bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epistemic and Aleatory Uncertainty in Recommended, Generic Rock Kd Values used in Performance Assessment Studies
Authors: Crawford James , Neretnieks Ivars , Moreno Luis 
Published: April 2011

ABSTRACTOver the past decade or so there has been an explosion in the number of sorption modelling approaches and applications of sorption modelling for understanding and predicting solute transport in natural systems. The most widely used and simplest of all models, however, is that employing a constant distribution coefficient (Kd) relating the sorbed concentration of a solute on a mineral surface and its aqueous concentration.There are a number of reasons why a constant partitioning coefficient is attractive to environmental modellers for predicting radionuclide retardation, and in spite of all the shortcomings and pitfalls associated with such an approach, it remains the leitmotif of most performance assessment transport modelling.This paper examines the scientific basis underpinning the Kd-approach and its broad defensibility in a performance assessment framework. It also examines sources of epistemic and aleatory uncertainty that undermine confidence in Kd-values reported in the open literature. The paper focuses particularly upon the use of so-called “generic” data for generalised rock types that may not necessarily capture the full material property characteristics of site-specific materials.From the examination of recent literature data, it appears that there are still a number of outstanding issues concerning interpretation of experimental laboratory data that need to be considered in greater detail before concluding that the recommended values used in performance assessments are indeed conservative.
Effects of Calcium Ion in Highly Alkaline Plume on Permeability Change of Flow-Path
Authors: Usui Hideo , Niibori Yuichi , Tanaka Koichi , Tochiyama Osamu , Mimura Hitoshi 
Published: April 2011

ABSTRACTFor the construction of the geological disposal system of radioactive wastes, a large amount of cement is used. Such a material alters the pH of groundwater to highly alkaline region [1-3]. The highly alkaline plume contains rich Ca ion compared to the surrounding environment, and the Ca ions reacts with soluble silicic acid. Its product would deposit on the surface of flow-paths in the natural barrier and decrease the permeability. In this study, the influence of Ca ion in highly alkaline plume on flow-paths has been examined by using packed bed column.The column was packed with the amorphous silica particles of 75-150 μm in diameter. The Ca(OH)2 solution (0.78 mM, 4.37 mM, and 8.48 mM, pH:12.2∼12.3) was continuously injected into the column at constant flow rate (1.1 mm/s), and the change of permeability was continuously monitored. At the same time, [Ca]total and [Si] in the eluted solution was measured by the inductively coupled plasma atomic emission spectrometry (ICP-AES). The Ca(OH)2 solutions were prepared with CO2-free pure water, and filtrated through 0.22 μm and 0.45 μm filter. The permeability was normalized by the initial permeability value.The experimental results showed that the permeability change and the chemical reactions in the packed bed depended on the concentration of Ca(OH)2 in the feed solution. The SEM images showed that the feed solution of 8.48 mM in [Ca]total apparently altered the particle surface with the products with Ca (deposition). Moreover, from the distribution of Ca on the cross section of packed particle (by EPMA), it was found that Ca deposited also in the inner pores of the particle. These results suggest that the deposition does not always change the permeability in the early stage of precipitation reaction. In the eluted solution, the concentrations of Ca and Si dramatically changed, depending on the concentration of Ca in the feed solution.
Development of Low Alkaline Cement Considering Pozzolanic Reaction for Support System in HLW Repository Construction
Authors: Nakayama Masashi , Iriya Keishiro , Fujishima Atsushi , Mihara Morihiro , Hatanaka Koichiro , Kurihara Yuji , Yui Mikazu 
Published: April 2011

ABSTRACTCementitious materials have been studied for their applicability as support and lining in the construction of shafts and tunnels of the underground facilities for HLW disposal system. However, in the case of Ordinary Portland Cement (OPC), the buffer materials and the host rock may be altered due to the high alkalinity of groundwater contacting the OPC in the long-term. Low alkaline cements with high content of pozzolanic material were developed in order to reduce such hyper alkaline alteration. This paper shows that the pH of the leaching solution of this cement is about 11, and that it can be applied for full scale lining and for shotcrete.
An Experimental Approach on the Effect of Rock Alteration on Sorption Behavior
Authors: Niibori Yuichi , Kasuga Yasunori , Yoshikawa Hiroaki , Tanaka Kouichi , Tochiyama Osamu , Mimura Hitoshi 
Published: April 2011

