(VI) (presence of precipitates or colloidal material) were studied prior to sorption and co-precipitation tests in order to determine the experimental U(VI) solubility limits. These U(VI) solubility limits were compared with the U(VI) solubilities obtained from thermodynamic speciation calculations assuming the presence of combinations of different solid U(VI) phases. The solid phase controlling U(VI) solubility in the present experiments was found to be CaUO4(s).The U(VI) uptake kinetics and sorption isotherms on C-S-H phases with different C:S ratios were determined under various chemical conditions; e.g., sorption and co-precipitation experiments and different pH’s. U(VI) was found to sorb fast and very strongly on C-S-H phases with distribution ratios (Rd values) ranging in value between 103 L kg-1 and 106 L kg-1. Both sorption and co-precipitation experiments resulted in Rd values which were very similar, thus indicating that no additional sorption sites for U(VI) were generated in the co-precipitation process. Furthermore, C-S-H synthesis procedures did not have a significant influence on U(VI) uptake. The U(VI) sorption isotherms were found to be non-linear, and further, increasing Ca concentrations resulted in increasing U(VI) uptake. The latter observation suggests that U(VI) uptake is controlled by a solubility-limiting process, while the former observation further indicates that pure Ca-uranate is not the solubility-limiting phase. It is proposed that a solid solution containing Ca and could control U(VI) uptake by C-S-H phases.
PHREEQC Modelling of Leaching of Major Elements and Heavy Metals From Cementitious Waste Forms
Authors: Martens Evelien , Jacques Diederik , Gerven Tom Van , Wang Lian , Mallants Dirk 
Published: April 2011

AbstractIn this study, Ca, Mg, Al, and Pb concentrations leached from uncarbonated and carbonated ordinary Portland cement – dried waste incinerator bottom ash samples during single extraction tests (EN12457 test) at a pH from 1 to 12, were modelled using the geochemical code PHREEQC. A good agreement was found between modelling results and experiments in terms of leached concentrations for Ca, Mg, and Al by defining a single set of pure mineralogical phases for both the uncarbonated and carbonated (three levels) samples. The model also predicted well the observed decrease in Ca leaching with increasing carbonation. Modelling results further revealed that leaching of Pb is not controlled by dissolution/precipitation of pure Pb containing minerals only (carbonates and (hydr)oxides). The addition of solid solutions (calcite-cerrusite and gibbsite-ferrihydrite-litharge solid solutions) and adsorption reactions on amorphous Fe- and Al-oxides improved the model representation of the experimentally observed amphoteric leaching profile of Pb from the cementitious material.
A New Natural Analogue Study of the Interaction of Low-Alkali Cement Leachates and the Bentonite Buffer of a Radioactive Waste Repository
Authors: Alexander W. Russell , Arcilla Carlo A. , McKinley Ian G. , Kawamura Hideki , Takahashi Yoshiaki , Aoki Kaz , Miyoshi Satoru 
Published: April 2011

AbstractBentonite plays a significant barrier role in many radioactive waste repository designs, where it has been chosen due to its favourable properties such as plasticity, swelling capacity, colloid filtration, low hydraulic conductivity and its stability in relevant geological environments. However, bentonite is unstable at high pH meaning that it could lose its favourable properties if interacted with hyperalkaline leachates from concrete construction materials (e.g. tunnel liners, grouts, etc.), seals and plugs and/or cementitious wastes in a repository. This fact has forced several national programmes to assess alternative construction and sealing materials such as low alkali cements. Recently, it has been assumed that the lower pH (typically pH 10-11) leachates of such cements will degrade bentonite to a much lesser degree than ‘standard’ OPC-based cement leachates (generally with an initial pH>13).To date, few laboratory orin situURL (underground rock laboratory) data are available to support the use of low alkali cements in conjunction with bentonites, partly because of the very slow kinetics involved. Consequently, a new project has focussed on finding an appropriate natural analogue site to provide long-term supporting data which will avoid the kinetic constraints of laboratory and URL experiments. Early results have identified an initial, very promising site at Mangatarem in the Philippines, where a quarry excavating bentonite and zeolites is found in the sedimentary carapace of the Zambales ophiolite. In the immediate vicinity of the quarry, ophiolite-derived hyperalkaline groundwaters are present and further field work (including geophysics surveys and borehole drilling) are now being planned to assess regional bentonite/hyperalkaline groundwater interaction. This paper presents an overview of the current status of the project and assesses the relevance of the study to improving understanding of low-alkali cement leachate/bentonite interaction.
Apparent Inversion of the Effect of Alloyed Molybdenum for Corrosion of Ordinary and Enhanced 316L Stainless Steel in Sulfuric Acid
Authors: Kwong Gloria , Carcea Anatolie , Newman Roger C. 
Published: April 2011

