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Journal Articles

Thermal-hydraulics technological strategy roadmap 2017; An Approach for continuous safety improvement of LWRs

Itoi, Tatsuya*; Iwaki, Chikako*; Onuki, Akira*; Kito, Kazuaki*; Nakamura, Hideo; Nishida, Akemi; Nishi, Yoshihisa*

Nippon Genshiryoku Gakkai-Shi, 60(4), p.221 - 225, 2018/04

no abstracts in English

Journal Articles

Unusual pressure evolution of the Meissner and Josephson effects in the heavy-fermion superconductor UPt$$_3$$

Gochi, Jun*; Sumiyama, Akihiko*; Yamaguchi, Akira*; Motoyama, Gaku*; Kimura, Noriaki*; Yamamoto, Etsuji; Haga, Yoshinori; Onuki, Yoshichika

Physical Review B, 93(17), p.174514_1 - 174514_5, 2016/05

 Times Cited Count:1 Percentile:88.02(Materials Science, Multidisciplinary)

Journal Articles

Thermal-hydraulics technological strategy roadmap that improves safety of LWRs

Arai, Kenji*; Umezawa, Shigemitsu*; Oikawa, Hirohide*; Onuki, Akira*; Nakamura, Hideo; Nishi, Yoshihisa*; Fujii, Tadashi*

Nippon Genshiryoku Gakkai-Shi, 58(3), p.161 - 166, 2016/03

no abstracts in English

Journal Articles

ROSA/LSTF tests and RELAP5 posttest analyses for PWR safety system using steam generator secondary-side depressurization against effects of release of nitrogen gas dissolved in accumulator water

Takeda, Takeshi; Onuki, Akira*; Kanamori, Daisuke*; Otsu, Iwao

Science and Technology of Nuclear Installations, 2016, p.7481793_1 - 7481793_15, 2016/00

AA2016-0048.pdf:5.15MB

 Times Cited Count:1 Percentile:76.09(Nuclear Science & Technology)

Journal Articles

Josephson effect and point-contact spectroscopy studies of the anomaly observed in the superconducting state of the heavy-fermion compound UBe$$_{13}$$

Gochi, Jun; Sumiyama, Akihiko*; Yamaguchi, Akira*; Motoyama, Gaku*; Haga, Yoshinori; Onuki, Yoshichika

Journal of the Physical Society of Japan, 84(9), p.094714_1 - 094714_5, 2015/09

 Times Cited Count:1 Percentile:81.9(Physics, Multidisciplinary)

Journal Articles

Experiments of coolant accumulation in SG U tube and analytical model development

Yamaji, Tatsuya*; Koizumi, Yasuo; Yamazaki, Kohei*; Otake, Hiroyasu*; Hasegawa, Koji*; Onuki, Akira*; Kanamori, Daisuke*

Konsoryu Shimpojiumu 2015 Koen Rombunshu (USB Flash Drive), 2 Pages, 2015/08

Experiments of condensing counter-current two-phase flow in a vertical pipe were performed. This study was intended to examine water accumulation in the up-flow side of steam generator U-tubes of a PWR during the reflux cooling stage of a small break LOCA. It has been apprehended that the water accumulation may result in temporary core liquid level depression. The inner diameter and the length of a test flow channel used in the experiments were 18 mm and 4 m, respectively. The experiments were performed by using steam and water at 0.1 MPa. Two kinds of experiments were conducted; visualization experiments by using a transparent test section and quantitative water accumulation evaluation experiments by using a brass test section. Even if water on the inner surface of the test pipe could not flow downward at the lower portion of the test pipe, a part of water became to flow downward at the upper portion of the test pipe since steam velocity decreased because of condensation. Thus, two-phase mixture level was formed in the upper portion of the test pipe, which resulted in the water accumulation in the pipe. The model to predict the water accumulation was proposed. It predicted the water accumulation reasonably well.

Journal Articles

RELAP5 code study of ROSA/LSTF experiments on PWR safety system using steam generator secondary-side depressurization

Takeda, Takeshi; Onuki, Akira*; Nishi, Hiroaki*

Journal of Energy and Power Engineering, 9(5), p.426 - 442, 2015/05

Journal Articles

Electronic structures of ferromagnetic superconductors UGe$$_{2}$$ and UCoGe studied by angle-resolved photoelectron spectroscopy

Fujimori, Shinichi; Okochi, Takuo*; kawasaki, Ikuto*; Yasui, Akira*; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; et al.

