Provided that the boundary value problem can be equivalently solved in conformally transformed domain, one can consider its mapping into unit disk domain. The problem can be solved for the new geometry and the solution can be retransformed back to the original problem domain. The paper presents this approach in order to validate whether it can be applied for improving ill-conditioning of the matrices and solutions obtained in indirect Trefftz methods.

This paper presents an interesting property of the matrices that may be obtained with the use of direct Trefftz method. It is proved analytically for 2D Laplace problem that values of the elements of matrices describing the capacitance of two scaled domains are inversely proportional to the scalability factor. As an example of the application the capacitance extraction problem is chosen. Concise description of the algorithm in which the scalability property can be utilized is given. Furthermore some numerical results of the algorithm are presented.

The dissociation constants of oxalic acid (Ox), and the stability constants of Am3+, Cm3+ and Eu3+ with Ox2− have been determined at 25°C, over a range of concentration varying from 0.1 to 6.60m NaClO4 using potentiometric titration and extraction techniques, respectively. The experimental data support the formation of complexes, M(Ox)n3−2n, where (M=Am3+, Cm3+ and Eu3+ and n=1 and 2). The dissociation constant and the stability constant values measured as a function of NaClO4 concentration were used to estimate the Pitzer parameters for the respective interactions of Am3+, Cm3+ and Eu3+ with Ox. Furthermore, the stability constants data of Am3+–Ox measured in NaClO4 and in NaCl solutions from the literature were simultaneously fitted in order to refine the existing actinide–oxalate complexation model that can be used universally in the safety assessment of radioactive waste disposal. The thermodynamic stability constant: log β0101=6.30±0.06 and log β0102=10.84±0.06 for Am3+ was obtained by simultaneously fitting data in NaCl and NaClO4 media. Additionally, log β0101=6.72±0.08 and log β0102=11.05±0.09 for the Cm3+ and log β0101=6.67±0.08 and log β0102=11.15±0.09 for the Eu3+ were calculated by extrapolation of data to zero ionic strength in NaClO4 medium only. For all stability constants, the Pitzer model gives an excellent representation of the data using interaction parameters β(0), β(1), and Cϕ determined in this work. The thermodynamic model developed in this work will be useful in accurately modeling the potential solubility of trivalent actinides and early lanthanides to ionic strength of 6.60m in low temperature environments in the presence of Ox. The work is also applicable to the accurate modeling transport of rare earth elements in various environments under the surface conditions.

The paper presents the algorithm of hierarchical capacitance extraction based on direct boundary methods. Three selected methods, i.e. Boundary Element Method, direct Trefftz method (based on TH-complete functions) and regular direct Boundary Element Method (direct Trefftz–Kupradze method), are compared for their effectiveness. The algorithm employs binary tree decomposition of the problem domain. Coupling capacitance matrix is calculated in hierarchical process with simultaneous dynamical updating library with basic element matrices. Numerical examples presented in the paper concern 2D planar transmission line structures composed of isotropic dielectric layers.

The dissociation constants of ethylenediaminetetraacetic acid (H4EDTA), and the stability constants of Am3+, Cm3+and Eu3+ with EDTA4− have been determined at 25°C, over a range of concentration varying from 0.1 to 6.60m NaClO4 using potentiometric titration and an extraction technique, respectively. The formation of only 1:1 complex, M(EDTA)−, where (M=Am3+, Cm3+ and Eu3+), was observed under the experimental conditions. The observed ionic strength dependencies of the dissociation constants and the stability constants have been described successfully over the entire ionic strength range using the Pitzer model. The thermodynamic stability constant: logβ1010=20.55±0.18 for Am3+, logβ1010=20.43±0.20 for Cm3+ and logβ1010=20.65±0.19 for Eu3+ were calculated by extrapolation of data to zero ionic strength in an NaClO4 medium. In addition, logβ1010 of 20.05±0.40 for Am3+ was obtained by simultaneously modeling data both in NaCl and NaClO4 media. For all stability constants, the Pitzer model gives an excellent representation of the data using interaction parameters β(0), β(1), and Cϕ determined in this work. The improved model presented in this work would enable researchers to model accurately the potential mobility of actinides (III) and light rare earth elements to ionic strength of 6.60m in low temperature environments in the presence of EDTA.

probabilities of sets of accidents; the consequences are calculated using the CRAC code appropriately modified for the material composition. Routine radiological risks to the public are estimated from the calculated release amounts; the effects are calculated using the CRAC code. Radiological occupational risks are determined from prior experience, projected standards, and estimates of accident risk. Nonradiological risks are calculated from the number of personnel involved, historical experience, and epidemiological studies. The result of this analysis is that the short-term risk of PT is 2.9 times greater than that of the Reference cycle, primarily due to the larger amount of industry. This conclusion is strongly dominated by the nonradiological risk, which is about 150 times greater than the radiological risk. The absolute risk as estimated for the fuel cycle portions considered in this report is 0.91 fatalities/GWe-year for the PT cycle and 0.34 fatalities/GWe-year for the Reference cycle. This should be compared with Inhaber's estimate of 1.5 for nuclear and 150 for coal. All of the risks assumed here are associated with the production of one billion watts of electricity (GWe) per year.

