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Journal Articles

Topological characterization of classical waves; The Topological origin of magnetostatic surface spin waves

Yamamoto, Kei; Thiang, G. C.*; Pirro, P.*; Kim, K.-W.*; Everschor-Sitte, K.*; Saito, Eiji*

Physical Review Letters, 122(21), p.217201_1 - 217201_5, 2019/05

JAEA Reports

Annual report on the environmental radiation monitoring around the Tokai Reprocessing Plant FY 2017

Nakano, Masanao; Fujita, Hiroki; Mizutani, Tomoko; Nemoto, Masashi; Tobita, Keiji; Kono, Takahiko; Hosomi, Kenji; Hokama, Tomonori; Nishimura, Tomohiro; Matsubara, Natsumi; et al.

JAEA-Review 2018-025, 171 Pages, 2019/02

JAEA-Review-2018-025.pdf:3.81MB

Environmental radiation monitoring around the Tokai Reprocessing Plant has been performed by the Nuclear Fuel Cycle Engineering Laboratories, based on "Safety Regulations for the Reprocessing Plant of Japan Atomic Energy Agency, Chapter IV - Environmental Monitoring". This annual report presents the results of the environmental monitoring and the dose estimation to the hypothetical inhabitant due to the radioactivity discharged from the plant to the atmosphere and the sea during April 2016 to March 2017. In this report, some data include the influence of the accidental release from the Fukushima Daiichi Nuclear Power Station of Electric Power Company Holdings, Inc. in March 2011. Appendices present comprehensive information, such as monitoring programs, monitoring methods, monitoring results and their trends, meteorological data and discharged radioactive wastes. In addition, the data which were influenced by the accidental release and were exceeded the normal range of fluctuation in the monitoring, were evaluated.

Journal Articles

Development of remote sensing technique using radiation resistant optical fibers under high-radiation environment

Ito, Chikara; Naito, Hiroyuki; Ishikawa, Takashi; Ito, Keisuke; Wakaida, Ikuo

JPS Conference Proceedings (Internet), 24, p.011038_1 - 011038_6, 2019/01

A high-radiation resistant optical fiber has been developed in order to investigate the interiors of the reactor pressure vessels and the primary containment vessels at the Fukushima Daiichi Nuclear Power Station. The tentative dose rate in the reactor pressure vessels is assumed to be up to 1 kGy/h. We developed a radiation resistant optical fiber consisting of a 1000 ppm hydroxyl doped pure silica core and 4 % fluorine doped pure silica cladding. We attempted to apply the optical fiber to remote imaging technique by means of fiberscope. The number of core image fibers was increased from 2000 to 22000 for practical use. The transmissive rate of infrared images was not affected after irradiation of 1 MGy. No change in the spatial resolution of the view scope by means of image fiber was noted between pre- and post-irradiation. We confirmed the applicability of the probing system, which consists of a view scope using radiation-resistant optical fibers.

Journal Articles

Quantum paramagnet near spin-state transition

Tomiyasu, Keisuke*; Ito, Naoko*; Okazaki, Ryuji*; Takahashi, Yuki*; Onodera, Mitsugi*; Iwasa, Kazuaki*; Nojima, Tsutomu*; Aoyama, Takuya*; Ogushi, Kenya*; Ishikawa, Yoshihisa*; et al.

Advanced Quantum Technologies (Internet), 1(3), p.1800057_1 - 1800057_7, 2018/12

Spin-state transition, also known as spin crossover, plays a key role in diverse systems. In theory, the boundary range between the low- and high-spin states is expected to enrich the transition and give rise to unusual physical states. However, no compound that realizes a nearly degenerate critical range as the ground state without requiring special external conditions has yet been experimentally identified. This study reports that the Sc substitution in LaCoO3 destabilizes its nonmagnetic low-spin state and generates an anomalous paramagnetic state accompanied by the enhancement of transport gap and magneto-lattice-expansion as well as the contraction of Co-O distance with the increase of electron site transfer. These phenomena are not well described by the mixture of conventional low- and high-spin states, but by their quantum superposition occurring on the verge of a spin-state transition.

