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Journal Articles

A Science-based mixed oxide property model for developing advanced oxide nuclear fuels

Kato, Masato; Oki, Takumi; Watanabe, Masashi; Hirooka, Shun; Vauchy, R.; Ozawa, Takayuki; Uwaba, Tomoyuki; Ikusawa, Yoshihisa; Nakamura, Hiroki; Machida, Masahiko

Journal of the American Ceramic Society, 107(5), p.2998 - 3011, 2024/05

Journal Articles

Uranium-plutonium-americium cation interdiffusion in polycrystalline (U,Pu,Am)O$$_{2 pm x}$$ mixed oxides

Vauchy, R.; Matsumoto, Taku; Hirooka, Shun; Uno, Hiroki*; Tamura, Tetsuya*; Arima, Tatsumi*; Inagaki, Yaohiro*; Idemitsu, Kazuya*; Nakamura, Hiroki; Machida, Masahiko; et al.

Journal of Nuclear Materials, 588, p.154786_1 - 154786_13, 2024/01

Journal Articles

Materials science and fuel technologies of uranium and plutonium mixed oxide

Kato, Masato; Machida, Masahiko; Hirooka, Shun; Nakamichi, Shinya; Ikusawa, Yoshihisa; Nakamura, Hiroki; Kobayashi, Keita; Ozawa, Takayuki; Maeda, Koji; Sasaki, Shinji; et al.

Materials Science and Fuel Technologies of Uranium and Plutonium mixed Oxide, 171 Pages, 2022/10

Innovative and advanced nuclear reactors using plutonium fuel has been developed in each country. In order to develop a new nuclear fuel, irradiation tests are indispensable, and it is necessary to demonstrate the performance and safety of nuclear fuels. If we can develop a technology that accurately simulates irradiation behavior as a technology that complements the irradiation test, the cost, time, and labor involved in nuclear fuel research and development will be greatly reduced. And safety and reliability can be significantly improved through simulation of nuclear fuel irradiation behavior. In order to evaluate the performance of nuclear fuel, it is necessary to know the physical and chemical properties of the fuel at high temperatures. And it is indispensable to develop a behavior model that describes various phenomena that occur during irradiation. In previous research and development, empirical methods with fitting parameters have been used in many parts of model development. However, empirical techniques can give very different results in areas where there is no data. Therefore, the purpose of this study is to construct a scientific descriptive model that can extrapolate the basic characteristics of fuel to the composition and temperature, and to develop an irradiation behavior analysis code to which the model is applied.

Journal Articles

Defect equilibria and thermophysical properties of CeO$$_{2-x}$$ based on experimental data and density functional theory calculation result

Watanabe, Masashi; Nakamura, Hiroki; Suzuki, Kiichi; Machida, Masahiko; Kato, Masato

Journal of the American Ceramic Society, 105(3), p.2248 - 2257, 2022/03

 Times Cited Count:1 Percentile:7.37(Materials Science, Ceramics)

Properties of CeO$$_{2}$$ were evaluated by DFT simulation to determine band gap, Frenkel defect formation energy and defect migration energy. Band gap and Frenkel defect formation energy were used to analyze defect equilibria. Oxygen partial pressure dependence of defect equilibria was evaluated based on oxygen potential experimental data and DFT calculation, and a Brouwer diagram was derived. The defect formation energies, including Frenkel defect, electron-hole pair and so on, were determined and used to evaluate the properties, including oxygen diffusion coefficients, electrical conduction, heat capacity and thermal conductivity. Mechanisms of various properties were discussed for a deeper understanding based on defect chemistry, and the relationship among properties were systematically described.

Journal Articles

Research and development on membrane IS process for hydrogen production using solar heat

Myagmarjav, O.; Iwatsuki, Jin; Tanaka, Nobuyuki; Noguchi, Hiroki; Kamiji, Yu; Ioka, Ikuo; Kubo, Shinji; Nomura, Mikihiro*; Yamaki, Tetsuya*; Sawada, Shinichi*; et al.