ABSTRACTIn the geological disposal of radioactive wastes, cement used for the repository construction alters the condition of groundwater to highly alkaline of pH about 13. Such alkaline groundwater around the repository would alter the surfaces of the rocks in the flow paths to the amorphous phase. Once the surface is altered, it takes a geological period (so much long time) to restore the surface to its former condition. This study examined the sorption behavior of europium (Eu-152 (tracer), Eu-151 (5×10-5 M, carrier) onto some silica minerals with polymeric silicic acid. Polymeric silicic acid also affects the alteration of the solid surface.The results showed that the kinds of silica minerals strongly affect the sorption behavior in the range of 5<pH<8. The main difference was due to the degree of crystallization of the solid phase, the specific surface area and the concentration of polymeric silicic acid. Since the amorphous silica or polymeric silicic acid takes a loose structure, the isoelectric point is high compared to the crystal ones such as opal-CT and cristobalite, which in turn decreases the sorption. The crystalline silica with polymeric silicic acid remarkably decreased the sorption of europium. This suggested that the surface of solid phase was altered by polymeric silicic acid.
Cathodoluminescence study of americium incorporation into calcite single crystals
Authors: Zamoryanskaya Maria V. , Burakov Boris E. , Kolesnikova Ekaterina V. , Zuykov Michael A. 
Published: April 2011

ABSTRACTIn order to study americium incorporation into calcite, CaCO3, under conditions of crystal growth, two samples of single crystal Am-doped calcite were synthesized and studied by cathodoluminescence (CL) spectroscopy in comparison with undoped and Eu-doped artificial calcite. Americium contents in calcite crystals were (in kBq/g): 1) 6.9; 2) 1.9(E+4). The CL emission of undoped and Am-Eu-doped calcitesamples was characterized by three broad bands at 2.03; 2.47 and 2.96 eV. Weak CL lines related to typical transitions 5D07F1,2,4 of Eu3+ and Am3+ions were observed at 1.68; 1.99, 2.06 eV and 1.60; 1.98 eV, respectively. Degrading of calcite structure under irradiation has been studied using CL emission of high power electron beam.
Silver Zeolites: Iodide Occlusion and conversion to Sodalite – a potential 129I waste form?
Authors: Sheppard Gareth P , Hriljac Joseph A , Maddrell Ewan R , Hyatt Neil C 
Published: April 2011

ABSTRACTSilver exchanged zeolites A, X and Y were used to occlude silver iodide (AgI) at 400°C. Heating to 900°C in a hot isostatic press caused decomposition of the zeolite materials and the formation of more dense phases. Silver zeolites A and X both formed sodalite, seen as a potential 129I waste form, while silver zeolite Y formed an x-ray amorphous phase containing AgI. Silver zeolite A produced the best potential waste form, a monolithic sodalite with negligible porosity.
Microchemical and crystallographic characterisation of fluorite-based ceramic wasteforms
Authors: Stennett Martin C. , Hyatt Neil C. , Maddrell Ewan R. , Gibb Fergus G. F. , Moebus Guenter , Lee William E. 
Published: April 2011

ABSTRACTA number of possible options have been proposed for the encapsulation and immobilisation of long lived actinide (Act) fractions in nuclear waste. Ceramics offer superior durability against chemical migration and the ability to be tailored to accommodate a variety ofdifferent waste streams. Research on the fabrication of dense, durable crystalline matrices for the safe disposal of fissile plutonium is ongoing and this study reports quantitative chemical, structural and spectroscopic analysis on fluorite based host phases.Ceramics based on the fluorite structure are known to be able to incorporate a variety of actinides and in this work two candidate ceramic matrices were investigated: a pyrochlore, Gd2Zr1.60Ce0.20Hf0.20O7; and a zirconolite, (Ca0.90Gd0.10)(Zr0.50Ce0.20Hf0.20Gd0.10)Ti2O7. The chemical compositions of the two major phases observed in the ‘zirconolite’ sample were consistent with the 2M and 4M zirconolite polytypes and the presence of the 4M structure was confirmed by Electron Diffraction (ED). The major phase in the ‘pyrochlore’ ceramic was confirmed by ED to have the pyrochlore structure. Electron Energy Loss Spectroscopy (EELS) data indicated the presence of both Ce3+ and Ce4+ in all the samples.
Porous Materials Based on Cenospheres of Coal Fly Ash for Fixation of Cs-137 and Sr-90 in Mineral-like Aluminosilicates
Authors: Vereshchagina Tatiana A. , Vasilieva Natalia G. , Vereshchagin Sergei N. , Paretskov Evgenyi N. , Zykova Irina D. , Kruchek Dmitryi M. , Manakova Ludmila F. , Tretyakov Alexander A. , Anshits Alexander G. 
Published: April 2011

