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Journal Articles

Settings of biospheric dose assessment parameters in safety assessment for final repository of short-lived radioactive waste in Sweden

Kato, Tomoko

KURNS-EKR-11, p.19 - 28, 2021/03

In order to extract the knowledge that will be helpful in setting the biospheric dose assessment parameters and their database for safety assessment of radioactive waste disposal in Japan, a methodology of setting the biospheric dose assessment parameters was surveyed in the safety assessment of the radioactive waste disposal in Sweden. In this study, the handling in the biospheric dose assessment in SR-PSU was specifically focused. SR-PSU was the project about the safety assessment for final repository of short-lived radioactive waste in Sweden, SFR.

Journal Articles

Analytical tool of evolution of topography and repository depth to assess impacts of uplift and erosion for HLW disposal

Yamaguchi, Masaaki; Kato, Tomoko; Suzuki, Yuji*; Makino, Hitoshi

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(2), p.72 - 82, 2020/12

An efficient analytical tool to calculate temporal change of topography and repository depth due to uplift and erosion was developed for use in performance assessment of high level radioactive waste geological disposal. The tool was developed as ArcGIS model, incorporating simplified landform development simulation, to enable trial calculation of various conditions such as initial topography, uplift rate and its distributions, and repository location. This tool enables to support decision on which processes, features, and their changes should be taken into account for performance assessment, by calculating topography change and repository depth change under various conditions.

Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.

Science, 364(6437), p.272 - 275, 2019/04

 Times Cited Count:140 Percentile:99.81(Multidisciplinary Sciences)

The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

JAEA Reports

Biosphere assessment methodology commonly applicable to various disposal concepts

Kato, Tomoko; Fukaya, Yukiko*; Sugiyama, Takeshi*; Nakai, Kunihiro*; Oda, Chie; Oi, Takao

JAEA-Data/Code 2019-002, 162 Pages, 2019/03

JAEA-Data-Code-2019-002.pdf:2.78MB

The radioactive waste generated from Fukushima Daiichi nuclear power station (FDNPS) accident have features such as wide range of radioactivity level (from low to high) and huge amount etc. It would be necessary for the waste from the FDNPS accident to develop suitable disposal concept and to be disposed safely and reasonably. When considering such appropriate disposal concepts in site-generic phase, it is necessary to appropriately develop models and parameters depending on the disposal concepts, such as disposal depth and specification of engineered barrier. In addition, it is desirable to evaluate the safety of repository with common models and parameters independent on the disposal concepts. In the safety assessment of disposal, it is useful to show the difference in performance of repository with "dose" as an indicator of safety assessment. Biosphere model and parameter set and flux-to-dose conversion factors calculated using them are originally dependent on the disposal concepts. However, the biosphere models and the parameter set in safety assessment of near-surface disposal, sub-surface disposal and geological disposal are prepared in each case, and are different according to the age and purpose of the discussion. In this study, an example of biosphere model and parameter-set of groundwater sceinario commonly applicable to various disposal concepts were shown, to calculate flux-to-dose conversion factors, as common indicators independent to disposal concept. And, a set of flux-to-dose conversion factors was also calculated by using the commonly available biosphere model and parameter set. By applying the flux-to-dose conversion factors, it is possible to compare the performance of disposal concepts to the waste generated from FDNPS accident, focusing on the parts depending on the disposal concepts.

Journal Articles

Incorporation of multinuclear copper active sites into nitrogen-doped graphene for electrochemical oxygen reduction

Kato, Masaru*; Muto, Marika*; Matsubara, Naohiro*; Uemura, Yohei*; Wakisaka, Yuki*; Yoneuchi, Tsubasa*; Matsumura, Daiju; Ishibara, Tomoko*; Tokushima, Takashi*; Noro, Shinichiro*; et al.