International Journal of Hydrogen Energy, 44(35), p.19141 - 19152, 2019/07

 Times Cited Count:16 Percentile:50.25(Chemistry, Physical)

Journal Articles

Crystal structure change of katoite, Ca$$_{3}$$Al$$_{2}$$(O$$_{4}$$D$$_{4}$$)$$_{3}$$, with temperature at high pressure

Kyono, Atsushi*; Kato, Masato*; Sano, Asami; Machida, Shinichi*; Hattori, Takanori

Physics and Chemistry of Minerals, 46(5), p.459 - 469, 2019/05

 Times Cited Count:4 Percentile:21.21(Materials Science, Multidisciplinary)

To reveal the decomposition mechanism with temperature under high-pressure, crystal structure of a hydrogrossular, katoite Ca$$_{3}$$Al$$_{2}$$(O$$_{4}$$D$$_{4}$$)$$_{3}$$ has been studied by in-situ neutron diffraction at 8 GPa. Although unusual expansion behavior was discerned at 200-400$$^circ$$C, the unit cell was continuously expanded up to 850$$^circ$$C. At 900$$^circ$$C, katoite was decomposed, indicating that pressure strongly increases dehydration temperature from 300$$^circ$$C to 900$$^circ$$C. On release of pressure, the katoite reappear together with corundum and portlandite. At 8 GPa, CaO$$_{8}$$ and AlO$$_{6}$$ polyhedra expand with temperature up to 850$$^circ$$C by about 8% and 13%, respectively. On the other hand, tetrahedral interstices are isotopically squeezed by about 10%: due to the expansion of above polyhedra. The neighboring D-D distance remains almost unchanged in this temperature range, while the O-D bond distance shrinks drastically just before decomposition. This finding suggests that the shortening of O-D distance caused by the D-D repulsion destabilizes the O-D bond, which induces the thermal decomposition of katoite.

Journal Articles

Defect chemistry and basic properties of non-stoichiometric PuO$$_{2}$$

Kato, Masato; Nakamura, Hiroki; Watanabe, Masashi; Matsumoto, Taku; Machida, Masahiko

Defect and Diffusion Forum, 375, p.57 - 70, 2017/05

The basic properties of PuO$$_{2-x}$$ were reviewed, and the equilibrium defects in PuO$$_{2-x}$$ were evaluated from the experimental data of the oxygen potential and electrical conductivity as well as the Ab-initio calculation results. Consistency among various properties was confirmed, and the mechanistic models for thermal property representations were derived.

Journal Articles

Phonons of Fe-based superconductor Ca$$_{10}$$Pt$$_4$$As$$_8$$(Fe$$_{1-x}$$Pt$$_x$$As)$$_{10}$$

Ikeuchi, Kazuhiko*; Kobayashi, Yoshiaki*; Suzukia, Kazunori*; Ito, Masayuki*; Kajimoto, Ryoichi; Bourges, P.*; Christianson, A. D.*; Nakamura, Hiroki; Machida, Masahiko; Sato, Masatoshi*

Journal of Physics; Condensed Matter, 27(46), p.465701_1 - 465701_7, 2015/11

 Times Cited Count:1 Percentile:4.84(Physics, Condensed Matter)

We report the results of inelastic neutron scattering measurements on particular phonons of a superconducting (SC) Ca$$_{10}$$Pt$$_4$$As$$_8$$(Fe$$_{1-x}$$Pt$$_x$$As)$$_{10}$$ with the onset transition temperature $$T_c sim 33$$ K to investigate mainly what roles orbital fluctuation plays in Cooper pairing, where we observed a slight softening of the in-plane transverse acoustic mode corresponding to the elastic constant $$C_{66}$$. This softening starts at temperature $$T$$ well above the SC $$T_c$$, as $$T$$ decreases. An anomalously strong change of the scattering intensity of in-plane optical modes was observed at the M point of the pseudo tetragonal reciprocal space in the range of 35 $$< omega <$$ 40 meV with decreasing $$T$$ from far above $$T_c$$. Because this $$omega$$ region mainly corresponds to the motion of Fe and As atoms in the FeAs planes, the finding presents information on the coupling between the orbital fluctuation of Fe $$3d$$ electrons and the lattice system, useful for studying the possible roles of orbital fluctuation in the pairing mechanism and/or the appearance of the so-called nematic phase.

