Muneaki Senoo

Thermal shock resistance of a simulated high-level waste glass

Abstract Thermal shock resistance of a simulated high-level waste glass was examined by water quenching in the range of the temperature difference up to 600°C. The observation of cracks revealed that there existed two critical temperature differences. One was the threshold temperature difference of 74°C above which surface cracks appeared. The other was the temperature difference of 600°C at which cracks were propagated markedly and the specimen broke down into many pieces. In the range of the temperature difference of 74°C to 600°C, the surface area of cracks on the surface of the quenched specimens increased with increasing temperature difference. However, the fractional release of sodium and cesium from the quenched specimens was almost constant in the range of the temperature difference up to 500°C, and it increased markedly at the temperature difference of 600°C. These facts indicate that sodium and cesium do not leach out from the cracks when the separation of fracture surfaces is small.

Sorption of Europium(III)-Humate Complexes onto a Sandy Soil

The sorption of Eu(III) by a sandy soil was studied by batch experiments at pH 7.5 in the presence of four humic acid (HAs) from different origins. Percentages of Eu sorbed onto the sandy soil were 95% in the absence of HA and 17-25% in the presence of HAs. The HA fraction with molecular weight (MW) of less than 5,000 daltons was remaining in the solution after the Eu-HA sorption experiments. Studies on fluorescence quenching of HAs indicated that the HA fraction was complexed with Eu(III). The sorption of Eu onto the sandy soil was decreased by the formation of complexes with the HAs.

Influence of humic acid on sorption of neptunium(V) onto soil

The pH dependence of the stability constant of Np(V)-humate and the sorption of Np(V) onto soil was studied to clarify the influence of dissolved organic carbon on the migration behavior of Np(V) in soil layer. The stability constant of Np(V)-humate was expressed by log{beta}{sub 1} = (0.35 {+-} 0.03)pH + 0.04 {+-} 0.01 in the pH region from 5.3 to 8.7, and the intrinsic stability constant by log{beta}*{sub 1} = 3.66 {+-} 0.05. The sorption of Np(V) increased with pH up to pH 7, and tended to reach maximum, about 95%, at pH 9 in the absence of humic acid. In the presence of humic acid more than 140 mg/l, the sorption of Np(V) was lower than that in the absence of humic acid above pH 7, while any influence of humic acid on the sorption of Np(V) onto soil was not observed below pH 7. The sorption behavior of Np(V) onto soil was explained by reversible sorption of NpO{sub 2}{sup +} and sorption of NpO{sub 2}CO{sub 3}{sup {minus}} and/or NpO{sub 2}OH. Further, the influence of the size distribution of Np(V) on the sorption onto soil was examined and discussed.

Distribution Coefficient in the Sorption of Radionuclides onto Ando Soil in the Presence of Humic Acid

Influence of humic acid (HA) on the sorption of 60Co, 85Sr and 241Am onto Ando soil was examined with respect to HA of various molecular sizes. Distribution coefficient (K d) in the sorption of 60Co on this type of soil was only slightly affected by the presence of HA. The K d of 85Sr as the HA concentration increased. The K d of 241Am decreased as the HA concentration increased and the K d of HA showed a similar trend. In the solution, 241Am selectively formed stable compounds with an HA ranging from 30,000 to 100,000 in molecular weight (MW), whereas 60Co and 85Sr Preferentially but weakly interacted with HA fractions smaller than 100,000MW. These results suggest that the K d in the case of 60Co and 85Sr is mainly controlled by sorption of both cationic species and humic compounds, while the K d of 241Am is controlled by the sorption of HA.

Redistribution of Neptunium(Y) During the Alteration of Ferrihydrite

Redistribution of neptunium(V) during an alteration of amorphous ferrihydrite to both goethite and hematite was studied at initial pH 6.0 and 7.7 at 90 °C. Sorption of neptunium(V) during the alteration was obtained as a function of contact time. At an initial pH of 7.7, the sorption neptunium(V) was nearly to 100% and remained constant during the alteration of amorphous ferrihydrite to hematite and goethite. On the other hand, at an initial pH of 6.0, the amounts of sorbed neptunium(V) decreased drastically when the amorphous ferrihydrite was converted to a crystalline structure. The sorption of neptunium on the altered product, a mixture of hematite and goethite, was studied by a sequential extraction technique in which 1 Μ MgCl2,1 Μ HCl and 6 Μ HCl solutions were used as the extraction reagents. Results of both initial pHs indicated that neptunium(V) sorbed on the altered products has changed during the alteration of amorphous ferrihydrite from a reversible form, that could extracted by 1 Μ MgCl2 solution to an incorporated form that could be not extractable by 1 Μ MgCl2 solution, but was by 6 Μ HCl solution.

