A tool to draw chemical equilibrium diagrams using SIT: Applications to geochemical systems and radionuclide solubility

2014 ◽  
Vol 1665 ◽  
pp. 111-116 ◽  
Author(s):  
I. Puigdomènech ◽  
E. Colàs ◽  
M. Grivé ◽  
I. Campos ◽  
D. García
Keyword(s):  
Experimental Data ◽  
Ionic Strength ◽  
Undergraduate Students ◽  
Nuclear Waste ◽  
Chemical Equilibrium ◽  
Equilibrium Constants ◽  
Nuclear Waste Repository ◽  
Wide Range ◽  
Java Programs ◽  
Institute Of Technology

ABSTRACTA set of computer programs has been developed to draw chemical-equilibrium diagrams. This new software is the Java-language equivalent to the Medusa/Hydra software (developed some time ago in Visual basic at the Royal Institute of Technology, Stockholm, Sweden). The main program, now named “Spana” calls Java programs based on the HaltaFall algorithm. The equilibrium constants that are needed for the calculations may be retrieved from a database included in the software package (“Database” program). This new software is intended for undergraduate students as well as researchers and professionals.The “Spana” code can be easily applied to perform radionuclide speciation and solubility calculations of minerals, including solubility calculations relevant for the performance assessment of a nuclear waste repository. In order to handle ionic strength corrections in such calculations several approaches can be applied. The “Spana” code is able to perform calculations based on three models: the Davies equation; an approximation to the model by Helgeson et al. (HKF); and the Specific Ion-Interaction Theory (SIT). Default SIT-coefficients may be used, which widens the applicability of SIT significantly.A comparison is made here among the different ionic strength approaches used by “Spana” (Davies, HKF, SIT) when modelling the chemistry of radionuclides and minerals of interest under the conditions of a geological repository for nuclear waste. For this purpose, amorphous hydrous Thorium(IV) oxide (ThO2(am)), Gypsum (CaSO4·2H2O) and Portlandite (Ca(OH)2) solubility at high ionic strengths have been modelled and compared to experimental data from the literature. Results show a good fitting between the calculated values and the experimental data especially for the SIT approach in a wide range of ionic strengths (0-4 M).

Ionic strength- and pH-dependence of calcium binding by terrestrial humic acids

2012 ◽  
Vol 9 (1) ◽  
pp. 89 ◽  
Author(s):  
Iso Christl
Keyword(s):  
Experimental Data ◽  
Ionic Strength ◽  
Humic Acids ◽  
Calcium Binding ◽  
Good Description ◽  
Ph Dependence ◽  
Wide Range ◽  
Electrostatic Binding ◽  
Carboxylic Groups ◽  
Terrestrial Environments

Environmental contextIn terrestrial environments, humic substances act as major sorbents for calcium, which is an essential nutrient for organisms. This study shows that calcium binding by terrestrial humic acids is strongly dependent on pH and ionic strength. The results indicate that calcium binding by humic acids is primarily controlled by electrostatic forces and specific binding to carboxylic groups. AbstractCalcium binding by two terrestrial humic acids was investigated at 25 °C as a function of pH, ionic strength and Ca2+ activity with calcium titration experiments. A Ca2+-selective electrode was used for Ca2+ measurements to cover a wide range of Ca2+ activities (10–8.5–10–2.5). Experimental data were quantitatively described with the NICA–Donnan model accounting for electrostatic and specific calcium binding. The results showed that calcium binding as a function of Ca2+ activity was strongly affected by variations of pH and ionic strength indicating that electrostatic binding is an important mechanism for calcium binding by humic acids. Data modelling providing a good description of experimental data for both humic acids suggested that electrostatic binding was the dominant calcium binding mechanisms at high Ca2+ activities often observed in terrestrial environments. Specific calcium binding being quantitatively predominant only at low Ca2+ activities was exclusively attributed to binding sites exhibiting a weak affinity for protons considered to represent mainly carboxylic groups. Since the negative charge of the humic acids being prerequisite for electrostatic calcium binding was found to be mainly due to deprotonation of carboxylic groups except under alkaline conditions, carboxylic groups were identified to primarily control calcium binding of humic acids.