ABSTRACTAmong the crystalline matrices being developed for immobilization of 137Cs and 90Sr are framework aluminosilicates like feldspars and feldspathoids. A novel approach to obtain mineral-like aluminosilicate forms of 137Cs and 90Sr with using porous materials based on hollow aluminosilicate microspheres of coal fly ash (cenospheres) has been demonstrated. Two modifications of microspherical porous materials have been developed, (i) moulded porous matrices based on consolidated cenospheres and (ii) zeolite sorbents obtained by hydrothermal zeolitization of cenospheres. The first includes impregnation of Cs- or Sr-containing solutions into porous matrices, drying and calcining at temperatures (700-900°C) lower than the softening point of the porous matrix material, at which solid phase crystallization takes place with formation of framework aluminosilicates, such as Cs-nepheline, pollucite or Sr-anorthite. Using zeolite sorbents, immobilization of Cs+ and Sr2+ proceeds through the step of trapping ions from the solution followed by drying and thermochemical solid-phase transformation of saturated zeolites into pollucite or Sr-anorthite over the same temperature range. Cenosphere-derived porous matrices and zeolite sorbents were tested in fixation of 137Cs using spiked simulants of actual radioactive waste. The durability of crystalline aluminosilicate 137Cs -forms obtained was shown to satisfy Russian (GOST P 50926-96) and international standards.
Leaching of Cesium and Uranium from Spent PWR fuel in the Gel-state Clays
Authors: Kim S. S. , Chun K. S. , Choi J. W. , Cho W. J. , Hahn P. S. 
Published: April 2011

ABSTRACTThe amounts of cesium and uranium released from crushed spent PWR fuel in the gel-state clays with a few ml of supernatant at hot cell temperature under Ar-atmosphere have been measured. The fractions of cesium dissolved from the fuel for 873 days were 0.29 and 0.25% in Boom clay/Boom-clay water and Ca-bentonite/synthetic granitic groundwater, respectively. These cesium fractions were very close to the gap inventory of cesium, which was determined to be around 0.30% in the previous experiment. The fraction of uranium released up to 193 days in the Boom clay media was 0.011% and this fraction has been retained until 873 days. Such this phenomenon was also obtained in the Ca-bentonite media even though the released fraction was higher than that in Boom clay. The increase of less than 0.001% in the dissolved uranium fraction between 193 and 873 days suggests that the long-term leach rate of uranium from spent fuel would be much less than 24 μg·m−2·day−1.
Long-Term Behavior of Embiez Archaeological Glass: Results after 1800 Years of Alteration in a Marine Environment
Authors: Gin Stéphane , Chouchan Jean-Louis , Foy Danièle 
Published: April 2011

ABSTRACTAn archaeological glass initially fractured and altered for 1800 years in a marine environment is now being examined by the CEA because of its strong morphological similarity to the nuclear glasses used for immobilization of long-lived radionuclides (i.e. the presence of fractures and cracks formed during cooling, which significantly increase the surface area accessible to water). The issue concerns glass alteration by water, and in particular the different behavior of the external surfaces in contact with a solution highly renewed and the internal surfaces, which constitute a much more confined medium.The preliminary results of this study are discussed. The cracks in the archaeological glass have been filled by crystallized alteration products formed jointly by elements from the glass and elements dissolved in seawater. The glass is distinctly less altered (by a factor of 10 to 100) on the internal surfaces generated by the cracks than on the external surfaces. The forward glass dissolution rate was measured at different temperatures on pristine glass samples and under conditions that allowed us to estimate the dissolution rate of the external surfaces under realistic conditions at about 200 μm in 1800 years. The implications of this study are then discussed.
Modelling The Alteration of Son-68 Glass with Nearfield Materials
Authors: de Combarieu G. , Barboux P. , Godon N. , Minet Y. , Gin S. 
Published: April 2011

