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Journal Articles

Distribution and fate of $$^{129}$$I in the seabed sediment off Fukushima

Otosaka, Shigeyoshi; Sato, Yuhi*; Suzuki, Takashi; Kuwabara, Jun; Nakanishi, Takahiro

Journal of Environmental Radioactivity, 192, p.208 - 218, 2018/12

 Percentile:100(Environmental Sciences)

From August 2011 to October 2013, the concentration of iodine-129 ($$^{129}$$I) in the seabed sediment collected from 26 stations located within 160 km from the Fukushima Daiichi Nuclear Power Plant was estimated. The concentrations of $$^{129}$$I in seabed sediment off Fukushima in 2011 ranged between 0.02 and 0.45 mBq/kg. Although iodine is a biophilic element, the accident-derived radioiodine negligibly affects the benthic ecosystem. Until October 2013, a slightly increased activity of $$^{129}$$I in the surface sediment in the shelf-edge region (bottom depth: 200-400 m) was observed. The increase of the $$^{129}$$I concentrations in the shelf-edge sediments was affected by the (1) transport of $$^{129}$$I-bound particles from the land through rivers and (2) re-deposition of $$^{129}$$I desorbed from the contaminated coastal sediment to the shelf-edge sediments, which were considered to be dominant processes.

Journal Articles

Standardization of stepping motor control system in J-PARC Linac and RCS

Takahashi, Hiroki; Sawabe, Yuki; Suzuki, Yasuo*; Suzuki, Takahiro*; Kawase, Masato*

Proceedings of 15th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1105 - 1108, 2018/08

J-PARC Linac and RCS Profile Monitor and etc. are devices consisting of moving parts and driving part. In these devices, in order to move the movable part to an appropriate position without damaging it, proper control of the stepping motor used for the driving part is important. Many of the control system hardware of these drive units are used since the early days of J-PARC operation, and there is concern about malfunctions due to aging. In addition, since both VME and PLC are used as controllers, it is necessary to prepare spare parts of both control equipment in maintenance and management. Besides, the control logic differs depending on the kind of controller, VME or PLC. Therefore, maintainability of both hardware and software is an important issue. Then, we decided to proceed with updating the drive unit control system which standardized control system hardware and software. In this paper, the standardization of stepping motor control system in Linac and RCS is detailed.

Journal Articles

Examination of evaluation method for fault activity based on morphological observation of fault planes

Tanaka, Yoshihiro*; Kametaka, Masao*; Okazaki, Kazuhiko*; Suzuki, Kazushige*; Seshimo, Kazuyoshi; Aoki, Kazuhiro; Shimada, Koji; Watanabe, Takahiro; Nakayama, Kazuhiko

Oyo Chishitsu, 59(1), p.13 - 27, 2018/04

This paper aims to develop a methodology for understanding the fault activity by observing exposed fault planes without covering younger strata. Based on purpose, faults developed in relatively homogeneous rocks such granitic types are investigated as follows; Gosuke Dam upstream outcrop of Gosukebashi Fault and Funasaka-nishi outcrop of Rokkou Fault were selected for the study of an active fault; and K-3 outcrop of Rokkou Houraikyo Fault was chosen for a non-active fault.

Journal Articles

Year-round variations in the fluvial transport load of particulate $$^{137}$$Cs in a forested catchment affected by the Fukushima Daiichi Nuclear Power Plant accident

Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 310(2), p.679 - 693, 2016/11

AA2015-0821.pdf:3.78MB

 Times Cited Count:5 Percentile:23.48(Chemistry, Analytical)

Particulate $$^{137}$$Cs in stream water was collected continuously for two years in order to assess the long-term trend of the $$^{137}$$Cs discharge from the forest environment. Sampling was conducted from December 2011 to December 2013 in a mountainous stream, which received the $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Plant accident. A seasonal increase in fluvial transport load of particulate $$^{137}$$Cs associated with suspended solids (SS) was observed in August and September when rainfall was abundant. The particulate $$^{137}$$Cs concentration decreased at a faster rate than the rate due to radioactive decay. This decrease might be resulted from redistribution of the easily eroded and polluted soil surface due to heavy rain events such as typhoons. These findings indicate that the particulate $$^{137}$$Cs load was subject to the inter-annual variations in rainfalls, and decreased gradually over a long period of time due to a decrease in $$^{137}$$Cs concentration in SS.

Journal Articles

Development of a control system at a 3 MeV linac in J-PARC

Sawabe, Yuki*; Ishiyama, Tatsuya; Takahashi, Daisuke; Kato, Yuko; Suzuki, Takahiro*; Hirano, Koichiro; Takei, Hayanori; Meigo, Shinichiro; Kikuzawa, Nobuhiro; Hayashi, Naoki

Proceedings of 13th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.647 - 651, 2016/11

In the J-PARC, a 3 MeV linac has been developed for the tests of beam scraper irradiation and charge exchange by high-power laser. To accomplish tests efficiently and safely, the control system for 3 MeV was designed and developed, and this system consists of four subsystems, personal protection system, machine protection system, timing system, and remote control system using the EPICS. In this paper, the details of control system for a 3 MeV linac are presented.