AbstractAn aging assessment of the OPG waste resin storage system predicted the potential for premature failure of the carbon steel resin liners. Consequently, resin liners made of 316L stainless steel with a minimum content of 2.5% molybdenum were selected to replace the carbon steel liners. The 2.5% Mo 316L stainless steel was specified to enhance pitting resistance in the spent resin environment. With the additional Mo, one would expect that a brief electrochemical corrosion test will reveal the superiority of such alloy over conventional 316L steel. This study reports a contrary experience
Observation of Diffusion Behavior of Trace Elements in Hardened Cement Pastes by LA-ICP-MS
Authors: Chida Taiji , Sugiyama Daisuke 
Published: April 2011

AbstractDiffusion coefficients of iodine (I), cesium (Cs) and strontium (Sr) in solid cement blocks of ordinary portland cement (OPC) and low-heat portland cement containing 30 wt% fly ash (FAC) are measured by in-diffusion experiment. By using “laser ablation inductively coupled plasma mass spectrometry”, the penetration profiles of trace elements by diffusion were obtained quantitatively in cement solids. The apparent diffusion coefficients of the near-surface of the cement samples were estimated to be about 10-13 m2 s-1for I, Cs and Sr. Lower diffusion coefficients were observed for FAC than those obtained for OPC.
Effect of thermal annealing on characteristics of polycrystalline silicon used for solar cells
Authors: Gou Xianfang , Li Xudong , xu Ying , Liang Xinqing , Zhao Yuwen 
Published: April 2011

AbstractBehavior of oxygen, carbon and minority-carrier lifetimes of multi-crystalline silicon (mc-Si) has been investigated by means of FTIR and QSSPCD after three step annealing. For comparison, the annealing of czochralski (CZ) silicon was also carried out under the same conditions. The results revalted that oxygen and carbon concentration pf mc-Si had a larger decrease than that of CZ -Si, which means the more oxygen precipitates in mc-Si were generated. High density defects of mc-Si such as grain boundaries and dislocations accelerated formation of oxygen precipates and defect complex compounds are generated after three step annealing, which could be suction center of defect, that reduced carrier decentralized recombination centers that resulted in improvement of lifetime of wafer. Tendency of difference of lifetime was correlated with interior structure of crystalline silicon.
Improvement of the interface quality between Zn (O,S,OH)x buffer and Cu(InGa)(SeS)2 surface layers to enhance the fill factor over 0.700
Authors: Kushiva K. , Tanaka Y. , Hakuma H. , Goushi Y. , Kijima S. , Aramoto T. , Fujiwara Y. , Tanaka A. , Chiba Y. , Sugimoto H. , Kawaguchi Y. , Kakegawa K. 
Published: April 2011

AbstractFor realizing the proof of mass production capablity or a move toward a GW/a production, 16%-efficiency project has been started setting the target of each parameter as V∝: 0.685 V/cell, FF: 0.735 and Jsc: 31.8mA/cm2. Up to FY2008, the target of each parameter independently has been achieved expect the efficiency. All of our research by adjusting the two resistance (Rsh and Rs) in the monolithically integrated 30cm×30cm-sized circuits. To improve the FF, double buffer structure with CBD-Zn(O,S,OH)x and MOCVD-ZnO is proposed and the thickness is adjusted by optimizing the Rs and the Rsh. As the result, FF of over 0.7 has been achieved for the first time in our CIS R&D since FY 1993.
Light-Induced Passivation of Si by Iodine Ethanol Solution
Authors: Sopori Bhushan , Rupnowski Przemyslaw , Appel Jesse , Guhabiswas Debraj , Anderson-Jackson LaTecia 
Published: April 2011

AbstractWe report on our observations of light-activated passivation (LIP) of Si surfaces by iodine-ethanol (I-E) solution. Based on our experimental results, the mechanism of passivation appears to be related to dissociation of iodine by the photo-carriers injected from the Si wafer into the I-E solution. The ionized iodine (I−) then participates in the formation of a Si-ethoxylate bond that passivates the Si surface. Experiments with a large number of wafers of different material parameters indicate that under normal laboratory conditions, LIP can be observed only in some samples–samples that have moderate minority-carrier lifetime. We explain this observation and also show that wafer cleaning plays an extremely important role in passivation.
Understanding Radionuclide Migration From the D1225 Shaft, Dounreay, Caithness, UK
Authors: Savage David , Watson Claire , Wilson James , Bond Alex , Jones Warren , Metcalfe Richard , Milodowski Tony , Munro Colin , Penfold James , Watson Sarah 
Published: April 2011

