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Journal Articles

A Comparative study of sampling techniques for dynamic probabilistic risk assessment of nuclear power plants

Kubo, Kotaro; Zheng, X.; Tanaka, Yoichi; Tamaki, Hitoshi; Sugiyama, Tomoyuki; Jang, S.*; Takata, Takashi*; Yamaguchi, Akira*

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.308 - 315, 2020/10

Dynamic probabilistic risk assessment (PRA) is a method for improving the realism and completeness of conventional PRA. However, enormous calculation costs are incurred by these improvements. One solution is to select an appropriate sampling method. In this paper, we applied the Monte Carlo, Latin hypercube, grid-point, and quasi-Monte Carlo sampling methods to the dynamic PRA of a simplified accident sequence and compared the results for each method. Quasi-Monte Carlo sampling was found to be the most effective method in this case.

Journal Articles

Formation and mobility of soil organic carbon in a buried humic horizon of a volcanic ash soil

Wijesinghe, J. N.*; Koarashi, Jun; Atarashi-Andoh, Mariko; Kokubu, Yoko; Yamaguchi, Noriko*; Sase, Takashi*; Hosono, Mamoru*; Inoue, Yuzuru*; Mori, Yuki*; Hiradate, Shuntaro*

Geoderma, 374, p.114417_1 - 114417_10, 2020/09

 Times Cited Count:0 Percentile:100(Soil Science)

Journal Articles

Neutron diffraction study on martensitic transformation under compressive stress in an ordered Fe$$_{3}$$Pt

Fukuda, Takashi*; Yamaguchi, Takashi*; Kakeshita, Tomoyuki*; Harjo, S.; Nakamoto, Tatsushi*

Journal of Applied Physics, 126(2), p.025107_1 - 025107_6, 2019/07

 Times Cited Count:1 Percentile:74.19(Physics, Applied)

Journal Articles

Development of semi-implicit particle method for simulating sodium-water chemical reaction

Li, J.*; Jang, S.*; Yamaguchi, Akira*; Uchibori, Akihiro; Takata, Takashi; Ohshima, Hiroyuki

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 4 Pages, 2018/11

The sodium-water reaction model is developed in particle methods. Two chemical reaction model, called surface reaction model and gas-phase reaction model are developed in the particle method. Validation on the case of vapor injection into liquid water is conducted and good consistency of jet velocity evolution along jet trajectory is obtained. Finally, sodium-water chemical reaction in a configuration of multiple tube bundles is simulated. Jet velocity, water vapor fraction and temperature are investigated and reasonable results are observed, which presents promising future of this methodology.

Journal Articles

Polarized neutrons

Hiraka, Haruhiro*; Yamaguchi, Yasuo*; Maruyama, Ryuji; Oku, Takayuki; Ino, Takashi*

Hamon, 28(3), p.144 - 149, 2018/08

no abstracts in English

Journal Articles

Evidence for momentum-dependent heavy fermionic electronic structures; Soft X-ray ARPES for the superconductor CeNi$$_{2}$$Ge$$_{2}$$ in the normal state

Nakatani, Yasuhiro*; Aratani, Hidekazu*; Fujiwara, Hidenori*; Mori, Takeo*; Tsuruta, Atsushi*; Tachibana, Shoichi*; Yamaguchi, Takashi*; Kiss, Takayuki*; Yamasaki, Atsushi*; Yasui, Akira*; et al.

Physical Review B, 97(11), p.115160_1 - 115160_7, 2018/03

AA2018-0003.pdf:1.65MB

 Times Cited Count:1 Percentile:87.28(Materials Science, Multidisciplinary)

Journal Articles

Numerical study on modeling of liquid film flow under countercurrent flow limitation in volume of fluid method

Watanabe, Taro*; Takata, Takashi; Yamaguchi, Akira*

Nuclear Engineering and Design, 313, p.447 - 457, 2017/03

 Times Cited Count:1 Percentile:79.72(Nuclear Science & Technology)

Countercurrent flow limitation (CCFL) in a heat transfer tube at a steam generator (SG) of pressurized water reactor (PWR) is one of the important issues on the core cooling under a loss of coolant accident(LOCA). In order to improve the prediction accuracy of the CCFL characteristics in numerical simulations using the volume of fluid (VOF) method with less computational cost, a thin liquid film flow in a countercurrent flow is modeled independently and is coupled with the VOF method. Then, we have carried out numerical simulations of a countercurrent flow in a vertical tube so as to investigate the CCFL characteristics and compare them with the previous experimental results. As a result, it has been concluded that the effect of liquid film entrainment by upward gas flux will cause the difference in the experiments.

