Chlorination of uranium metal to uranium trichloride using ammonium chloride

Journal of Radioanalytical and Nuclear Chemistry - Given that the most feasible option for fabricating chloride-based molten salt fuel for molten-salt reactors (MSRs) is to use uranium/transuranic...     

Consecutive recovery of uranium oxides from uranyl-containing molten alkali metal sulfate electrolytes

The oxygen coefficient (atomic ratio O/U) of a cathode product and the cathode current yield in consecutive recovery of uranium oxides from molten salt mixtures (nLi₂SO₄ + (1 ? n)Cs₂SO₄) + UO₂SO₄ and (Li,Na,K)₂SO₄ + UO₂SO₄ in air were analyzed as dependent on the electrolyte and the mean solvent-salt cation radius. The increasing mean solvent-salt cation radius and decreasing UO₂SO₄ concentration in the electrolyte during long-term electrolysis suppress the solvolysis of uranyl ions and decrease the oxygen coefficient in the cathode product. The cathode current yield decreases systematically during electrolysis and drops to zero long before the uranium is completely recovered from the melt. The ultimate uranium recovery increases as the mean solvent-salt cation radius increases.     

Reactions of HCl and D2O with molten alkali carbonates

The acidic oxide SO? and protic acid HCl are among the gases released in the combustion of coal and the incineration of municipal waste. They are typically removed by wet or dry scrubbing involving calcium carbonate or calcium hydroxide. The molten alkali carbonate eutectic provides a liquid-state alternative that readily absorbs SO? and HCl and does not become covered with a passivating layer. Gas-liquid scattering experiments utilizing the eutectic mixture (44 mol % Li?CO?, 31 mol % Na?CO?, 25 mol % K?CO?) reveal that the reaction probability for HCl(g) + CO?2? → CO?(g) + OH? + Cl? is 0.31 ± 0.02 at 683 K and rises to 0.39 at 783 K. Gaseous CO? is formed within 10?? s or less, implying that the reaction takes place in a liquid depth of less than 1000 ?. When the melt is exposed to D?O, the analogous reaction D?O(g) + CO?2? → CO?(g) + 2OD? occurs too slowly to measure and no water uptake is observed. Together with previous studies of SO?(g) + CO?2? → CO?(g) + SO?2?, these results demonstrate that molten carbonates efficiently remove both gaseous HCl and SO? while reacting at most weakly with water vapor. The experiments further highlight the remarkable ability of hot CO?2? ions to behave as a base in reactions with protic and Lewis acids.     

Electrode processes of uranium ions and electrodeposition of uranium in molten LiCl-KCl

In the first part, LiCl-KCl-UCl₃ and LiCl-KCl-UCl₃-UCl₄ molten salts were prepared, which were studied employing cyclic voltammetry and chronopotentiometry techniques, respectively. It was determined that the reduction of U(IV) to uranium metal takes two steps. Firstly, U(IV) is reduced to U(III). Then, the reduction of U(III) to uranium metal occurs in a step with a global exchange of three electrons. Cyclic voltammetry studies indicated that at low sweep rates, the reduction of U(III) to uranium is reversible. However, a mixed control of both diffusion and electrontransfer is observed as the sweep rate increases. The diffusion coefficient of U(III) and the formal potential of U(III)/U versus Ag/AgCl reference electrode in these two salt systems were calculated respectively. In second part, based on the data of the electrode processes of uranium ions, electrodeposition of uranium metal was carried out. Uranium deposits were prepared adopting a 304 stainless steel electrode in the molten LiCl-KCl-UCl₃ and LiCl-KCl-UCl₃-UCl₄, respectively by employing suitable electrolytic techniques. The morphology of the deposits and the cross-section of the cathode were investigated by SEM. It was determined that at the beginning of the deposition process, uranium product alloys with stainless steel and forms a thin layer, and then uranium begins to grow adhering to the layer.     

Activation of uranium metal

Treatment of uranium with hydrochloric or hydrobromic acid produces an adherent layer of hydride on the metal surface. When this hydride is decomposed by heat in a vacuum, the resulting metal surface reacts immediately with hydrogen at ambient temperature.Mound is operated by Monsanto Researh Corporation for the U.S. Department of Energy under Contract No. DE-AC04-76-DP00053.     

