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Journal Articles

Phase stability of Cs-Si-O and Cs-Si-Fe-O compounds on stainless steel

Suzuki, Chikashi; Nakajima, Kunihisa; Osaka, Masahiko

Journal of Nuclear Science and Technology, 59(3), p.345 - 356, 2022/03

 Times Cited Count:1 Percentile:0.01(Nuclear Science & Technology)

During a severe accident (SA) such as the Fukushima Daiichi Nuclear Power Plant accident, fission products (FP) can be retained on the surface of structural materials in reactors. Cesium (Cs) is an important FP, and various Cs compounds such as Cs silicates are formed on the surface of stainless steel (SS) in a reactor during a SA. We calculated total energies of Cs-Si-O compounds for evaluation on phase stability within an adiabatic approximation. The calculations indicate that Cs$$_{6}$$Si$$_{10}$$O$$_{23}$$ is the most stable of the Cs-Si-O compounds. We calculated, furthermore, total energies of Cs-Si-Fe-O compounds. These calculations indicate that Cs-Si-Fe-O compounds are more stable than C-Si-O compounds and that CsSi$$_{2}$$FeO$$_{6}$$ is the most stable of these C-Si-O and Cs-Si-Fe-O compounds within an adiabatic approximation. The results of our present calculations and our previous experiments lead to the conclusion that Cs-Si-Fe-O compounds can be stably formed on SS surface by Cs chemisorption.

Journal Articles

Cesium chemisorbed species onto stainless steel surfaces; An Atomistic scale study

Miradji, F.; Suzuki, Chikashi; Nakajima, Kunihisa; Osaka, Masahiko

Journal of Physics and Chemistry of Solids, 136, p.109168_1 - 109168_9, 2020/01

 Times Cited Count:2 Percentile:16.85(Chemistry, Multidisciplinary)

Journal Articles

Evaluation of electronic state of Cs-adsorbed clay minerals by NEXAFS analysis using DFT calculations

Suzuki, Chikashi; Yaita, Tsuyoshi; Suzuki, Shinichi; Pacold, J.*; Altman, A. B.*; Minasian, S. G.*; Tyliszczak, T.*; Shuk, D. K.*; Yoshida, Hiroyuki; Osaka, Masahiko

Journal of Physics and Chemistry of Solids, 127, p.169 - 177, 2019/04

 Times Cited Count:4 Percentile:25.98(Chemistry, Multidisciplinary)

A combined method of NEXAFS measurement and DFT-calculation was employed for Cs evaluation in clay minerals. The Cs M$$_{4,5}$$ NEXAFS spectra of Cs halides were analyzed using the DFT-calculations, and were well reproduced by incorporating the core-hole strength. The Cs M$$_{4,5}$$ NEXAFS spectrum of clay minerals was well-reproduced by the DFT-calculations including the major transitions and tail structures with the established method. The further evaluation of this spectrum by charge density suggests that these major transitions and the tail structures likely reflect bonding states and local environments around the Cs atoms. Comparison of electronic states of Cs in the clay mineral with those in the Cs halides by DFT-calculations has shown that the interaction between Cs and the nearest-neighbor atom is largest in the clay mineral, because the energy level of Cs-5s and 5p is closer to that of O-2s and 2p than the s and p orbitals of other alkali metal and alkali earth metal elements.

Journal Articles

Modelling of cesium chemisorption under nuclear power plant severe accident conditions

Miradji, F.; Suzuki, Chikashi; Nishioka, Shunichiro; Suzuki, Eriko; Nakajima, Kunihisa; Osaka, Masahiko; Barrachin, M.*; Do, T. M. D.*; Murakami, Kenta*; Suzuki, Masahide*

Proceedings of 9th Conference on Severe Accident Research (ERMSAR 2019) (Internet), 21 Pages, 2019/03

Journal Articles

Results and progress of fundamental research on FP chemistry

Osaka, Masahiko; Nakajima, Kunihisa; Miwa, Shuhei; Di Lemma, F. G.*; Miyahara, Naoya; Suzuki, Chikashi; Suzuki, Eriko; Okane, Tetsuo; Kobata, Masaaki