ACS Applied Energy Materials (Internet), 1(5), p.2358 - 2364, 2018/05

 Times Cited Count:4 Percentile:26.29(Chemistry, Physical)

Journal Articles

NIRS3; The Near Infrared Spectrometer on Hayabusa2

Iwata, Takahiro*; Kitazato, Kohei*; Abe, Masanao*; Otake, Makiko*; Arai, Takehiko*; Arai, Tomoko*; Hirata, Naru*; Hiroi, Takahiro*; Honda, Chikatoshi*; Imae, Naoya*; et al.

Space Science Reviews, 208(1-4), p.317 - 337, 2017/07

 Times Cited Count:33 Percentile:72.27(Astronomy & Astrophysics)

NIRS3: The Near Infrared Spectrometer is installed on the Hayabusa2 spacecraft to observe the target C-type asteroid 162173 Ryugu at near infrared wavelengths of 1.8 to 3.2 micrometer. It aims to obtain reflectance spectra in order to detect absorption bands of hydrated and hydroxide minerals in the 3 micrometer-band. We adopted a linear-image sensor with indium arsenide (InAs) photo diodes and a cooling system with a passive radiator to achieve an optics temperature of 188 K, which enables to retaining sufficient sensitivity and noise level in the 3 micrometer wavelength region. We conducted ground performance tests for the NIRS3 flight model (FM) to confirm its baseline specifications. The results imply that the properties such as the signal-to-noise ratio (SNR) conform to scientific requirements to determine the degree of aqueous alteration, such as CM or CI chondrite, and the stage of thermal metamorphism on the asteroid surface.

Journal Articles

Development of a method of safety assessment for geological disposal considering long-term evolution of geological and topographical environment by uplift and erosion

Wakasugi, Keiichiro; Yamaguchi, Masaaki; Koo, Shigeru*; Nagao, Fumiya; Kato, Tomoko; Suzuki, Yuji*; Ebashi, Takeshi; Umeki, Hiroyuki*; Niibori, Yuichi*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 16(1), p.15 - 33, 2017/03

This study provides a method of safety assessment for the geological disposal of HLW to evaluate the effects of uplift and erosion which are widespread phenomena identified on regional and global scales, and are more or less difficult to avoid in Japan. This method enables to deal with different uplift rate and erosion rate, and to evaluate repository depth, the time required for a repository to reach the weathered zone and surface of the ground, and the number of waste packages eroded as a function of time by using a landform evolution model. Based on trial analysis, the result shows that the maximum dose in the Base Case (uplift rate: 0.3 mm/y) is less than the targeted criterion suggested by the international organization even if the repository reaches the ground surface. Furthermore, the diversifying effect on timing the waste packages to reach to weathered zone due to heterogeneity on altitude of bottom of weathered zone reduces one order magnitude of result of the existed dose assessment. The new method is applicable to evaluate safety of geological disposal based on realistic phenomena of uplift and erosion and to quantify a safety margin and robustness of the disposal system.

JAEA Reports

A Compartment model of radionuclide migration in environment based on exposure pathways

Kurikami, Hiroshi; Niizato, Tadafumi; Tsuruta, Tadahiko; Kato, Tomoko; Kitamura, Akihiro; Kanno, Mitsuhiro*; Kurosawa, Naohiro*

JAEA-Research 2016-020, 50 Pages, 2017/01

JAEA-Research-2016-020.pdf:6.02MB

In this report, we developed a compartment model of radionuclide migration in environment based on exposure pathways in a river basin scale and performed a preliminary calculation. The results showed good agreement with some measurement, although the comparison of bed sediment, transportation to outer sea and to agricultural products with the measurement was not enough. We continue to validate the model.