U(IV) chalcogenolates synthesized via oxidation of uranium metal by dichalcogenides

Treatment of uranium metal with dichalcogenides in the presence of a catalytic amount of iodine in pyridine affords molecular U(IV) chalcogenolates that do not require stabilizing ancillary ligands. Oxidation of U(0) by PhEEPh yields monomeric seven-coordinate U(EPh)4(py)3 (E = S(1), Se(2)). The dimeric eight-coordinate complexes [U(EPh)2(mu2-EPh)2(CH3CN)2]2 (E = S(3), Se(4)) are obtained by crystallization from solutions of 1 and 2 dissolved in acetonitrile. Oxidation of U(0) by pySSpy and crystallization from thf yields nine-coordinate U(Spy)4(thf) (5). Incorporation of elemental selenium into the oxidation of U(0) by PhSeSePh results in the isolation of [U(py)2(SePh)(mu3-Se)(mu2-SePh)]4.4py (6), a tetrameric cluster in which each U(IV) ion is eight-coordinate and the U4Se4 core forms a distorted cube. The compounds were analyzed spectroscopically and the single-crystal X-ray structures of 1 and 3-6 were determined. The isolation of 1-6 represents six new examples of actinide chalcogenolates and allows insight into the nature of "hard" actinide ion-"soft" chalcogen donor interactions.     

Properties of molten alkali metal trifluoracetates

We have studied the thermal stabilities of the alkali metal trifluoroacetates by means of DTA and TG, and shown that they are stable in the solid form, with the exception of the lithium salt. We have determined the enthalpies of melting of these five salts. We have also studied the kinetics of decomposition of CF₃COONa, of CF₃COOK and of their mixture. This decomposition is in all cases of the first order. The mixture decomposes in two steps, the first one corresponding to the decomposition of the sodium salt.

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Zusammenfassung Die ThermostabilitÄt der Alkalitrifluoracetate wurde durch DTA und TG untersucht und festgestellt, da\ diese in der festen Form mit Ausnahme des Lithiumsalzes stabil sind. Die Schmelzenthalpie dieser fünf Salze wurde bestimmt. Die Kinetik der Zersetzung von CF₃COONa, CF₃COOK und ihrer Gemische wurde ebenfalls untersucht. Diese Zersetzung ist in allen FÄllen ein Vorgang erster Ordnung. Die Gemische werden in zwei Stufen zersetzt, wobei die erste Stufe der Thermolyse des Natriumsalzes entspricht.

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Résumé Nous avons étudié la stabilité thermique des trifluoroacétates alcalins par ATD et TG, et montré que seul le sel de lithium se décompose avant la fusion. Nous avons déterminé les enthalpies de fusion de ces cinq sels. Nous avons également étudié la cinétique de décomposition de CF₃COONa, CF₃COOK et de leurs mélanges. Cette décomposition est dans tous les cas d'ordre 1. Les mélanges se décomposent en deux étapes, la première correspondant à la thermolyse complète du sel de sodium.

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. , . , . CF₃COOK, CF₃COONa . . , .

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We are grateful to Miss H. Lartigue for technical assistance. Thanks are due to Prof. A. Buchs, Director of the Mass-spectrometry Laboratory.     

Properties of molten alkali metal trifluoroacetates

The CF₃COOK-CF₃COONa phase diagram was studied by DTA between 100% and 50 wt. % CF₃COOK; the thermal decomposition of CF₃COONa-rich samples prevents the complete determination of the phase diagram. Two eutectics were found:E ₁ at 89.5 wt. % CF₃COOK andE ₂ at 62 wt. %, with melting points at 122–123 and 112–113, respectively, representing a temperature approximately 30 lower than the m. p. of pure CF₃COOK (140.5). The presence of a compound between these two eutectics is not formally established, but is probable at about 85 or 87 wt. % CF₃COOK, melting at 124–125. DTA has shown that the fused mixtures solidify into a metastable state, the phase diagram of which presents a labile eutectic at 75 wt. % CF₃COOK, melting at 88.