scholarly journals Corium Experimental Thermodynamics: A Review and Some Perspectives

Thermo ◽  
2021 ◽  
Vol 1 (2) ◽  
pp. 179-204
Author(s):  
Marc Barrachin
Keyword(s):  
Experimental Data ◽  
Equilibrium Constants ◽  
Research Area ◽  
Severe Accident ◽  
Model Parameters ◽  
Joint Research ◽  
Research Perspectives ◽  
Wide Range ◽  
Simple Physical Model ◽  
Water Reactors

More than 30 years ago a specialist meeting was held at Joint Research Center Ispra (Italy) from 15 to 17 January 1990 to review the current understanding of chemistry during severe accidents in light water reactors (LWR). Let us consider that, at the end of the 1980s, thermodynamics introduced in the severe accident codes was really poor. Only some equilibrium constants for a few simple reactions between stoichiometric compounds were used as well as some simple correlations giving estimates of solidus and liquidus temperatures. In the same time, the CALPHAD method was developed and was full of promise to approximate the thermodynamic properties of a complex thermochemical system by the way of a critical assessment of experimental data, a definition of a simple physical model and an optimisation procedure to define the values of the model parameters. It was evident that a nuclear thermodynamic database had to be developed with that new technique to obtain quite rapidly prominent progress in the knowledge of thermochemistry in the severe accident research area. Discussions focused on the important chemical phenomena that could occur across the wide range of conditions of a damaged nuclear plant. The most pressing need for improved chemical models is identified with condensed phase mixtures to model the corium progression. This paper reviews more than 30 years of experimental data production in the field of corium thermodynamics. This work has been conducted through multiple international programs (EURATOM, ISTC, OECD) as well as through more specific studies conducted at the national scale. This research has been capitalised in specific databases such as NUCLEA and TAF-ID, databases developed at IRSN and at CEA, respectively, and are now used in degradation models of the severe accident simulation codes. This research is presented in this paper. In the conclusion, we outline the research perspectives that need to be considered in order to address today’s and tomorrow’s issues.

scholarly journals Determination of complex formation constants of neptunium(V) with propionate and lactate in 0.5–2.6 m NaCl solutions at 22–60°C using a solvent extraction technique

2019 ◽  
Vol 107 (7) ◽  
pp. 623-634
Author(s):  
Aleksandr N. Vasiliev ◽  
Nidhu L. Banik ◽  
Rémi Marsac ◽  
Stepan N. Kalmykov ◽  
Christian M. Marquardt
Keyword(s):  
Solvent Extraction ◽  
Complex Formation ◽  
Nuclear Waste ◽  
Equilibrium Constants ◽  
Extraction Technique ◽  
Nuclear Waste Repository ◽  
Clay Rock ◽  
Complex Formation Constants ◽  
Solvent Extraction Technique

Abstract Natural clay rocks like Opalinus (OPA) and Callovo-Oxfordian (COx) clay rock are considered as potential host rocks for deep geological disposal of nuclear waste. However, small organic molecules such as propionate and lactate exist in clay rock pore water and might enhance Np mobility through a complexation process. Therefore, reliable complex formation data are required in the frame of the Safety Case for a nuclear waste repository. A solvent extraction technique was applied for the determination of ${\rm{NpO}}_2^ + $ complexation with propionate and lactate. Extraction was conducted from isoamyl alcohol solution containing 10−3 M TTA and 5 · 10−4 M 1,10-phenanthroline. Experiments were performed in 0.5–2.6 m NaCl solutions at temperatures ranging from 22 to 60 °C. Formation of 1:1 Np(V) complexes for propionate and lactate was found under the studied conditions. The SIT approach was applied to calculate equilibrium constants β°(T) at zero ionic strength from the experimental data. Log β°(T) is found linearly correlated to 1/T for propionate and lactate, evidencing that heat capacity change is near 0. Molal reaction enthalpy and entropy ( ${\Delta _{\rm{r}}}H_{\rm{m}}^ \circ $ and ${\Delta _{\rm{r}}}S_{\rm{m}}^ \circ $ ) could therefore be derived from the integrated van’t Hoff equation. Data for log β° (298.15 K) are in agreement with literature values for propionate and lactate. Np(V) speciation was calculated for concentrations of acetate, propionate and lactate measured in clay pore waters of COx. In addition, the two site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model was applied to quantitatively describe the influence of Np(V) complexation on its uptake on Na-illite, a relevant clay mineral of OPA and COx.