Journal Articles

Development of inspection and repair techniques for reactor vessel of experimental fast reactor "Joyo"; Replacement of upper core structure

Takamatsu, Misao; Kawahara, Hirotaka; Ito, Hiromichi; Ushiki, Hiroshi; Suzuki, Nobuhiro; Sasaki, Jun; Ota, Katsu; Okuda, Eiji; Kobayashi, Tetsuhiko; Nagai, Akinori; et al.

Nippon Genshiryoku Gakkai Wabun Rombunshi, 15(1), p.32 - 42, 2016/03

In the experimental fast reactor Joyo, it was confirmed that the top of the irradiation test sub-assembly of "MARICO-2" (material testing rig with temperature control) had been broken and bent onto the in-vessel storage rack as an obstacle and had damaged the upper core structure (UCS). This paper describes the results of the in-vessel repair techniques for UCS replacement, which are developed in Joyo. UCS replacement was successfully completed in 2014. In-vessel repair techniques for sodium cooled fast reactors (SFRs) are important in confirming its safety and integrity. In order to secure the reliability of these techniques, it was necessary to demonstrate the performance under the actual reactor environment with high temperature, high radiation dose and remained sodium. The experience and knowledge gained in UCS replacement provides valuable insights into further improvements for In-vessel repair techniques in SFRs.

Journal Articles

Fluvial discharges of particulate and dissolved radiocesium from a forest and its monthly trend

Muto, Kotomi; Atarashi-Andoh, Mariko; Takeuchi, Erina; Nishimura, Shusaku; Koarashi, Jun; Tsuzuki, Katsunori; Nakanishi, Takahiro; Matsunaga, Takeshi

KEK Proceedings 2015-4, p.252 - 257, 2015/11

As a result of the Fukushima Daiichi Nuclear Power Plant accident, a large amount of radiocesium released into the atmosphere was deposited in forests. This study estimated the monthly trend in the fluvial discharges of radiocesium from a forest. The study site was a forested catchment in Kitaibaraki City. Radiocesium in river water was collected with a filtration system as both particulate and dissolved components. Filters and columns including dissolved Cs absorbent were replaced every month. The collected suspended solids were sieved into 2000-3000 $$mu$$m, 500-2000 $$mu$$m, 75-500 $$mu$$m, and $$<$$75 $$mu$$m fractions. The $$^{137}$$Cs concentrations in the samples were measured using $$gamma$$-ray spectrometry with Ge semiconductor detectors. The $$^{137}$$Cs discharge increased with the river water discharge. The particulate $$^{137}$$Cs discharge was dominant in both 2013 and 2014. The $$^{137}$$Cs discharge rate of the dissolved component increased in winter, when the river water discharge decreased.

Journal Articles

SiC coating as hydrogen permeation reduction and oxidation resistance for nuclear fuel cladding

Usui, Takahiro*; Sawada, Akihiko; Amaya, Masaki; Suzuki, Akihiro*; Chikada, Takumi*; Terai, Takayuki*

Journal of Nuclear Science and Technology, 52(10), p.1318 - 1322, 2015/10

 Times Cited Count:9 Percentile:15.14(Nuclear Science & Technology)

SiC coating is one of countermeasures for the prevention of oxidation and hydrogen embrittlement of fuel claddings because SiC has high resistance of oxidation and hydrogen permeation. Hydrogen permeation and oxidation experiments for the cladding materials with SiC coatings were conducted in unirradiated conditions. The sputtering method was employed to make SiC coatings. In the hydrogen permeation experiment, SUS316 was used as a base material of the coating. SUS316 with SiC coatings showed hydrogen permeation reduction by one order of magnitude. In the oxidation experiments, Zry-4 and SUS316 were used as base materials of the coatings. The weight gain of the Zry-4 specimens with a SiC coating decreased by about one-fifth compared to the uncoated ones. This phenomenon was observed for SUS316 at 750 $$^{circ}$$C as well. The peel-off of the coating was observed in some experiments, and it is considered that the peel-off was caused by the difference of the thermal expansions between coatings and base materials. Thicker coatings showed better oxidation resistance, but thinner coatings showed more tolerance of peel-off.