Proceedings of 8th European Review Meeting on Severe Accident Research (ERMSAR 2017) (Internet), 11 Pages, 2017/05

Fundamental research on fission product (FP) chemistry is underway at Japan Atomic Energy Agency. The purpose is to establish a FP chemistry database in each region of a LWR under severe accident conditions. Improvement of FP chemical models based on this database is also an important task of the research. Research outputs are reflected to the research and development of decommissioning of Fukushima Daiichi Nuclear Power Station (1F) and the enhancement of LWR safety. Four research items have thus been established considering the specific issues of 1F and the priority in the source term research area, as follows: - Effects of boron (B) release kinetics and thermal-hydraulic conditions on FP behavior, - Cesium (Cs) chemisorption and reactions with structural materials, - Establishment of a thermodynamic and thermophysical properties database for FP compounds, - Development of experimental and analytical techniques for the reproduction of FP behavior. In this paper, results and progress of the research are presented.

JAEA Reports

Results and progress of fundamental research on fission product chemistry; Progress report in 2015

Osaka, Masahiko; Miwa, Shuhei; Nakajima, Kunihisa; Di Lemma, F. G.*; Suzuki, Chikashi; Miyahara, Naoya; Kobata, Masaaki; Okane, Tetsuo; Suzuki, Eriko

JAEA-Review 2016-026, 32 Pages, 2016/12


A fundamental research program on fission product (FP) chemistry has started since 2012 for the purpose of establishment of a FP chemistry database in each region of LWR under severe accident and improvement of FP chemical models based on the database. Research outputs are reflected as fundamental knowledge to both the research and development of decommissioning of Fukushima Daiichi Nuclear Power Station (1F) and enhancement of LWR safety. Four research items have thus been established considering the specific issues of 1F and the priority in the source term research area, as follows: effects of boron (B) release kinetics and thermal-hydraulic conditions on FP behavior, cesium (Cs) chemisorption and reactions with structural materials, enlargement of a thermodynamic and thermophysical properties database for FP compounds and development of experimental and analytical techniques for the reproduction of FP behavior and for direct measurement methods of chemical form of FP compounds. In this report, the research results and progress for the year 2015 are described. The main accomplishment was the installation of a reproductive test facility for FP release and transport behavior. Moreover, basic knowledge about the Cs chemisorption behavior was also obtained. In addition to the four research items, a further research item is being considered for deeper interpretation of FP behavior by the analysis of samples outside of the 1F units.

Journal Articles

NEXAFS analysis and electronic state of cesium in clay minerals

Suzuki, Chikashi; Yoshida, Hiroyuki; Shuk, D. K.*; Suzuki, Shinichi; Yaita, Tsuyoshi

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

We evaluated Cs M$$_{4,5}$$ near edge X-ray absorption fine structure (NEXAFS) of Cs halides and clay minerals containing Cs using DFT calculation with the NEXAFS of the clay minerals measured. The evaluation of Cs halides indicated that the core-hole strength (CHS) in the NEXAFS measurement was reduced to 0.6, taking into account the strength interaction of the core-hole with the valence-band electrons. On the basis of this result, Cs M$$_{4,5}$$ NEXAFS of the clay mineral was well reproduced including the dominant peak and tail structures using DFT calculation. Moreover the calculation showed that the NEXAFS clearly changed with the displacement of Si atoms to Al in the six-membered ring of clay minerals and little did with the coexist of K atoms with Cs between layers of the clay mineral. In addition, we examined the electronic state of CsCl and the clay mineral containing Cs.

Journal Articles

Electronic structure of BaTiO$$_{3}$$ using resonant X-ray emission spectroscopy at the Ba-L$$_{3}$$ and Ti K absorption edges

Yoshii, Kenji; Yoneda, Yasuhiro; Jarrige, I.*; Fukuda, Tatsuo; Nishihata, Yasuo; Suzuki, Chikashi; Ito, Yoshiaki*; Terashima, Takahito*; Yoshikado, Shinzo*; Fukushima, Sei*

Journal of Physics and Chemistry of Solids, 75(3), p.339 - 343, 2014/03

 Times Cited Count:9 Percentile:40.44(Chemistry, Multidisciplinary)