The solubility of uranium(VI) was determined in WIPP-relevant brines as a function of pC(H+) and ionic strength, in the absence of carbonate. Carbonate concentration was below 2 x 10(-5) M, measured using the gas chromatography method. In the absence of carbonate, the uranium(VI) solubilities were about 10(-6) M in GWB at pC(H+) >= 7 and about 10(-8)-10(-)7 M in ERDA-6 brine at pC(H+) >= 8. Solubility of uranium(VI) was also measured in NaCl media at the same levels as in ERDA-6 brine. The data established a uranium solubility that was 10-100 times lower than published results from Diaz-Arocas and Grambow [13], and they are in good agreement with modeling results and other literature data [11, 12]. In the absence of carbonate, hydrolysis was the main complexation and precipitation mechanisms for uranium(VI) solubility at high ionic strength and pC(H+) >= 7. However, the effect of borate complexation was noticeable at pC(H+) similar to 8-9.

AbstractThe dissociation constants of citric acid (Cit), and the stability constants of Am3+, Cm3+and Eu3+with Cit were determined as a function of ionic strength (NaClO4) using potentiometric titration and an extraction technique, respectively. The results have shown the presence of both 1:1 and 1:2 complexes under the experimental conditions. A thermodynamic model was constructed to predict the apparent stability constants at different ionic strengths by applying the Pitzer ionic interaction parametersβ(0),β(1), and Cφwhich were obtained to fit the experimental data. Thermodynamic stability constants of M(Cit) and M(Cit)23-(where M = Am3+, Cm3+or Eu3+) were calculated to belog β0101 = 9.91 ± 0.10,log β0102 = 14.47 ± 0.14for Am3+,log β0101 = 9.53 ± 0.16,log β0102 = 14.46 ± 0.16for Cm3+andlog β0101 = 9.82 ± 0.14,log β0102 = 13.31 ± 0.12for Eu3+as obtained by extrapolation to zero ionic strength.

Iron and Pu Reduction: (1) Very different appearances in iron reaction products were noted depending on pH, brine and initial iron phase; (2) Plutonium was associated with the Fe phases; (3) Green rust was often noted at the higher pH; (4) XANES established the green rust to be an Fe2/3 phase with a bromide center; and (5) This green rust phase was linked to Pu as Pu(IV).

The aim of this paper is to review and compare the existing direct boundary methods. Each method is briefly characterised. Similarity of these methods is pointed out by showing their common origin (which is the inverse variational formulation) and much the same way of obtaining final matrices. The accuracy and efficiency of the methods are compared in numerical experiments of two-dimensional Laplace problem.

Four pillared metal(IV) phosphate-phosphonate ion exchange materials were synthesized and characterized. Studies were conducted to determine their affinity for the lanthanides (Ln's) and actinides (An's). It was determined that by simply manipulating the metal source (Zr or Sn) and the phosphate source (H3PO4 or Na3PO4) large differences were seen in the extraction of the Ln and An species. K-d values higher than 4 x 10(5) were observed for the AnO(2)(2+) species in nitric acid at pH 2. These basic uptake experiments are important, as the data they provide may indicate the possibility of a separation of Ln's from An's or even more notably americium from curium and Ln's.

The extraction of trivalent lanthanides from an aqueous phase containing 1 M NaClO4 into the room temperature ionic liquid 1-butyl-3-methylimidazolium nonafluoro-1-butanesulfonate by the beta-diketone extractant 2-thenoyltrifluoroacetone (Htta) was studied. Radiotracer distribution, absorption spectroscopy, time-resolved laser-induced fluorescence spectroscopy, and X-ray absorption fine structure measurements point to the extraction of multiple lanthanide species. At low extractant concentrations, fully hydrated aqua cations of the lanthanides are present in the ionic liquid phase. As the extractant concentration is increased 1:2 and 1:3 lanthanide:tta species are observed. In contrast, 1:4 Ln:tta complexes were observed in the extraction of lanthanides by Htta into 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

Abstract Closing the nuclear fuel cycle in the US poses many challenges, one of which is found in the waste streams, which contain both trivalent lanthanides and actinides. The separation of americium from the raffinate will dramatically reduce the long-term radiotoxicity of the waste. The sorption of americium in both the tri- and pentavalent oxidation states was observed for four M(IV) phosphate-phosphonate ion exchange materials in nitric acid at pH 2. High selectivity was observed for reduced Am(III) with Kd values ca. 6×105 mL/g, while the Kd values for Am(V) were much lower. A new method of synthesizing and stabilizing AmO2+ to yield a lifetime of at least 24 h in acidic media using a combination of sodium persulfate and calcium hypochlorite will be described.

The subsurface chemistry of multivalent actinide contaminants is highly dependent on their oxidation state distribution and associated redox conditions. These redox conditions are established by coupled direct and indirect subsurface processes such as microbial activity, geochemical reactions with the host rock, and the chemical effects of other co-contaminants present. The ability to predict actinide migration, especially over the very long times that are typically of concern, is directly linked to the ability to establish the nature, stability, and mobility of dissolved species formed within the bounds of the prevailing redox conditions. The measurement of system-specific redox conditions (Eh) can be problematic under the most ideal groundwater conditions but is especially problematic in high ionic strength systems such as brines with I > 5 M. The redox chemistry and key assumptions pertaining to the key multivalent metals and actinides present in the WIPP underground, which is expected to be a strongly reducing high ionic-strength brine system, is presented. Long-term actinide solubility studies and redox kinetics of lower-valent iron show varied degrees of correlation between Pu(III)/Pu(IV) and Fe(II)/Fe(III) concentration ratios with Eh measurements. Linkages between the observed microbial activity and redox chemistry of neptunium were also observed. Overall, these system-specific results are discussed and interpreted in the context of their broader application to understanding the redox chemistry and migration behavior of multivalent metals and actinides in high ionic-strength brine systems and salt-based repositories.