Incorporation of Radioactive Metals and Trace Metals into Phosphate “Anhydrous” Autunite: Thermodynamic Evaluation

2002 ◽  
Vol 757 ◽  
Author(s):  
Huifang Xu ◽  
Yifeng Wang
Keyword(s):  
Environmental Remediation ◽  
Order Approximation ◽  
Fission Products ◽  
Monovalent Cation ◽  
Nuclear Waste Repository ◽  
Linear Free Energy Relationship ◽  
Thermodynamic Evaluation ◽  
Spent Fuel ◽  
Free Energies ◽  
Linear Free Energy

ABSTRACTThe prediction of heavy metal solubility in the presence of phosphate is the key for designing a successful environmental remediation strategy or for the performance assessment of a nuclear waste repository. In order to evaluate the possibility for solubilities and incorporation of U and its fission products, such as Cs, Np, Pu, it is important to have the Gibbs free energies of formation of possible end-member phases. In this paper, we use a linear free energy relationship to calculate the Gibbs free energies of formation of divalent cation “anhydrous” autunite phases [M2+(UO2)2(PO4)2] and monovalent cation “anhydrous” autunite phases [M+2(UO2)2(PO4)2]. Based on predicted Gibbs free energies of formation for autunite phases, an equilibrium calculation indicates that it is feasible to incorporate NpO2+ into the autunite phases. If concentration of Cs+ is high, Cs+ will be incorporated into the autunite phases. However, it is not feasible to incorporate low concentration Cs+ released from spent fuel into the uranyl phosphate phases with layered structure and interlayer water (such as autunite phases, boltwoodite phases, and uranophane phases) as previously proposed. The predicted data can be considered as a first order approximation.

The Effect of Waste Package Components on Radionuclides Released from Spent Fuel Under Hydrothermal Conditions

1987 ◽  
Vol 112 ◽  
Author(s):  
Shirley A. Rawson ◽  
William L. Neal ◽  
James R. Burnell
Keyword(s):  
Low Carbon Steel ◽  
Fission Products ◽  
Nuclear Waste Repository ◽  
Low Carbon ◽  
Spent Fuel ◽  
Hydrothermal Conditions ◽  
Waste Package ◽  
Dissolved Species ◽  
Radionuclide Release ◽  
Time Invariant

AbstractThe Basalt Waste Isolation Project has conducted a series of hydrothermal experiments to characterize waste/barrier/rock interactions as a part of its study of the Columbia River basalts as a potential medium for a nuclear waste repository. Hydrothermal tests of 3–15 months duration were performed with light water reactor spent fuel and simulated groundwater, in combination with candidate container materials (low-carbon steel or copper) and/or basalt, in order to evaluate the effect of waste package materials on spent fuel radionuclide release behavior. Solutions were filtered through 400 and 1.8 nm filters to distinguish colloidal from dissolved species. In all experiments, 14C, 129I, and 137Cs occurred only as dissolved species, whereas the actinides occurred in 400 nm filtrates primarily as spent fuel particles. Actinide concentrations in 1.8 nm filtrates were below detection in steel-bearing experiments. In the system spent fuel + copper, apparent time-invariant concentrations of 14C and 137Cs were obtained, but in the spent fuel + steel system, the concentrations of 14C and 137Cs increased gradually throughout the experiments. In experiments containing basalt or steel + basalt, 137Cs concentrations decreased with time. In tests with copper + basalt, 14C and 129I concentrations attained time-invariant values and 137Cs concentrations decreased. Concentrations for the actinides and fission products measured in these experiments were below those calculated from Federal regulations governing radionuclide release.

scholarly journals Rationalisation of the activities of phenolic (vitamin E-type) antioxidants

2003 ◽  
Vol 17 (4) ◽  
pp. 753-762
Author(s):  
Christopher J. Rhodes ◽  
Thuy T. Tran ◽  
Philip Denton ◽  
Harry Morris
Keyword(s):  
Free Energy ◽  
Vitamin E ◽  
Gibbs Free Energy ◽  
State Theory ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Gibbs Free Energy Change ◽  
Linear Free Energy ◽  
Free Energy Of Activation ◽  
Enthalpy And Entropy

Using Transition-State Theory, experimental rate constants, determined over a range of temperatures, for reactions of vitamin E type antioxidants are analysed in terms of their enthalpies and entropies of activation. It is further shown that computational methods may be employed to calculate enthalpies and entropies, and hence Gibbs Free Energies, for the overall reactions. Within the Linear Free Energy Relationship (LFER) assumption, that the Gibbs Free Energy of activation is proportional to the overall Gibbs Free Energy change for the reaction, it is possible to rationalise, and even to predict, the relative contributions of enthalpy and entropy for reactions of interest, involving potential antioxidants.