Physical Review B, 91(17), p.174503_1 - 174503_9, 2015/05

 Times Cited Count:13 Percentile:28.28(Materials Science, Multidisciplinary)

The electronic structures of the ferromagnetic superconductors UGe$$_2$$ and UCoGe in the paramagnetic phase were studied by angle-resolved photoelectron spectroscopy using soft X-rays ($$h nu$$ = 400-500 eV). The quasi-particle bands with large contributions from U 5$$f$$ states were observed in the vicinity of EF, suggesting that the U 5$$f$$ electrons of these compounds have an itinerant character. Their overall band structures were explained by the band-structure calculations treating all the U 5$$f$$ electrons as being itinerant. Meanwhile, the states in the vicinity of EF show considerable deviations from the results of band-structure calculations, suggesting that the shapes of Fermi surface of these compounds are qualitatively different from the calculations, possibly caused by electron correlation effect in the complicated band structures of the low-symmetry crystals. Strong hybridization between U 5$$f$$ and $$mathrm{Co} 3d$$ states in UCoGe were found by the $$mathrm{Co}$$ 2p-3d resonant photoemission experiment, suggesting that $$mathrm{Co} 3d$$ states have finite contributions to the magnetic, transport, and superconducting properties.

Journal Articles

Probing strongly correlated 4$$f$$-orbital symmetry of the ground state in Yb compounds by linear dichroism in core-level photoemission

Mori, Takeo*; Kitayama, Satoshi*; Kanai, Yuina*; Naimen, Sho*; Fujiwara, Hidenori*; Higashiya, Atsushi*; Tamasaku, Kenji*; Tanaka, Arata*; Terashima, Kensei*; Imada, Shin*; et al.

Journal of the Physical Society of Japan, 83(12), p.123702_1 - 123702_5, 2014/12

 Times Cited Count:11 Percentile:28.13(Physics, Multidisciplinary)

We show that the strongly correlated 4$$f$$-orbital symmetry of the ground state is revealed by linear dichroism in core-level photoemission spectra, as we have discovered for YbRh$$_{2}$$Si$$_{2}$$ and YbCu$$_{2}$$Si$$_{2}$$. Theoretical analysis shows us that the linear dichroism reflects the anisotropic charge distributions resulting from a crystalline electric field. We have successfully determined the ground-state 4$$f$$ symmetry for both compounds from the polarization-dependent angle resolved core-level spectra at a temperature well below the first excitation energy. The excited-state symmetry is also probed by temperature dependence of the linear dichroism where the high measurement temperatures are on the order of the crystal-field-splitting energies.

Journal Articles

RELAP5 code study of ROSA/LSTF validation tests for PWR safety system using SG secondary-side depressurization

Takeda, Takeshi; Onuki, Akira*; Nishi, Hiroaki*

Proceedings of 10th International Topical Meeting on Nuclear Thermal Hydraulics, Operation and Safety (NUTHOS-10) (USB Flash Drive), 13 Pages, 2014/12

Journal Articles

Angle resolved photoelectron spectroscopy study of heavy fermion superconductor UPd$$_{2}$$Al$$_{3}$$

Fujimori, Shinichi; kawasaki, Ikuto*; Yasui, Akira*; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; et al.

JPS Conference Proceedings (Internet), 3, p.011072_1 - 011072_5, 2014/06

In this presentation, we review some of our recent photoemission studies on uranium superconductors by means of soft X-ray synchrotron radiation ARPES (SX-ARPES). Results of SX-ARPES study on URhGe and UPd$$_{2}$$Al$$_{3}$$ will be presented. URhGe is a ferromagnetic superconductor with $$T_{rm Curie}$$ = 9.5 K and $$T_{rm SC}$$ = 0.26 K while UPd$$_{2}$$Al$$_{3}$$ is an antiferromagnetic superconductor with $$T_{rm N}$$ = 14 K and $$T_{rm SC}$$ = 1.8 K. We have revealed the three-dimensional electronic structures of those compounds by SX-ARPES, and they are compared with those calculated by LDA.

Journal Articles

Josephson effect between UPt$$_3$$ and conventional superconductors under pressure

Gochi, Jun*; Sumiyama, Akihiko*; Yamaguchi, Akira*; Motoyama, Gaku*; Kimura, Noriaki*; Yamamoto, Etsuji; Haga, Yoshinori; Onuki, Yoshichika

JPS Conference Proceedings (Internet), 3, p.011067_1 - 011067_6, 2014/06

Journal Articles

Itinerant magnetism in URhGe revealed by angle-resolved photoelectron spectroscopy

Fujimori, Shinichi; kawasaki, Ikuto*; Yasui, Akira*; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi*; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; et al.

