Potential of indigenous bacteria driven U(VI) reduction under relevant deep geological repository (DGR) conditions.

Understanding the biogeochemical U redox processes is crucial for controlling U mobility and toxicity under conditions relevant to deep geological repositories (DGRs). In this study, we examined the microbial reduction of aqueous hexavalent uranium U(VI) [U(VI)] by indigenous bacteria in U-contaminated groundwater. Three indigenous bacteria obtained from granitic groundwater at depths of 44-60 m (S1), 92-116 m (S2), and 234-244 m (S3) were used in U(VI) bioreduction experiments.

Structural and spectroscopic studies of spontaneously formed crystalline Eu(iii)-aliphatic dicarboxylates at room temperature.

Complexation of actinides and lanthanides with carboxylic organic ligands is a critical issue affecting radionuclide migration from deep geological disposal systems of spent nuclear fuel. A series of Eu(iii)-aliphatic dicarboxylate compounds, as chemical analogs of radioactive Am(iii) species, Eu(Ox)(HO), Eu(Mal)(HO), and Eu(Suc)(HO), were synthesized and characterized using X-ray crystallography and time-resolved laser fluorescence spectroscopy to examine the ligand-dependent binding modes and the corresponding changes in spectroscopic properties. Powder X-ray crystallography results confirmed that all of the compounds presented a crystalline polymer structure with a trigonal prism square-face tricapped polyhedron geometry centered on Eu(iii) in a nine-coordinate environment involving nine oxygen atoms.

Spectroscopic Study into Lanthanide Speciation in Deep Eutectic Solvents.

Deep eutectic solvents are a new class of green solvents that are being explored as an alternative for used nuclear fuel and critical material recycling. However, there is a paucity of knowledge regarding metal behavior in them. This paper explores the underlying chemistry of rare-earth elements in choline chloride-based deep eutectic solvents by using a multi-technique spectroscopic methodology.

Studies of aqueous U(iv) equilibrium and nanoparticle formation kinetics using spectrophotometric reaction modeling analysis.

Hydrolysis of tetravalent uranium (U(iv)) and U(iv)-nanoparticle formation kinetics were examined over a wide range of temperatures using spectrophotometric reaction modeling analysis. The characteristic absorption bands representing U, U(OH), and a proposed oxohydroxo species were newly identified in the UV region (190-300 nm). Dynamic absorption band changes in the UV and visible regions (360-800 nm) were explored to reevaluate the binary ion interaction coefficients for U(iv) ions and the thermodynamic constants of the primary hydrolysis reaction, including complexation constants, enthalpy, and entropy.

Study of Aqueous Am(III)-Aliphatic Dicarboxylate Complexes: Coordination Mode-Dependent Optical Property and Stability Changes.

The thermodynamics of Am(III) complex formation in natural groundwater systems is one of the major topics of research in the field of high-level radioactive waste management. In this study, we investigate the absorption and luminescence properties of aqueous Am(III) complexes with a series of aliphatic dicarboxylates in order to learn the thermodynamic complexation behaviors in relation to binding geometries. The formation of Am(III) complexes with these carboxylate ligands induced distinct red shifts in the absorption spectra, which enabled chemical speciation.

Hydrolysis of trivalent plutonium and solubility of Pu(OH) (am) under electrolytic reducing conditions.

The aim of this work is to determine the solubility product of plutonium hydroxide under reducing conditions and to ascertain the stability of Pu(OH) (am) in water. Hydrolysis of Pu(iii) and solubility of Pu(OH) (am) were investigated at a constant ionic strength of 0.1 M NaClO.

Factors affecting measurement of channel thickness in asymmetrical flow field-flow fractionation.

Asymmetrical flow field-flow fractionation (AF4) has been considered to be a useful tool for simultaneous separation and characterization of polydisperse macromolecules or colloidal nanoparticles. AF4 analysis requires the knowledge of the channel thickness (w), which is usually measured by injecting a standard with known diffusion coefficient (D) or hydrodynamic diameter (dh). An accurate w determination is a challenge due to its uncertainties arising from the membrane's compressibility, which may vary with experimental condition.

Retention behavior of microparticles in gravitational field-flow fractionation (GrFFF): effect of ionic strength.

Retention behavior of micron-sized particles in gravitational field-flow fractionation (GrFFF) was studied in this study. Effects of ionic strength and flow rate as well as the viscosity of the GrFFF carrier liquid was investigated on the size-based selectivity (Sd), retention ratio (R), and plate height (H) of micron-sized particles using polystyrene latex beads as model particles. It was found that the retention ratio of microparticles increases with increasing flow rate or the viscosity of the carrier liquid as the particles are forced away from the accumulation wall by increased hydrodynamic lift forces (HLF).

