Liquid Uranium Research Articles

U + N 2 Reaction layer growths

Reaction layers were formed on uranium at various temperatures up to 2400 °C in nitrogen (0.003 to 2.0 atm). Reaction with solid uranium is propagated by spalling and is most rapid near 800 °C. Reaction with liquid uranium occurs by two parallel processes, diffusion through and fracturing of UN layers. From observed thicknesses of fracture-free layers, concentration-gradient chemical interdiffusion coefficients are calculated. Marker experiments indicate that the UN layers form by inward diffusion of nitrogen atoms from which are deduced nitrogen self-diffusion coefficients represented by the equation D ̄ S N[cm 2/sec] = 12exp−(120 ± 25)[kcal/mole]/RT . Nitrogen selfdiffusion coefficients are also deduced from estimated nitrogen activity gradients and these exhibit a dependence on nitrogen pressure. Uranium-saturated UN compositions range from N/ U = 0.991 to 0.997 ± 0.006 at temperatures above 1600 °C. Change in N/U ratio across the UN phase is 0.005 at about 1600 °C.

Measurement of the equilibrium oxygen, carbon and uranium activities associated with the uranium oxycarbide phase

The composition of uranium oxycarbide in equilibrium with pure liquid uranium and appropriate oxygen partial pressures (10 −25 > po 2 [ atm] > 10 −35) has been determined by chemical and X-ray analyses for the temperatures 1473 °K, 1573 °K and 1648 °K. The oxygen partial pressures were established using an isopiestic technique in conjunction with the calciumcalcium oxide equilibria. A similar investigation along the oxycarbide-uranium dioxide phase boundary involved isothermal equilibration with uranium-gold alloys to establish the relevant uranium activities and oxygen partial pressures. The experimental values were analysed by treating the uranium oxycarbide phase as a pseudo-binary solid solution of UO-UC, and it was concluded that a simple regular solution model adequately described the data. Calculations based on this model provided information about the free energy of formation of UO ( ΔG° = −121 200 + 22.46 T kcal/ mole), and about the carbon monoxide pressures associated with various oxycarbide compositions. Where it was possible to check the calculated values they were in good agreement with measured data.

Les diagrammes de phases U-UN-UO 2 et UO 2-UN-N 2

Previous results have been complemented and gathered to establish the phase diagram of the system UO 2-UN-N 2 at one atmosphere. A theoretical perspective view of the diagram is proposed. Experiments performed in argon allow the determination of the limiting compositions of the dioxide and of the mononitride simultaneously in equilibrium with liquid uranium. The main properties of the U-UN-UO 2 phase diagram have been specified.

Vaporization of Uranium Mononitride and Heat of Sublimation of Uranium

The vaporization of uranium mononitride UN has been investigated by the Knudsen effusion technique in combination with a mass spectrometer. The vaporization occurs incongruently by preferential loss of nitrogen forming the two-phase system nitrogen-saturated liquid uranium–uranium-saturated nonstoichiometric uranium mononitride. The vapor pressures of U and N2 have been obtained by silver calibration over the two-phase system UN0.4–UN0.9 in the temperature range 1910–2230°K. The enthalpies ΔH°298 for the simplified reaction (1) UN(s)=U(g)+0.5 N2 (g) and its partial reactions (2) UN(s)=U(l)+0.5 N2(g) and (3) U(l)=U(g) have been obtained from second- and third-law treatments. The experimental third-law value of Partial Reaction (3) of 130.7 ± 2.2 kcal mole−1 may be considered an upper value for the heat of vaporization of uranium metal. The third-law enthalpy of Partial Reaction (2) of 68.9 ± 0.4 kcal mole−1 is in general agreement with literature data for this reaction. The selected value for the enthalpy of Reaction (1) of ΔH°298 = 200.3 ± 4.0 kcal mole−1 yields with appropriate literature data a heat of atomization ΔH°298 = 313.3 ± 4.5 kcal mole−1 for solid UN, and a heat of vaporization ΔH°298 = 127.9 ± 4.9 kcal mole−1 for uranium. The difference of 2.8 kcal mole−1 between this value and the directly measured value for Partial Reaction (3) is attributed to an activity decrease of uranium in nitrogen-saturated liquid uranium that is in equilibrium with the UN phase.