We have studied the electronic properties of ferroelectric BaTiO$$_{3}$$ using two complementary bulk-sensitive spectroscopic probes, resonant X-ray emission spectroscopy (RXES) and X-ray absorption spectroscopy in the partial fluorescence mode (PFY-XAS). Contrary to a previous study, we found no temperature change of a PFY-XAS spectrum at the Ba L$$_{3}$$ edge between room temperature and 150$$^{circ}$$C. This result is not supportive of the possible presence of the displacement around Ba$$^{2+}$$ at the Curie temperature. RXES spectra were measured at the Ti K edge for BaTiO$$_{3}$$, along with SrTiO$$_{3}$$ and La-doped metallic SrTiO$$_{3}$$. The photon energy of the emission peak is found to be nearly constant throughout the absorption edge for all three compounds. We deduce the Ti 3d states to have a delocalized character, in contrast with the Ba 5d states, a property which is consistent with the proposed scenario of the formation of electric dipoles in BaTiO$$_{3}$$.

Journal Articles

DFT study on the electronic structure and chemical state of americium in an (Am,U) mixed oxide

Suzuki, Chikashi; Nishi, Tsuyoshi; Nakada, Masami; Tsuru, Tomohito; Akabori, Mitsuo; Hirata, Masaru; Kaji, Yoshiyuki

Journal of Physics and Chemistry of Solids, 74(12), p.1769 - 1774, 2013/12

 Times Cited Count:12 Percentile:50.24(Chemistry, Multidisciplinary)

We investigated the electronic state of a CaF$$_{2}$$-type (Am,U) mixed oxide using the all-electron full potential linear augmented plane wave method and compared it with those of Am$$_{2}$$O$$_{3}$$, AmO$$_{2}$$, UO$$_{2}$$, and La$$_{0.5}$$U$$_{0.5}$$O$$_{2}$$. The valence of Am in the mixed oxide was close to that of Am$$_{2}$$O$$_{3}$$ and the valence of U in the mixed oxide was pentavalent. The electronic structure of AmO$$_{2}$$ was different from that of Am$$_{2}$$O$$_{3}$$, particularly just above the Fermi level. In addition, the electronic states of Am and U in the mixed oxide were similar to those of trivalent Am and pentavalent U oxides. These electronic states reflected the high oxygen potential of AmO$$_{2}$$ and the heightened oxygen potential resulting from the addition of Am to UO$$_{2}$$ and also suggested the occurrence of charge transfer from Am to U in the solid solution process.

Journal Articles

X-ray emission spectroscopy of Ta-related oxides

Yoneda, Yasuhiro; Yoshii, Kenji; Suzuki, Chikashi

Transactions of the Materials Research Society of Japan, 37(4), p.579 - 582, 2012/12

We performed X-ray Emission spectroscopy (XES) by using a double crystal spectrometer. Ta-L$$_{alpha 1}$$ and L$$_{alpha 2}$$ emission lines of Ta-related materials of Ta-metal, Ta$$_2$$O$$_5$$, LiTaO$$_3$$, and KTaO$$_3$$ were measured. XES is one of the most important spectroscopies to make a remarkable progress utilizing third generation synchrotron radiation sources. Here, I discuss some aspects of XES in Ta compounds of recent experimental data. We also discuss an azimuth dependence of resonant X-ray emission spectra (RXES) of a single-crystal KTaO$$_3$$. The precise measurement by the double crystal spectrometer has observed change of the electronic structure by crystal orientation. Since electronic structure observation is a local probe, it can detect minute lattice deformation.

Journal Articles

Probing the Ba 5d states in BaTiO$$_{3}$$ and BaSO$$_{4}$$; A Resonant X-ray emission study at the Ba-L$$_{3}$$ edge

Yoshii, Kenji; Jarrige, I.; Suzuki, Chikashi; Matsumura, Daiju; Nishihata, Yasuo; Yoneda, Yasuhiro; Fukuda, Tatsuo; Tamura, Kazuhisa; Ito, Yoshiaki*; Mukoyama, Takeshi*; et al.