Journal Articles

Isotope-selective microscale imaging of radioactive Cs without isobaric interferences using sputtered neutral mass spectrometry with two-step resonant ionization employing newly-developed Ti:Sapphire lasers

Sakamoto, Tetsuo*; Morita, Masato*; Kanenari, Keita*; Tomita, Hideki*; Sonnenschein, V.*; Saito, Kosuke*; Ohashi, Masaya*; Kato, Kotaro*; Iguchi, Tetsuo*; Kawai, Toshihide*; et al.

Analytical Sciences, 34(11), p.1265 - 1270, 2018/11

 Percentile:100(Chemistry, Analytical)

Journal Articles

Effect of porosity distribution on two-phase pressure drop in a packed bed

Kurisaki, Tatsuya*; Ito, Daisuke*; Ito, Kei*; Saito, Yasushi*; Imaizumi, Yuya; Matsuba, Kenichi; Kamiyama, Kenji

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 3 Pages, 2018/11

In the evaluation of the in-place cooling which is for the residual core materials in the severe accident of sodium-cooled fast reactors, pressure loss of two-phase flow in debris bed is one of the important factors. Although Lipinski model is already proposed for the pressure loss evaluation, the accuracy would decrease when the porosity is not homogeneous. Thus, experiment to measure the pressure loss in a packed bed of non-homogeneous porosity distribution was conducted, and the Lipinski model was modified dividing the cross section to evaluate the pressure loss in it. As a result, it was confirmed that agreement of the experimental values with the values by modified Lipinski model was better than that with the original Lipinski model.

Journal Articles

Local magnetic states of the weakly ferromagnetic iron-based superconductor Sr$$_{2}$$VFeAsO$$_{3-delta}$$ studied by X-ray magnetic circular dichroism

Horio, Masafumi*; Takeda, Yukiharu; Namiki, Hiromasa*; Katagiri, Takao*; Wakabayashi, Yuki*; Sakamoto, Shoya*; Nonaka, Yosuke*; Shibata, Goro*; Ikeda, Keisuke*; Saito, Yuji; et al.

Journal of the Physical Society of Japan, 87(10), p.105001_1 - 105001_2, 2018/10

 Times Cited Count:1 Percentile:49.95(Physics, Multidisciplinary)

Journal Articles

Cation distribution and magnetic properties in ultrathin (Ni$$_{1-x}$$Co$$_{x}$$)Fe$$_{2}$$O$$_{4}$$ (x=0-1) layers on Si(111) studied by soft X-ray magnetic circular dichroism

Wakabayashi, Yuki*; Nonaka, Yosuke*; Takeda, Yukiharu; Sakamoto, Shoya*; Ikeda, Keisuke*; Chi, Z.*; Shibata, Goro*; Tanaka, Arata*; Saito, Yuji; Yamagami, Hiroshi; et al.

Physical Review Materials (Internet), 2(10), p.104416_1 - 104416_12, 2018/10

Journal Articles

Study on simulation of thermal desorption spectra for a tempered martensitic steel with vacancies induced by hydrogen and strain

Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*

"Suiso Zeika No Kihon Yoin To Tokusei Hyoka" Kenkyukai Hokokusho, p.57 - 61, 2018/09

no abstracts in English

Journal Articles

Estimation of porosity and void fraction profiles in a packed bed of spheres using X-ray radiography

Ito, Daisuke*; Ito, Kei*; Saito, Yasushi*; Aoyagi, Mitsuhiro; Matsuba, Kenichi; Kamiyama, Kenji

Nuclear Engineering and Design, 334, p.90 - 95, 2018/08

 Percentile:100(Nuclear Science & Technology)

Two-phase flow through porous media must be well understood to develop a severe accident analysis code not only for light water reactor but also sodium-cooled fast reactor. When a core disruptive accident occurs in sodium-cooled fast reactor, the fuel inside the core become melted and interacts with the coolant. As a result, gas-liquid two-phase flow will be formed in the debris bed, which may have porous nature depending on the cooling process. In such condition, the local porosity and its distribution are very important to characterize two-phase flow field in the porous media. In this study, X-ray radiography was applied to measure the local porosity in the packed bed of spheres. The radial profiles were estimated from the chordal profiles measured by the X-ray method and compared with the previous porosity model. In addition, the void fraction radial profiles were also obtained in air-water two-phase flow.