Vapor pressure of liquid uranium; effects of dissolved tantalum, phosphorus, sulfur, carbon, and oxygen

Vapor pressure of liquid uranium; effects of dissolved tantalum, phosphorus, sulfur, carbon, and oxygen

Densities and molar volumes of isotopically altered liquid uranium hexafluoride

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDensities and molar volumes of isotopically altered liquid uranium hexafluorideWalter D. HedgeCite this: J. Chem. Eng. Data 1969, 14, 1, 65–67Publication Date (Print):January 1, 1969Publication History Published online1 May 2002Published inissue 1 January 1969https://doi.org/10.1021/je60040a008RIGHTS & PERMISSIONSArticle Views33Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (309 KB) Get e-Alerts Get e-Alerts

Molecular Motion and 19F Relaxation in the Liquid Hexafluorides of Molybdenum, Tungsten, and Uranium

In order to study molecular motion in liquid molybdenum, tungsten, and uranium hexafluorides, we have undertaken a 19F relaxation study in these liquids. Measurements of the relaxation times as a function of resonance frequency show that the dominant relaxation mechanism is the modulation of the spin—rotation interaction by the molecular motions. It is shown that the strengths of the spin—rotation interactions, which have not been measured directly, can be deduced very simply from the chemical-shift tensors if some approximations are made. The molecular motion is discussed with the help of a generalized Langevin equation in which it is not required that the particle under consideration be much heavier than the molecules interacting with it. It is thus found that the hexafluoride molecules in the liquid phase can rotate through an angle of about 1 rad at 70°C before their angular velocity changes and that this intermediate degree of rotation is consistent both with the low values of the entropies of fusion, which indicate that the rotations do not occur freely, and with the appearance of rotation—vibration structures in their infrared absorption spectra. The self-diffusion coefficients were also measured as a function of temperature. The relationship between the diffusion coefficients and the longitudinal relaxation times is not in agreement with Hubbard's theory, and this is attributed to the failure of both the Stokes' equation and the rotational diffusion model.

The viscosities of liquid uranium, gold and lead

The viscosity of liquid uranium metal was measured by an absolute method in an oscillating cup viseosirnetor. To verify the accuracy of the viscosimeter, the viscosities of liquid gold and lead metals wore measured for comparison with reported values. The viscosity of the liquid 99.97 % pure lead decreased linearly on a plot of log viscosity as a function of reciprocal absolute temperature from 2.47 centipoises at 337° C to 0.95 centipoiso at 1114° C. The viscosity of molten 99.97 + % pure gold decreased from 4.84 to 3.58 centipoises over a 1063° to 1364° C temperature interval. The viscosity of 99.9 + % pure uranium was measured at five temperatures between 1141° and 1248° C. A least squares analysis of the data showed that the viscosity decreased from 6.5 to 5.4 ± 0.2 centipoises between 1133° and 1248° C with an activation energy for viscous flow ( E vis ) of 7260 cal/g-atom. Liquid self-diffusion, calculated from the viscosity data, increased from 1.92 × 10 −5 cm 2/see to 2.51 × 10 −5 cm 2/sec between 1138° and 1248° C. The experimental melting point viscosity and E vis compared favorably with the 5.9 centipoises and 7540 cal/g-atom values predicted from theoretical considerations. The 6.5 centipoises for uranium at its melting temperature is the highest viscosity reported in the literature for a pure liquid metal.

