M. Hara

Group separation of trivalent actinides and lanthanides by tertiary pyridine-type anion-exchange resin embedded in silica beads

The separation of trivalent actinides and lanthanides was studied by using newly developed tertiary pyridine-type anion-exchange resin embedded in silica beads. Chromatographic elution experiments were carried out by using a packed column of the new resin and methanol-hydrochloric acid solution as an effluent. We confirmed that the actinides were eluted well from the elution bands of lanthanides. Actinides and lanthanides were eluted according to the reverse order of their atomic number.

Chromatographic Separation of Trivalent Actinides by Using Tertiary Pyridine Resin with Methanolic Nitric Acid Solutions

Chromatographic separation of trivalent actinides (Am, Cm and Cf) was performed by using a tertiary pyridine resin embedded in silica beads with methanolic nitric acid solutions. The trivalent actinides were eluted from the resin column in the reverse order of atomic numbers (Cf-Cm-Am). Higher concentration of methanol in the mixed solution accelerated both the adsorption of these elements on the resin and the separability for these elements. Americium was clearly separated from Cm and Cf by using a 1 cm-ø × 10 cm-height column with a 60vol% of methanol/40 vol% of concentrated nitric acid mixed solution at ambient temperature.

Oxidation of americium(III) with sodium bismuthate

The oxidation of americium(III) with sodium bismuthate has been investigated in a nitric acid solution. The lower the acidity, the more rapidly the oxidation of americium(III) to americium(VI) proceeds, especially at higher temperatures. Based on this finding, a procedure was developed to oxidize americium(III) completely at low concentrations. The americium(VI) free from the excess oxidant has been found to be stable only at 0°C, irrespective of the acidity, but to be more unstable at the temperature higher than 10°C, especially at lower acidities.

Effects of Calcium Ions on the Sorption of Am(III) and Eu(III) onto Kaolinite in the Presence of Humic Acid

The sorption of actinides onto minerals depending on groundwater chemistry plays an important role in the safety aspects of geological disposal of high-level waste. The effects of Ca(II) on the sorption of Am(III) and Eu(III) onto kaolinite in the presence of humic acid (HA) were examined in this study. Distribution coefficients (Kd) of Am(III) and Eu(III), and the fractional adsorption (fHA) of HA on kaolinite were determined by a batch method under initial Ca(II) concentrations of 0 to 1.0 × 10-3 M at a constant ionic strength of 0.1 M (NaClO4) and pH region from 3.5 to 10 in an N2 atmosphere at 298 K. The Kd increased with increasing Ca(II) concentrations in regions higher than 1.0 X10-4 M and in the range of pH 7 to 10. In this pH region, fHA was also enhanced by introducing Ca(II). Concentrations higher than 1.0 × 10-4 M Ca(II) can be regarded as a bridge between kaolinite and HA. It is very likely that the increase in the adsorbed HA on kaolinite, where the HA includes very stable Am(III) and Eu(M) humates, results in an increase in the Am(III) and Eu(IH) distribution coefficients.

Alpha-decay from the 3.5 eV isomer of 229Th

The alpha-decay of a low energy isomer of 229Th at about 3.5 eV was sought by producing it through the (g,n) reaction on a 230Th target. Thorium isotopes in the reaction products were isolated and purified by anion exchange chromatography in a concentrated nitric acid medium to remove lanthanides fission products. The thorium fraction was further purified by samarium fluoride coprecipitation and the precipitate was mounted as a source for a-spectroscopy. Decaying a-signals were observed in the energy region that was expected for 229mTh, i.e., between 4.83 and 5.08 MeV. The half-life of the decaying component was determined from repeated experiments to be 13.9±3 hours.

The JCO criticality accident at Tokai-mura, Japan: An overview of the sampling campaign and preliminary results

A criticality accident occurred on September 30, 1999 at the uranium conversion facility of the JCO Company Ltd. in Tokai-mura, Japan. A collaborating scientific investigation team was organized in two groups, the first to carry out research on the environmental impact (the environmental research group) and the second to assess the radiation effects on residents (the biological research group). This report concerns only the activities of the environmental research group. Four investigative teams were sent on different dates to the accident site and its vicinity to collect samples. About 400 samples were collected and subjected to analysis. An outline of the sampling campaign is presented here along with a brief chronology of the accident and the preliminary key results obtained by the independent research group are summarised in this Special Issue of the Journal of Environmental Radioactivity.

Structure and magnetic properties of U2Co15Ge2 and related compounds

Abstract Ternary compounds of U 2 T 15 Ge 2 (TFe, Co and Ni) are crystallized in the hexagonal Th 2 Ni 17 -type structure. The Curie temperatures were determined for U 2 Fe 15 Ge 2 , U 2 Co 15 Ge 2 and the alloy U 2 Co 15− x Fe x Ge 2 ( x = 3, 6, 9, 12), and were found to be as high as 540–750 K. The magnetocrystalline anisotropy of U 2 Fe 15 Ge 2 and U 2 Co 15 Ge 2 was studied on single crystals.

Complexation of americium(III) with humic acid by cation exchange and solvent extraction

Complexation of Am(III) with humic acid was studied at various pHs in 0.1M NaClO4. The stability constants of the Am(III)—humate complexes were determined by a cation-exchange method. The values of logβ1 and logβ2 increased slightly with increases of pH from 4 to 6 and were found to be 6.9 and 11.6, respectively, at a pH of 5. Markedly larger values than these were obtained by a solvent extraction method. This discrepancy was also revealed by summarizing data from several literature sources. It is very likely that this can be ascribed to decreases in either humic acid and/or the extractant from the extraction system due to humate interactions at the aqueous-organic interface.

Diffusion Behavior of Iron Corrosion Products In Buffer Materials

Carbon steel is one of the candidate overpack materials for high-level waste disposal and is expected to assure complete containment of vitrified waste glass during an initial period of 1000 years in Japan. The lifetime of the carbon steel overpack will depend on its corrosion rate. The corrosion rate of carbon steel is reduced by the presence of buffer material such as bentonite. Buffer material will delay the supply of corrosive materials and discharge of corrosion products through it. Carbon steel overpack will be corroded by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. The reducing condition will be expected to retard the migration of redox-sensitive radionuclides by lowering their solubilities. Therefore, the diffusion of corrosion products of iron in buffer material is important to discuss the corrosion rate of overpack, migration of redox-sensitive radionuclides and properties of buffer material. The purpose of this paper is to study diffusion behavior of a corrosion product of iron in compacted bentonites under a reducing condition with a carbon steel. The diffusion mechanism of iron in the compacted bentonites were discussed by estimation of iron species in the bentonite pore water. There were two diffusion paths of iron in the compacted bentonites used in this study; the fast path has low capacity of iron, ca. 1wt%, and large apparent diffusion coefficient, ca. 10 −12 m 2 /s and the slow path has high capacity of iron, ca. 10wt%, and small apparent diffusion coefficient, ca. 10 −14 m 2 /s.

Measurement of neutron emission from a Ti−D2 system

Neutron emission from the d-d nuclear fusion reaction, D/d,n/3He, in and on titanium metals /titanium sponge and the mixture of titanium powder/ trapped deuterium at about 1 atm has been ascertained by using a high resolution liquid scintillation detector. The neutron emissions from 11 samples which were provided under wide varieties of conditions were measured by temperature change in the range of liquid nitrogen temperature to 350 °C. As a result, it was proved that the neutron emission observed can be divided into two types, such as cooling and heating, by the evolved conditions. Moreover, by estimating the neutron emission efficiencies of samples, it was suggested that the neutron emission reactions are closely related to the deuterium trapped in the surface of titanium metal.