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Zusammenfassung Das CF₃COOK-CF₃COONa Phasendiagramm wurde mittels DTA, zwischen 100 und 50 Gew. % CF₃COOK untersucht; die thermische Zersetzung CF₃COONa-reicher Proben macht die Bestimmung des vollständigen Phasendiagramms unmöglich. Zwei Eutektika wurden gefunden:E ₁ bei 89.5 Gew. % CF₃COOK undE ₂ bei 62 Gew. %, mit den entsprechenden Schmelzpunkten bei 122–123 und 112–113, welche bei um etwa 30 niedrigeren Temperaturen liegen als der Schmelzpunkt des reinen CF₃COOK (140.5). Die Existenz einer Verbindung zwischen diesen beiden Eutektika wurde zwar nicht genau bewiesen, sie liegt aber wahrscheinlich bei etwa 85 oder 87 Gew. % CF₃COOK und schmilzt bei 124–125. Mittels der DTA konnte nachgewiesen werden, daß die geschmolzenen Gemische in einen metastabilen Festkörperzustand übergehen, dessen Phasendiagramm ein labiles Eutektikum bei 75 Gew. % CF₃COOK mit einem Schmelzpunk bei 88 aufweist.

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Résumé Le diagramme de phases CF₃COOK-CF₃COONa a été établi par ATD entre CF₃COOK et le mélange à 50% poids; la décomposition thermique des échantillons riches en CF₃COONa empÊche la détermination complète du diagramme de phases. On observe deux eutectiques:E ₁ à 89.5 % poids en CF₃COOK etE ₂ à 62% poids, fondant respectivement à 122–123 et 112–113, ce qui représente un abaissement d'environ 30 C par rapport au P. F. de CF₃COOK pur (140.5). L'existence d'un composé entre ces deux eutectiques n'a pu Être montrée formellement. Il se situe vraisemblablement vers 85 ou 87 % poids en CF₃COOK et fond à 124–125. L'ATD a montré que les mélanges fondus se solidifient dans un état métastable, dont le diagramme de phases présente un eutectique labile à 75% poids en CF₃COOK fondant à 88.

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CF₃COOK—OF₃COONa CF₃COOK 100 50 .%. CF₃COONa, . :E ₁ CF₃COOK 89,5 .% ₂-62 .% 122–123 112–113, 30 , . . CF₃COOK (140,5). , , , CF₃COOK 85 87 .% 124–125. , , CF₃COOK 75 .% 88.

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This paper is based on part of the Dissertation (No. 1721) of R. Dallenbach, University of Geneva.

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Thanks are due to Professor R. Monnier and Dr. J. J. Duruz for useful discussions.     

XAFS analyses of molten metal fluorides

X-ray absorption fine structure studies of molten metal fluorides containing the materials related to nuclear engineering are intensively summarized. By using XAFS spectra data of divalent and trivalent cation metal fluorides in molten state which have been collected by authors’ group for a few years, local structure have been extracted and discussed systematically in conjunction with other spectroscopic studies and numerical calculations. In molten divalent fluorides, tetrahedral coordination of fluorides around a cation is predominant. In the case of pure molten trivalent fluorides, structure with more than 6-coordination has been suggested in some cases, but octahedral coordination structure is much stabilized at heavier rare earth metal fluorides. By mixing with alkali metal fluorides, it is a general trend that inter-ionic distances keep constant, but coordination number of fluorides decreases. In experimental chapter, all the details of sample preparation, furnace installation, X-ray optics setups and data analyses procedures are explained. Finally, future expectations of XAFS technique are also suggested.     