JAEA Reports

Development of the method of biosphere modeling according to surface environmental conditions

Nagao, Fumiya; Kato, Tomoko; Suzuki, Yuji*; Itazu, Toru*

JAEA-Research 2016-003, 80 Pages, 2016/05

JAEA-Research-2016-003.pdf:14.15MB

In the performance assessment study in the geological disposal of the high-level radioactive waste in Japan, the assessment technique that can treat local characteristics is examined, and establishing the method for the biosphere modeling using specific local information is aimed. In this report, the basic matrices were compiled which contain transport and exposure processes in the surface environment from a generic point of view. And the method was shown to construct the steady-state biosphere model in the actual surface environments by the combination of the basic matrices. To confirm applicability of the method, the biosphere modeling for the hypothetical site was tried. In addition, the important issues to describe the surface environmental condition and human lifestyle were identified to extract future problems and viewpoints by referring to the earlier study of the biosphere assessment at the actual repository site in Sweden.

Journal Articles

Exposure dose from natural radiation sources

Kato, Tomoko

Hosha Kagaku No Jiten, p.204 - 205, 2015/09

no abstracts in English

Journal Articles

Mathematical Modeling of Radioactive Contaminants in the Fukushima Environment

Kitamura, Akihiro; Kurikami, Hiroshi; Yamaguchi, Masaaki; Oda, Yoshihiro; Saito, Tatsuo; Kato, Tomoko; Niizato, Tadafumi; Iijima, Kazuki; Sato, Haruo; Yui, Mikazu; et al.

Nuclear Science and Engineering, 179(1), p.104 - 118, 2015/01

 Times Cited Count:8 Percentile:65.81(Nuclear Science & Technology)

The prediction of the distribution and fate of radioactive materials eventually deposited at surface in the Fukushima area is one of the main objectives and expected to be achieved in an efficient manner. In order to make such prediction, a number of mathematical models of radioactive contaminants, with particular attention on cesium, on the land and in rivers, lakes, and estuaries in the Fukushima area are developed. Simulation results are examined with the field investigations simultaneously implemented. The basic studies of the adsorption/absorption mechanism of cesium and soils have been performed to shed light on estimating distribution coefficient between dissolved contaminant and particulate contaminant.

Journal Articles

Trial synthesis of Li$$_{2}$$Be$$_{2}$$O$$_{3}$$ for high-functional tritium breeders

Hoshino, Tsuyoshi; Oikawa, Fumiaki; Natori, Yuri*; Kato, Kenichi*; Sakka, Tomoko*; Nakamura, Mutsumi*; Tatenuma, Katsuyoshi*

Fusion Engineering and Design, 88(9-10), p.2268 - 2271, 2013/10

 Times Cited Count:1 Percentile:12.53(Nuclear Science & Technology)

Lithium titanate with additional Li (Li$$_{2+x}$$TiO$$_{3+y}$$) and lithium orthosilicate (Li$$_{4}$$SiO$$_{4}$$) is one of the most promising candidates for use in a tritium breeder because of its good chemical and mechanical stabilities. Currently, mixtures of tritium breeder pebble and neutron multiplier (Be or Be$$_{12}$$Ti) pebble are being considered for use in increasing the tritium breeding ratio in a breeding blanket. However, lithium and beryllium are gradually reacted under practical operating conditions, and therefore a high-functional tritium breeder such as lithium beryllium oxide (Li$$_{2}$$Be$$_{2}$$O$$_{3}$$) needs to be developed to compensate for this reactive characteristic under high temperature use. In this study, methods of synthesizing Li$$_{2}$$Be$$_{2}$$O$$_{3}$$ have been extensively investigated by means of solid-phase reaction. The solid-phase reaction of LiOH(H$$_{2}$$O) and BeO is a suitable synthesis method for lithium beryllium oxide (Li$$_{2}$$Be$$_{2}$$O$$_{3}$$). It is expected that single-phase Li$$_{2}$$Be$$_{2}$$O$$_{3}$$ will be stable under the mixture conditions of a tritium breeder and neutron multiplier in the blanket region at high temperatures.