The Salton Sea Geothermal Field as a Natural Analog for the Near-Field in a Salt High-Level Nuclear Waste Repository

1984 ◽  
Vol 44 ◽  
Author(s):  
Wilfred A. Elders ◽  
Judith B. Moody
Keyword(s):  
Nuclear Waste ◽  
Near Field ◽  
Geothermal Field ◽  
Salton Sea ◽  
High Level Waste ◽  
Nuclear Waste Repository ◽  
Natural Analog ◽  
Naturally Occurring ◽  
Wide Range ◽  
High Level

AbstractThe Salton Sea Geothermal Field (SSGF), on the delta of the Colorado River in southern California, is being studied as a natural analog for the near-field environment of proposed nuclear waste repositories in salt. A combination of mineralogical and geochemical methods is being employed to develop a three dimensional picture of temperature, salinity, lithology, mineralogy, and chemistry of reactions between the reservoir rocks and the hot brines. Our aim is to obtain quantitative data on mineral stabilities and on mobilities of the naturally occurring radionuclides of concern in Commercial High-Level Waste (CHLW). These data will be used to validate the EQ3/6 geochemical code under development to model the salt near-field repository behavior.Maximum temperatures encountered in wells in the SSGF equal or exceed peak temperatures expected in a salt repository. Brines produced from these wells have major element chemistry similar to brines from candidate salt sites. Relative to the rocks, these brines are enriched in Na, Mn, Zn, Sr, Ra and Po, depleted in Ba, Si, Mg, Ti, and Al, and strongly depleted in U and Th. However the unaltered rocks contain only about 2–3 ppm of U and 4–12 ppm of Th, largely in detrital epidotes and zircons. Samples of hydrothermally altered rocks from a wide range of temperature and salinity show rather similar uniform low concentrations of these elements, even when authigenic illite, chlorite, epidote and feldspar are present. These observations suggest that U and Th are relatively immobile in these hot brines. However Ra, Po, Cs and Sr are relatively mobile. Work is continuing to document naturally occurring radionuclide partitioning between SSGF minerals and brine over a range of temperature, salinity, and lithology.

scholarly journals Uranyl oxalate species in high ionic strength environments: stability constants for aqueous and solid uranyl oxalate complexes

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Yongliang Xiong ◽  
Yifeng Wang
Keyword(s):  
Ionic Strength ◽  
Stability Constants ◽  
Nuclear Waste ◽  
Waste Disposal ◽  
Infinite Dilution ◽  
Uranyl Ion ◽  
Natural Environments ◽  
Wide Range ◽  
Oxalate Complexes ◽  
Uranyl Oxalate

Abstract Uranyl ion, UO2 2+, and its aqueous complexes with organic and inorganic ligands can be the dominant species for uranium transport on the Earth surface or in a nuclear waste disposal system if an oxidizing condition is present. As an important biodegradation product, oxalate, C2O4 2−, is ubiquitous in natural environments and is known for its ability to complex with the uranyl ion. Oxalate can also form solid phases with uranyl ion in certain environments thus limiting uranium migration. Therefore, the determination of stability constants for aqueous and solid uranyl oxalate complexes is important not only to the understanding of uranium mobility in natural environments, but also to the performance assessment of nuclear waste disposal. Here we developed a thermodynamic model for the UO2 2+–Na+–H+–Cl––ClO4 ––C2O4 2––NO3 ––H2O system to ionic strength up to ∼11 mol•kg−1. We constrained the stability constants for UO2C2O4(aq) and UO2(C2O4)2 2− at infinite dilution based on our evaluation of the literature data over a wide range of ionic strengths up to ∼11 mol•kg−1. We also obtained the solubility constants at infinite dilution for solid uranyl oxalates, UO2C2O4•3H2O, based on the solubility data over a wide range of ionic strengths. The developed model will enable for the accurate stability assessment of oxalate complexes affecting uranium mobility under a wide range of conditions including those in deep geological repositories.