Journal Articles

First-principles calculation of phonon and Schottky heat capacities of plutonium dioxide

Nakamura, Hiroki; Machida, Masahiko; Kato, Masato

Journal of the Physical Society of Japan, 84(5), p.053602_1 - 053602_5, 2015/05

 Times Cited Count:2 Percentile:20.53(Physics, Multidisciplinary)

Plutonium dioxide (PuO$$_2$$) is a key ingredient of mixed oxide (MOX) and advanced nuclear fuels. Its thermophysical data is crucial in understanding the high-temperature behaviors of nuclear fuels. In particular, the high-temperature heat capacity is of great importance for their safety and performance analyses. Here, we evaluate the main contributions to the heat capacity of PuO$$_2$$ from 0 to 1400 K through suitable first-principles calculations. Consequently, we successfully obtain a temperature dependence in good agreement with experimental measurements. This success mainly results from accurate calculations of the Schottky heat capacity caused by the excited levels of $$f$$-electrons of Pu. Our calculations resolve the mystery of why previous works failed to reproduce the measurement data. This study extends the possibility of performing simulation-based nuclear-fuel research instead of difficult measurements.

Journal Articles

Thermal expansion measurement and heat capacity evaluation of hypo-stoichiometric PuO$$_{2.00}$$

Kato, Masato; Uchida, Teppei; Matsumoto, Taku; Sunaoshi, Takeo*; Nakamura, Hiroki; Machida, Masahiko

Journal of Nuclear Materials, 451(1-3), p.78 - 81, 2014/08

 Times Cited Count:9 Percentile:57.39(Materials Science, Multidisciplinary)

Linear thermal expansion of PuO$$_{2-x}$$ was measured by dilatometry in an oxygen partial pressure-controlled atmosphere. The measured data of PuO$$_{2-x}$$ slightly increased with deviation $$x$$. The linear thermal expansion of PuO$$_{2-x}$$ was determined as a function of temperature and O/M ratio, and the equation for the thermal expansion coefficient was derived. Heat capacity of PuO$$_{2-x}$$ was evaluated using this equation. The effect of O/M ratio on heat capacity was small. In addition to the vibration and dilatational terms, it is important to analyze the Schottky term in evaluating heat capacity of PuO$$_{2}$$.

Journal Articles

Fabrication of polymer optical waveguides for the 1.5-$$mu$$m band using focused proton beam

Miura, Kenta*; Machida, Yuki*; Uehara, Masato*; Kiryu, Hiromu*; Ozawa, Yusuke*; Sasaki, Tomoyuki*; Hanaizumi, Osamu*; Sato, Takahiro; Ishii, Yasuyuki; Koka, Masashi; et al.

Key Engineering Materials, 497, p.147 - 150, 2012/00

 Times Cited Count:7 Percentile:95.17

Journal Articles

Fabrication of polymer optical waveguides for the 1.5-$$mu$$m band using focused proton beam

Miura, Kenta*; Machida, Yuki*; Uehara, Masato*; Kiryu, Hiromu*; Ozawa, Yusuke*; Sasaki, Tomoyuki*; Hanaizumi, Osamu*; Sato, Takahiro; Ishii, Yasuyuki; Koka, Masashi; et al.

Key Engineering Materials, 497, p.147 - 150, 2011/12

 Times Cited Count:6 Percentile:2.48

Journal Articles

$$s_{pm}$$-like spin resonance in the iron-based nodal superconductor BaFe$$_2$$(As$$_{0.65}$$P$$_{0.35}$$)$$_2$$ observed using inelastic neutron scattering

Ishikado, Motoyuki; Nagai, Yuki; Kodama, Katsuaki; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Wakimoto, Shuichi; Nakamura, Hiroki; Machida, Masahiko; Suzuki, Katsuhiro*; et al.