ABSTRACTThe model tested in this paper couples glass dissolution rate and geochemistry in the surrounding environment, thus leading to the comprehensive description of the interactions between the glass and the minerals and their transformations. Leaching of glass is simulated at 90°C and S/V=80 cm-1 in pure water or with iron from the canister and overpack or with argillite. The glass dissolution is described with an affinity law with respect to a nontronite-like phase, which saturation state depends on Si, Al, Fe, Na and Ca activities. The simulations results allow to reproduce both the decrease of the initial alteration rate and the so-called residual regime while the composition of the alteration layers are explained in terms of precipitated phases. In presence of metallic iron, the corrosion does not affect much glass dissolution rate if silica sorption is neglected. On the contrary, in presence of argillite, the alteration is enhanced by the dissolution of primary clay minerals and the precipitation of feldspar, K-zeolite and clay minerals.
Immobilisation of Simulated Plutonium-Contaminated Material in Phosphate Glass: An Initial Scoping Study
Authors: Bingham Paul A. , Hand Russell J. , Scales Charlie R. 
Published: April 2011

ABSTRACTVitrification is a potential route for the immobilisation of Plutonium Contaminated Material (PCM). This is an Intermediate Level Waste (ILW) arising from operations in which there is contact with Pu isotopes. PCM consists of low levels of Pu combined with metals, masonry, glass, ceramics, polymers and other carbonaceous materials. Simulated PCM containing CeO2 as a PuO2 surrogate was mixed with a phosphate precursor and vitrified. Pre-oxidation of PCM simulant prior to vitrification minimised the violence of batch reactions. No pre-oxidation produced inhomogeneous slag-like materials with high residual metals and particulates. Pre-oxidation at 600°C in air and at 1200°C in an O2-rich atmosphere produced more favourable results, with increasingly vitreous products resulting from more oxidised PCM simulant. The most oxidised PCM simulant produced phosphate glasses with low levels of particulate inclusions, as confirmed by x-ray diffraction and scanning electron microscopy. Particulates included iron-rich metallics and aluminous oxides. Increased melting times and temperatures may have reduced the number of inclusions slightly, but O2 bubbling during melting resulted in little additional benefit. Waste loading equivalent to ∼60 weight % of untreated waste may be possible. There was little evidence of Ce partitioning, indicating that it was immobilised within the glass matrix and had little preference for metallic or crystalline phases. These results demonstrate the potential feasibility for vitrification of PCM in phosphate glass, justifying further investigation into this potentially novel solution.
Chemical durability and performance of assessment of spent fuel and high level waste forms under simulated repository conditions – Spanish contribution to IAEA project
Authors: Martínez-Esparza Aurora , Gago José Antonio , Quiñones Javier , Iglesias Eduardo , Cera Esther , Merino Juan , de Pablo Joan , Casas Ignasi 
Published: April 2011

ABSTRACTChemical durability of spent fuel under repository conditions is one of the main topics of interest in national and international projects from the last two decades. During the last decade there have been growing the activities in Enresa related to the deep disposal concept with the aim of developing a spent fuel alteration model for the understanding of the behaviour of this nuclear waste under repository conditions. In this context, the development and utilisation of models and sub-models based on experimental work have been of great importance.Experimental studies with spent fuel(in Collaboration Agreement with ITU) and spent fuel analogues in several environmental conditions have been carried out into Enresa R+D Programmes in order to reach a better knowledge of the relevant processes and to quantify the spent fuel chemical durability under repository conditions.In this work, it is showed the utility of data provided from experiments with spent fuel analogues to test the mechanisms and the influence of relevant parameters in the spent fuel alteration under repository conditions.The evolution of irradiated fuel under interim storage conditions and in deep geologic storage and its oxygen to metal ratio (O/M) before the water access to the fuel is another factor of great influence on enhanced spent fuel leaching. This effect has been also studied by means of spent fuel analogues and by using simulated (artificially) aged fuel.
Particle Size Control, Structure and Magnetic Characterization of Cobalt Nanoparticles
Authors: Singh Abhishek , Parekh Nirav , Young Gregory , Parvin Kiumars , Kaur Maninder , Bruck David , Wong Spencer , Varasteh Mehdi 
Published: April 2011