Transport of Gaseous 14C in a Partially Saturated, Fractured, Porous Medium

1989 ◽  
Vol 176 ◽  
Author(s):  
W. B. Light ◽  
P. L. Chambré ◽  
W. W.-L. Lee ◽  
T. H. Pigford
Keyword(s):  
Porous Medium ◽  
Nuclear Waste ◽  
Ground Surface ◽  
Yucca Mountain ◽  
Nuclear Waste Repository ◽  
Release Rates ◽  
Partially Saturated ◽  
Wide Range ◽  
Waste Repository ◽  
Porous Medium Model

ABSTRACTWe predict the transport of 14C from the proposed nuclear waste repository at Yucca Mountain using a porous medium model. Use of this model is justified if the Peclet number, which indicates equilibrium between gas in fractures and liquid in rock pores, is much less than unity. For the assumed release rates, maximum predicted concentrations of 14CO2 in rock near the ground surface are comparable to the USNRC limit for unrestricted areas. Furthermore, dilution near the ground surface as the 14CO2 enters the atmosphere will lower the concentrations by several orders of magnitude. Travel times from the repository to the surface are predicted to be hundreds to thousands of years. For a wide range of the parameters, the release rate from the source has negligible effect on the maximum concentrations at the ground surface.

Extraction of strontium with dicarbolide in the presence of polyethylene glycol

1979 ◽  
Vol 44 (1) ◽  
pp. 157-166 ◽  
Author(s):  
Petr Vaňura ◽  
Jiří Rais ◽  
Pavel Selucký ◽  
Miroslav Kyrš
Keyword(s):  
Experimental Data ◽  
Polyethylene Glycol ◽  
Ionic Strength ◽  
Aqueous Phase ◽  
Organic Phase ◽  
Distribution Ratio ◽  
Equilibrium Constants ◽  
Electrostatic Charge ◽  
Peg 400 ◽  
Order Of Magnitude

The extraction of microquantities of 85Sr in the presence of 3 . 10-4 - 0.25 mol l-1 polyethylene glycol (PEG 400) (L) with solutions of dicarbolide ({(π-(3)-1,2-B9C2H11)2Co}-) in nitrobenzene (10-3 - 10-2M) was investigated. The occurrence of the maxima (up to one order of magnitude) on the plots of the strontium distribution ratio vs the total PEG concentration was explained in terms of the competition between the charged strontium-PEG complex (SrL2+) and protonized PEG (HL+) during the balancing of the dicarbolide electrostatic charge in the organic phase. Theoretical relations were derived for the shape of this dependence, for the effect of the acid concentration in the aqueous phase and that of the dicarbolide concentration in the organic phase, as well as for the positions of the corresponding maxima. The theoretical dependences are in accordance with the experimental data. The values of the concentration equilibrium constants of the reactions Sr2+ + L + 2 H+ ##e SrL2+ + 2 H+ (Kex(SrL2+)) and H+ + L ##e HL+ (Kex(HL+)) (for variable ionic strength) are Kex(SrL2+) = 3.26 . 108 and Kex(HL+) = 538 at 25 °C.

Coprecipitation of Ni With Calcite: An Experimental Study

1997 ◽  
Vol 506 ◽  
Author(s):  
T. Carlsson ◽  
H. Aalto
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Nuclear Waste ◽  
Liquid Scintillation Counting ◽  
Liquid Scintillation ◽  
Solid Phase ◽  
Scintillation Counting ◽  
Nuclear Waste Repository ◽  
Eds Analysis ◽  
Waste Repository

