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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

https://doi.org/10.1111/jace.19609

Times Cited Count：0 Percentile：0.01(Materials Science, Ceramics)

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

https://doi.org/10.1016/j.jnucmat.2023.154786

Times Cited Count：1 Percentile：68.31(Materials Science, Multidisciplinary)

Journal Articles

Progress of evaluation of beam coupling impedance reduction for the Eddy-current type septum magnet in J-PARC MR

Kobayashi, Aine*; Toyama, Takeshi*; Nakamura, Takeshi*; Shobuda, Yoshihiro; Ishii, Koji*; Tomizawa, Masahito*; Takeuchi, Yasunao*; Sato, Yoichi*

Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.19 - 23, 2023/01

https://www.pasj.jp/web_publish/pasj2022/proceedings/PDF/TUOB/TUOB01.pdf

In the J-PARC main ring, density modulation due to longitudinal beam instability occurs during the debunching process of coasting beams. This leads to the generation of an electron cloud, which in turn causes transverse beam instabilities. The transverse beam instability causes beam loss and the electron cloud is assumed to cause vacuum degradation, both of which hinder the beam intensity enhancement, so it is essential to clarify the causes and countermeasures. In particular, the longitudinal impedance of several hundred MHz has been investigated as relevant, and measures to reduce the impedance of individual devices are underway. The Eddy-current type septum magnet, newly installed this year, was found to have a large impedance by simulation. Therefore, we are investigating a method to reduce the impedance by a flange loaded with SiC radio wave absorber, which can be applied to locations where there is no spatial margin to install a taper. In this report, we will discuss the characterization of SiC to be used in actual devices, impedance simulation reflecting the results of SiC evaluation, and evaluation of the effect of impedance countermeasures by impedance measurement using the wire method, and progress in evaluating the effect on the beam by beam simulation and beam study.

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

https://doi.org/10.1201/9781003298205

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

https://doi.org/10.1111/jace.18249

Times Cited Count：1 Percentile：6.56(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

Single crystal growth and unique electronic states of cubic chiral EuPtSi and related compounds

Onuki, Yoshichika*; Kakihana, Masashi*; Iha, Wataru*; Nakaima, Kenri*; Aoki, Dai*; Nakamura, Ai*; Honda, Fuminori*; Nakashima, Miho*; Amako, Yasushi*; Gochi, Jun*; et al.

JPS Conference Proceedings (Internet), 29, p.012001_1 - 012001_9, 2020/02

https://doi.org/10.7566/JPSCP.29.012001

Journal Articles

Design loads and structural member modelling to shock-resistant design of buildings

Ikawa, Nozomu*; Mukai, Yoichi*; Nishida, Akemi; Hamamoto, Takuji*; Kano, Toshiya*; Ota, Toshiro*; Nakamura, Naohiro*; Komuro, Masato*; Takeuchi, Masato*

Proceedings of 12th International Conference on Shock and Impact Loads on Structures (SI 2017) (USB Flash Drive), p.259 - 268, 2017/06

Accidental actions on building structures involve impact and explosion loads. The design loads due to impact are determined by experiment data, impact simulation and energetics approach. These loads are presented in the form of load-time (F-t) curves caused by collision and explosion. It is assumed that the structure is rigid and immovable and that impacting body absorbs all the energy (i.e., hard impact condition is supposed), because this assumption gives conservative results in general. Responses of individual structural members directly-subjected to an impulsive load are evaluated. These responses are classified into three types; impulsive response, dynamic response, and quasi-static response. The maximum responses are basically estimated by direct integration method with a single-degree-of-freedom (SDOF) model. The procedure of the SDOF modelling based on the classification of types of members and failure modes is proposed in AIJ guideline.

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

http://doi.org/10.4028/www.scientific.net/DDF.375.57

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

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

https://doi.org/10.7566/JPSJ.84.053602

Times Cited Count：2 Percentile：20.35(Physics, Multidisciplinary)

Plutonium dioxide (PuO) 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 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 -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

https://doi.org/10.1016/j.jnucmat.2014.03.021

Times Cited Count：9 Percentile：57.01(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 . 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

Current status of a new polarized neutron reflectometer at the intense pulsed neutron source of the Materials and Life Science Experimental Facility (MLF) of J-PARC

Takeda, Masayasu; Yamazaki, Dai; Soyama, Kazuhiko; Maruyama, Ryuji; Hayashida, Hirotoshi; Asaoka, Hidehito; Yamazaki, Tatsuya; Kubota, Masato; Aizawa, Kazuya; Arai, Masatoshi; et al.

