OXYGEN ISOTOPE FRACTIONATION IN URANIUM OXIDES

Thermodynamic oxygen isotope factors for uranium oxides have been calculated by means of the modified increment method. The sequence of 18￣O-enrichment in the uranium oxides with respect to the common rock-forming minerals is predicted as follows: spinel < uraninite brannerite hematite < rutile < pitchblende <cassiterite uranium blacks coffinite sedovite UO3 < illite. Two sets of selfconsistent fractionation factors between the uranium oxides and water and between the uranium oxides and the other minerals have been obtained for 0～ 1200℃. The theoretical results are applicable to the isotopic geothermometry of uranium ores when pairing with other gangue minerals in hydrothermal uranium deposits.

The structural and spectroscopic properties for uranium oxides

The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO2, UO3, and U2O3 molecules are systematically investigated using the density functional theory （DFT） with the method of generalized gradient approximation （GGA）. The bond lengths and the vibrational frequencies of the ground states of UO, UO2, and UO3 molecules are all in agreement with available experimental data. For U2O3 molecules, our calculations indicate that the ground state of the U203 molecule is an XTA1 state with Dah （trigonal bipyramid） symmetry （R1 （U O）=0.2113 nm, R2（U1 U2）=0.2921 nm, ZU1OU2 = 87.5° , dihedral angle O（U,O1,O2,O3）=62.40°）. The harmonic frequency, the IR intensity and the spin density of the U2Oa molecule are all obtained for the first time in theory. For the ground state of U203 molecules, the vibrational frequencies are 178.46 （Ai）, 276.79 （E1＇＇）, 310.77 （EL）, 396.63 （AS＇）, 579.15 （El）, and 614.98 （A1＇） cm-1. The vibrational modes corresponding to the IR maximum peaks are worked out for UO3 and U203 molecules. Besides, the results of Gophinatan-Jng bond order indicate that UO, UO2, and UO3 molecules possess U=O double bonds and that the U203 molecule possesses U O single bonds and a U-U single bond.

Depleted uranium oxide supported nickel catalyst for autothermal CO_(2)methanation in non-adiabatic reactor under induction heating

Undoped nickel-based catalysts supported on depleted uranium oxide allow one to carry out CO_(2)methanation process under extremely low reaction temperature under atmospheric pressure and powered by a contactless induction heating.By adjusting the reaction conditions,the catalyst is able to perform CO_(2)methanation reaction under autothermal process operated inside a non-adiabatic reactor,without any external energy supply.Such autothermal process is possible thanks to the high apparent density of the UO_x which allows one to confine the reaction heat in a small catalyst volume in order to confine the exothermicity of the reaction inside the catalyst and to operate the reaction at equilibrium heat in-heat out.Such autothermal operation mode allows one to significantly reduce the complexity of the process compared to that operated using adiabatic reactor,where complete insulation is required to prevent heat disequilibrium,in order to reduce as much as possible,the heat exchange with the external medium.The catalyst displays an extremely high stability as a function of time on stream as no apparent deactivation.It is expected that such new catalyst with unprecedented catalytic performance could open new era in the field of heterogeneous catalysis where traditional supports show their limitations to operate catalytic processes under severe reaction conditions.

Study on the surface of hydrous titanium oxide adsorbent for extracting uranium from seawater-Ⅱ. The surface of HTO

This is second paper summarizing the study on the hydrous titanium oxide absorbent for extracting uranium fromseawater. The investigation is performed by means of X- ray photoelectronic energy spectroscopy for chemical analysis ( ESC A ) , determination of surface hydroxy radical, Fourier-transfer infrared spectrophotometry (FT-IR ) , electron paramagnetic resonance (EPR), inductively coupled Plasma torch (ICP), etc. The emphasis is laid upon the exploration of HTO surface and a discussion about the adsorption micromechanism.

Potential Function and Thermodynamic Property of UO

Potential energy scan for uranium oxide （UO） was performed by ab initio configuration inter- action （CI） method and density functional theory methods at the PBE1 and the B3LYP levels in combination with the （ECPSOMWB_AVQZ＋2f） basis set for uranium and 6-311＋G＊ for oxygen. The dissociation energies of UO, after being corrected for the zero-point vibrational energy, are 2.38, 3.76, and 3.31 eV at the CI, PBE1, and BaLYP levels, respectively. The calculated energy was fitted to potential functions of Morse, Lennard-Jones, and Rydberg. Only the Morse function is eligible for the potential. The anharmonieity constant is 0.00425. The anharmonic frequency is 540.95 em-1 deduced from the PBE1 results. Thermodynamic properties of entropy and heat capacity at 298.2-1500 K were calculated using DFT-UPBE1 results and Morse parameters. The relationship between entropy and temperature was established.

A Methodology for Producing Uniform Distribution of UO2 in a Tungsten Matrix

We report a method to produce a uniform mixture of uranium dioxide spherical particles in a tungsten matrix. This method involves mixing 0.5 weight percent of high density polyethylene binder with 60 volume percent uranium dioxide spheres and 40 volume percent tungsten powders. Initially, hafnium oxide spheres were used as a surrogate for uranium dioxide spheres. The HfO2/W/PE powders were thoroughly mixed in a Turbula, then mixed on a hot plate above the drop point of the binder. These powders were then densified using spark plasma sintering. Microstructure was evaluated using scanning electron microscopy, density was measured and hardness measurements were made. Initial carbon content of the powders were measured and carbon content of the sintered materials was measured. Subsequently, W/UO2/Binder powders were mixed using the same methodology to ensure the process could be used for this system. These powders were sintered using hot isostatic pressing and microstructures evaluated. The resultant microstructures contained uniform distribution of HfO2 and UO2 particles in the tungsten matrix with very low carbon content.

Synthesis and catalytic property of urania-palladium-graphene nanohybrids

ABSTRACT Urania-paUadium-graphene nanohybrids were synthesized via a solvothermal process in ethylene glycol. With the solvothermal treatment, the Pd nanocrystals sur- rounded by well-crystallized urania supported on graphene oxide was obtained. This ternary hybrid showed consid- erably higher catalytic activity than palladium-graphene hybrids toward the reduction of 4-nitrophenol by NaBH4. Besides the smaller sizes of palladium nanoparticles in the ternary hybrids, in which the aggregation of Pd nanoparticles was prevented by urania, the charge transfer between the nano-structured Pd and urania may also contribute to the enhancement of catalytic activity by offering more active sites for adsorption and reaction.

U-Doped Y-Ba-Cu-O Melt-Processed Superconductor

Large grain Y-Ba-Cu-O (YBCO) superconductors doped with various amounts of depleted uranium oxide have been fabricated by top seeded melt growth (TSMG). The effect of depleted UO2 on the large grain microstructure has been studied systematically in samples with and without added Pt. Addition of uranium oxide results in the formation of U-phase particles of dimensions of a few hundred nanometers with an approximately spherical morphology in the superconducting YBa2Cu3O7-δ(Y-123) phase matrix. Addition of Y2O3 to the uranium doped precursor powder, rather than Y-211, yields a significantly finer distribution of second phase particles. The chemical composition of the U-phase particles, found in samples with no Pt addition, has been identified as Y2Ba4CuUOy, which exhibits paramagnetic behaviour. It has been confirmed experimentally that this phase forms during the peritectic solidification process. Magnetic measurements show that U-doped melt processed YBCO exhibits improved critical current densities and trapped fields compared to un-doped material.