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Journal Articles

Evaluation of sediment and $$^{137}$$Cs redistribution in the Oginosawa River catchment near the Fukushima Dai-ichi Nuclear Power Plant using integrated watershed modeling

Sakuma, Kazuyuki; Malins, A.; Funaki, Hironori; Kurikami, Hiroshi; Niizato, Tadafumi; Nakanishi, Takahiro; Mori, Koji*; Tada, Kazuhiro*; Kobayashi, Takamaru*; Kitamura, Akihiro; et al.

Journal of Environmental Radioactivity, 182, p.44 - 51, 2018/02

 Times Cited Count:7 Percentile:42.65(Environmental Sciences)

The Oginosawa River catchment lies 15 km south-west of the Fukushima Dai-ichi nuclear plant. The General-purpose Terrestrial Fluid-flow Simulator (GETFLOWS) code was used to study sediment and $$^{137}$$Cs redistribution within the catchment. Cesium-137 input to watercourses came predominantly from land adjacent to river channels and forest gullies. Forested areas far from the channels only made a minor contribution to $$^{137}$$Cs input to watercourses, total erosion of between 0.001-0.1 mm from May 2011 to December 2015. The 2.3-6.9% y$$^{-1}$$ decrease in the amount of $$^{137}$$Cs in forest topsoil over the study period can be explained by radioactive decay (approximately 2.3% y$$^{-1}$$), along with a migration downwards into subsoil and a small amount of export. The amount of $$^{137}$$Cs available for release from land adjacent to rivers is expected to be lower in future than compared to this study period, as the simulations indicate a high depletion of inventory from these areas.

Journal Articles

Characteristics of radio-cesium transport and discharge between different basins near to the Fukushima Dai-ichi Nuclear Power Plant after heavy rainfall events

Sakuma, Kazuyuki; Kitamura, Akihiro; Malins, A.; Kurikami, Hiroshi; Machida, Masahiko; Mori, Koji*; Tada, Kazuhiro*; Kobayashi, Takamaru*; Tawara, Yasuhiro*; Tosaka, Hiroyuki*

Journal of Environmental Radioactivity, 169-170, p.137 - 150, 2017/04

 Times Cited Count:18 Percentile:69.64(Environmental Sciences)

This paper describes watershed modeling of catchments surrounding the Fukushima Dai-ichi Nuclear Power Plant to understand radio-cesium redistribution by water flows and sediment transport. We extended our previously developed three-dimensional hydrogeological model of the catchments to calculate the migration of radio-cesium in both sediment-sorbed and dissolved forms. The simulations cover the entirety of 2013, including nine heavy rainfall events, as well as Typhoon Roke in September 2011. Typhoons Man-yi and Wipha were the strongest typhoons in 2013 and had the largest bearing on radio-cesium redistribution. The simulated $$^{137}$$Cs discharge quantities over the nine events in 2013 are in good agreement with field monitoring observations. Deposition mainly occurs on flood plains and points where the river beds broaden in the lower basins, and within dam reservoirs along the rivers. Differences in $$^{137}$$Cs discharge ratios between the five basins are explained by differences in the initial fallout distribution within the basins, the presence of dam reservoirs, and the input supply to watercourses. It is possible to use these simulation results to evaluate future radioactive material distributions in order to support remediation planning.

Journal Articles

Redistribution and export of contaminated sediment within eastern Fukushima Prefecture due to typhoon flooding

Kitamura, Akihiro; Kurikami, Hiroshi; Sakuma, Kazuyuki; Malins, A.; Okumura, Masahiko; Machida, Masahiko; Mori, Koji*; Tada, Kazuhiro*; Tawara, Yasuhiro*; Kobayashi, Takamaru*; et al.