Physical Review B, 84(14), p.144517_1 - 144517_5, 2011/10

 Times Cited Count:26 Percentile:70.8(Materials Science, Multidisciplinary)

We performed inelastic neutron scattering on a powder sample of iron-based superconductor BaFe$$_2$$(As$$_{0.65}$$P$$_{0.35}$$)$$_2$$ with $$T_c$$ = 30 K. Although this system is expected to have line nodes in its superconducting order parameter, we have observed spin resonance at the same scattering vector as that appeared in the $$s_{pm}$$-wave iron-based superconductors without line nodes. Moreover, the resonance enhancement, which can be a measure of the area of sign reversal between the hole and electron Fermi surfaces (FSs), is comparable to those without line nodes. These facts indicate that the sign reversal between the FSs is still dominant in this system, and the line nodes should create only limited area of sign-reversal on a single FS. Hence the system can hold higher Tc than the other iron-based superconductors with nodal symmetry, such as LaFePO$$_{1-y}$$ and KFe$$_2$$As$$_2$$ ($$T_c <$$ 10 K).

Journal Articles

LDA+$$U$$ study on plutonium dioxide with spin-orbit couplings

Nakamura, Hiroki; Machida, Masahiko; Kato, Masato

Progress in Nuclear Science and Technology (Internet), 2, p.16 - 19, 2011/10

Plutonium dioxide is a main component of mixed oxide fuels. We perform first-principles density functional calculations on plutonium dioxides considering proper relativistic effects and strong correlations. Though this material is a paramagnetic insulator, standard calculations predict metallic states. The reason of this failure is often considered lack of strong correlations in LDA. However, even if strong correlation effects on plutonium $$f$$-orbital electrons are taken into account using the LDA+$$U$$ method, an insulating state cannot be obtained. In this paper, we point out that not only strong correlations but also spin-orbit couplings as relativistic effects are necessary to obtain paramagnetic insulating states. Based on this proper method, we calculate several physical properties of plutonium dioxide and compare them with other calculations and experiments. We also discuss the effects of oxygen deficiency on the electronic structures and thermal properties.

Journal Articles

Soft and isotropic phonons in PrFeAsO$$_{1-y}$$

Fukuda, Tatsuo; Baron, A. Q. R.*; Nakamura, Hiroki; Shamoto, Shinichi; Ishikado, Motoyuki; Machida, Masahiko; Uchiyama, Hiroshi*; Iyo, Akira*; Kito, Hijiri*; Mizuki, Junichiro; et al.

Physical Review B, 84(6), p.064504_1 - 064504_13, 2011/08

 Times Cited Count:9 Percentile:39.45(Materials Science, Multidisciplinary)

Journal Articles

Phonon spectra of PrFeAsO$$_{1-y}$$ via inelastic X-ray scattering

Fukuda, Tatsuo; Baron, A. Q. R.*; Nakamura, Hiroki; Shamoto, Shinichi; Ishikado, Motoyuki; Machida, Masahiko; Uchiyama, Hiroshi*; Iyo, Akira*; Kito, Hijiri*; Mizuki, Junichiro; et al.

Journal of the Physical Society of Japan, 80(Suppl.B), p.SB015_1 - SB015_4, 2011/01

 Times Cited Count:1 Percentile:11.37(Physics, Multidisciplinary)

We have investigated phonons of PrFeAsO$$_{1-y}$$ using high-resolution inelastic X-ray scattering and $$ab-initio$$ calculations. Extensive measurements show that there are some changes in phonon spectra with temperature and/or doping. However, we compare our data with several calculations and find that the experimentally observed changes are much smaller than differences between the experiment. data and the calculations. Agreement is improved if magnetism is included in the calculations. However, still in disagreement even in the parent sample below T$$_N$$. We consider several modifications of the $$ab-initio$$ calculations. The best agreement is obtained from modifying the nonmagnetic calculation. by softening only the in-plane nearest-neighbor Fe-As force constant. Fluctuating magnetism may be a partial explanation for the failure of the calculations, but seems incomplete in the face of the similarity of the measured phonon response in all the systems investigated including those known to have static magnetism.