Some quantitative relationships for ionization reactions at high pressures

1975 ◽  
Vol 28 (5) ◽  
pp. 945 ◽  
Author(s):  
BS El'yanov ◽  
SD Hamann
Keyword(s):  
High Pressures ◽  
Good Description ◽  
Ionization Constants ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Ion Hydration ◽  
Linear Free Energy ◽  
Linear Relationships ◽  
Wide Range ◽  
Ionization Equilibria

A simple formula is proposed to describe the pressure dependence of the variable Φ in El?yanov and Gonikberg's linear free energy relationship for ionization reactions in solution at high pressure. ��� The expression, given in equations (10) and (12), provides a good description of the influence of pressure on ionization equilibria in aqueous solutions. It permits El'yanov's general linear relationships between Φ and ionization free energies, enthalpies and entropies, pH and Hammett's p parameter, to be expressed in terms of the pressure in convenient analytical forms. ��� The formula is shown to be consistent with the simple electrostatic theory of ion hydration, allowing for the effect of pressure on the dielectric constant of water. Combined with the theory, it provides a general means of predicting ionization constants over a wide range of pressures and temperatures simply from knowledge of the changes in molar volume, enthalpy and entropy which accompany the reactions at atmospheric pressure.

Hot Cell Preparation of Tesiing Materials

1984 ◽  
Vol 44 ◽  
Author(s):  
R. E. Thornhill ◽  
C. A. Knox
Keyword(s):  
Fission Products ◽  
Materials Characterization ◽  
High Level Waste ◽  
Nuclear Waste Repository ◽  
Spent Fuel ◽  
Cell Preparation ◽  
High Radiation ◽  
High Level ◽  
Commercial Reactor ◽  
Simulated High Level Waste

AbstractIt is important in nuclear waste repository development that testing be done with materials containing a radionuclide spectrum representative of actual wastes. To meet the need for such materials, the Materials Characterization Center (MCC) has prepared simulated high level waste (HLW) glasses with radionuclides representative of about 10-, 300-, and 1000-year-old waste. A quantity of well characterized spent fuel also has been acquired for the same purpose. Glasses containing 10- and 300-year-old wastes, and the spent fuel specimens, must be fabricated in a hot cell. Hot cell conditions (high radiation field, remote operation, and difficulty of repairs) require that procedures and equipment normally used in materials preparation out-of-cell be modified for hot cell applications.This paper discusses the fabrication of two glasses, and the preparation of test specimens of these glasses and spent fuel. One of the glasses is a 76–68 composition, which is fully loaded with actual commercial reactor fission product waste. The other glass contains simulated Barnwell Nuclear Fuel Plant waste, doped with different combinations of fission products and actinides. The spent fuel is a 10-year-old PWR material. Special techniques have been used to achieve high quality, well characterized testing materials, including specimens in the form of segments, wafers, cylinders, and powders of these materials.

Solvation of ions. XXII. Solvation of cations by hard N,N-dimethylformamide and soft N,N-dimethylthioformamide

1974 ◽  
Vol 27 (5) ◽  
pp. 933 ◽  
Author(s):  
R Alexander ◽  
DA Owensby ◽  
AJ Parker ◽  
WE Waghorne
Keyword(s):  
Electrochemical Cell ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Univalent Cations ◽  
Liquid Junction Potential ◽  
Liquid Junction ◽  
Linear Free Energy ◽  
Solvation Of Ions ◽  
Solvation Mechanisms ◽  
Junction Potential