Earth Surface Processes and Landforms, 41(12), p.1708 - 1726, 2016/09

 Times Cited Count:14 Percentile:62.25(Geography, Physical)

Sediment erosion and transport processes that are considered to be important in predicting the future radioactive material distribution through sediment-sorbed form in Fukushima Prefecture are simulated. Since large portion of the sediment is considered to be supplied into the rivers, it is important to trace their migration process in terms of each river basin. We choose five river basins, namely the Odaka, the Ukedo, the Maeda, the Kuma, and the Tomioka, from north to south, because of their importance in contamination aspects and prediction studies. The results are summarized as comprehensive dataset of sediment migration for particular river basins in typical typhoon events that account for the most of annual soil erosion. Detail calculations implemented for the amount of sediment supplied in to the river, deposited on river and dam beds, and exported to the ocean.

Journal Articles

Non-destructive evaluation methods for degradation of IG-110 and IG-430 graphite

Shibata, Taiju; Sumita, Junya; Tada, Tatsuya; Hanawa, Satoshi; Sawa, Kazuhiro; Iyoku, Tatsuo

Journal of Nuclear Materials, 381(1-2), p.165 - 170, 2008/10

 Times Cited Count:13 Percentile:68.01(Materials Science, Multidisciplinary)

The lifetime extension of in-core graphite components is one of the key technologies for the VHTR. The residual stress in the graphite components caused by neutron irradiation at high temperatures affects their lifetime. Although oxidation damage in the components would not be significant in reactor normal operation, it should be checked as well. To evaluate the degradation of the graphite components directly by non-destructive way, the applicability of the micro-indentation and ultrasonic wave methods were investigated. The fine-grained isotropic graphites of IG-110 and IG-430, the candidate grades for the VHTR, were used in this study. The following results were obtained. (1) The micro-indentation behavior was changed by applying the compressive strain on the graphite. It suggested that the residual stress would be measured directly. (2) The change of ultrasonic wave velocity with 1 MHz by the uniform oxidation could be evaluated by the wave-propagation analysis with wave-pore interaction model. (3) The trend of oxidation-induced strength degradation on IG-110 was expressed by using the proposed uniform oxidation model. The importance of the un-uniformity consideration was indicated.

Journal Articles

Development of non-destructive evaluation methods for degradation of HTGR graphite components

Shibata, Taiju; Sumita, Junya; Tada, Tatsuya; Sawa, Kazuhiro

Journal of Nuclear Materials, 381(1-2), p.204 - 209, 2008/10

 Times Cited Count:6 Percentile:43.18(Materials Science, Multidisciplinary)

To develop the non-destructive evaluation methods for degradation of HTGR graphite components, the applicability of the micro-indentation method to detect the residual stress was studied. The IG-110 and IG-430 graphites were used. (1) The residual stress in a graphite block at the HTTR in-core condition was analyzed. For the components in the VHTR which would be used at much severer condition, the development of lifetime extension methods was suggested as an important subject. (2) Micro-indentation behavior at stress free condition was investigated with some indenters. The spherical indenter R0.5 mm with indentation load of 5 and 10 N was selected to detect the specimen surface condition sensitively. (3) The relationship between the average indentation depth and compressive stress of the specimen was expressed by an empirical formula. It would be possible to evaluate the residual stress by the indentation. It is necessary to assess the data with statistic method in the future study.

JAEA Reports

Development of oxidation damage evaluation method for HTGR graphite component by ultrasonic-wave propagation characteristics, 1 (Contract research)

Tada, Tatsuya; Shibata, Taiju; Sumita, Junya; Sawa, Kazuhiro

JAEA-Research 2007-079, 22 Pages, 2008/01

JAEA-Research-2007-079.pdf:13.34MB

Graphite materials used for in-core components of High Temperature Gas-cooled Reactor are gradually oxidized by quite small amount of impurities in primary coolant during long term operation. The oxidation damage is addressed one of crucial factors to determine their lifetime, and it is important to evaluate the damage for components lifetime extension. Since ultrasonic-waves are propagated through interactions with pores in porous ceramics including graphite, it is possible to evaluate the porous condition by propagation characteristics such as velocity and attenuation. We are now developing the oxidation damage evaluation method non-destructively by the wave propagation characteristics. This report shows evaluation formulas to evaluate uniform oxidation condition of graphite. They are obtained experimental data of wave propagation characteristics for parametrically oxidized IG-110 and IG-430 graphite specimens.