JAEA Reports

Annual report on the environmental radiation monitoring around the Tokai Reprocessing Plant FY2010

Sumiya, Shuichi; Watanabe, Hitoshi; Nakano, Masanao; Takeyasu, Masanori; Nakada, Akira; Fujita, Hiroki; Isozaki, Tokuju; Morisawa, Masato; Mizutani, Tomoko; Kokubun, Yuji; et al.

JAEA-Review 2012-015, 166 Pages, 2012/05

JAEA-Review-2012-015.pdf:3.53MB

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 2010 to March 2011. In this report, some data include the influence of the accidental release from the Fukushima Daiichi Nuclear Power Plant on Tokyo Electric Power Co. in 2011 March. Appendices present comprehensive information, such as monitoring program, monitoring methods, monitoring results and their trends, meteorological data and discharged radioactive wastes. In addition, the data exceeded the normal range of fluctuation by the accidental release was evaluated in the appendices.

JAEA Reports

Results of the environmental radiation monitoring following the accident at the Fukushima Daiichi Nuclear Power Plant; Interim report (Ambient radiation dose rate, radioactivity concentration in the air and radioactivity concentration in the fallout)

Furuta, Sadaaki; Sumiya, Shuichi; Watanabe, Hitoshi; Nakano, Masanao; Imaizumi, Kenji; Takeyasu, Masanori; Nakada, Akira; Fujita, Hiroki; Mizutani, Tomoko; Morisawa, Masato; et al.

JAEA-Review 2011-035, 89 Pages, 2011/08

JAEA-Review-2011-035.pdf:2.97MB

As a correspondence to the accident at the Fukushima Daiichi Nuclear Power Plant, the environmental radiation monitoring was performed at the Nuclear Fuel Cycle Engineering Laboratories, JAEA. This report presented the measurement results of ambient radiation dose rate, radioactivity concentration in the air and radioactivity concentration in fallout and meteorological observation result until May 31, 2011. The ambient radiation dose rate increased, with the peak dose rate of several thousand nGy/h at 7 o'clock in March 15, at 5 o'clock in March 16, and at 4 o'clock in March 21. The variation on the radioactivity concentration in the air and in fallout showed the almost same tendency as that of the dose rate. The concentration ratio of I-131/Cs-137 in the air increased to about 100. The dose was estimated resulting from internal exposure due to inhalation.

Journal Articles

Study of advection-dispersion calculation method by using the random-walk method for the purpose of application to biosphere assessment for geological disposal of radioactive waste

Itazu, Toru; Kato, Tomoko; Maekawa, Keisuke

Nihon Chikasui Gakkai 2011-Nen Shunki Koenkai Koen Yoshi, p.34 - 39, 2011/05

Biosphere assessment, which is a part of safety assessment for geological disposal of radioactive waste, addresses the migration of radionuclide from underground to near the ground surface. Advection-dispersion calculation for this purpose must take into the consideration the following factors: long-distance migration of solute, a requirement to calculate the inflow of solute into the rivers or sea bed supposed to be the final position, demand to control numerical dispersion in heterogeneous field. In this study, we adopt the Random-Walk Method having functions required to biosphere assessment and developed a program available to groundwater analysis by using MODFLOW. The program is verified by comparison with the analytical solution and studied about application method to biosphere assessment.

JAEA Reports

Annual report on the environmental radiation monitoring around the Tokai Reprocessing Plant FY2009

Sumiya, Shuichi; Matsuura, Kenichi; Watanabe, Hitoshi; Nakano, Masanao; Takeyasu, Masanori; Fujita, Hiroki; Isozaki, Tokuju; Morisawa, Masato; Mizutani, Tomoko; Kokubun, Yuji; et al.

JAEA-Review 2011-004, 161 Pages, 2011/03

JAEA-Review-2011-004.pdf:4.09MB

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 2009 to March 2010. Appendices present comprehensive information, such as monitoring program, monitoring methods, monitoring results and their trends, meteorological data and discharged radioactive wastes.

