Shinzo Ueta

Radiolysis of aqueous phenol solutions with nanoparticles. 1. Phenol degradation and TOC removal in solutions containing TiO2 induced by UV, γ-ray and electron beams

Aqueous phenol solutions containing TiO(2) nanoparticles were irradiated with ultraviolet (UV), gamma-ray and electron beams. Organic compounds were fully removed by each type of radiation in the presence of the particles. The absorbed energy of the ionizing radiation (gamma-ray and electron beams) needed for removal was much lower than that of UV photocatalysis. Phenol was decomposed by the ionizing radiation in the absence of the nanoparticles and the addition of TiO(2) had no significant effect on phenol decomposition rate. Instead, total organic carbon (TOC) removal using the ionizing radiation was accelerated drastically by TiO(2). It is suggested that TiO(2) particles affect the intermediate compounds produced through the decomposition of phenol. The amount of removed TOC per absorbed energy were compared in the absence and the presence of TiO(2) nanoparticles. Radiolysis with the nanoparticles showed consistently high rate and high efficiency of TOC removal.

Uranium(IV) solubility and hydrolysis constants under reduced conditions

The solubility of UO{sub 2}(S) was examined in dilute NaCl solutions at room temperature and in the ph range from 2 to 12. Dissolution equilibrium showed good agreements between the data obtained by oversaturation and undersaturation experiments. The dissolution reactions that control the solubility of U[IV] are estimated as UO{sub 2} (s) + 4H{sup +} + 2H{sub 2}O and UO{sub 2} (s) + 2H{sub 2}O {yields} U(OH){sub 4}{sup 0}. The log K at zero ionic strength are yielded 0.34 {+-} 0.4 and {minus}8.7 {+-} 0.4, respectively. The hydrolysis constant (log {beta}{sub 14}) is calculated {minus}9.0 {+-} 0.5 for the hydrolysis reaction of U{sup 4+} + 4H{sub 2}O {yields} U(OH){sub 4}{sup 0} + 4H{sup +}. Contribution of the other uranium species to the solubility are of minor importance. The crystallization of the precipitations of UO{sub 2}(s) progressed gradually in the oversaturation experiments. Nevertheless the progress of crystallization had little effect on the solubility.

In-situ measurement of dissolution of anorthite in Na-Cl-OH solutions at 22 °C using phase-shift interferometry

Abstract In-situ measurements of anorthite dissolution in Na-Cl-OH solutions at an ionic strength (IS) of 0.5 mol/L (M) and in artificial seawater (IS = 0.7 M) were conducted at 22 °C using white-light, phase-shift interference microscopy (PSI-M). Nanometer-scale surface topography by PSI-M revealed three-dimensionally inhomogeneous surface dissolution, which is commonly observed as retreating steps on anorthite surfaces. Continuous dissolution of the anorthite cleavage surface (010) was successfully measured within a day. The vertical dissolution velocity was 4.3 × 10-5 to 1.4 × 10-3 nm/s. The obtained dissolution rates showed a typical dependency on pH with a reaction order of 0.191, and could be consistently extended to the previous data obtained under acidic conditions (Luttge et al. 1999). In-homogeneities in the vertical dissolution velocities at each pH condition could be interpreted by the step dynamics explained by the Burton-Cablera-Frank (BCF) theory (Burton et al. 1951). These results emphasize that the velocity of step retreat is a strong function of the step density, which has to be taken into account when describing the global dissolution phenomena on mineral surfaces

A novel technique of in situ phase-shift interferometry applied for faint dissolution of bulky montmorillonite in alkaline solution

