The Geochemical Behaviour of Nickel in the Repository Environment

1994 ◽  
Vol 353 ◽  
Author(s):  
David Savage
Keyword(s):  
Solid Solution ◽  
Trace Elements ◽  
Radioactive Waste ◽  
Performance Assessment ◽  
Solid Solutions ◽  
Near Field ◽  
Solubility Data ◽  
Geochemical Behaviour ◽  
Chemical Conditions ◽  
Selection Of

Abstract59Ni may make significant contributions to calculated doses in performance assessment (PA) studies of geological repositories for radioactive waste, due principally to the adoption of relatively high near-field solubilities. Ni concentration values used in PA are typically 1–6 orders of magnitude greater than those measured in natural groundwaters. This difference is a result of the utilisation in PA of solubility data for pure nickeliferous solids, and in some instances, the selection of solids chemically incompatible with the disposal environment. The geochemical behaviour of Ni is reviewed. It is considered highly unlikely that Ni will form discrete pure solids in the repository near-field, so that partition as a trace element into solid solutions should be considered. Henry’s law behaviour of trace elements is discussed and geochemically-realistic Ni solubility values for HLW and L/ILW disposal scenarios calculated. It is concluded that Ni will behave according to the chemical conditions of the disposal environment, which should be reflected in the choice of solubility data for PA. The adoption of solid solution modelling for other elements of interest to PA should be considered.

The Coupling of Chemical and Transport Processes in Near-Field Modelling

1986 ◽  
Vol 84 ◽  
Author(s):  
S.M. Sharland ◽  
P.W. Tasker ◽  
C.J. Tweed
Keyword(s):  
Radioactive Waste ◽  
Chemical Equilibrium ◽  
Near Field ◽  
Transport Processes ◽  
Primary Interest ◽  
Field Modelling ◽  
Long Time ◽  
Waste Repository ◽  
Solid Phases ◽  
Chemical Conditions

AbstractNear-field modelling is concerned with the description of the migration, chemical and degradation processes that may occur within an engineered radioactive waste repository and its immediate environs. The object is to gain understanding of such processes in order to predict the long-time evolution of the repository and to assess the degree of containment provided by the proposed engineered construction. The conditions of primary interest to our programme concern the waste contained within a steel canister and buried in a concrete environment within a clay geology. The chemistry of the near-field is controlled in that it is the consequence of the choice of near-field components, but it may be extremely complex. Intrusion of external groundwater and degradation of the chosen materials will lead to variations in the chemistry in both space and time. It is vitally important to understand these changing chemical conditions since they determine the solubility and sorption of any released radionuclides. In this paper, we describe the computer program CHEQMATE (CHemical EQuilibrium with Migration And Transport Equations), which has many applications in modelling various changes in chemistry in the near-field. The program combines an ionic migration code with the geochemical program PHREEQE [1]. The program maintains local chemical equilibrium in the system as the transport processes evolve. The program includes automatic mineral accounting; solid phases are added or removed from the equilibrium as precipitation or dissolution occurs. We illustrate the use of the CHEQMATE program with an example of a coupled chemical and transport problem, particularly relevant to the near-field of a waste repository.

Thermodynamic Modelling and Aqueous Chemistry in the CaO-Al2O3-SiO2-H2O System

1990 ◽  
Vol 212 ◽  
Author(s):  
A. Atkinson ◽  
J. A. Hearne ◽  
C. F. Knights
Keyword(s):  
Experimental Data ◽  
Solid Solution ◽  
Radioactive Waste ◽  
Solid Solutions ◽  
Chemical Properties ◽  
Average Composition ◽  
Radioactive Waste Repositories ◽  
Waste Repositories ◽  
Hydrolysis Of ◽  
Main Influence

ABSTRACTThe chemical properties of the CaO-Al2O3-SiO2-H2O system are important for understanding and predicting the behaviour of Portland cements in cementitious wasteforms and radioactive waste repositories. Solids of known average composition in this system have been synthesised by the co-hydrolysis of mixed alkoxides. The solids have been equilibrated with water at 25°C and the composition of the aqueous phase characterised. A thermodynamic model for the system has been developed by extending an earlier model of solid solutions in amorphous gels to include aluminium compounds. The model accounts for most of the experimental data and predicts that the main influence of aluminium is to form a hydrogarnet solid solution of general composition C3AH6−2xSx The model can be used to predict the chemistry of hydrated cements and the interaction of cements with groundwaters.