Journal of Physics and Chemistry of Solids, 73(9), p.1106 - 1110, 2012/09

 Times Cited Count:11 Percentile:45.32(Chemistry, Multidisciplinary)

We have directly probed the Ba 5d states in the ferroelectric barium titanate BaTiO$$_{3}$$ using resonant X-ray emission spectroscopy (RXES) and X-ray absorption spectroscopy in the partial fluorescence mode (PFY-XAS) at the Ba-L$$_{3}$$ edge. The results are compared with those of the non-ferroelectric BaSO$$_{4}$$. While the RXES spectra point to a localized character for the Ba 5d states in both compounds, the main peak of the PFY-XAS spectrum, corresponding to the dipolar transitions from 2p to 5d, is found to be significantly broader for BaTiO$$_{3}$$ than for BaSO$$_{4}$$. On the basis of band structure calculations, this broadening is ascribed to strong hybridization between the unoccupied Ba 5d and O 2p states in the ferroelectric. This suggests that the hybridization between the conduction states of the Ba$$^{2+}$$ and O$$^{2-}$$ ions, and not only Ti$$^{4+}$$ and O$$^{2-}$$, plays a central role in determining the electronic structure of BaTiO$$_{4}$$.

Journal Articles

Core-hole effect on XANES and electronic structure of minor actinide dioxides with fluorite structure

Suzuki, Chikashi; Nishi, Tsuyoshi; Nakada, Masami; Akabori, Mitsuo; Hirata, Masaru; Kaji, Yoshiyuki

Journal of Physics and Chemistry of Solids, 73(2), p.209 - 216, 2012/02

 Times Cited Count:24 Percentile:67.29(Chemistry, Multidisciplinary)

The authors investigated theoretically core-hole effects on X-ray absorption near-edge structures (XANES) of Np and Am L$$_{III}$$ in neptunium dioxide (NpO$$_{2}$$) and americium dioxide (AmO$$_{2}$$) with CaF$$_{2}$$-type crystal lattices using the all-electron full-potential linearized augmented plane-wave (FP-LAPW) method. The peak creation mechanism of XANES was shown by examining the electronic structures of these oxides, which indicated that core-hole screening was more marked for AmO$$_{2}$$ than for NpO$$_{2}$$ because of the difference in the charge transfer between these oxides. Furthermore, the results of charge density analysis suggested that the white line was assigned to the quasi-bound state composed of the localized Np d or Am d components and O components, and that the tail structure was created as a result of delocalized standing waves between the Np or Am atoms.

Journal Articles

Fast calculation approach to semi-empirical molecular orbital method using real space division method

Igarashi, Takahiro; Nakazawa, Tetsuya; Suzuki, Chikashi; Tsuru, Tomohito; Kaji, Yoshiyuki

Computational Materials Science, 50(12), p.3346 - 3349, 2011/12

 Times Cited Count:1 Percentile:4.7(Materials Science, Multidisciplinary)

The authors have developed a new approach for large-scale systems including over 100,000 atoms to obtain physical strength from the viewpoint of atom-atom bonding energy. In this study, the authors applied this method to SiH$$_{4}$$ molecule and crystalline silica system, and carried out bond order and bonding energy analyses. In this analysis, the developed method offered almost the same analytical accuracy as the first principle method, while its calculation speed was much faster than that of the latter.

Journal Articles

Valence state of Am in (U$$_{0.95}$$Am$$_{0.05}$$)O$$_{2.0}$$

Nishi, Tsuyoshi; Nakada, Masami; Suzuki, Chikashi; Shibata, Hiroki; Okamoto, Yoshihiro; Akabori, Mitsuo; Hirata, Masaru

Journal of Nuclear Materials, 418(1-3), p.311 - 312, 2011/11

 Times Cited Count:19 Percentile:81.43(Materials Science, Multidisciplinary)

The XAFS measurements at U-L$$_{3}$$ and Am-L$$_{3}$$ absorption edge of (U$$_{0.95}$$Am$$_{0.05}$$)O$$_{2.0}$$ were performed in transmission mode. Moreover, to clarify the valence state of Am in (U,Am)O$$_{2-x}$$, the XANES spectrum of Am-L$$_{3}$$ absorption edge of (U$$_{0.95}$$Am$$_{0.05}$$)O$$_{2.0}$$ was verified using those of Am-L$$_{3}$$ absorption edge of AmO$$_{2}$$ and Am$$_{2}$$O$$_{3}$$. It was found that the XANES spectrum of the Am-L$$_{3}$$ edge of (U$$_{0.95}$$Am$$_{0.05}$$)O$$_{2.0}$$ is in good accordance with that of Am$$_{2}$$O$$_{3}$$. Thus, Am in (U$$_{0.95}$$Am$$_{0.05}$$)O$$_{2.0}$$ is almost trivalent state.