Physical Review B, 89(10), p.104518_1 - 104518_7, 2014/03

 Times Cited Count:16 Percentile:26.37(Materials Science, Multidisciplinary)

The electronic structure of the ferromagnetic superconductor URhGe in the paramagnetic phase has been studied by angle-resolved photoelectron spectroscopy using soft X rays ($$hnu$$ = 595-700 eV). Dispersive bands with large contributions from U 5$$f$$ states were observed in the ARPES spectra, and form Fermi surfaces. The band structure in the paramagnetic phase is partly explained by the band-structure calculation treating all U 5$$f$$ electrons as being itinerant, suggesting that an itinerant description of U 5$$f$$ states is a good starting point for this compound. On the other hand, there are qualitative disagreements especially in the band structure near the Fermi level ($$E$$$$_{rm B}$$ $$_sim^{<}$$ 0.5 eV). The experimentally observed bands are less dispersive than the calculation, and the shape of the Fermi surface is different from the calculation. The changes in spectral functions due to the ferromagnetic transition were observed in bands near the Fermi level, suggesting that the ferromagnetism in this compound has an itinerant origin.

Journal Articles

Measurement of the Josephson effect of heavy-fermion superconductor UPt$$_3$$ as a test of the odd-parity order parameter

Gochi, Jun*; Sumiyama, Akihiko*; Motoyama, Gaku*; Yamaguchi, Akira*; Kimura, Noriaki*; Yamamoto, Etsuji; Haga, Yoshinori; Onuki, Yoshichika

Journal of the Physical Society of Japan, 81(11), p.113701_1 - 113701_4, 2012/11

 Times Cited Count:5 Percentile:54.14(Physics, Multidisciplinary)

Journal Articles

Electronic structure of heavy fermion uranium compounds studied by core-level photoelectron spectroscopy

Fujimori, Shinichi; Okochi, Takuo*; Kawasaki, Ikuto; Yasui, Akira; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; et al.

Journal of the Physical Society of Japan, 81(1), p.014703_1 - 014703_9, 2012/01

 Times Cited Count:27 Percentile:16.55(Physics, Multidisciplinary)

High-energy-resolution core-level and valence-band photoelectron spectroscopic studies were performed for the heavy Fermion uranium compounds UGe$$_2$$, UCoGe, URhGe, URu$$_2$$Si$$_2$$, UNi$$_2$$Al$$_3$$, UPd$$_2$$Al$$_3$$, and UPt$$_3$$ as well as typical localized and itinerant uranium compounds to understand the relationship between the uranium valence state and their core-level spectral line shapes. The core-level spectra of UGe$$_2$$, UCoGe, URhGe, URu$$_2$$Si$$_2$$, and UNi$$_2$$Al$$_3$$ are rather similar to those of itinerant compounds, suggesting that U 5$$f$$ electrons in these compounds are well hybridized with ligand states. On the other hand, the core-level spectra of UPd$$_2$$Al$$_3$$ and UPt$$_3$$ show considerably different spectral line shapes from those of the itinerant compounds, suggesting that U 5$$f$$ electrons in UPd$$_2$$Al$$_3$$ and UPt$$_3$$ are less hybridized with ligand states, leading to the correlated nature of U 5$$f$$ electrons in these compounds.

Journal Articles

Itinerant U 5$$f$$ nature in antiferromagnet U(Ru$$_{0.97}$$Rh$$_{0.03}$$)$$_{2}$$Si$$_{2}$$; Soft X-ray angle-resolved photoemission spectroscopy

Kawasaki, Ikuto; Fujimori, Shinichi; Okane, Tetsuo; Yasui, Akira; Saito, Yuji; Yamagami, Hiroshi*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika*

Journal of the Physical Society of Japan, 80(12), p.124710_1 - 124710_5, 2011/12

 Times Cited Count:2 Percentile:75.59(Physics, Multidisciplinary)

We have carried out soft X-ray angle-resolved photoemission spectroscopy experiments on U(Ru$$_{0.97}$$Rh$$_{0.03}$$)$$_{2}$$Si$$_{2}$$, which shows antiferromagnetic (AFM) ordering at low temperatures. We have revealed that U 5$$f$$ electrons contribute to the formation of the energy band as well as Fermi surface. This suggests that the AFM ordering is caused by a spin density wave of itinerant U 5$$f$$ electrons. The observed band dispersion and Fermi surface are nearly identical to those of URu$$_{2}$$Si$$_{2}$$. Therefore, the AFM ordering vector $$Q$$ = (1,0,0) can be a possible ordering vector of the hidden order phase in URu$$_{2}$$Si$$_{2}$$.