Surface Tension of Liquid Uranium and Thorium Tetrafluorides and a Discussion on the Relationship between the Surface Tension and Critical Temperature of Salts1

Surface Tension of Liquid Uranium and Thorium Tetrafluorides and a Discussion on the Relationship between the Surface Tension and Critical Temperature of Salts¹

The surface tension of liquid uranium from its melting point, 1406°K to 1850°K

The surface tension of liquid uranium was measured from its melting point (1406°K) to 1850°K by the maximum bubble pressure method with a probable error of 40 dyn/cm, or 2·5 per cent at the melting point. Impervious aluminium oxide tubes having a tip measuring 2 mm o.d. × 0·3 mm wall × 5 mm long were immersed in the liquid uranium which was held in a thorium dioxide crucible contained in a molybdenum tube under argon. Extrapolation of the data to the melting point (1406°K) gave a preliminary value of 1550 dyn/cm. From the experimental points and the relationship Δσ ΔT = σ m.·p. (T c − T m.·p. ) −1 , the following tentative equations for the surface tension of liquid uranium were determined. σ dyn/cm = 1747 − 0·14 T(° K) or σ dyn/cm = 1550 − 0·14(T − 1406° K)

Raoult's Law Study of Vanadium Pentafluoride in Uranium Hexafluoride

Binary systems of liquid vanadium pentafluoride dissolved in liquid uranium hexafluoride are non-ideal, with negative deviations from Raoult's law in the temperature range 75 degrees to 92 degrees C.

Phase Relations in the System Uranium—Nitrogen

To supplement efforts to develop UN as a nuclear fuel material, a study of the phase relations in the system uranium‐nitrogen was conducted. The decomposition behavior and melting point of UN was studied in a controlled nitrogen‐pressure apparatus in which cast specimens of UN were heated and observed. UN decomposed at pressures of nitrogen below 2.5 atm at temperatures below 2850° C and melted congruently at 2850° C and pressures of 2.5 atm or greater. The nitrogen content of the liquid uranium phase in equilibrium with UN was determined by heating uranium in a UN crucible and then quenching and analyzing the equilibrated phase. The solubility of nitrogen in atomic percent can be expressed as S = 2.45 × 104 exp (‐38,800/RT) for temperatures in OK. Studies in the region U2N3‐UN2 of the system which were performed using a Sievert‐type apparatus showed that although these compounds are structurally dissimilar, they form a series of continuous solid solutions. Only UN2 formed at high pressures and low temperatures. A pressure‐temperature schematic diagram and a temperature‐composition schematic diagram for a nitrogen pressure of 1 atm for the system uranium‐nitrogen are presented. At this pressure, UN decomposed at 2800° C and U2N3 decomposed at 1345° C.

DENSITY OF LIQUID URANIUM1

The density of pure liquid U was determined by the Archimedean method, from its melting point (l406 deg K) to about 1900 deg K. The equation of the density of liquid uranium, determined by the method of least squares, is Dliq in g/cm3 == It was concluded that liquid density is a straight line function of temperature far beyond the metal's normal boiling point, because the saturated vapor density of metal, which according to the law of rectilinear diameter causes deviation from linearity, assumes significant values only substantially above the normal boiling point. From the data tabulated, liquid densities of pure U235, U233, and U238 can be calculated. (P.C.H.)

The density of molten thorium and uranium tetrafluorides

Using molybdenum crucibles and sinkers, the liquid densities of liquid uranium and thorium tetrafluorides were determined by the immersed-sinker method from 1300 to 1700°K. and are represented by the equations D ThF 4(1) = 7·108 − 7·590 × 10 −4 T D UF 4(1) = 7·784 − 9·920 × 10 −4 T The liquid molar volumes and thermal coefficients of expansions were calculated from the liquid densities.