ABSTRACTCobalt nanoparticles were synthesized by means of a hot metal reduction reaction with cobalt chloride as precursor material. The size of cobalt nanoparticles was controlled by the choice of surfactant and the molar ratio of surfactant-to-reagent. Surfactants with larger alkane side chains yielded a smaller average nanoparticle size (diameter) and tighter size distribution, as these chains provided steric hindrance to the growth of the nanoparticles after initial nucleation. For each alkane side chain, a high molar ratio of surfactant-to-reagent (HSR) rendered nanoparticles with smaller particle size, while a low molar ratio of surfactant-to-reagent (LSR) produced larger nanoparticles. Measurements on transmission electron microscope images of cobalt particles synthesized with tri-octylphosphine revealed an average particle size of 6.9 nm (HSR) and 9.1 nm (LSR), while particles synthesized with tri-butylphosphine had a mean diameter of 12.5 nm (HSR) and 14.9 nm (LSR). X-ray diffraction profiles indicated that particles had metastable ε-cobalt structure. Room temperature magnetization measurements showed ferromagnetic behavior with highly square M-H loops indicative of single domain particles with coercive fields in the range of 400–500 Oe.
Effects of FM/NM Interfaces on Spin Accumulation in Free Layer of Pseudo-Spin-Valve Structure
Authors: Hu Jiuning , Ren Min , Zhang Lei , Deng Ning , Dong Hao , Chen Peiyi 
Published: April 2011

ABSTRACTThe ferromagnetic/nonmagnetic (FM/NM) interfacial effects on the spin accumulation in the free layer were studied in a pseudo-spin-valve structure (PSVs) consisting of two FM layers separated by a NM spacer layer. We developed a spin current model for the current-induced magnetic switching (CIMS) effect based on the spin diffusion equations and appropriate boundary conditions, and derived a new formula for the spin-dependent electrochemical potentials that are related to the spin-dependent density of states. The results indicate that the spin accumulation in the free layer mainly depends on the interfacial spin asymmetry coefficient Ξ?which originates from the spin-dependent interfacial conductance. In the parallel (anti-parallel) configuration of the magnetization direction for the free and fixed layer, the positive (negative) electron current (electrons from the free layer to the fixed layer and vice versa) drives the spin current polarization factor at the interface between the top electrode and the free layer to vary from Ξ? (-Ξ?) to 0, while at the interface between the free layer and the spacer layer the spin current polarization factor vary from Ξ? (0) to Ξ?/2, which means the total spin current polarization factor in the free layer varies from 0 (Ξ?) to Ξ?/2. These results show that the anti-parallel configuration has a less critical switching current than that of the parallel configuration. Thus, we can design PSVs with symmetrical critical current based on the model.
Nonlinear Damping Generated by Spin Injection in a Pseudo-spin-valve Structure
Authors: Ren Min , Zhang Lei , Hu Jiuning , Deng Ning , Dong Hao , Chen Peiyi 
Published: April 2011

ABSTRACTThe current induced magnetic dynamics of a nano-scale pseudo-spin-valve (PSV) structure was theoretically studied. The spin relaxation mechanisms and the influence of ferromagnetic/nonmagnetic (FM/NM) interfaces on the current polarization were investigated, and a modified magnetic dynamic equation was developed. Both the free layer's local magnetic moments and itinerant electrons' spins were regarded as a macro-spin, whose movement was resulted from two items: spin relaxation due to the magnetic damping and spin accumulation due to the polarized current. The injected current not only produces a spin transfer torque, but also alters the effective magnetic field, and thus affects the damping. Therefore, the damping is nonlinear and correlated to the current. Based on the analysis of the competition between magnetic damping and spin accumulation, the dynamic behaviors of magnetization switching and oscillation can be explained.
Using Sheep to Control Purple Loosestrife (Lythrum salicaria)
Authors: Kleppel G. S. , LaBarge Erin 
Published: April 2011

AbstractWe investigated the use of sheep for controlling the spread of purple loosestrife in a wet meadow in upstate New York from June to August 2008. Changes in the purple loosestrife population and vascular plant community structure were monitored as a function of the grazing of two ewes, “rotated” through four “experimental” paddocks at 2- to 3-d intervals. Comparative data were collected in “reference” paddocks from which sheep were excluded. Purple loosestrife was heavily grazed and most plants did not flower in experimental paddocks. Purple loosestrife cover declined by 40.7% in the experimental paddocks but did not change significantly in the reference paddocks. After grazing, species richness was 20% higher in experimental than reference paddocks.