scholarly journals Preparation and Morphological Studies of Epitaxial Layers of a Solid Solution Si1–xGex

2020 ◽  
Vol 15 (2) ◽  
pp. 84-91
Author(s):  
Amin S. Saidov ◽  
Alozhon Sh. Razzokov
Keyword(s):  
Solid Solution ◽  
Dislocation Density ◽  
Solid Solutions ◽  
Epitaxial Layers ◽  
Optimal Process ◽  
Exponential Relationship ◽  
Process Regime ◽  
Morphological Studies ◽  
Dislocation Densities ◽  
Selection Of

The article shows the selection of the optimal process regime for the growth of epitaxial layers of Si1–xGex solid solutions from tin and gallium solution – melt on a Si<111> substrate, with the lowest dislocation densities that we experimentally achieved. An exponential relationship was found between the values of the dislocation density and the film thickness.With a smooth variable composition of the structure, respectively, by smoothly changing the lattiece parameters of the graded-gap solid solution, structurally perfect epitaxial layers Si1–xGex (0 < x < 1) were obtained

Real-time Approximation of Photometric Polygonal Lights

2020 ◽  
Vol 3 (1) ◽  
pp. 1-18
Author(s):  
Christian Luksch ◽  
Lukas Prost ◽  
Michael Wimmer
Keyword(s):  
Real Time ◽  
Specular Reflection ◽  
Near Field ◽  
Measurement Data ◽  
Data Sets ◽  
Photometric Measurement ◽  
Integration Technique ◽  
Time Approximation ◽  
Light Emitter ◽  
Selection Of

We present a real-time rendering technique for photometric polygonal lights. Our method uses a numerical integration technique based on a triangulation to calculate noise-free diffuse shading. We include a dynamic point in the triangulation that provides a continuous near-field illumination resembling the shape of the light emitter and its characteristics. We evaluate the accuracy of our approach with a diverse selection of photometric measurement data sets in a comprehensive benchmark framework. Furthermore, we provide an extension for specular reflection on surfaces with arbitrary roughness that facilitates the use of existing real-time shading techniques. Our technique is easy to integrate into real-time rendering systems and extends the range of possible applications with photometric area lights.

scholarly journals A Multiple Criteria Decision Making Method to Weight the Sustainability Criteria of System Selection for Surface Mining

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3066
Author(s):  
Michał Patyk ◽  
Przemysław Bodziony ◽  
Zbigniew Krysa
Keyword(s):  
Decision Making ◽  
Performance Assessment ◽  
Multiple Criteria Decision Making ◽  
Surface Mining ◽  
Open Pit ◽  
Mining Equipment ◽  
Surface Mines ◽  
Mining Conditions ◽  
And Performance ◽  
Selection Of

Selection and assessment of mining equipment used in open pit rock mines relies chiefly on estimates of overall exploitation cost. The rational arrangement of mining equipment and systems comprising loading machines, haul trucks and crushing plants should be preceded by a thorough analysis of technical and economic aspects, such as investment outlays and the costs of further exploitation, which largely determine the costs of mining operations and the deposit value. Additionally, the operational parameters of the mining equipment ought to be considered. In this study, a universal set of evaluation criteria has been developed, and an evaluation method has been applied for the selection of surface mining equipment and the processing system to be operated in specific mining conditions, defined by the user. The objective of this study is to develop and apply the new methodology of multi-criteria selection of open pit rock mining equipment based on multiple criteria decision-making (MCDM) procedures, to enable the optimization of loading, handling and crushing processes. The methodology, underpinned by the principles of MCDM, provides the dedicated ranking procedures, including the ELECTRE III. The applied methodology allows the alternative options (variants) to be ranked accordingly. Ultimately, a more universal methodology is developed, applicable in other surface mines where geological and mining conditions are similar. It may prove particularly useful in selection and performance assessment of mining equipment and process line configurations in mining of low-quality rock deposits. Therefore, we undertook to develop universal criteria and applications for the selection and performance assessment of process machines for surface mines, taking into account environmental aspects as well as deposit quality.

scholarly journals Synthesis of Ce1−xPdxO2−δ Solid Solution in Molten Nitrate

Catalysts ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 640
Author(s):  
Hideaki Sasaki ◽  
Keisuke Sakamoto ◽  
Masami Mori ◽  
Tatsuaki Sakamoto
Keyword(s):  
Electron Microscopy ◽  
Solid Solution ◽  
Solid Solutions ◽  
Photoelectron Spectroscopy ◽  
Synthesis Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Co Precipitation ◽  
Ionic States