Journal Articles

Theoretical study on segregation of Cu, Mo and W impurities and stability of impurity-vacancy pairs in bcc Fe

Tsuru, Tomohito; Abe, Yosuke; Suzuki, Chikashi; Nakazawa, Tetsuya; Kaji, Yoshiyuki; Tsukada, Takashi

Journal of Nuclear Materials, 417(1-3), p.1054 - 1057, 2011/10

 Times Cited Count:1 Percentile:10.97(Materials Science, Multidisciplinary)

Reduced activation ferritic steel is one of the leading structural material candidates for a nuclear fusion reactor. Since the solute impurities have an effect on the embrittlement through segregation under irradiation, the stability of impurity elements should be elaborated. In the present study the segregation characteristics of tungsten and some general solute impurities in bcc iron were investigated nonempirically by first principle calculations, where the equilibrium segregation was considered via a regular solution model and the change in enthalpy for segregation were directly evaluated for comparison. Subsequently the energetic stabilities of impurity-impurity and impurity-vacancy pair were evaluated. The segregation enthalpy is influenced by the electronic interaction between the d-electron of Fe and the outer electron of the impurity element, and molybdenum and tungsten tend to prevent from the impurity segregation.

Journal Articles

Evaluation of solute-atom clusters segregated in $$alpha$$-Fe

Suzuki, Chikashi; Tsuru, Tomohito; Kaji, Yoshiyuki

Progress in Nuclear Science and Technology (Internet), 2, p.34 - 37, 2011/10

no abstracts in English

Journal Articles

Resonant inelastic X-ray scattering at Ba-L$$_{3}$$ edge in BaTiO$$_{3}$$

Yoshii, Kenji; Jarrige, I.; Matsumura, Daiju; Nishihata, Yasuo; Suzuki, Chikashi; Ito, Yoshiaki*; Mukoyama, Takeshi*; Tochio, Tatsunori*; Shinotsuka, Hiroshi*; Fukushima, Sei*

Japanese Journal of Applied Physics, 50(9), p.09NE03_1 - 09NE03_4, 2011/09

 Times Cited Count:2 Percentile:10.06(Physics, Applied)

Resonant X-ray inelastic scattering experiments have been performed at the Ba-L$$_{3}$$ edge in ferroelectric BaTiO$$_{3}$$ using synchrotron radiation at the BL15XU of SPring-8. An X-ray absorption spectrum of this material was found to be broader than non-ferroelectric BaSO$$_{4}$$. Molecular orbital calculations showed the formation of Ba-O bands in BaTiO$$_{3}$$, suggesting an important role of the Ba-O hybridization in the ferroelectric transition of this material. X-ray emission spectra at the edge showed a localized character of Ba-5d orbitals in BaTiO$$_{3}$$ in spite of the hybridization with O-3p. A few possible applications of the measurement will be also discussed.

Journal Articles

Relativistic density-functional study of solid solubitilty of tansiton metal/$$gamma$$-uranium alloys; The Roll of d-d orbital interactions

Kurihara, Masayoshi*; Onoe, Jun*; Hirata, Masaru; Suzuki, Chikashi

Journal of Alloys and Compounds, 509(4), p.1152 - 1156, 2011/01

 Times Cited Count:3 Percentile:24.74(Chemistry, Physical)

