The Interaction of Borosilicate Glass and Grawodiorite at 100°C, 50 Mpa: Implications For Models Of Radionuclide Release

1981 ◽  
Vol 11 ◽  
Author(s):  
David Savage ◽  
Jane E. RObbins

An essential component of any assessment of HLRW geological disposal options is the quantitative prediction of radionuclide release rates from the near-field over time spans of the order of 103-106 years. Fundamental to this assessment is the investigation of the interaction of potential wasteforms with groundwater under repository conditions of temperature, pressure, and groundwater flow-rate. Consequently, many studies world-wide have been initiated to examine the kinetics of wasteform dissolution over a wide range of physical and chemical conditions. Although these studies have provided a considerable amount of invaluable data on wasteform-fluid interactions, they have tended to focus on breakdown of the wasteform itself, and not on the fate of released waste components in the nearfield. For example, effects of saturation of species in solution, precipitation of secondary minerals or amorphous gels, and the effect of host rock chemistry on the products (solid and fluid) of waste-fluid interaction have largely been ignored or even specifically excluded in laboratory experiments. This is despite growing evidence from source term modelling studies which suggest that the above processes may well be the chief factors in governing rates of radionuclide release from the near-field, bearing in mind the limited availability of ground

2019 ◽  
Vol 489 (1) ◽  
pp. 708-713 ◽  
Author(s):  
Kaijun Li ◽  
Aigen Li ◽  
F Y Xiang

ABSTRACT The carriers of the still (mostly) unidentified diffuse interstellar bands (DIBs) have been a long-standing mystery ever since their first discovery exactly 100 yr ago. In recent years, the ubiquitous detection of a large number of DIBs in a wide range of Galactic and extragalactic environments has led to renewed interest in connecting the occurrence and properties of DIBs to the physical and chemical conditions of the interstellar clouds, with particular attention paid to whether the DIB strength is related to the shape of the interstellar extinction curve. To shed light on the nature and origin of the DIB carriers, we investigate the relation between the DIB strength and RV, the total-to-selective extinction ratio, which characterizes how the extinction varies with wavelength (i.e. the shape of the extinction curve). We find that the DIB strength and RV are not related if we represent the strength of a DIB by its reddening-normalized equivalent width (EW), in contrast to the earlier finding of an anticorrelation in which the DIB strength is measured by the extinction-normalized EW. This raises a fundamental question about the appropriate normalization for the DIB EW. We argue that the hydrogen column density is a more appropriate normalization than extinction and reddening.


The paper addresses the physical and chemical processes that can serve to immobilize waste radionuclides within the confines of an underground repository. These processes, which can be made largely independent of the chemical nature of the host rock, depend for their efficacy upon the maintenance of a very low flow rate of groundwater through the repository constituents. The very long-lived waste products, in particular the actinides, are very insoluble in water under conditions of alkalinity and oxygen potential that will exist in a repository when cement is used as a backfill or as a matrix for the waste. The same chemical conditions tend to favour a fairly long life for steel containers. The paper suggests how these factors may be used to immobilize wastes and draws some conclusions on the relative value of the various engineered features of a repository. Some natural geological analogues are explored as a means of assisting the extrapolation of waste behaviour over very long times.


Minerals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 737 ◽  
Author(s):  
Anatoly M. Sazonov ◽  
Sergey A. Silyanov ◽  
Oleg A. Bayukov ◽  
Yuriy V. Knyazev ◽  
Yelena A. Zvyagina ◽  
...  