Journal Articles

Estimation of mitigation effects of sodium nanofluid for SGTR accidents in SFR

Ichikawa, Kenta*; Kanda, Hironori; Yoshioka, Naoki*; Ara, Kuniaki; Saito, Junichi; Nagai, Keiichi

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 6 Pages, 2018/07

Studies on the suppression of the reactivity of sodium itself have been performed on the basis of the concept of suspended nanoparticles in liquid sodium (sodium nanofluid). According to the experimental and theoretical results of studies for sodium nanofluid, velocity and heat of sodium nanofluid-water reaction are lower than those of the pure sodium-water reaction. The analytical model for the peak temperature of a sodium nanofluid-water reaction jet has been developed in consideration of these suppression effects by the authors. In this paper, the prediction method for mitigation effects for a damage of adjacent tubes in a steam generator tube rupture (SGTR) accidents is arranged by applying this analytical model for the peak temperature of the reaction jet. On the assumption that the sodium nanofluid is used for the secondary coolant of sodium-cooled fast reactor (SFR), mitigation effects under the design-base accident (DBA) condition and the design-extension condition (DEC) of SGTR are estimated by using this method. As a result, there is a possibility to reduce the number of damaged tubes and to suppress the pressure generated by SGTR accidents by using sodium nanofluid in the secondary coolant.

Journal Articles

The Development of method for extinguishing / treating metallic sodium using calcium chloride

Abe, Yuta; Nagai, Keiichi; Maie, Mitsuyoshi*; Nakano, Natsuko*; Kawashima, Yuichi*; Takesue, Naohisa*; Saito, Junichi

Dai-23-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (USB Flash Drive), 5 Pages, 2018/06

no abstracts in English

Journal Articles

Spin colossal magnetoresistance in an antiferromagnetic insulator

Qiu, Z.*; Hou, D.*; Barker, J.*; Yamamoto, Kei; Gomonay, O.*; Saito, Eiji*

Nature Materials, 17(7), p.577 - 580, 2018/05

 Times Cited Count:12 Percentile:3.52(Chemistry, Physical)

Colossal magnetoresistance (CMR) refers to a large change in electrical conductivity induced by a magnetic field in the vicinity of a metal-insulator transition. CMR occurs due to a correlation between the magnetic structure and electron conduction and has inspired extensive studies for decades. Here, in the antiferromagnetic insulator Cr$$_{2}$$O$$_{3}$$, we found a sharp transition between conducting and nonconducting states for spin currents at room temperature. The spin-current transmission changes by two orders of magnitude within a narrow temperature window of 14K around the Neel temperature. The spin conductor-nonconductor transition can be modulated by a magnetic field, giving an isothermal change of spin-current transmission of up to 500%, effectively an on-off switch for spin currents.

Journal Articles

Preferred site occupation of 3$$d$$ atoms in Ni$$_{x}$$Fe$$_{4-x}$$N (${it x}$ = 1 and 3) films revealed by X-ray absorption spectroscopy and magnetic circular dichroism

Takata, Fumiya*; Ito, Keita*; Takeda, Yukiharu; Saito, Yuji; Takanashi, Koki*; Kimura, Akio*; Suemasu, Takashi*

Physical Review Materials (Internet), 2(2), p.024407_1 - 024407_5, 2018/02

Journal Articles

New precise measurement of muonium hyperfine structure interval at J-PARC

Ueno, Yasuhiro*; Aoki, Masaharu*; Fukao, Yoshinori*; Higashi, Yoshitaka*; Higuchi, Takashi*; Iinuma, Hiromi*; Ikedo, Yutaka*; Ishida, Keiichi*; Ito, Takashi; Iwasaki, Masahiko*; et al.