ABSTRACTAt the Finnish candidate sites for a nuclear waste repository calcite (CaCO3) is a common fracture mineral, that may participate in coprecipitation processes. The objective of this work was to study the coprecipitation of the trace element Ni with CaCO3 under controlled conditions. The experiments were carried out at 30 °C in vessels closed to the atmosphere. Calcite-saturated 0.05 M NaCI solutions containing trace amounts of Ni2+ were contacted with calcite for periods of up to 42 days. The experimental data indicate that Ni coprecipitates with calcite as a result of recrystallization. The amounts of coprecipitated Ni and recrystallized calcite were determined using liquid scintillation counting and the isotopes 63Ni and 45Ca. The results are supported by a complementary SEM/EDS analysis of the solid phase.

scholarly journals Diffusive transport of uranium and americium through clay rock down to ultra-trace levels

2021 ◽  
Vol 1 ◽  
pp. 153-154
Author(s):  
Daniel Glückman ◽  
Karin Hain ◽  
Claudia Joseph ◽  
Volker Metz ◽  
Francesca Quinto ◽  
...  
Keyword(s):  
Nuclear Waste ◽  
Host Rock ◽  
Diffusion Profile ◽  
Thin Layers ◽  
Opalinus Clay ◽  
Nuclear Waste Repository ◽  
Clay Rock ◽  
Wide Range ◽  
Ultra Trace ◽  
Geological Formations

Abstract. Clay rock is a potential host rock for the final disposal of nuclear waste in deep geological formations. In the scenario of ground water intrusion into the nuclear waste repository and subsequent corrosion of canisters and waste, possibly released actinides, such as uranium (U) and americium (Am), would be transported through the engineered barrier and clay host rock mainly by diffusion. Actinides are known to exhibit low solubility and are strongly sorbing under the reducing conditions of deep geological formations. Diffusion experiments are therefore difficult to perform due to analytical constraints. To our knowledge, the diffusion of U in clay rock has not been investigated below concentrations of 10-7molkg-1 clay (e.g., Joseph et al., 2013) and for Am, no diffusion experiments have been performed in a clay rock, considered suitable as host rock, such as Opalinus clay (OPA). This work aimed at the investigation of the diffusive behavior of U and Am down to ultra-trace concentrations (≪10-7molkg-1) in OPA. Laboratory-scale diffusion experiments were conducted with samples of OPA, obtained from the Mont Terri underground laboratory, Switzerland for up to 240 d. The OPA samples were placed in contact with synthetic pore water (I=0.22molL-1, pH=7.24), spiked with 5×10-9molL-1 of 233U and 243Am, respectively. After termination of the experiment, the OPA samples were segmented into thin layers of 20–400 µm. The obtained clay segments were analyzed for the 233U and 243Am content with accelerator mass spectrometry. Concentration profiles were determined down to 10-12molkg-1 clay for 233U and 5×10-10molkg-1 clay for 243Am. U showed a typical diffusion profile which can be interpreted by applying Fick's laws, while the Am profile was more complex, requiring further investigation of transport modes. These results will provide relevant insights into the transport behavior of U and Am in OPA over a wide range of concentrations down to ultra-trace levels.

scholarly journals Design of a Production Process for Poly(oxymethylene) Dimethyl Ethers from Dimethyl Ether and Trioxane

2021 ◽  
Author(s):  
Christian Frederik Breitkreuz ◽  
Niklas Schmitz ◽  
Eckhard Stöfer ◽  
Jakob Burger ◽  
Hans Hasse
Keyword(s):  
Experimental Data ◽  
Production Process ◽  
Dimethyl Ether ◽  
Diesel Fuel ◽  
Diesel Engines ◽  
Chemical Equilibrium ◽  
Process Simulation ◽  
Soot Formation ◽  
Equilibrium Constants ◽  
Synthetic Fuels

Abstract Poly(oxymethylene) dimethyl ethers (OME) are promising synthetic fuels. When compared to fossil diesel fuel, OME reduce the soot formation in diesel engines. OME can be produced from the C1 platform syngas via different routes. This work investigates an OME production process via dimethyl ether and trioxane. The process is simulated and optimized using process simulation with varying model depth. As no experimental data are available on the chemical equilibrium of the reaction of dimethyl ether and trioxane, chemical equilibrium constants are partly estimated from formation data of the reactants.

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