The Mössbauer spectroscopy method was used to study the ligand microstructure of natural arsenopyrite (31 specimens) from the ores of the major gold deposits of the Yenisei Ridge (Eastern Siberia, Russia). Arsenopyrite and native gold are paragenetic minerals in the ore; meanwhile, arsenopyrite is frequently a gold carrier. We detected iron positions with variable distribution of sulfur and arsenic anions at the vertexes of the coordination octahedron {6S}, {5S1As}, {4S2As}, {3S3As}, {2S4As}, {1S5As}, {6As} in the mineral structure. Iron atoms with reduced local symmetry in tetrahedral cavities, as well as iron in the high-spin condition with a high local symmetry of the first coordination sphere, were identified. The configuration {3S3As} typical for the stoichiometric arsenopyrite is the most occupied. The occupation degree of other configurations is not subordinated to the statistic distribution and varies within a wide range. The presence of configurations {6S}, {3S3As}, {6As} and their variable occupation degree indicate that natural arsenopyrites are solid pyrite {6S}, arsenopyrite {3S3As}, and loellingite {6As} solutions, with the thermodynamic preference to the formation of configurations in the arsenopyrite–pyrite–loellingite order. It is assumed that in the variations as part of the coordination octahedron, the iron output to the tetrahedral positions and the presence of high-spin Fe cations depend on the physical and chemical conditions of the mineral formation. It was identified that the increased gold concentrations are typical for arsenopyrites with an elevated content of sulfur or arsenic and correlate with the increase of the occupation degree of configurations {5S1As}, {4S2As}, {1S5As}, reduction of the share of {3S3As}, and the amount of iron in tetrahedral cavities.


2006 ◽  
Vol 932 ◽  
Author(s):  
Sarah P Watson ◽  
David P Hodgkinson ◽  
Peter C Robinson ◽  
Lucy EF Bailey ◽  
Mike J Poole

ABSTRACTUK Nirex has supported a programme of work to develop models describing the postclosure evolution of intermediate-level waste packages with the objectives of:• providing support and justification for the parameters and representations used in performance assessment models;• informing future model development and packaging advice.Scenarios for the potential evolution of a waste package were developed and modelled taking explicit account of waste package heterogeneity and the time-dependence of the physical and chemical characteristics of the system. The modelling work highlighted the treatment of organic complexants and the representation of physical containment as two areas in which the impacts of time dependence and package scale heterogeneity might be particularly significant.A subsequent study of the impact of organic complexants emphasised the importance of heterogeneity in package inventory in determining the radionuclide release from the near field.The degree of containment afforded by the wasteform and the waste container has been investigated as part of a study to develop a preliminary understanding of the mixing scales within the repository. The study suggests that the most important control on the release of radionuclides from the waste packages is the integrity of the waste encapsulation grout. Interactions between neighbouring packages are to be expected, but the degree to which homogeneous (well mixed) conditions develop may be limited in both time and space.


2020 ◽  
pp. 823-845
Author(s):  
Stuart F. Simmons ◽  
Benjamin M. Tutolo ◽  
Shaun L.L. Barker ◽  
Richard J. Goldfarb ◽  
François Robert

Abstract Epithermal, Carlin, and orogenic Au deposits form in diverse geologic settings and over a wide range of depths, where Au precipitates from hydrothermal fluids in response to various physical and chemical processes. The compositions of Au-bearing sulfidic hydrothermal solutions across all three deposit types, however, are broadly similar. In most cases, they comprise low-salinity waters, which are reduced, have a near-neutral pH, and CO2 concentrations that range from <4 to >10 wt %. Experimental studies show that the main factor controlling the concentration of Au in hydrothermal solutions is the concentration of reduced S, and in the absence of Fe-bearing minerals, Au solubility is insensitive to temperature. In a solution containing ~300 ppm H2S, the maximum concentration of Au is ~1 ppm, representing a reasonable upper limit for many ore-forming solutions. Where Fe-bearing minerals are being converted to pyrite, Au solubility decreases as temperature cools due to the decreasing concentration of reduced S. High Au concentrations (~500 ppb) can also be achieved in strongly oxidizing and strongly acidic chloride solutions, reflecting chemical conditions that only develop during intense hydrolytic leaching in magmatic-hydrothermal high-sulfidation epithermal environments. Gold is also soluble at low to moderate levels (10–100 ppb) over a relatively wide range of pH values and redox states. The chemical mechanisms which induce Au deposition are divided into two broad groups. One involves achieving states of Au supersaturation through perturbations in solution equilibria caused by physical and chemical processes, involving phase separation (boiling), fluid mixing, and pyrite deposition via sulfidation of Fe-bearing minerals. The second involves the sorption of ionic Au on to the surfaces of growing sulfide crystals, mainly arsenian pyrite. Both groups of mechanisms have capability to produce ore, with distinct mineralogical and geochemical characteristics. Gold transport and deposition processes in the Taupo Volcanic Zone, New Zealand, show how ore-grade concentrations of Au can accumulate by two different mechanisms of precipitation, phase separation and sorption, in three separate hydrothermal environments. Phase separation caused by flashing, induced by depressurization and associated with energetic fluid flow in geothermal wells, produces sulfide precipitates containing up to 6 wt.% Au from a hydrothermal solution containing a few ppb Au. Sorption on to As-Sb-S colloids produces precipitates containing tens to hundreds of ppm Au in the Champagne Pool hot spring. Sorption on to As-rich pyrite also leads to anomalous endowments of Au of up to 1 ppm in hydrothermally altered volcanic rocks occurring in the subsurface. In all of these environments, Au-undersaturated solutions produce anomalous concentrations of Au that match and surpass typical ore-grade concentrations, indicating that near-saturated concentrations of dissolved metal are not a prerequisite for generating economic deposits of Au. The causes of Au deposition in epithermal deposits are related to sharp temperature-pressure gradients that induce phase separation (boiling) and mixing. In Carlin deposits, Au deposition is controlled by surface chemistry and sorption processes on to rims of As-rich pyrite. In orogenic deposits, at least two Au-depositing mechanisms appear to produce ore; one involves phase separation and the other involves sulfidation reactions during water-rock interaction that produces pyrite; a third mechanism involving codeposition of Au-As in sulfides might also be important. Differences in the regimes of hydrothermal fluid flow combined with mechanisms of Au precipitation play an important role in shaping the dimensions and geometries of ore zones. There is also a strong link between Au-depositing mechanisms and metallurgical characteristics of ores.