Characterization of uranium isotopic abundances in depleted uranium metal assay standard 115

Certified reference material (CRM) 115, Uranium (Depleted) Metal (Uranium Assay Standard), was analyzed using a TRITON Thermal Ionization Mass Spectrometer to characterize the uranium isotope-amount ratios. The certified ²³⁵U/²³⁸U “major” isotope-amount ratio of 0.0020337 (12) in CRM 115 was determined using the total evaporation (TE) and the modified total evaporation (MTE) analytical techniques. In the MTE method, the total evaporation process is interrupted on a regular basis to allow correction of background from peak tailing, internal calibration of the secondary electron multiplier detector versus the Faraday cups, peak-centering, and ion source re-focusing. For the “minor” ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratio measurements using MTE, precision and accuracy comparable to conventional analyses are achieved, without compromising the quality of the ²³⁵U/²³⁸U isotope-amount ratios. Characterized values of the ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratios in CRM 115 are 0.000007545 (10) and 0.000032213 (84), respectively. The ²³³U/²³⁸U isotope-amount ratio in CRM 115 is estimated to be <5 × 10^?9. The homogeneity of the CRM 115 materials is established through the absence of any statistically significant unit-to-unit variation in the uranium isotope-amount ratios. The measurements leading to the certification of uranium isotope-amount ratios are discussed.     

Radiological chronometry of uranium metal samples

Radiological chronometry is an important tool in nuclear forensics that uses several methods to determine the length of time that has elapsed since a material was last purified. One of the chronometers used in determining the age of metallic uranium involves measuring the fractional ingrowth of ²³⁰Th from its parent ²³⁴U with the assumption that the uranium metal contained no impurities, especially thorium, when it was purified. The affects of different etching procedures were evaluated for the removal of surface oxidation with three different types of uranium metal samples to determine whether the etching procedure affects the radiological age. The sample treated with a rigorous etching procedure had exhibited the most reliable radiological age while less rigorous etching yields a radiological age from 15 years to hundreds of years older than the known age. Any excess thorium on the surface of a uranium metal sample presents a bias in age determination and the sample will appear older than the true age. Although this research demonstrates the need for rigorous surface etching, a bias in the radiological age could have arisen if the uranium in the metal was heterogeneously distributed.     

Nonstoichiometric spinel ferrites obtained from alpha-NaFeO2 via molten media reactions

Different solid/liquid "exchange" reactions involving divalent cations, protons, or ammonium ions have been performed at low/moderate temperatures (between 80 and 500 degrees C) on alpha-NaFeO2 dipped in molten salts (or acid) media. Several ferrites have been obtained which are nonstoichiometric with partially inverse spinel structures. When sodium is replaced by divalent cations (Mg2+, Co2+, Ni2+, and Zn2+), the obtained ferrites are hyperstoichiometric (cation/oxygen ratio higher than 3/4) whereas proton or ammonium reactions result in hypostoichiometric materials (cation/oxygen lower than 3/4). All these ferrites present a platelet-like morphology and show ferrimagnetic, soft magnet behavior.     

Reductive Chlorination and Bromination of Ketones via Trityl Hydrazones

A method is presented for the direct transformation of a ketone to the corresponding reduced alkyl chloride or bromide. The process involves the reaction of a ketone trityl hydrazone with tBuOCl to give a diazene which readily collapses to the α‐chlorocarbinyl radical, reduction of which by a hydrogen atom source gives the alkyl chloride product. The use of N‐bromosuccinimide provides the corresponding alkyl bromide. This unique transformation provides a reductive halogenation that complements Barton's redox‐neutral vinyl halide synthesis.     

Reactions of metal ions with dithizone in molten naphthalene

A comparative study has been made of the reactions of metal ions with dithizone in the two media, chloroform and molten naphthalene. The absorption spectra of several metal dithizonates, prepared in molten naphthalene, were recorded and were found to be the same as those of the dithizonates obtained by extraction of metal ions from aqueous solution with chloroform dithizone.     

A novel method for the preparation of uranium metal,oxide and carbide via electrolytic amalgamation

A solid uranium amalgam was prepared electrolytically using a two-compartment cell separated with an ion exchange membrane for the purpose of regulating pH value within a narrowly restricted region of 2 to 3. The mercury cathode was kept at −1.8 vs SCE during electrolysis. The thereby obtained amalgam containing as high as 1.9 gm U/ml Hg is easily converted into uranium metal by heating in vacuo above 1300°C. Uranium dioxide and uranium monocarbide could be easily obtained at relatively low temperature by reacting the amalgam with water vapor and methane.