Journal Articles

Spin excitations in iron oxypnictide superconductor system

Shamoto, Shinichi; Ishikado, Motoyuki; Wakimoto, Shuichi; Kodama, Katsuaki; Kajimoto, Ryoichi; Arai, Masatoshi; Fukuda, Tatsuo; Nakamura, Hiroki; Machida, Masahiko; Eisaki, Hiroshi*

Physica C, 470(Suppl.1), p.S284 - S287, 2010/12

 Times Cited Count:4 Percentile:22.02(Physics, Applied)

Journal Articles

Effects of spin-orbit coupling and strong correlation on the paramagnetic insulating state in plutonium dioxides

Nakamura, Hiroki; Machida, Masahiko; Kato, Masato

Physical Review B, 82(15), p.155131_1 - 155131_6, 2010/10

 Times Cited Count:33 Percentile:76.26(Materials Science, Multidisciplinary)

We perform first-principles calculations taking account of both relativistic and strong correlation effects on plutonium dioxides in order to numerically obtain its observed ground state, i.e., the paramagnetic insulating state and properly calculate the material properties. Generally, it is known for plutonium dioxides that the standard LDA calculations give metallic states and even LDA + $$U$$ considering the strong correlation on Pu $$f$$-orbitals fails to attain the paramagnetic insulating state. In this paper, we clarify that inclusion of the spin-orbit coupling in addition to the strong correlation is responsible for the paramagnetic insulating state. Using the obtained paramagnetic insulating state, we calculate various material properties and claim that the proper state preparation is essential for quantitative evaluation of the material properties.

Journal Articles

Lattice dynamics of LaFeAsO$$_{1-x}$$F$$_x$$ and PrFeAsO$$_{1-y}$$ via inelastic X-ray scattering and first-principles calculation

Fukuda, Tatsuo; Baron, A. Q. R.*; Shamoto, Shinichi; Ishikado, Motoyuki; Nakamura, Hiroki; Machida, Masahiko; Uchiyama, Hiroshi*; Tsutsui, Satoshi*; Iyo, Akira*; Kito, Hijiri*; et al.

Journal of the Physical Society of Japan, 77(10), p.103715_1 - 103715_4, 2008/10

 Times Cited Count:41 Percentile:82.89(Physics, Multidisciplinary)

The lattice dynamics of LaFeAsO$$_{1-x}$$F$$_x$$ ($$x$$=0, 0.1) and PrFeAsO$$_{1-y}$$ ($$ysim$$0.1) are investigated using inelastic X-ray scattering. Measurements of powder samples provide an approximation to the phonon DOS, while dispersion is measured from a single crystal of PrFeAsO$$_{1-y}$$. A model that agrees reasonably well with all of the data at room temperature is built from results of ab-initio calculations by reducing the strength of the Fe-As bond by 30%.

Journal Articles

Superconducting MgB$$_2$$ thin film detector for neutrons

Ishida, Takekazu*; Nishikawa, Masatoshi*; Fujita, Yoshifumi*; Okayasu, Satoru; Katagiri, Masaki*; Sato, Kazuo*; Yotsuya, Tsutomu*; Shimakage, Hisashi*; Miki, Shigehito*; Wang, Z.*; et al.

Journal of Low Temperature Physics, 151(3-4), p.1074 - 1079, 2008/05

 Times Cited Count:36 Percentile:78.12(Physics, Applied)

The superconducting neutron detector using high-quality $$^{10}$$B-enriched MgB$$_2$$ thin films at higher operating temperatures has been proposed, where a resistance change induced by the nuclear reaction of neutron and $$^{10}$$B in MgB$$_2$$ is used to detect a neutron. Cold neutrons from a nuclear research reactor irradiated the MgB$$_2$$ detector, and the output voltage was clearly observed through a low-noise amplifier by using a digital oscilloscope. The out-of-equilibrium thermodynamics was investigated by means of the time-dependent Ginzburg-Landau equations by using the Earth Simulator.

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