JAEA Reports

Development of safety assessment model based on TRU-2 report using GoldSim

Ebina, Takanori*; Inagaki, Manabu*; Kato, Tomoko

JAEA-Data/Code 2010-029, 41 Pages, 2011/03

JAEA-Data-Code-2010-029.pdf:5.79MB

The safety assessment model at "Second Progress Report on Research and Development for TRU Waste Disposal in Japan" (TRU-2 report) was designed using the numerical code TIGER, that allows the physical and chemical properties within the system to vary with time. At the analysis using TIGER, the migration (i.e engineered barrier system, host rock and fault) have to be analysed independently at each region, consequently the huge number of complicated parameter setting have been required. On the other hand, by using numerical code GoldSim, all regions are analyzed synchronously and parameters can be defined at same model. In future, safety analyses of TRU waste package disposal will be carried out according as study of an optimization of nuclear fuel cycle. Therefor, safety assessment model for TRU waste disposal using GoldSim was designed, and calculation results were verified by comparing with the result of TRU-2 report.

JAEA Reports

Study plan on biosphere assessment for geological disposal of radioactive waste; 5-year plan for fiscal years 2010-2014

Kato, Tomoko; Itazu, Toru; Suzuki, Yuji*

JAEA-Review 2010-075, 42 Pages, 2011/02

JAEA-Review-2010-075.pdf:4.11MB

As the biosphere assessment of geological disposal covers an extremely long time period, it is difficult to predict the future human environment and lifestyles. IAEA-TECDOC addresses that a stylized approach is proposed for selecting critical groups and biospheres in future situations where human behaviour or biosphere conditions cannot be known with any certainty, although it is possible to construct biosphere models based on the characteristics and evolution of the surface environment at the actual site in shorter time period. BIOMASS methodology is especially effective for treating uncertainty of biosphere in these situations. To address the approaches of biosphere modelling, time period after closure of repository was divided; period 0 to 100 years, 100 years to 10,000 years and beyond them. Critical issues of biosphere modelling were specified through summarising the past progresses in domestic and foreign institutes. Based on the critical issues specified, 5-year research plan on biosphere assessment were identified.

Journal Articles

Dissolution techniques with microwave heating devices for radiochemical analysis of ash and cement-solidified product samples

Haraga, Tomoko; Ishimori, Kenichiro; Kato, Kenichi; Kameo, Yutaka; Takahashi, Kuniaki

Bunseki Kagaku, 60(1), p.87 - 90, 2011/01

 Times Cited Count:0 Percentile:0(Chemistry, Analytical)

In order to dissolve radioactive ash (fly ash and bottom ash) and cement-solidified product of radioactive liquid wastes, a dissolution method using microwave heating devices was developed. In present method, most metal elements in samples were extracted with HCl and HNO$$_{3}$$ to sample solution and a precipitate with silica as the main ingredient was decomposed with HF and HNO$$_{3}$$. As a result, fluoride residue was sufficiently reduced and more than 99% of radionuclides were recovered to sample solution. The ash and cement-solidified product samples were successfully dissolved in a shorter time as compared with a conventional method by external heating.

JAEA Reports

International trends on stylization of biosphere evolution and future human activity for performance assessment of geological disposal

Kato, Tomoko

JAEA-Review 2009-052, 23 Pages, 2010/02

JAEA-Review-2009-052.pdf:1.52MB

It is difficult to assume future evaluations of surface environments and human activities accurately and to describe them in a biosphere assessment scenario of geological disposal. Accurate assumption on their evolution is not necessary, because a biosphere assessment aims to illustrate the radiological impact to human as an index of performance for repository. Consequently, it is important to develop the methodology to describe the biosphere system with long-term evolution of geosphere according to a regulatory guideline or an assessment purpose, that is, the methodology to stylize evaluations of surface environments and human activities. In this report, we reviewed regulatory guidelines and scenarios of performance assessment applied to natural processes and human intrusion in foreign countries, and discussed the view-points when evolution of biosphere and future human activity are stylized in performance assessment of geological disposal.

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