Journal Articles

Circular dichroism in resonant angle-resolved photoemission spectra of LaNi$$_{2}$$Ge$$_{2}$$

Nakatani, Yasuhiro*; Fujiwara, Hidenori*; Aratani, Hidekazu*; Mori, Takeo*; Tachibana, Shoichi*; Yamaguchi, Takashi*; Kiss, Takayuki*; Yamasaki, Atsushi*; Yasui, Akira*; Yamagami, Hiroshi*; et al.

Journal of Electron Spectroscopy and Related Phenomena, 220, p.50 - 53, 2017/01

 Times Cited Count:1 Percentile:83.16(Spectroscopy)

We report the soft X-ray angle-resolved photoemission study for LaNi$$_{2}$$Ge$$_{2}$$ to reveal the electronic structures derived from non-4$$f$$ bands of the heavy fermion compound CeNi$$_{2}$$Ge$$_{2}$$. The photoemission spectra recorded at the La M$$_{4,5}$$ absorption edges clearly show the enhancement of the La 5$$d$$ components in the valence band spectra. The circular dichroism of photoemission spectra reveals the band-dependent dichroic response due to the orbital symmetry.

Journal Articles

Electronic structures of ferromagnetic CeAgSb$$_{2}$$; Soft X-ray absorption, magnetic circular dichroism, and angle-resolved photoemission spectroscopies

Saito, Yuji; Fujiwara, Hidenori*; Yamaguchi, Takashi*; Nakatani, Yasuhiro*; Mori, Takeo*; Fuchimoto, Hiroto*; Kiss, Takayuki*; Yasui, Akira*; Miyawaki, Jun*; Imada, Shin*; et al.

Journal of the Physical Society of Japan, 85(11), p.114713_1 - 114713_7, 2016/11

 Times Cited Count:7 Percentile:38.94(Physics, Multidisciplinary)

We report on the electronic structures of ferromagnetic CeAgSb$$_{2}$$ using soft X-ray absorption (XAS), magnetic circular dichroism (XMCD), and angle-resolved photoemission (ARPES) spectroscopies. The Ce $$M_{4,5}$$ XAS spectra show very small satellite structures, reflecting a strongly localized character of the Ce 4${it f}$ electrons. The linear dichroism effects in the Ce $$M_{4,5}$$ XAS spectra demonstrate the ground-state Ce 4${it f}$ symmetry of $$Gamma$$$$_{6}$$, the spatial distribution of which is directed along the ${it c}$-axis. Nevertheless, ARPES spectra at the Ce 3$$d$$-4$$f$$ resonance show the momentum dependence of the intensity ratio between Ce 4$$f^{1}_{5/2}$$ and 4$$f^{1}_{7/2}$$ peaks in a part of the Brillouin zone, suggesting the non negligible momentum-dependent hybridization effect between the Ce 4${it f}$ and the conduction electrons. This is associated with the moderate mass enhancement in CeAgSb$$_{2}$$.

Journal Articles

Study on self-wastage phenomenon at heat transfer tube in steam generator of sodium-cooled fast reactor with consideration of thermal coupling of fluid and structure

Kojima, Saori*; Uchibori, Akihiro; Takata, Takashi; Ohno, Shuji; Fukuda, Takeshi*; Yamaguchi, Akira*

Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 8 Pages, 2016/11

Analytical evaluation on a self-wastage phenomenon at heat transfer tubes in the steam generator of sodium cooled fast reactors has been performed by using the sodium-water reaction analysis code SERAPHIM. In this study, a fluid-structure thermal coupling model was developed and incorporated in the SERAPHIM code to evaluate heat transfer between the sodium-side reacting flow and the outer surface of the heat transfer tube. The effect of the fluid-structure thermal coupling model on the temperature field was demonstrated through the numerical analyses.

Journal Articles

Dynamic and interactive approach to level 2 PRA using continuous Markov process with Monte Carlo Method

Jang, S.*; Yamaguchi, Akira*; Takata, Takashi

Proceedings of 13th Probabilistic Safety Assessment and Management Conference (PSAM-13) (USB Flash Drive), 11 Pages, 2016/10

The current approach to Level 2 probabilistic risk assessment (PRA) using the conventional event-tree (ET)/fault-tree (FT) methodology requires pre-specifications of event order occurrence and component failure probabilities which may vary significantly in the presence of uncertainties. In the present study, a new methodology is proposed to quantify the level 2 PRA in which the accident progression scenarios are dynamic and interactive with the instantaneous plant state and related phenomena. The accident progression is treated as a continuous Markov process and the transition probabilities are evaluated based on the computation of plant system thermal-hydraulic dynamics. A Monte Carlo method is used to obtain the resultant probability of the radioactive material release scenarios. The methodology is applied to the protected loss of heat sink accident scenario of the level 2 PRA of a generation IV fast reactor.