The effect of alkaline pH on the dissolution rate of bulky aggregated montmorillonite samples at 23 °C was investigated for the first time by using an enhanced phase-shift interferometry technique combined with an internal refraction interferometry method developed for this study. This technique was applied to provide a molecular resolution during the optical observation of the dissolution phenomena in real time and in situ while remaining noninvasive. A theoretical normal resolution limit of this technique was 0.78 nm in water for opaque material, but was limited to 6.6 nm for montmorillonite due to the transparency of the montmorillonite crystal. Normal dissolution velocities as low as 1 × 10−4 to 1 × 10−3 nm/s were obtained directly by using the measured temporal change in height of montmorillonite samples set in a reaction cell. The molar dissolution fluxes of montmorillonite obtained in this study gave considerably faster dissolution rates in comparison to those obtained in previous investigations by solution analysis methods. The pH dependence of montmorillonite dissolution rate determined in this study was qualitatively in good agreement with those reported in the previous investigations. The dissolution rates to be used in safety assessments of geological repositories for radioactive wastes should be obtained for bulky samples. This goal has been difficult to achieve using conventional powder experiment technique and solution analysis method, but has been shown to be feasible using the enhanced phase-shift interferometry.

Experimental and Numerical Studies on Colloid-Enhanced Radionuclide Transport - The Effect of Kinetic Radionuclide Sorption onto Colloidal Particles -

Numerous studies have shown that colloidal particles in groundwater can facilitate radionuclide transport in subsurface environments. A series of laboratory experiments was conducted to investigate the effects of radionuclide sorption onto colloids and the surfaces of rock fractures. This research especially focused on the kinetic behavior of the sorption process. A mixed solution of Cs and clay colloids was injected into a single artificial fracture in a granite column. Simulations were also performed to analyze the experimental results using a numerical code, COLFRAC, which describes colloid-facilitated solute transport in discretely-fractured media. The code allows for either equilibrium or kinetic sorption onto the colloidal particles. The experimental and analytical results indicate that transport of Cs is facilitated by the colloidal particles, which can sorb Cs and transport through the fracture. The analyses also illustrate the importance of evaluating parameters that describe kinetic sorption onto colloids. Furthermore, radionuclide transport is likely to be retarded as colloidal particles that sorb radionuclides are filtered on the fracture surface.

Interlayer dissolution of montmorillonite observed by internal refraction interferometry

Dissolution behavior of a clay mineral such as montmorillonite is one of the most important phenomena for a long-term safety of high-level radioactive waste disposal. Dissolution rates of aggregated montmorillonite samples in basic solutions at room temperature were investigated in flow-through experiments by using internal refraction interferometry with an enhanced phase-shift interferometry. Conventional solution analysis methods cannot measure the effects of dissolution occurring within the interlayer of montmorillonite. Internal refraction interferometry can measure the crystal dissolution of montmorillonite, including both the dissolution of the outer surface and the interlayer of montmorillonite. The dissolution rate of montmorillonite in the interlayer was first observed. It was slower than the dissolution rate of outer surface. As the number of the montmorillonite crystal laminations increased, the montmorillonite dissolution rate in the interlayer decreased. Montmorillonite dissolution rates showed limited dependence on pH in the alkaline solutions. This can be explained by the effect of the laminated structure of montmorillonite crystal on the dissolution rate, especially in highly alkaline solution.

Procedure and Results of Decommissioning of R&D Facility of Uranium Fuel

From 1998 through 2005, the facilities for research and development (R&D) of uranium ore-dressing and uranium fuel etc. were decommissioned and soil contaminated by uranium was collected. All the pieces of apparatus in the nuclear facilities which might be contaminated with uranium were treated as radioactive wastes. At the time of the decommissioning activity, there was no specific value to judge as radioactive wastes. So MMC considered and adopted the pragmatic procedure to judge that soil was radioactive waste or not. During decommissioning facilities and collecting soil, the environmental monitoring was conducted. And it was confirmed that these activities had no influence on the surrounding areas. All decommissioning activities were finished with no difficulty. The wastes generated from the decommissioning activities were packed in the steel containers and have been stored safely in the storehouse built in the same area. In this report, the details of decommissioning activities are described.© 2010 ASME