Thermodynamic properties of Uranium-Bismuth alloys

Thermodynamic properties of uranium-bismuth alloys were determined by measuring the vapor pressure of bismuth in equilibrium with the condensed phase. Classical methods based on the rate of sublimation, rate of evaporation or rate of effusion could not be used since each method requires an accurate knowledge of the molecular weight of the vapor. The molecular weight of bismuth is not accurately known, but the presence of Bi and Bi 2 species has been established. An optical absorption technique was used to determine the concentration of each species independently. Briefly, this method consists of measuring concentrations in a vapor by the quantity of light absorbed at certain characteristic frequencies by the species in the vapor. The amount of each species present, which is related to the pressure, was determined by measuring the diminution of intensity at 3067 and 2731 Å. The amount of radiation absorbed was found to be dependent on the thickness of the vapor space and the concentration of the bismuth vapor. The thermodynamic activity of bismuth was measured at temperatures from 725 to 875°C in the regions: U 3Bi 4 + UBi 2, UBi 2 + liquid and the one-phase, liquid region. In order to obtain measurable quantities in the regions UBi + U and UBi + U 3Bi 4 it was necessary to work at temperatures from 800 to 1000°C. From a measure of the activity of bismuth, the activity of uranium was calculated for the entire system. The liquid uranium—bismuth alloys were found not to be regular solutions. The Henry's law parameter (3.49 × 10 −3 at 1064°K) was found to be valid for uranium concentrations of less than 2 mole % uranium. From a complete knowledge of the activities of uranium and bismuth in the system the partial molar quantities and integral molar quantities were calculated at five temperatures: 1018, 1041, 1064, 1089 and 1115°K.

Extraction of Plutonium from Uranium by Liquid Magnesium

The partition of plutonium between liquid magnesium and uranium or uranium-chromium alloy was investigated. The extraction was found to be reversible and essentially independent of concentration up to 1 wt.% plutonium. The molar partition coefficients for both systems can be expressed as a function of temperature by the equation log K = 1887/T 2.010. (auth)

The vapour pressure of uranium tetrafluoride

The vapour pressure of liquid uranium tetrafluoride was measured between 4 and 180 mm Hg (1018–1302°C) by a combination of the quasi-static method of Rodebush and Dixon and a boiling point technique. The data are consistent with the extrapolation of the effusion measurements by Ryon and Twichell on solid UF 4. The vapour pressures of the liquid can be represented by the equation: log P( mm Hg) = 16,840 ± 44 T − 7·549 log T + 37·086 ± 0·03 Extrapolation of the data to the normal boiling point of 1729°K, with the assumption of a ΔCp of vaporization of −15 cal/deg mole, gives a heat of vaporization of 51·2 ± 0·2 kcal/mole at the boiling point. The entropy of vaporization at the normal boiling temperature is 29·7 e.u. in reasonable agreement with those of other heavy metal tetrafluorides. The close agreement between the extrapolated effusion measurements (assuming the vapour species to be monomeric) and the total pressures measured in the present study indicates the absence of associated molecules in the vapour phase.

The Melt Refining of Irradiated Uranium: Application to EBR-II Fast Reactor Fuel. IV. Interaction of Uranium and Its Alloys with Refractory Oxides

Sessile drops of liquid uranium on five refractory oxide substrates were studied photographically. The volume expansion on melting ( approximately 3%), the contact angles (135 plus or minus 3 deg in each case), and the surface tension of the liquid (826 plus or minus 10% dynes/cm) were determined. The reactions of liquid uranium with alumina or magnesia proceed stoichiometrically to the expected prcducts. The reactions with zirconia, thoria, and beryllia yield oxygen-deficient substrares and only small amounts of the corresponding metal in solution. The kinetics and reaction mechanism are discussed. Some effects of alloying on these phenomena are also noted. (auth)

Vapor Pressure of Uranium

The vapor pressures and the heat of vaporization of liquid uranium have been measured by collecting a known fraction of the vapor effusing from a Knudsen cell. The deposits were ``weighed'' by comparing the number of fissions upon thermal neutron irradiation with the fissions from a standard. The measured rate of vaporization is extremely sensitive to the residual pressure of oxygen in the vacuum at background pressures of the order of 10—7 mm Hg. With the aid of a theoretically derived expression the effusion rate can be extrapolated to zero oxygen pressure to yield for the vapor pressure the result that logp(mm)=−(23330±21)T+(8.583±0.011),,over the temperature range 1630 to 1970°K. This expression, together with heat capacity data for solid uranium, yields a value of 116.6 kcal/mole for the heat of sublimation at 0°K and predict a value of about 4.7 kcal/mole for the heat of fusion.