Chinese Journal of Physics, 50(2), p.161 - 170, 2012/04

http://psroc.org/cjp/issues.php?vol=50&num=2

Journal Articles

LDA+ 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

https://doi.org/10.15669/pnst.2.16

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 -orbital electrons are taken into account using the LDA+ 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

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

https://doi.org/10.1103/PhysRevB.82.155131

Times Cited Count：33 Percentile：76.04(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 + considering the strong correlation on Pu -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

Possible existence of magnetic polaron in nearly ferromagnetic semiconductor -US

Ikeda, Shugo*; Sakai, Hironori; Tateiwa, Naoyuki; Matsuda, Tatsuma; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; Ota, Yuki*; et al.

Journal of the Physical Society of Japan, 78(11), p.114704_1 - 114704_10, 2009/11

https://doi.org/10.1143/JPSJ.78.114704

Times Cited Count：12 Percentile：58.92(Physics, Multidisciplinary)

Journal Articles

Pressure effect on paramagnet -US

Ikeda, Shugo; Sakai, Hironori; Matsuda, Tatsuma; Tateiwa, Naoyuki; Nakamura, Akio; Yamamoto, Etsuji; Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; Hedo, Masato*; et al.

Physica B; Condensed Matter, 403(5-9), p.893 - 894, 2008/04

https://doi.org/10.1016/j.physb.2007.10.059

Times Cited Count：6 Percentile：30.28(Physics, Condensed Matter)

Single crystals of paramagnetic semiconductor -US with the orthorhombic () crystal structure were grown by chemical transport method. We measured the electrical resistivity under high pressure, and magnetization. With increasing pressure, the temperature dependence of approaches to semimetallic behavior and a kink anomaly appears at $T_{rm a}$ . $T_{rm a}$ shifts to higher temperature with increasing pressure. From the comparison with ferromagnetic semimetal UTeS having the same crystal structure, it seems that $T_{rm a}$ is a ferromagnetic transition.

Journal Articles

Pressure effect on ferromagnet UTeS

Ikeda, Shugo*; Sakai, Hironori; Matsuda, Tatsuma; Tateiwa, Naoyuki; Aoki, Dai*; Homma, Yoshiya*; Nakamura, Akio; Yamamoto, Etsuji; Shiokawa, Yoshinobu*; Hedo, Masato*; et al.

Journal of the Physical Society of Japan, 77(Suppl.A), p.359 - 361, 2008/00

https://doi.org/10.1143/JPSJS.77SA.359

Times Cited Count：1 Percentile：11.65(Physics, Multidisciplinary)

The ferromagnet UTeS was studied by measurement the resistivity under high pressure. The Curie temperature $T_{rm C}$ rapidly increases from 87 K to 166 Kat 8 GPa. The result suggests that there is a correlation between the electrical conductivity and magnetic transition temperature, implying the strong hybridization.

Journal Articles

Effect of pressure on the electronic state in antiferromagnets UPtSi and UIrSi

Ikeda, Shugo; Nakashima, Miho*; Matsuda, Tatsuma; Tateiwa, Naoyuki; Yamamoto, Etsuji; Nakamura, Akio; Haga, Yoshinori; Hedo, Masato*; Uwatoko, Yoshiya*; Onuki, Yoshichika*

Journal of the Physical Society of Japan, 75(12), p.125003_1 - 125003_2, 2006/12

https://doi.org/10.1143/JPSJ.75.125003

Times Cited Count：2 Percentile：19.44(Physics, Multidisciplinary)

We measured the electrical resistivity under pressures up to 8 GPa in antiferromagnets UPtSi ( $T_{rm N}$ = 34 K) and UIrSi ( $T_{rm N}$ = 6.3 K). The Nel temperature is found to decrease slowly as a function of pressure in UPtSi. The critical pressure $P_{rm c}$ ( $T_{rm N}rightarrow$ 0) is roughly estimated as $P_{rm c}$ 10 GPa. On the other hand, the Nel temperature is unchanged in UIrSi.