Study on steric transition in asymmetrical flow field-flow fractionation and application to characterization of high-energy material.

In field-flow fractionation (FFF), there is the 'steric transition' phenomenon where the sample elution mode changes from the normal to steric/hyperlayer mode. Accurate analysis by FFF requires understanding of the steric transition phenomenon, particularly when the sample has a broad size distribution, for which the effect by combination of different modes may become complicated to interpret. In this study, the steric transition phenomenon in asymmetrical flow FFF (AF4) was studied using polystyrene (PS) latex beads.

Quantitative analysis of uranium in aqueous solutions using a semiconductor laser-based spectroscopic method.

A simple analytical method based on the simultaneous measurement of the luminescence of hexavalent uranium ions (U(VI)) and the Raman scattering of water, was investigated for determining the concentration of U(VI) in aqueous solutions. Both spectra were measured using a cw semiconductor laser beam at a center wavelength of 405 nm. The empirical calibration curve for the quantitative analysis of U(VI) was obtained by measuring the ratio of the luminescence intensity of U(VI) at 519 nm to the Raman scattering intensity of water at 469 nm.

Evaluation of the behavior of uranium peroxocarbonate complexes in Na-U(VI)-CO3-OH-H2O2 solutions by Raman spectroscopy.

In this work, the formation of uranium species and their stabilities in Na-U(VI)-CO(3)-OH-H(2)O(2) solutions at different pHs are studied by Raman spectroscopy. In this solution, the UO(2)(O(2))(CO(3))(2)(4-) species was formed together with three other uranium species of UO(2)(O(2))(2)(2-), UO(2)(CO(3))(3)(4-), and a speculated uranium species of the uranyl carbonate hydroxide complex, UO(2)(CO(3))(x)(OH)(y)(2-2x-y), which showed remarkable Raman peaks at approximately 769, 848, 811, and 727 cm(-1), respectively. The UO(2)(O(2))(CO(3))(2)(4-) species disappeared at pH conditions where bicarbonate dominated, and its Raman peak could be clearly observed in only a narrow pH range from approximately 9 to 12.

Synthesis and size characterization of silica nanospheres using sedimentation field-flow fractionation (SdFFF).

Silica nanoparticles were synthesized by a conventional emulsion polymerization by mixing ethanol, ammonium hydroxide, water and tetra ethyl orthosilicate (TEOS). A new reaction apparatus was assembled for a large scale synthesis of silica nanospheres in the laboratory, which was designed for uniform mixing of the reactants. The apparatus was equipped with a disc type agitator with six rectangular propellers.

Adsorption behavior of Eu(III) on partially Fe(III)- or Ti(IV)-coated silica.

The adsorption behavior of Eu(III) onto silica surface, which was partially coated with Fe(III) or Ti(IV), was investigated to determine Fe(III) or Ti(IV) effects on the surface reaction of lanthanides on mineral surfaces in groundwater. Compared with a parallel uncoated silica, the Fe(III)-coated silica did not enhance the adsorption of Eu(III). However, enhanced adsorption of Eu(III) on the Ti(IV)-coated silica was observed by increasing the amount of Ti(IV) on the silica surface.

Isotope correlations for determining the isotopic composition of plutonium in high burnup pressurized water reactor (PWR) samples.

Correlations among the alpha activity ratios of (238)Pu/((239)Pu+(240)Pu), the alpha specific activities of Pu and the atom % abundances of Pu isotopes were derived for the plutonium samples obtained from high burnup fuel samples from pressurized water reactors. Using the alpha activity ratios of (238)Pu/((239)Pu+(240)Pu) determined by alpha spectrometry, the alpha specific activities of Pu as well as the atom % abundances of the plutonium isotopes in the unknown samples were calculated without depending on mass spectrometry. The calculated alpha specific activities of Pu agreed with those determined by experiment within 2%, and the atom % abundances of the Pu isotopes agreed within 4% for (238)Pu, 5% for (239)Pu, 7% for (240)Pu and 5% for (242)Pu, respectively.

Development of a 756 nm, 3 W injection-locked cw Ti:sapphire laser.

We have developed a 756 nm, 3 W single-frequency cw Ti:sapphire laser by using the technique of injection locking. A cw Ti:sapphire laser in a ring-type configuration was forced to lase unidirectionally by use of an optical diode to prevent a high-power backward laser from disturbing the injection laser. A master laser was amplified by a broad-area laser diode and coupled into a single-mode fiber to generate a 50 mW injection laser with a Gaussian beam profile, which was enough to lock the Ti:sapphire laser at full power of 3 W.