Journal Articles

Molecular gyrotops with a five-membered heteroaromatic ring; Synthesis, temperature-dependent orientation of dipolar rotors inside the crystal, and its birefringence change

Masuda, Toshiyuki*; Arase, Junko*; Inagaki, Yusuke*; Kawahara, Masatoshi*; Yamaguchi, Kentaro*; Ohara, Takashi; Nakao, Akiko*; Momma, Hiroyuki*; Kwon, E.*; Setaka, Wataru*

Crystal Growth & Design, 16(8), p.4392 - 4401, 2016/08

 Times Cited Count:18 Percentile:10.99(Chemistry, Multidisciplinary)

Journal Articles

Numerical investigation of self-wastage phenomena in steam generator of sodium-cooled fast reactor

Jang, S.*; Takata, Takashi; Yamaguchi, Akira*; Uchibori, Akihiro; Kurihara, Akikazu; Ohshima, Hiroyuki

Proceedings of 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16) (USB Flash Drive), p.4275 - 4288, 2015/08

Numerical analysis of the self-wastage phenomenon was carried out using a multi-dimensional computational code called SERAPHIM. Several steps of numerical analysis were constructed to reproduce transient self-wastage phenomenon caused by Sodium Water Reaction (SWR). Numerical analysis of multiphase flow with chemical reaction near the initial crack is firstly performed. The wastage amount is evaluated based on hypothetical Arrhenius equation by using the temperature and molar concentration of sodium hydroxide. New analytical grid is created by exchanging the solid cells to fluid cells in the reaction based on the wastage amount evaluation. These series of procedure is repeated. The width and the shape of the enlarged crack showed good agreement with the experimental results.

Journal Articles

Utilization status of the electron accelerator and the $$gamma$$-ray irradiation facilities

Agematsu, Takashi; Hanaya, Hiroaki; Yamagata, Ryohei; Seito, Hajime; Nagao, Yuto; Kaneko, Hirohisa; Yamaguchi, Toshiyuki*; Kawashima, Ikuo*; Yagi, Norihiko*; Takagi, Masahide*; et al.

JAEA-Review 2014-050, JAEA Takasaki Annual Report 2013, P. 183, 2015/03

The electron accelerator and the three $$gamma$$-ray irradiation facilities were operated for various research subjects according to the operation plan in FY 2013. The number of research subjects at the electron accelerator and at the $$gamma$$-ray irradiation facilities kept constant from FY 2012. Among these research subjects, 47 and 91 ones respectively performed at the electron accelerator and the $$gamma$$-ray irradiation facilities were relevant to recovery from the Fukushima Daiichi nuclear disaster.

Journal Articles

Operation of the electron accelerator and the $$gamma$$-ray irradiation facilities

Agematsu, Takashi; Hanaya, Hiroaki; Yamagata, Ryohei; Seito, Hajime; Nagao, Yuto; Kaneko, Hirohisa; Yamaguchi, Toshiyuki*; Kawashima, Ikuo*; Yagi, Norihiko*; Takagi, Masahide*; et al.

JAEA-Review 2014-050, JAEA Takasaki Annual Report 2013, P. 182, 2015/03

The electron accelerator and the $$gamma$$-ray irradiation facility have been operated approximately smoothly. The annual operation time in FY 2013 for the electron accelerator, the first, the second cobalt irradiation facility and food irradiation facility are 1242 h, 18,900 h, 11,804 h and 6,587 h, respectively. Typically repairs were next ones. The SF$$_{6}$$ gas withdrawal system was renewed at the electron accelerator. The 600 m$$^{3}$$ water storage tank was installed to keep pool-water for the cobalt facilities maintenance. New pieces of $$^{60}$$Co sources were purchased and loaded to the first and the second irradiation facility. The maintenance check was done for the food irradiation facility.

Journal Articles

Experimental and numerical reaction analysis on sodium-water chemical reaction field

Deguchi, Yoshihiro*; Takata, Takashi*; Yamaguchi, Akira*; Kikuchi, Shin; Ohshima, Hiroyuki

Mechanical Engineering Journal (Internet), 2(1), p.14-00029_1 - 14-00029_11, 2015/02

In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes. This process ends up damages on the heat transport equipment in the SFR. Therefore, the study on sodium-water chemical reactions is of paramount importance for security reasons. This study aims to clarify the sodium-water reaction mechanisms using an elementary reaction analysis. From analytical results, the main reaction was Na + H$$_{2}$$O = NaOH + H at gas-phase reaction.