Journal Articles

Electronic structure of YbCu$$_2$$Ge$$_2$$ studied by soft X-ray angle-resolved photoemission spectroscopy

Yasui, Akira; Fujimori, Shinichi; Kawasaki, Ikuto; Okane, Tetsuo; Takeda, Yukiharu; Saito, Yuji; Yamagami, Hiroshi; Sekiyama, Akira*; Settai, Rikio*; Matsuda, Tatsuma; et al.

Physical Review B, 84(19), p.195121_1 - 195121_6, 2011/11

 Times Cited Count:7 Percentile:59.49(Materials Science, Multidisciplinary)

We have measured three-dimensional band structure and Fermi surfaces (FSs) of YbCu$$_2$$Ge$$_2$$, which has recently become recognized as a nearly divalent Yb-based compound, by using soft X-ray angle-resolved photoemission spectroscopy. We clarified that the bands with finite Yb 4$$f$$ contribution cross the Fermi level and are slightly involved in the formation of the FSs, in line with the valence-fluctuating state of YbCu$$_2$$Ge$$_2$$. The obtained valence-band dispersions and the FSs are well explained by a relativistic band-structure calculation based on a local-density-approximation (LDA). These results suggest that the LDA calculation is a good starting point for understanding of the electronic state of YbCu$$_2$$Ge$$_2$$ as well as nearly divalent Yb-based compounds.

Journal Articles

Soft X-ray angle-resolved photoemission study of YbCu$$_2$$Ge$$_2$$

Yasui, Akira; Fujimori, Shinichi; Kawasaki, Ikuto; Okane, Tetsuo; Takeda, Yukiharu; Saito, Yuji; Yamagami, Hiroshi; Sekiyama, Akira*; Settai, Rikio*; Matsuda, Tatsuma; et al.

Journal of Physics; Conference Series, 273, p.012067_1 - 012067_4, 2011/02

 Times Cited Count:2 Percentile:38.07

Soft X-ray photoemission spectroscopies have been performed on YbCu$$_2$$Ge$$_2$$, which is thought to be a Yb divalent system, to investigate its bulk electronic structure including Yb 4$$f$$ electrons. Small but finite Yb$$^{3+}$$ multiplet peaks were found at 6$$sim$$12 eV in the angle-integrated spectrum, suggesting that it is a valence fluctuation compound. An "anti-crossing" Yb 4$$f$$ bands with conduction bands were observed in the angle-resolved spectrum. This is the evidence that the Yb 4$$f$$ electrons form a band state through the hybridization with Ge 4$$p$$ and Cu 3$$d$$ electrons.

Journal Articles

Magnetic and superconducting properties of CeRhGe$$_2$$ and CePtSi$$_2$$

Hirose, Yusuke*; Nishimura, Naoto*; Honda, Fuminori*; Sugiyama, Kiyohiro*; Hagiwara, Masayuki*; Kindo, Koichi*; Takeuchi, Tetsuya*; Yamamoto, Etsuji; Haga, Yoshinori; Matsuura, Masato*; et al.

Journal of the Physical Society of Japan, 80(2), p.024711_1 - 024711_12, 2011/02

 Times Cited Count:5 Percentile:54.24(Physics, Multidisciplinary)

Journal Articles

Observation of itinerant Ce 4$$f$$ electronic states in CeIrSi$$_3$$ studied by angle-resolved Ce 3$$drightarrow 4f$$ resonance photoemission spectroscopy

Okochi, Takuo*; Toshimitsu, Takafumi*; Yamagami, Hiroshi; Fujimori, Shinichi; Yasui, Akira; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi; Miyauchi, Yuichiro*; et al.

Journal of the Physical Society of Japan, 78(8), p.084802_1 - 084802_6, 2009/08

 Times Cited Count:8 Percentile:45.17(Physics, Multidisciplinary)

We have applied angle-resolved Ce 3$$d{rightarrow}$$4$$f$$ resonance photoemission spectroscopy to the non-centrosymmetric pressure-induced superconductor CeIrSi$$_3$$ and obtained the 4$$f$$ band-structure and Fermi surfaces. We have found that the Ce 4$$f$$ states are located mainly near the Fermi level and that the photoemission intensity derived from the dispersive conduction bands across the Fermi level shows considerable resonant enhancement. In addition, the band structure and Fermi surfaces of CeIrSi$$_3$$ are different from those of the non-$$f$$ reference compound, LaIrSi$$_3$$ and the difference is well explained by the band structure calculated within the local density approximation (LDA). These results strongly suggest that the Ce 4$$f$$ electrons in CeIrSi$$_3$$ are well hybridized with conduction bands and form itinerant electronic states.

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