CeO2-based solid solutions in which Pd partially substitutes for Ce attract considerable attention, owing to their high catalytic performances. In this study, the solid solution (Ce1−xPdxO2−δ) with a high Pd content (x ~ 0.2) was synthesized through co-precipitation under oxidative conditions using molten nitrate, and its structure and thermal decomposition were examined. The characteristics of the solid solution, such as the change in a lattice constant, inhibition of sintering, and ionic states, were examined using X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM−EDS), transmission electron microscopy (TEM)−EDS, and X-ray photoelectron spectroscopy (XPS). The synthesis method proposed in this study appears suitable for the easy preparation of CeO2 solid solutions with a high Pd content.

Electron microprobe study of turquoise-group solid solutions in the Neyshabour and Meydook mines, northeast and southern Iran

2020 ◽  
Vol 58 (1) ◽  
pp. 71-83
Author(s):  
Elahe Mansouri Gandomani ◽  
Nematollah Rashidnejad-Omran ◽  
Amir Emamjomeh ◽  
Pietro Vignola ◽  
Tahereh Hashemzadeh
Keyword(s):  
Solid Solution ◽  
Solid Solutions ◽  
Electron Microprobe ◽  
Electron Probe Microanalysis ◽  
Electron Probe ◽  
Major Elements ◽  
Point Of View ◽  
Chemical Compositions ◽  
Light Blue ◽  
Quaternary Solid Solution

ABSTRACT Turquoise, CuAl6(PO4)4(OH)8·4H2O, belongs to the turquoise group, which consists of turquoise, chalcosiderite, aheylite, faustite, planerite, and UM1981-32-PO:FeH. In order to study turquoise-group solid solutions in samples from the Neyshabour and Meydook mines, 17 samples were selected and investigated using electron probe microanalysis. In addition, their major elements were compared in order to evaluate the feasibility of distinguishing the provenance of Persian turquoises. The electron microprobe data show that the studied samples are not constituted of pure turquoise (or any other pure endmember) and belong, from the chemical point of view, to turquoise-group solid solutions. In a turquoise–planerite–chalcosiderite–unknown mineral quaternary solid solution diagram, the chemical compositions of the analyzed samples lie along the turquoise–planerite line with minor involvement of chalcosiderite and the unknown mineral. Among light blue samples with varying hues and saturations from both studied areas, planerite is more abundant among samples from Meydook compared with samples from Neyshabour. Nevertheless, not all the light blue samples are planerite. This study demonstrates that distinguishing the deposit of origin for isochromatic blue and green turquoises, based on electron probe microanalysis method and constitutive major elements, is not possible.

Geochemical behaviour and risk assessment of trace elements in a tropical river, Northwest Borneo

Chemosphere ◽  
2020 ◽  
Vol 252 ◽  
pp. 126430 ◽  
Author(s):  
K. Prabakaran ◽  
S. Eswaramoorthi ◽  
R. Nagarajan ◽  
A. Anandkumar ◽  
F. Merlin Franco
Keyword(s):  
Risk Assessment ◽  
Trace Elements ◽  
Tropical River ◽  
Geochemical Behaviour

Epitaxial Solid-Solution Films of Immiscible MgO and CaO

1994 ◽  
Vol 341 ◽  
Author(s):  
E. S. Hellman ◽  
E. H. Hartford
Keyword(s):  
Solid Solution ◽  
Molecular Beam Epitaxy ◽  
Lattice Constant ◽  
Solid Solutions ◽  
Molecular Beam ◽  
Building Blocks ◽  
Layer Growth ◽  
Growth Mode ◽  
Miscibility Gap ◽  
Layer By Layer

AbstractMetastable solid-solutions in the MgO-CaO system grow readily on MgO at 300°C by molecular beam epitaxy. We observe RHEED oscillations indicating a layer-by-layer growth mode; in-plane orientation can be described by the Matthews theory of island rotations. Although some films start to unmix at 500°C, others have been observed to be stable up to 900°C. The Mgl-xCaxO solid solutions grow despite a larger miscibility gap in this system than in any system for which epitaxial solid solutions have been grown. We describe attempts to use these materials as adjustable-lattice constant epitaxial building blocks

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