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Condensed-matter Chemistry in Actinides


Heavy elements that have f-electron orbitals, which are called lanthanide and actinide, show particular chemical characteristics under various conditions.

The objective of our research is to study the chemical characteristics of f-elements under the condition of various liquids, such as aqueous solution, highly concentrated salt solution, molten salt, and liquid metal. Some unique chemical effects of them, such as chemical isotope effect and interaction with biological materials, are studied also. For these studies, analytical methods using electrochemistry, spectrophotometry, chromatography, mass-analysis, and radiochemical analysis are adopted. By clarifying the chemical phenomena and their mechanisms, we want to expand them to the development of new chemical separation and purification technique for "recycling technology". One of the technological objectives of our study is the advancement of the process for the reprocessing of spent nuclear fuels and radioactive waste management.

Academic Staff

Tomoo YAMAMURA

Professor (Institute for Integrated Radiation and Nuclear Science)

Research Theme

Contact Information

TEL: +81-72-451-2442
FAX: +81-72-451-2442
E-mail: yamamura@* (Add "rri.kyoto-u.ac.jp" after @)

Chihiro TABATA

Assistant professor (Institute for Integrated Radiation and Nuclear Science)

Research Theme: Magnetism of actinide compounds

Research Topics

Study on chemical properties of f-elements in high temperature melts and aqueous solutions.

Physicochemical properties of actinides and lanthanides in various solvents (molten salt, liquid metal, water, organic compound, etc.) are evaluated by electrochemical and spectroscopic studies. Chemical reactions of actinides and lanthanides in each solvent can be understood.

Figure 1 indicates an apparatus for electrochemical measurement in molten salt system placed in Ar gas atmosphere glove box. Since, light beam travels through the quartz cell in the apparatus and UV/Vis/NIR spectra of the molten salt phase can be obtained, the dissolved state of various elements in the molten salt at temperatures up to 900°C can be analyzed. Figure 2 shows molten alkali chloride containing neptunium(V) at 650°C in the quartz cell.

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Figure 1:Electrochemical and spectrophotometric measurement system for high temperature melts.

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Figure 2:Neptunium chloride in NaCl-2CsCl at 650°C.

Scientific and technological research on an advanced chemical processing of nuclear fuels and radioactive wastes

As an example, we introduce our study on electrochemical deposition of uranium by using highly concentrated electrolytes.  Generally, it is quite difficult to reduce uranyl ion (UO22+) in aqueous solution to uranium dioxide (UO2) by electrolysis, because the decomposition of H2O dominantly occurs.  Using highly concentrated electrolytes named hydrate melts enables us to recover UO2 by electrolytic reduction without the decomposition of H2O.  Figure 3 shows a concentrated solution of UO2Cl2 and Figure 4 the recovered UO2 by electrolytic reduction in a hydrate melt system.  We also investigate the chemical behavior of nuclides in aqueous reprocessing systems.  Furthermore, for the purpose of developing a database necessary for the transmutation technology of radionuclides, we participate a collaboration study for the measurement of the cross sections of neutron reactions of radioactive nuclides. In this study, we contribute to the radiochemical and analytical tasks for supporting physical measurements. For these tasks, we study the radiochemical technique for target preparation of radio-nuclides, and for the recovery of the long-lived fission products from high active waste solutions.

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Figure 3:A concentrated solution of hydrated uranyl dichloride.

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Figure 4: UO2 recovered by reduction electrolysis in a hydrate melt system.

Study on mechanism of the mass-independent isotope effects in chemical exchange reactions

Isotopes of an element have similar chemical properties, but these are slightly different. Chemical exchange method (e.g., fractional distillation, liquid-liquid extraction, liquid chromatography, and so on) is one of isotope separation methods, which is based on the difference in the chemical properties of isotopes. Macrocyclic polyethers named crown ether and cryptand are good complex-forming compounds. Large isotope effects can be observed in chemical exchange systems with macrocyclic polyethers. We are studying the mass-dependent and mass-independent isotope effects in the chemical exchange systems using macrocyclic polyethers or other complex-forming reagents. The mass-independent isotope effect would be the result from the isotopic differences in the nuclear size and shape and the nuclear spin. We are studying the detailed mechanism of the mass-independent isotope effects.

Figure 5 shows isotope fractionation factors of Cd found in a laboratory-scale experiment.  The results were normalized for an isotope pair 110Cd-114Cd.  Deviation from zero means the existence of mass-independent isotope fractionation.  Similarly to the isotope fractionation, mean-square nuclear charge radii normalized are shown together.  Both showed a quite similar staggering pattern, and from this, it is assumed that the mass-independent isotope fractionation correlates with the interaction between nuclear radius and orbital electrons.

We also study the contribution of the nuclear size and shape to unusual isotope fractionations found in nature, for example, in meteorites.

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Figure 5 :Isotope fractionation of Cd.