The alloying behavior of transition metals (TMs) in solid $$gamma$$-phase uranium ($$gamma$$-U), which is expected to be used as fuel for next-generation nuclear reactors, is investigated using the discrete-variational Dirac-Fock-Slater molecular orbital method. Using a model cluster, U$$_{8}$$/TM, as the minimum unit of $$gamma$$-U/TM alloys, we evaluate the d-orbital energy of the TM (Md), the bond order between the TM and U atoms, and the orbital overlap population (OOP) between the atomic orbitals of the TM and U atoms. We subsequently examine the effect of these quantities on the maximum solid solubility (MSS) of the $$gamma$$-U/TM alloys. Md and the OOP (U 6d-TM d) exhibit good correlations with the MSS for $$gamma$$-U/TM alloys, so that the interaction between the U-6d and TM-d atomic orbitals is found to play a key role in determining the MSS of the $$gamma$$-U/TM alloys. The magnitude of the MSS can be explained in terms of the stabilization energy caused by U 6d-TM d orbital interactions for $$gamma$$ -U/TM alloys, which is affected by the Md and the OOP. The exponential dependence of the MSS on Md and the OOP is explained in terms of the equilibrium constant obtained using a substitution cluster model for $$gamma$$-U/TM alloys. We also map the MSS of $$gamma$$-U/TM alloys using the Md and the OOP as the alloying parameters. These results will assist the quantum design of nuclear fuel materials for other alloy systems besides the present alloy system.

Journal Articles

The Configuration and electronic state of SO$$_{3}$$ adsorbed on Au surface

Suzuki, Chikashi; Nakagiri, Toshio

Journal of Physics and Chemistry of Solids, 72(1), p.10 - 16, 2011/01

 Times Cited Count:4 Percentile:21.48(Chemistry, Multidisciplinary)

We evaluated the adsorption of SO$$_{3}$$ molecule on the Au (111) surface using the first-principles calculations by a slab model with a periodic boundary condition. We find that there are six stable adsorption configurations on the Au surface, where SO$$_{3}$$ molecules are adsorbed above the three-fold fcc and hcp hallow sites and atop site. In two of these configurations, S and two O atoms are bound to the Pt atoms, and in two other of them, all the three O atoms are bound to Pt surface atoms, and then, S atom is bound to Au surface atom on the atop site and O atoms are situated on the hallow sites. In addition, it is found that molecular orbitals of SO$$_{3}$$ and those of Au surface are hybridized in the active metal d-bands region, that the localized molecular orbitals in SO$$_{3}$$ are stabilized, and that the charge is transferred from Au to S 3p by SO$$_{3}$$ adsorption on Au surface though the other interaction of S and O (bound to Au) component with Au is little. In addition, the bond between S and O bound to Au become weak by SO$$_{3}$$ adsorption on Au surface because the charge polarization to O-Au bond weakens the bond between S and O bound to Au. This interaction is assumed to encourage the breakage of S-O bond.

Journal Articles

Local and electronic structure of Am$$_{2}$$O$$_{3}$$ and AmO$$_{2}$$ with XAFS spectroscopy

Nishi, Tsuyoshi; Nakada, Masami; Suzuki, Chikashi; Shibata, Hiroki; Ito, Akinori; Akabori, Mitsuo; Hirata, Masaru

Journal of Nuclear Materials, 401(1-3), p.138 - 142, 2010/06

 Times Cited Count:26 Percentile:85.09(Materials Science, Multidisciplinary)

XAFS studies were performed in a study of americium sesquioxide (Am$$_{2}$$O$$_{3}$$) with A-type rare earth oxide structure and americium dioxide (AmO$$_{2}$$) with fluorite structure. EXAFS results for Am-L$$_{3}$$ absorption edge of Am$$_{2}$$O$$_{3}$$ and AmO$$_{2}$$ were good agreement with the crystallographic data from X-ray diffraction analysis. In order to characterize XANES in aspect of the electronic states, the theoretical assignments for the Am$$_{2}$$O$$_{3}$$ and AmO$$_{2}$$ were performed with the all-electron full potential linearized augmented plane wave (FP-LAPW) method. The theoretical XANES spectra of Am$$_{2}$$O$$_{3}$$ and AmO$$_{2}$$ well reproduced the experimental ones. In addition, it was found that the white line peak was created due to the interaction between Am-d and O-p components, and the broad peak and the tail peak were created due to the interaction between Am-d and O-d component.

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