The free energies of transfer of some univalent cations from N,N-dimethylformamide to N,N- dimethylthioformamide at 25� are Li+, 64.0; Na+, 50.2; K+, 37.2; Cs+, 23.4; TI+, -4.2 and Ag+, - 87.0 kJ g-ion-1. The values are based on the assumption of negligible liquid junction potential in an electrochemical cell. Certain ones of these values can be interpreted in terms of general interactions of hard and soft cations with hard and soft basic solvents. A linear free energy relationship, ΔGtr(M+) = mΔGtr(K+), is roughly obeyed by many cations for transfer to a variety of solvents. Deviations from this relationship, for example ΔGtr(Ag2+) to acetonitrile, ΔGtr (Ph4As+) to water and ΔGtr (Ag+) to N,N-dimethylthioformamide, allow specific solvation mechanisms to be detected.

Using Linear Free Energy Relationship to Predict the Stability Constants of Aqueous Complexes of Metal-Organic Ligands

2004 ◽  
Vol 824 ◽  
Author(s):  
Huifang Xu ◽  
Yifeng Wang
Keyword(s):  
Free Energy ◽  
Metal Complexes ◽  
Stability Constants ◽  
Metal Cation ◽  
Dissociation Constants ◽  
Natural Environments ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Linear Free Energy ◽  
The Stability

AbstractThe Sverjensky-Molling linear free energy relationship was originally developed to correlate the Gibbs free energies of formation of an isostrutural family of solid phases to the thermodynamic properties of aqueous cations. In this paper, we demonstrate that the similar relationship also exists between metal complexes and simple metal cations in aqueous solutions. We extend the Sverjensky-Molling relationship to predict the Gibbs free energies of formation or dissociation constants for a family of metal complexes with a given complexing ligand. The discrepancies between the predicted and experimental data are generally less than 1.5 kcal/mol (or one log unit for stability constants). The use of this linear free energy correlation can significantly enhance our ability to predict the speciation, mobility, and toxicity of heavy metals in natural environments. According the obtained results, Gibbs free energies of formation of cations (δG0f, Mn+) can be used as an indicator for the hardness/softness of a metal cation (acid). The higher negative value of a metal cation, the harder acid it will be. It is logical to postulate that the coefficient a*ML characterizes the softness of a complexing ligand (base).

scholarly journals Substrate analogues as probes of the catalytic mechanism of l-mandelate dehydrogenase from Rhodotorula graminis

1994 ◽  
Vol 297 (3) ◽  
pp. 647-652 ◽  
Author(s):  
O Smékal ◽  
G A Reid ◽  
S K Chapman
Keyword(s):  
Transition State ◽  
Catalytic Mechanism ◽  
Activation Parameters ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Linear Free Energy ◽  
Kinetic Isotope ◽  
Substrate Analogues ◽  
Reaction Constant ◽  
Delta G

A detailed kinetic analysis of the oxidation of mono-substituted mandelates catalysed by L-(+)-mandelate dehydrogenase (L-MDH) from Rhodotorula graminis has been carried out to elucidate the role of the substrate in the catalytic mechanism. Values of Km and kcat. (25 degrees C, pH 7.5) were determined for mandelate and eight substrate analogues. Values of the activation parameters, delta H++ and delta S++ (determined over the range 5-37 degrees C), for mandelate and all substrate analogues were compensatory resulting in similar low values for free energies of activation delta G++ (approx. 60 kJ.mol-1 at 298.15 K) in all cases. A kinetic-isotope-effect value of 1.1 +/- 0.1 was observed using D,L-[2-2H]mandelate as substrate and was invariant over the temperature range studied. The logarithm of kcat. values for the enzymic oxidation of mandelate and all substrate analogues (except 4-hydroxymandelate) showed good correlation with Taft's dual substituent constant omega (where omega = omega I + 0.64 omega +R) and gave a positive reaction constant value, rho, of 0.36 +/- 0.07. This linear free-energy relationship was verified by analysing the data using isokinetic methods. These findings support the hypothesis that the enzyme-catalysed reaction proceeds via the same transition state for each substrate and indicates that this transition state is relatively nonpolar but has an electron-rich centre at the alpha-carbon position.

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