AbstractA 65 m vertical shaft was sunk at Dounreay in the 1950s to build a tunnel for the offshore discharge of radioactive effluent from the various nuclear facilities then under construction. In 1959, the Shaft was licensed as a disposal facility for radioactive wastes and was routinely used for the disposal of ILW until 1970. Despite the operation of a hydraulic containment scheme, some radioactivity is known to have leaked into the surrounding rocks. Detailed logging, together with mineralogical and radiochemical analysis of drillcore has revealed four distinct bedding-parallel zones of contamination. The data show that Sr-90 dominates the bulk beta/gamma contamination signal, whereas Cs-137 and Pu-248/249 are found only to be weakly mobile, leading to very low activities and distinct clustering around the Shaft. The data also suggest that all uranium seen in the geosphere is natural in origin. At the smaller scale, contamination adjacent to fracture surfaces is present within a zone of enhanced porosity created by the dissolution of carbonate cements from the Caithness flagstones during long-term rockwater interactions. Quantitative modelling of radionuclide migration, using the multiphysics computer code QPAC shows the importance of different sorption mechanisms and different mineralogical substrates in the Caithnesss flagstones in controlling radionuclide migration.
The methodology followed in Belgium to investigate the compatibility with geological disposal of Eurobitum bituminized intermediate-level radioactive waste
Authors: Valcke Elie , Marien An , Geet Maarten Van 
Published: April 2011

AbstractIn Belgium, Eurobitum intermediate-level long-lived bituminized radioactive waste containing large amounts of NaNO3, which is a hygroscopic and soluble salt, is to be disposed of in an underground repository in a geologically stable clay formation. The Boom Clay is studied as a potential host formation because of its favourable properties to limit and delay the migration of the leached radionuclides and other contaminants (heavy metals, NaNO3, organic molecules) to the biosphere. The emplacement of the bituminized waste will induce multiple processes that could have a significant effect on the key properties of the clay. Because several of these processes are interdependent, the study of the compatibility of Eurobitum with geological disposal is complex. To structure the research and to identify possible knowledge gaps, the Belgian Radioactive Waste Management Agency ONDRAF/NIRAS developed a new methodology based on safety functions and safety statements. In this paper, this methodology is briefly explained, with reference to the disposal of Eurobitum. Experimental results obtained at the Belgian Nuclear Research Centre SCK•CEN are presented and discussed in the light of the safety functions and safety statements approach. The importance of the interdependence of the processes is highlighted. Special attention is given to the evolution of the disposal design as a result of the improved understanding of key processes.
Estimation of seismic observation records in the vicinity of large earthquakes and its impact on geological disposal program
Authors: Tsuchi Hiroyuki , Oouchi Taishi , Ichikawa Yoshikazu , Okutsu Kazuo , Sasaki Toru 
Published: April 2011

AbstractJapan is located at the converging plate boundaries and is one of the most earthquake-prone zones in the world. In order to ensure the safety of a geological repository against earthquakes, a site with a high possibility of direct destruction by active faults should be excluded, and the relationship between the characteristics of seismic ground motion, subsurface structures, geological disposal system and the propagation characteristics of seismic ground motion should be fully investigated. Earthquake-resistant design based on the latest technology is also very important for ensuring the safety of a geological repository.Following rapid improvement of seismic observation networks after the Hyogoken Nanbu earthquake in 1995, numerous seismic observation records have been obtained in the vicinity of large earthquakes. According to these seismic observations, some phenomena that might affect the safety of a geological disposal system have occurred. Some earthquakes occurred in the areas where active faults had not been identified, while some records showed that seismic motion in the deep underground environment was greater than that at the surface. We have identified the implications from the latest information concerning large earthquakes for the geological disposal program. This study made it clear that detailed investigation incorporating state-of-the-art technologies could reduce the likelihood of missing active faults to an extremely low level and a more practical analysis of seismic ground motion could be achieved by taking the latest information into account.
French Industrial Vitrification Plant: 30 Years Old and Still Innovating
Authors: Chauvin E. , Ladirat C. , Quang R. Do 
Published: April 2011

AbstractIn 2008, AREVA NC Industrial Vitrification of High-Level Liquid Waste blows out its 30th candle, with always two main objectives during all the time: containment of the long lived fission products and reduction of the final volume of waste. During all this time AREVA with the French Atomic Energy Commission (CEA) developed and use in their industrial installations a selection of borosilicate glass that have been demonstrated as the most suitable containment matrix for waste from spent nuclear fuel. Consistent and long-term R&D programs associated to industrial feed back from operation have enabled continuous improvement of the process: throughput and waste loading factor enhancement. The Vitrification Process used and currently implemented in the AREVA facilities will be described.
Iron Aluminium Silico-Phosphate Glasses Including U3O8
Authors: Oliver Carlos J.R. Gonzalez , Russo Diego O. , Lovey Francisco C. , Romero Maximina , Rincon Jesus Ma. 
Published: April 2011