2020 ◽  
Vol 20 (2) ◽  
pp. 40
Author(s):  
I Wayan Juliawan ◽  
I Wayan Arthana ◽  
Endang Wulandari Suryaningtyas

Batur Lake is one of the lakes located in the Kintamani sub-district, Bali. This lake has abundant biodiversity, one of them is Red Devil fish (Amphilophus sp) which is a competitor of native and introduced fish. The research aims to find out the pattern of growth, size structure, and the physical and chemical conditions of waters. The method used was descriptive quantitative by using two trapping devices that were fishing rods and nets. Calculation results showed that a wide range of growth patterns of Red Devil (Amphilophus sp) fish on both trapping devices (fishing rods and nets) were grouped (Id<1). The highest sized structure value on the trapping devices (fishing rod) found in the water of Trunyan Village that was total length (TL) of  9,3 cm, Standard length (SL) of 7,3 cm, and weight: 16,5 gr. On the trapping devices (net) the highest value was found in the water of Songan Village that was total length (TL) of 13,5, SL of 11,1, and weight: 48,8 gr. The growth patterns of Red Devil (Amphilophus sp) fish based on length and weight analysis showed that were partly positive allometric and partly negative allometric. The result of the water quality  measurement in the water of Batur Lake was about 26,3°C – 29,1°C (temperature), 5,36 mg/L – 6 mg/L, (DO), 7,2 – 7,8 (pH), and 87,1 cm – 147,8 cm (brightness).


1993 ◽  
Vol 265 (2) ◽  
pp. H543-H552 ◽  
Author(s):  
Y. Yuan ◽  
W. M. Chilian ◽  
H. J. Granger ◽  
D. C. Zawieja

This study reports measurements of albumin permeability in isolated coronary venules. The isolated microvessel technique allows the quantification of transmural exchange of macromolecules under tightly controlled physical and chemical conditions. Transvenular exchange of albumin was studied in isolated coronary venules during alterations in filtration rate caused by changes in intravascular pressure. The apparent permeability coefficient of albumin (Pa) at an intraluminal pressure of 11 cmH2O was 3.92 +/- 0.43 x 10(-6) cm/s. Elevating intraluminal pressure to 16 and 21 cmH2O increased Pa to 5.13 +/- 0.57 x 10(-6) and 6.78 +/- 0.66 x 10(-6) cm/s, respectively. Calculation of the true diffusive permeability coefficient of albumin (Pd) at zero filtration rate was 1.54 x 10(-6) cm/s. The product of hydraulic conductance (Lp) and (1 - sigma), where sigma is the solute reflection coefficient, was 3.25 x 10(-7) cm.s-1 x cmH2O-1. At a net filtration pressure of 4-5 cmH2O, diffusion accounts for > 60% of total albumin transport across the venular wall. Transmural albumin flux is very sensitive to filtration rate, rising 6.7% for each cmH2O elevation of net filtration pressure. At 11 cmH2O net filtration pressure, convection accounts for nearly 70% of net albumin extravasation from the venular lumen. We suggest that the isolated coronary venule is a suitable preparation for the study of solute exchange in the heart.