Journal Articles

Oxidation damage evaluation by non-destructive method for graphite components in High Temperature Gas-cooled Reactor

Shibata, Taiju; Tada, Tatsuya; Sumita, Junya; Sawa, Kazuhiro

Journal of Solid Mechanics and Materials Engineering (Internet), 2(1), p.166 - 175, 2008/00

To develop non-destructive evaluation methods for oxidation damage on graphite components in High Temperature Gas-cooled Reactors (HTGRs), the applicability of ultrasonic wave and micro-indentation methods were investigated. IG-110 and IG-430 graphites, candidates for Very High Temperature Reactor (VHTR), were uniformly oxidized for experiments. (1) Ultrasonic wave velocities were decreased with increasing the oxidation. It can be expressed empirically by exponential formulas to oxidation weight loss. (2) A wave propagation analysis with a wave-pore interaction model showed slightly less velocity reduction than experimental data of the oxidized IG-110. The possibility of the non-uniform oxidation effect was suggested. (3) Although micro-indentation characteristics were changed to show oxidation-induced degradation, it is necessary to assess the variation of the test data with statistic method to specify the oxidation damage in the next study.

JAEA Reports

Development of evaluation method of residual stress for graphite component of HTGR by micro-indentation method, 1 (Contract research)

Sumita, Junya; Shibata, Taiju; Tada, Tatsuya; Sawa, Kazuhiro

JAEA-Research 2007-073, 17 Pages, 2007/11

JAEA-Research-2007-073.pdf:5.72MB

In High Temperature Gas-cooled Reactor (HTGR), graphite materials are used as core internal structural components. The neutron irradiation and thermal gradient induce residual stress of graphite components which is a crucial factor to determine the lifetime of them. It is hence important to measure and assess the stress for lifetime extension of the components. Since the residual stress gives characteristics change to the micro-indentation behavior, it is possible to evaluate the residual stress to measure indentation depth. Therefore, in order to evaluate the change of residual stress of graphite components non-destructively, we are now developing the indentation method to evaluate it. This report showed the relationship between indentation depth and residual stress based on experimental data obtained by changing the stress condition of graphite specimen parametrically.

Journal Articles

Analytical study on micro-indentation method to integrity evaluation for graphite components in HTGR

Sumita, Junya; Hanawa, Satoshi; Shibata, Taiju; Tada, Tatsuya; Iyoku, Tatsuo; Sawa, Kazuhiro

Proceedings of 14th International Conference on Nuclear Engineering (ICONE-14) (CD-ROM), 8 Pages, 2006/07

An analytical study on micro-indentation method to integrity evaluation for graphite components was carried out. The indentation method is used as simplicity test to measure mechanical properties of materials. This method is thought to be applicable to evaluate the residual stress from the relationship between indentation load and indentation depth. In this study, in order to confirm the applicability of the micro-indentation method for lifetime evaluation of the graphite component, indentation load-depth behavior under stress/strain condition was evaluated taking account of the specified minimum ultimate strength of IG-110 graphite. Moreover, analytical investigations of indentation load-depth behavior for oxidized graphite and oxidized graphite with residual strain were also carried out. As a result, it can be said that the indentation method is potentially applicable to evaluate the integrity of graphite components.

Journal Articles

Safety design concepts for ITER-tritium facility; Toward construction in Japan

Ohira, Shigeru; Tada, Eisuke; Hada, Kazuhiko; Neyatani, Yuzuru; Maruo, Takeshi; Hashimoto, Masayoshi*; Araki, Takao*; Nomoto, Kazuhiro*; Tsuru, Daigo; Ishida, Toshikatsu*; et al.