Hyperfine Interactions, 238(1), p.14_1 - 14_6, 2017/11

 Times Cited Count:1 Percentile:17.79

Journal Articles

Experiments on gas entrainment phenomena due to free surface vortex induced by flow passing beside stagnation region

Ezure, Toshiki; Ito, Kei; Tanaka, Masaaki; Ohshima, Hiroyuki; Kameyama, Yuri*

Proceedings of 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17) (USB Flash Drive), 9 Pages, 2017/09

In the design of sodium cooled fast reactors, cover gas entrainment into sodium coolant (gas entrainment) is one of significant thermal hydraulic issues. This paper describes experimental results on surface vortex type gas entrainment which occurs in a share flow area where flow passes beside the stagnation region. In the experiment, the relationship between the free surface dimple shape and the velocity distribution around the free surface vortex was simultaneously grasped under several horizontal and suction velocity conditions by means of visualization measurement and Particle Image Velocimetry measurement. As the results, quantitative relationships among circulation, vertical velocity gradient and the gas core length were obtained in time-trends as fundamental data to develop the evaluation method of gas entrainment. Furthermore, it was confirmed that the evaluation method based on a vortex model, was an effective way to evaluate gas entrainment.

Journal Articles

Reduction and resource recycling of high-level radioactive wastes through nuclear transmutation; Isolation techniques of Pd, Zr, Se and Cs in simulated high level radioactive waste using solvent extraction

Sasaki, Yuji; Morita, Keisuke; Ito, Keisuke; Suzuki, Shinichi; Shiwaku, Hideaki; Takahashi, Yuya*; Kaneko, Masaaki*; Omori, Takashi*; Asano, Kazuhito*

Proceedings of International Nuclear Fuel Cycle Conference (GLOBAL 2017) (USB Flash Drive), 4 Pages, 2017/09

no abstracts in English

Journal Articles

Structure of the magnetic excitations in the spin-1/2 triangular-lattice Heisenberg antiferromagnet Ba$$_{3}$$CoSb$$_{2}$$O$$_{9}$$

Ito, Saya*; Kurita, Nubuyuki*; Tanaka, Hidekazu*; Kawamura, Seiko; Nakajima, Kenji; Ito, Shinichi*; Kuwahara, Keitaro*; Kakurai, Kazuhisa*

Nature Communications (Internet), 8, p.235_1 - 235_6, 2017/08

 Times Cited Count:11 Percentile:19.69(Multidisciplinary Sciences)

Journal Articles

Extraction and separation of Se, Zr, Pd, and Cs including long-lived radionuclides

Sasaki, Yuji; Morita, Keisuke; Suzuki, Shinichi; Shiwaku, Hideaki; Ito, Keisuke; Takahashi, Yuya*; Kaneko, Masaaki*

Solvent Extraction Research and Development, Japan, 24(2), p.113 - 122, 2017/06

The solvent extraction of Se, Zr, Pd, and Cs from nitric acid into 1-octanol (OC) and dodecane has been performed. These elements include long-lived radionuclides in spent nuclear fuels, so a simple separation method is indispensable for the development of the treatment of high-level liquid radioactive waste. It was found that Se can be extracted using phenylenediamine, Zr can be extracted using tetraoctyl diglycolamide and di-2-ethylhexyl phosphoric acid, and Pd can be extracted using (methylimino)bis(dioctylacetamide) and hexaoctylnitrilotriacetamide. These elements can be recovered in over 90% yield by these extractants from nitric acid into OC. A distribution ratio of Cs of greater than 1 can be obtained using di-t-butyldibenzo-18-crown-6. It is clear that 90% recovery of Cs can be achieved using an extraction solvent with ten times the volume of the aqueous phase.

Journal Articles

Coupling the advection-dispersion equation with fully kinetic reversible/irreversible sorption terms to model radiocesium soil profiles in Fukushima Prefecture

Kurikami, Hiroshi; Malins, A.; Takeishi, Minoru; Saito, Kimiaki; Iijima, Kazuki

Journal of Environmental Radioactivity, 171, p.99 - 109, 2017/05

 Times Cited Count:2 Percentile:69.03(Environmental Sciences)

A modified diffusion-sorption-fixation model (mDSF) is proposed to describe the vertical migration of radiocesium in soils following fallout. The model introduces kinetics for reversible sites, meaning that the exponential-shape radiocesium distribution can be reproduced immediately following fallout. The initial relaxation mass depth of the distribution is determined by the diffusion length, which depends on the distribution coefficient, sorption rate and dispersion coefficient. The model captures the long tails of the radiocesium distribution at large depths. These tails are caused by different rates for kinetic sorption and desorption.

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