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Thermodynamic models of the solution chemistry in a homogeneous reactor used for molybdenum-99 (sub 99Mo) production are being developed at Argonne National Laboratory (Argonne) to aid in the optimization of molybdenum generation ...
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Thermodynamic models of the solution chemistry in a homogeneous reactor used for molybdenum-99 (sub 99Mo) production are being developed at Argonne National Laboratory (Argonne) to aid in the optimization of molybdenum generation and recovery processes. The models calculate concentrations of aqueous species and saturation states of possible uranium and fission product precipitates (e.g., uranyl oxide hydrates, peroxides, molybdates) over a relevant range of pH values, oxidization/reduction potentials, and component concentrations. Predicting conditions under which precipitation may occur is particularly important because solids formed in the reactor solution could complicate 99Mo recovery and have deleterious effects on reactor operation. Results presented in this paper indicate that, for uranyl nitrate based reactors, the radiolytic decomposition of nitrate (loss of nitrogen to off-gas) could cause the precipitation of uranyl and/or fission products due to an increase in pH. This precipitation process is readily counteracted by the addition of nitric acid. The modeling results presented help quantify the optimal pH envelope for a uranyl nitrate solution reactor used for 99Mo production and highlight the need for future experimental studies to address uncertainties in the thermodynamic models.
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This document reports on the work done by the Nuclear Waste Management Section of the Chemical Technology Division of Argonne National Laboratory in the period of October 1996 through September 1997. Studies have been performed to...
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This document reports on the work done by the Nuclear Waste Management Section of the Chemical Technology Division of Argonne National Laboratory in the period of October 1996 through September 1997. Studies have been performed to evaluate the behavior of nuclear waste glass and spent fuel samples under the unsaturated conditions (low-volume water contact) that are likely to exist in the Yucca Mountain environment being considered as a potential site for a high-level waste repository. Tests with actinide-doped waste glasses, in progress for over 11 years, indicate that the transuranic element release is dominated by colloids that continuously form and span from the glass surface. The nature of the colloids that form in the glass and spent fuel testing programs is being investigated by dynamic light scattering to determine the size distribution, by autoradiography to determine the chemistry, and by zeta potential to measure the electrical properties of the colloids. Tests with UO(sub 2) have been ongoing for 12 years. They show that the oxidation of UO(sub 2) occurs rapidly, and the resulting paragenetic sequence of secondary phases forming on the sample surface is similar to that observed for uranium found in natural oxidizing environments. The reaction of spent fuel samples in conditions similar to those used with UO(sub 2) have been in progress for over six years, and the results suggest that spent fuel forms many of the same alteration products as UO(sub 2). With spent fuel, the bulk of the reaction occurs via a through-grain reaction process, although grain boundary attack is sufficient to have reacted all of the grain boundary regions in the samples. New test methods are under development to evaluate the behavior of spent fuel samples with intact cladding: the rate at which alteration and radionuclide release occurs when water penetrates fuel sections and whether the reaction causes the cladding to split. Alteration phases have been formed on fine grains of UO(sub 2) in contact with small volumes of water within a several month period when the radiolysis product H(sub 2)O(sub 2) is added to the groundwater solution. The test setup has been mocked up for operation with spent fuel in the hot-cell.
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Quasielastic neutron scattering measurements on the Zintl alloy NaSn show that the high-temperature solid phase discovered by Hume-Rothery is a plastic crystal characterized by rapid rotations of the Sn(sub 4)(sup (4(minus))) Zint...
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Quasielastic neutron scattering measurements on the Zintl alloy NaSn show that the high-temperature solid phase discovered by Hume-Rothery is a plastic crystal characterized by rapid rotations of the Sn(sub 4)(sup (4(minus))) Zintl ions. The reorientations are similar to those previously observed in CsPb but have a markedly different wave vector dependence, indicating a different behaviour of the alkali metal ions.
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Zintl compounds of lead and tin with the heavier alkali metals are semiconductors with surprising and unusual properties in both solid and liquid states. These are ascribed to the formation of tetrahedral complex anions arising fr...
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Zintl compounds of lead and tin with the heavier alkali metals are semiconductors with surprising and unusual properties in both solid and liquid states. These are ascribed to the formation of tetrahedral complex anions arising from charge transfer and covalent bonding around the polyvalent metal ions. The tetrahedra exhibit both rotational and translational order, leading to a variety of complex dynamical behaviors in both solid and liquid phases. The changes in order have dramatic effects on electrical transport properties.
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摘要 :
Zintl compounds of lead and tin with the heavier alkali metals are semiconductors with surprising and unusual properties in both solid and liquid states. These are ascribed to the formation of tetrahedral complex anions arising fr...
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Zintl compounds of lead and tin with the heavier alkali metals are semiconductors with surprising and unusual properties in both solid and liquid states. These are ascribed to the formation of tetrahedral complex anions arising from charge transfer and covalent bonding around the polyvalent metal ions. The tetrahedra exhibit both rotational and translational order, leading to a variety of complex dynamical behaviors in both solid and liquid phases. The changes in order have dramatic effects on electrical transport properties.
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In this paper a review of the thermodynamic, electrical and structural properties of liquid alkali-tellurium alloys is presented with a special emphasis on the interplay between these properties. The thermodynamic properties indic...
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In this paper a review of the thermodynamic, electrical and structural properties of liquid alkali-tellurium alloys is presented with a special emphasis on the interplay between these properties. The thermodynamic properties indicate ordering of the solutions at compositions corresponding to about 12, 50, and 67 atom% of alkali atoms. The electrical conductivity and thermopower data confirm that these liquids are true semiconductors. The neutron diffraction patterns coupled with the above information indicate that in the case of liquid K(sub 0.12)Te(sub 0.88) the measured structure is dominated by the Te-Te contribution, and is remarkably similar to that of pure liquid tellurium, while the equiatomic alloy K(sub 0.50)Te(sub 0.50) is shown to contain mostly Te pairs which are identified with Zintl ions, Te(sub 2)(sup 2(minus)).
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