2021 ◽  
pp. 204141962199349
Author(s):  
Jordan J Pannell ◽  
George Panoutsos ◽  
Sam B Cooke ◽  
Dan J Pope ◽  
Sam E Rigby

Accurate quantification of the blast load arising from detonation of a high explosive has applications in transport security, infrastructure assessment and defence. In order to design efficient and safe protective systems in such aggressive environments, it is of critical importance to understand the magnitude and distribution of loading on a structural component located close to an explosive charge. In particular, peak specific impulse is the primary parameter that governs structural deformation under short-duration loading. Within this so-called extreme near-field region, existing semi-empirical methods are known to be inaccurate, and high-fidelity numerical schemes are generally hampered by a lack of available experimental validation data. As such, the blast protection community is not currently equipped with a satisfactory fast-running tool for load prediction in the near-field. In this article, a validated computational model is used to develop a suite of numerical near-field blast load distributions, which are shown to follow a similar normalised shape. This forms the basis of the data-driven predictive model developed herein: a Gaussian function is fit to the normalised loading distributions, and a power law is used to calculate the magnitude of the curve according to established scaling laws. The predictive method is rigorously assessed against the existing numerical dataset, and is validated against new test models and available experimental data. High levels of agreement are demonstrated throughout, with typical variations of <5% between experiment/model and prediction. The new approach presented in this article allows the analyst to rapidly compute the distribution of specific impulse across the loaded face of a wide range of target sizes and near-field scaled distances and provides a benchmark for data-driven modelling approaches to capture blast loading phenomena in more complex scenarios.


Life ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 539
Author(s):  
Benton C. Clark ◽  
Vera M. Kolb ◽  
Andrew Steele ◽  
Christopher H. House ◽  
Nina L. Lanza ◽  
...  

Although the habitability of early Mars is now well established, its suitability for conditions favorable to an independent origin of life (OoL) has been less certain. With continued exploration, evidence has mounted for a widespread diversity of physical and chemical conditions on Mars that mimic those variously hypothesized as settings in which life first arose on Earth. Mars has also provided water, energy sources, CHNOPS elements, critical catalytic transition metal elements, as well as B, Mg, Ca, Na and K, all of which are elements associated with life as we know it. With its highly favorable sulfur abundance and land/ocean ratio, early wet Mars remains a prime candidate for its own OoL, in many respects superior to Earth. The relatively well-preserved ancient surface of planet Mars helps inform the range of possible analogous conditions during the now-obliterated history of early Earth. Continued exploration of Mars also contributes to the understanding of the opportunities for settings enabling an OoL on exoplanets. Favoring geochemical sediment samples for eventual return to Earth will enhance assessments of the likelihood of a Martian OoL.


Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1891
Author(s):  
Antonio Reina ◽  
Trung Dang-Bao ◽  
Itzel Guerrero-Ríos ◽  
Montserrat Gómez

Metal nanoparticles have been deeply studied in the last few decades due to their attractive physical and chemical properties, finding a wide range of applications in several fields. Among them, well-defined nano-structures can combine the main advantages of heterogeneous and homogenous catalysts. Especially, catalyzed multi-step processes for the production of added-value chemicals represent straightforward synthetic methodologies, including tandem and sequential reactions that avoid the purification of intermediate compounds. In particular, palladium- and copper-based nanocatalysts are often applied, becoming a current strategy in the sustainable synthesis of fine chemicals. The rational tailoring of nanosized materials involving both those immobilized on solid supports and liquid phases and their applications in organic synthesis are herein reviewed.


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