Journal Articles

Long-term observation of fog chemistry and estimation of fog water and nitrogen input via fog water deposition at a mountainous site in Hokkaido, Japan

Yamaguchi, Takashi*; Katata, Genki; Noguchi, Izumi*; Sakai, Shigekatsu*; Watanabe, Yoko*; Uematsu, Mitsuo*; Furutani, Hiroshi*

Atmospheric Research, 151, p.82 - 92, 2015/01

 Times Cited Count:10 Percentile:57.56(Meteorology & Atmospheric Sciences)

To evaluate water and nitrogen input via fog water deposition, fog chemistry and deposition around a crater lake (Mashu) in northern Japan were investigated in the growing seasons of trees in 2006-2012. The fog samples were collected using an active fog collector and droplet size distribution was measured by a droplet size spectrometer. Compared to previous iterature of exposure experiments of acid mist on plants, fog acidity in this study did not seem to injure plant leaves. The visibility (VIS)-liquid water content of fog (LWC) relationship differed between summer and autumn. Fog water deposition was calculated from LWC empirically derived from past VIS data and deposition velocity estimated using wind speed and vegetation parameters. The water and nitrogen inputs via fog water deposition accumulated for each growing season were estimated as 107-161 mm and 20-41 meq m$$^{-2}$$, respectively.

Journal Articles

Numerical study on inert gas behavior in fast reactor primary coolant system; Inert gas accumulation at HPP and consideration of gas elimination system

Takata, Takashi*; Konaka, Yuji*; Yamaguchi, Akira*; Ito, Kei; Ohno, Shuji; Ohshima, Hiroyuki

Proceedings of 9th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-9) (CD-ROM), 7 Pages, 2014/11

In this paper, a model of bubble transport at entrance nozzle has been developed based on theoretical and computational methods. For this purpose, a three-dimensional analysis of dynamic bubbles behavior has been carried out by using one-way bubble tracking method which is specified to a bubble flow under a low void fraction. A commercial CFD tool, FLUENT Ver. 6.3.26 is used for three-dimensional flow field analyses. Then the gas accumulation at a high pressure plenum (HPP) of sodium-cooled fast rector has been quantitatively-assessed by implementing the developed model in SYRENA code. Furthermore, gas elimination (bubble removal) systems have been considered and the quantitatively-assessment has been carried out in order to investigate the effect of each measure to the accumulation of gas at the HPP.

Journal Articles

Numerical quantification of self-wastage phenomena in sodium-cooled fast reactor

Jang, S.*; Takata, Takashi; Yamaguchi, Akira*; Uchibori, Akihiro; Kurihara, Akikazu; Ohshima, Hiroyuki

Proceedings of 9th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-9) (CD-ROM), 8 Pages, 2014/11

Numerical quantification of the self-wastage phenomenon has been carried out using a multi-dimensional computational code: SERAPHIM. The width of the completely enlarged crack was investigated in this study. Several steps of numerical calculations were devised to reproduce transient self-wastage phenomenon caused by Sodium Water Reaction (SWR). In the analyses, 2-dimensional calculation was carried out to obtained thermal hydraulic properties in the reaction zone. The wastage amount was evaluated based on hypothetical Arrhenius equation by using the temperature and molar concentration of Sodium hydroxide. New analytical grid was created by exchanging the solid cells to fluid cells in the reaction based on the wastage amount evaluation. These series of procedure have been repeated. The width and the shape of the enlarged crack showed good agreement with the experimental results.

Journal Articles

Aerosol deposition and the behavior of aerosol particles deposited on the foliar surface of trees in cool-temperate forests in Hokkaido

Watanabe, Yoko*; Yamaguchi, Takashi*; Katata, Genki

Earozoru Kenkyu, 29(S1), p.176 - 182, 2014/04

The concentrations of atmospheric aerosols were measured by filter pack method from spring to autumn in eastern Hokkaido. Furthermore, the components of fog water collected by an active string fog collector and the diameter of fog droplets by fog monitor were analyzed in the same area. The concentrations of SO$$_4^{2-}$$ and NH$$^{4+}$$ in aerosols were highest during the growing period of forest trees in eastern Hokkaido. Mean diameter of fog droplets was larger than that in other areas. This suggests that fog deposition velocity would increase in this area. On the other hand, the shape and components of aerosols deposited on the surfaces of leaves of white birch trees were observed by SEM-EDX. Soil particles and particles including S, and NaCl particles were found. Washing treatment of the leaf surfaces of white birch showed that many particles deposited on the leaf surface are possible to be washed with raindrops.

249 (Records 1-20 displayed on this page)