Fusion Science and Technology, 41(3), p.642 - 646, 2002/05

no abstracts in English

Journal Articles

Study on decay heat removal of compact ITER

Tsuru, Daigo; Neyatani, Yuzuru; Araki, Takao*; Nomoto, Kazuhiro*; Ohira, Shigeru; Maruo, Takeshi; Hashimoto, Masayoshi*; Hada, Kazuhiko; Tada, Eisuke

Fusion Engineering and Design, 58-59, p.985 - 989, 2001/11

 Times Cited Count:3 Percentile:28.03(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Safety activities in JAERI related to ITER

Ohira, Shigeru; Tada, Eisuke; Hada, Kazuhiko; Neyatani, Yuzuru; Maruo, Takeshi; Hashimoto, Masayoshi*; Araki, Takao*; Nomoto, Kazuhiro*; Tsuru, Daigo; Ishida, Toshikatsu*; et al.

Fusion Engineering and Design, 54(3-4), p.515 - 522, 2001/04

 Times Cited Count:3 Percentile:28.03(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

Temperature effect on radiation shielding for HTTR primary upper shield

Takada, Eiji*; Sumita, Junya; Sawa, Kazuhiro; Tada, Keiko*

JAERI-Tech 2000-020, p.65 - 0, 2000/03

JAERI-Tech-2000-020.pdf:2.12MB

no abstracts in English

Oral presentation

Development of non-destructive damage evaluation method for nuclear graphite

Shibata, Taiju; Sumita, Junya; Hanawa, Satoshi; Tada, Tatsuya; Sawa, Kazuhiro; Ishihara, Masahiro; Iyoku, Tatsuo

no journal, , 

no abstracts in English

Oral presentation

Development of evaluation techniques for residual stress and oxidation damage on graphite components in nuclear reactors

Shibata, Taiju; Sumita, Junya; Hanawa, Satoshi; Tada, Tatsuya; Sawa, Kazuhiro; Iyoku, Tatsuo

no journal, , 

no abstracts in English

Oral presentation

Investigation on lifetime extension and waste reduction methods for graphite components

Sumita, Junya; Hanawa, Satoshi; Shibata, Taiju; Tada, Tatsuya; Iyoku, Tatsuo; Sawa, Kazuhiro

no journal, , 

In order to extend the lifetime of the graphite components in HTGR, an important technical issue on graphite waste was extracted by investigating the method for disposing of graphite waste and an investigation of the technology for confirming integrity of the graphite components was carried out.

Oral presentation

Investigation of evaluation method for residual stress of graphite component of HTGR using micro-indentation method

Sumita, Junya; Shibata, Taiju; Tada, Tatsuya; Sawa, Kazuhiro

no journal, , 

It was shown that the relationship between indentation depth and residual stress based on experimental data obtained by changing the stress condition of graphite specimen parametrically.

Oral presentation

Development of evaluation method of degradation for graphite component in HTGR using non-destructive method

Tada, Tatsuya; Shibata, Taiju; Sumita, Junya; Sawa, Kazuhiro

no journal, , 

To develop non-destructive evaluation methods for oxidation damage on graphite components in High Temperature Gas-cooled Reactors (HTGRs), the applicability of ultrasonic wave and micro-indentation methods were investigated. As the results of investigation, the relationship between ultrasonic wave velocities and burn-off, oxidation weight loss of graphite, can be expressed empirically by exponential formulas and a wave propagation analysis with a wave-pore interaction model showed slightly less velocity reduction than experimental data of the oxidized graphite. Moreover, micro-indentation characteristics on the graphite samples were changed to show oxidation-induced degradation.

Oral presentation

Long-term assessment of transport of radioactive contaminant in the environment of Fukushima (F-TRACE Project), 13; Numerical analysis of water, sediment and radioactive cesium transport during rainfall events in a catchment scale

Kurikami, Hiroshi; Malins, A.; Kitamura, Akihiro; Mori, Koji*; Tada, Kazuhiro*; Kobayashi, Takamaru*

no journal, , 

We added models of erosion, transport and deposition of sediment due to surface flow and corresponding radioactive cesium transport into GETFLOWS, GEneral purpose Terrestrial fluid-FLOW Simulator. The application of the model showed results in good agreement with the monitored turbidity and radioactive cesium concentrations in rivers.

19 (Records 1-19 displayed on this page)
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