Sorption of 60 Co, 85 Sr, 137 Cs, 237 Np and 241 Am on Soil Under Coexistence of Humic Acid: Effects of Molecular Size of Humic Acid

Sorption experiments have been performed by a batch method, to study the effects of humic acid of different molecular size on the complexing stability with 60 Co, 85 Sr, 137 Cs, 237 Np and 241 Am, and on the sorption behavior of these radionuclides on a sandy soil. Equilibrium constants K in the sorption of 137 Cs and 237 Np onto the soil were not changed at different concentrations of humic acid since 137 Cs and 237 Np do not interact with humic acid, while those of 60 Co and 241 Am decreased with increasing humic acid concentration due to forming humic complexes. However, the K of 85 Sr was not changed at different humic acid concentrations, despite 85 Sr interacts with humic acid. This contradiction was probably caused from that a main binding of 85 Sr with humic acid is not based on coordination bond but electrostatic force, due to relatively high concentration of non–radioactive strontium. The theoretical sorption model taking account of the interaction of 60 Co and 241 Am with humic acid could well reproduce the values of K for each radionuclide at different concentrations of humic acid. Concentration profiles of the radionuclides in each size fraction of the solution before and after the sorption experiments were examined by ultrafiltration technique. The reduction of concentration of 60 Co in the fraction less than 300,000 of cutoff molecular weight (MW) and that of concentration of 241 Am in the fraction larger than 100,000MW, respectively, by the sorption onto the soil decreased with increasing humic acid concentration. This decrease resulted in the decrease in the K of 60 Co and 241 Am with increasing humic acid concentration.

A simplified method for preparation of 137Cs pollucite γ-ray source

A simple method for preparing a pollucite 137Cs γ-ray source pellet is presented. An original pellet forming commercial synthetic (NH4Na)A zeolite is calcined at 600°C for 2 h, and impregnated with 137CsNO3 solution of appropriate radioactive concentration, followed by heating at 1100°C for 2 h, for synthesizing the pollucite and sintering the source pellet. The pellet thus obtained with bulk density of about 2.4 gcm−3 and specific activity up to about 12 Cig−1, has prominent properties such as high resistivity for heating and insolubility to water.

New Method for Synthesis of Strontium Titanate

A new method is presented for synthesizing strontium titanate. The reaction between strontium nitrate and meta-titanic acid or titanium dioxide (anatase or rutile) has been studied with use made of thermo-gravimetry and differential thermal analysis, and the compound produced was identified by X ray diffractometry. A mixture of strontium nitrate and meta-titanic acid is converted to strontium titanate at about 600°C by an apparently endothermic reaction. This process can be applied advantageously to the preparation of sources of radiation and heat that utilize radioactive strontium obtained from nuclear fission products.

A simplified procedure in radioisotope dilution method for the mercury inventory of electrolytic chlorine cells

Abstract Concerning the radioisotope dilution method for determining the mercury amount in electrolytic cells in the soda industry, a simple and safe procedure with high accuracy was investigated. The procedure developed is based on the scrupulous supply by the Japan Atomic Energy Research Institute of the aliquots of radioactive mercury, i.e. 197 Hg, precisely weighed and the standard reference sample accurately diluted. The intended purpose is achieved with the s.d. in the determination less than 1%

Particle size determination by use of 55Fe X-ray absorption

Abstract Application of 55Fe X-ray source to the particle size analysis is proposed in combination with small sedimentation cell of 3 mm X-ray path length, X-ray detector and beam scanning device. Feasibility test of the method showed good agreement with results by other different methods and also the certificated values of a standard powder sample. The analyser is applicable to particulate materials in wide ranges of size from 0.2 to 50 μm and of elements of atomic number higher than magnesium.