Journal Articles

Report on ITPA (International Tokamak Physics Activity) meeting, 49

Shinohara, Koji; Isayama, Akihiko; Suzuki, Takahiro; Yoshida, Maiko

Purazuma, Kaku Yugo Gakkai-Shi, 91(7), p.494 - 496, 2015/07

AA2015-0141.pdf:0.38MB

no abstracts in English

Journal Articles

Assessment of the accuracy of plasma shape reconstruction by the Cauchy condition surface method in JT-60SA

Miyata, Yoshiaki; Suzuki, Takahiro; Takechi, Manabu; Urano, Hajime; Ide, Shunsuke

Review of Scientific Instruments, 86(7), p.073511_1 - 073511_13, 2015/07

 Times Cited Count:2 Percentile:79.6(Instruments & Instrumentation)

It is essential for a stable plasma equilibrium control to reconstruct an accurate plasma boundary in tokamak devices. Cauchy Condition Surface (CCS) method is a numerical approach to calculate the spatial distribution of the magnetic flux outside a hypothetical plasma surface and reconstruct the plasma boundary from the magnetic measurements located outside the plasma. It is found that the optimum number of unknown parameters and shape of the CCS for minimizing errors in the reconstructed plasma shape increase in proportion to the plasma size. It is shown that the accuracy of the plasma shape reconstruction greatly improves by using the optimum number of unknown parameters. The assessment of accuracy of plasma shape reconstruction by CCS method in JT-60SA is reported.

Journal Articles

Advance in integrated modelling towards prediction and control of JT-60SA plasmas

Hayashi, Nobuhiko; Honda, Mitsuru; Shiraishi, Junya; Miyata, Yoshiaki; Wakatsuki, Takuma; Hoshino, Kazuo; Toma, Mitsunori; Suzuki, Takahiro; Urano, Hajime; Shimizu, Katsuhiro; et al.

Europhysics Conference Abstracts (Internet), 39E, p.P5.145_1 - P5.145_4, 2015/06

Journal Articles

Current ramp-up scenario with reduced central solenoid magnetic flux consumption in JT-60SA

Wakatsuki, Takuma; Suzuki, Takahiro; Hayashi, Nobuhiko; Shiraishi, Junya; Ide, Shunsuke; Takase, Yuichi*

Europhysics Conference Abstracts (Internet), 39E, p.P5.144_1 - P5.144_4, 2015/06

Journal Articles

Simulation of plasma current ramp-up with reduced magnetic flux consumption in JT-60SA

Wakatsuki, Takuma; Suzuki, Takahiro; Hayashi, Nobuhiko; Shiraishi, Junya; Ide, Shunsuke; Takase, Yuichi*

Plasma Physics and Controlled Fusion, 57(6), p.065005_1 - 065005_12, 2015/06

 Times Cited Count:6 Percentile:48.28(Physics, Fluids & Plasmas)

Journal Articles

Replacement of upper core structure in experimental fast reactor Joyo, 1; Existing damaged upper core structure jack-up test

Ito, Hiromichi; Suzuki, Nobuhiro; Kobayashi, Tetsuhiko; Kawahara, Hirotaka; Nagai, Akinori; Sakao, Ryuta*; Murata, Chotaro*; Tanaka, Junya*; Matsusaka, Yasunori*; Tatsuno, Takahiro*

Proceedings of 2015 International Congress on Advances in Nuclear Power Plants (ICAPP 2015) (CD-ROM), p.1058 - 1067, 2015/05

In the experimental fast reactor Joyo (Sodium-cooled Fast Reactor (SFR)), it was confirmed that the top of the irradiation test sub-assembly had bent onto the in-vessel storage rack as an obstacle and had damaged the upper core structure (UCS). There is a risk of deformation of the UCS and guide sleeve (GS) caused by interference between them unless inclination is controlled precisely. To mitigate the risk, special jack-up equipment for applying three-point suspension was developed. The existing damaged UCS (ed-UCS) jack-up test using the jack-up equipment was conducted on May 7, 2014. As a result of this test, it was confirmed that the ed-UCS could be successfully jacked-up to 1000 mm without consequent overload. The experience and knowledge gained in the ed-UCS jack-up test provides valuable insights and prospects not only for UCS replacement but also for further improving and verifying repair techniques in SFRs.

JAEA Reports

Enhancement of the methodology of repository design and post-closure performance assessment for preliminary investigation stage, 3; Progress report on NUMO-JAEA collaborative research in FY2013 (Joint research)

Shibata, Masahiro; Sawada, Atsushi; Tachi, Yukio; Makino, Hitoshi; Wakasugi, Keiichiro; Mitsui, Seiichiro; Kitamura, Akira; Yoshikawa, Hideki; Oda, Chie; Ishidera, Takamitsu; et al.