AbstractThe obtention of iron aluminium silicate- phosphate glasses including U3O8 oxide has been carried out and the study of crystalline phases formation. A serie of these original glasses have been investigated by thermal cycles at 780? C for promoting the nucleation and growth of crystalline phases of iron aluminium phosphates including U3O8 in the 5.1- 13.71 wt% range. Thermal expansion and DTA/G analysis have been carried out showing behaviour trend to crystallization of these glasses. The glass with higher uranium oxide content shows liquid phase in phase separation which change of microstructure during HREM observations. It seems produced a pulsed order- disorder processing which takes place under the electron beam. This effect first observed in TEM-HREM on phase separation droplets is discussed.
Quantifying Conservatism of Performance Assessment Calculations by Sorption Model Reduction: Case Study on Near Field Cs Migration in Callovo-Oxfordian Clay
Authors: Weetjens Eef , Martens Evelien , Jacques Diederik 
Published: April 2011

AbstractImplementation of full thermodynamic models in performance assessment (PA) calculations (large domain and very large timescales) is practically unfeasible due to excessive computational times. The complex competitive sorption processes of radionuclides are often simplified.In this paper, such simple sorption models (i.e. linear Kd and Langmuir isotherms) were compared with more complex thermodynamic models for a reduced geometry and relatively short timescales (compared to traditional PA calculations).Within the context of a safety case the value of this study is twofold. Primarily, it provides support information on how to choose adequate parameter values in a consistent simplified analysis for compliance with safety criteria. For the cases studied in this paper it became clear that a linear model is sufficient to represent sorption, but a proper choice of the Kd values is critical. Secondly, the comparison of results from these compliance calculations with more realistic analyses demonstrates quantitatively the safety margin implicitly present in PA calculations through model abstraction.
Mathematical Modelling of Transport Phenomena in Concrete Porous Media
Authors: Plecas Ilija B. , Dimovic Slavko D. 
Published: April 2011

AbstractTwo fundamental concerns must be addressed when attempting to isolate low-level waste in a disposal facility on land. The first concern is isolating the waste from water, or hydrologic isolation. The second is preventing movement of the radionuclides out of the disposal facility, or radionuclide migration. Particularly, we have investigated here the latter modified scenario.To assess the safety for disposal of radioactive waste-concrete composition, the leakage of 137Cs from a waste composite into a surrounding fluid has been studied. Leakage tests were carried out by original method, developed in Vinca Institute [1,2,3,4,5]. Transport phenomena involved in the leaching of a radioactive material from a cement composite matrix are investigated using three methods based on theoretical equations [6,10]. These are: the diffusion equation for a plane source an equation for diffusion coupled to a first-order equation, and an empirical method employing a polynomial equation‥ The results presented in this paper are from a 25-year mortar and concrete testing project that will influence the design choises for radioactive waste packaging for a future Serbian radioactive waste disposal center.
Characterisation of Granite Fractures From the In-Situ FEBEX Experiment (Grimsel, Switzerland): ossible Effects on Bentonite Colloid and Radionuclide Transport
Authors: Alonso Ursula , Missana Tiziana , Garcia-Gutierrez Miguel , Patelli Alessandro , Albarran Nairoby , Lopez-Torrubia Trinidad , Ceccato Daniele , Rigato Valentino 
Published: April 2011

AbstractThe FEBEX in-situ experiment, installed in 1997 at the Grimsel Test Site (GTS, Switzerland) 400 m depth under the Swiss Alps, simulates a high level radioactive waste repository (HLWR) emplaced in granite. Its initial aim was to study the performance of a bentonite engineered barrier but recently, two new boreholes were drilled in the granite to study the possible bentonite colloid formation and their migration in the granite.This study presents the characterization performed, at the micrometer scale, of the threemain water conductive fractures that were identified on the granite cores extracted from the newboreholes. These fractures are possible pathways for bentonite colloid transport (or retention),may be source of natural colloids and may condition colloid stability. The nuclear ion beamtechniques µ-Particle X-Ray Emission (µPIXE) and Rutherford Backscattering Spectrometry(RBS) were applied for visualizing and quantifying the elemental composition of the fracturessurface and of the surrounding micro-fractures, as support of the bentonite colloid analyses.