JAEA-Research 2014-030, 457 Pages, 2015/03

JAEA-Research-2014-030.pdf:199.23MB

JAEA and NUMO have conducted a collaborative research work which is designed to enhance the methodology of repository design and post-closure performance assessment in preliminary investigation stage. With regard to (1) study on rock suitability in terms of hydrology, based on some examples of developing method of hydro-geological structure model, acquired knowledge are arranged using the tree diagram, and model uncertainty and its influence on the evaluation items were discussed. With regard to (2) study on scenario development, the developed approach for "defining conditions" has been reevaluated and improved from practical viewpoints. In addition, the uncertainty evaluation for the effect of use of cementitious material, as well as glass dissolution model, was conducted with analytical evaluation. With regard to (3) study on setting radionuclide migration parameters, based on survey of precedent procedures, multiple-approach for distribution coefficient of rocks was established, and the adequacy of the approach was confirmed though its application to sedimentary rock and granitic rock. Besides, an approach for solubility setting was developed including the procedure of selection of solubility limiting solid phase. The adequacy of the approach was confirmed though its application to key radionuclides.

Journal Articles

A Passive collection system for whole size fractions in river suspended solids

Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; Nagao, Seiya*

Journal of Radioanalytical and Nuclear Chemistry, 303(2), p.1291 - 1295, 2015/02

 Times Cited Count:3 Percentile:53.75(Chemistry, Analytical)

An innovative, yet simple method for the passive collection of radioactive materials in river water has been developed and validated. The method employes large filter vessels, containing multiple cartridge filters. River water is led to the system naturally using a drop of the riverbed by hose from upstream. This method makes long-term, unmanned monitoring possible. In addition to regular radioactivity analyses, this method provides an opportunity for the characterization of suspended materials based on its ample collection quantities (more than several tens of grams). This method may also be applicable to sediment-bound chemicals.

Journal Articles

High-power test of annular-ring coupled structures for the J-PARC linac energy upgrade

Tamura, Jun; Ao, Hiroyuki; Nemoto, Yasuo; Asano, Hiroyuki*; Suzuki, Takahiro*

Journal of the Korean Physical Society, 66(3), p.399 - 404, 2015/02

 Percentile:100(Physics, Multidisciplinary)

ACSs are going to increase the beam energy of the J-PARC linac from 181 to 400 MeV. The 2011 Tohoku earthquake damaged the J-PARC facilities and the cavity conditioning was interrupted for two years. After the restoration of the facility, the two ACS cavities (M01 and M11) were conditioned. They achieved to 15-20% above the designed accelerating field of 4.2 MV/m. Since M01 was conditioned six years ago, the conditioning time required for M01 was drastically reduced from that for the first time. During the high-power operation for M11, which is an unique cavity equipped with a capacitive iris in a waveguide, no significant increase of the temperature and the discharge rate around the capacitive iris was observed. The vacuum pressure was sufficiently low (4$times10$^{-6}$$ Pa) even from the view point of beam loss due to residual gas scattering. The more stable operation can be expected through one-month conditioning before beam commissioning.

Journal Articles

Vertical and lateral transport of particulate radiocesium off Fukushima

Otosaka, Shigeyoshi; Nakanishi, Takahiro; Suzuki, Takashi; Sato, Yuhi; Narita, Hisashi*

Environmental Science & Technology, 48(21), p.12595 - 12602, 2014/11

 Times Cited Count:11 Percentile:45.16(Engineering, Environmental)

From August 2011 to July 2013, a sediment trap was deployed at 100 km east of the Fukushima Daiichi Nuclear Power Plant and sinking particles were collected. Sinking flux of $$^{137}$$Cs decreased over time with seasonal fluctuation. The $$^{137}$$Cs fluxes were mainly affected by two principal modes. One was a rapid sinking of radiocesium-bound particles (moderate mode). This mode was dominant especially in the early post-accident stage, and was presumed to establish the distribution of radiocesium in the offshore seabed. Another was the secondary transport of particles attributed to turbulence near the seabed and was observed in winter (turbulence mode). Although the latter process would not drastically change the distribution of sedimentary radiocesium, attention should be paid as this key process redistributing the accident-derived radiocesium may cumulatively affect the long-term distribution.

Journal Articles

Safety managements of the linear IFMIF/EVEDA prototype accelerator

Takahashi, Hiroki; Maebara, Sunao; Kojima, Toshiyuki; Narita, Takahiro; Tsutsumi, Kazuyoshi; Sakaki, Hironao; Suzuki, Hiromitsu; Sugimoto, Masayoshi

Fusion Engineering and Design, 89(9-10), p.2066 - 2070, 2014/10

 Percentile:100(Nuclear Science & Technology)

Journal Articles

Development of timing system for RF ion source & RFQ III test stand

Sawabe, Yuki; Ito, Yuichi; Kawase, Masato; Fukuta, Shimpei; Suzuki, Takahiro*; Kikuzawa, Nobuhiro; Ouchi, Nobuo

Proceedings of 11th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.748 - 751, 2014/10

no abstracts in English

386 (Records 1-20 displayed on this page)