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Journal Articles

Development of field estimation technique and improvement of environmental tritium behavior model

Yokoyama, Sumi*; Takahashi, Tomoyuki*; Ota, Masakazu; Kakiuchi, Hideki*; Sugihara, Shinji*; Hirao, Shigekazu*; Momoshima, Noriyuki*; Tamari, Toshiya*; Shima, Nagayoshi*; Atarashi-Andoh, Mariko; et al.

Plasma and Fusion Research (Internet), 14(Sp.2), p.3405099_1 - 3405099_4, 2019/06

The Large Helical Device of the National Institute for Fusion Science started D-D experiments in 2017. To ensure the safety of the facility, it is important to develop evaluation methods for environmental tritium transfer. Tritiated water (HTO) in atmosphere and soil is transferred to plants, and organically bound tritium (OBT) is formed by photosynthesis. Prediction of OBT formation is important, because OBT accumulates in plants and causes dose through ingestion. The objective of this study is to estimate environmental tritium transfer using a simple compartment model and practical parameters. We proposed a simple compartment model consisting of air-soil-plant components, and tried to validate the model by comparison with a sophisticated model, SOLVEG. In this study, we plan to add wet deposition to the model and obtain parameters from measurements of soil permeability and tritium concentrations in air, soil and plants. We also establish rapid pretreatment methods for OBT analysis.

Journal Articles

Model intercomparison of atmospheric $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Plant accident; Simulations based on identical input data

Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qu$'e$lo, D.*; et al.

Journal of Geophysical Research; Atmospheres, 123(20), p.11748 - 11765, 2018/10

A model intercomparison of the atmospheric dispersion of $$^{137}$$Cs emitted following the Fukushima Daiichi Nuclear Power Plant accident was conducted by 12 models to understand the behavior of $$^{137}$$Cs in the atmosphere. The same meteorological data, horizontal grid resolution, and an emission inventory were applied to all the models to focus on the model variability originating from the processes included in each model. The multi-model ensemble captured 40% of the observed $$^{137}$$Cs events, and the figure-of-merit in space for the total deposition of $$^{137}$$Cs exceeded 80. Our analyses indicated that the meteorological data were most critical for reproducing the $$^{137}$$Cs events. The results also revealed that the differences among the models were originated from the deposition and diffusion processes when the meteorological field was simulated well. However, the models with strong diffusion tended to overestimate the $$^{137}$$Cs concentrations.

Journal Articles

Reconstruction of the atmospheric releases of $$^{131}$$I and $$^{137}$$Cs resulting from the Fukushima Daiichi Nuclear Power Plant accident

Chino, Masamichi; Terada, Hiroaki; Katata, Genki; Nagai, Haruyasu; Nakayama, Hiromasa; Yamazawa, Hiromi*; Hirao, Shigekazu*; Ohara, Toshimasa*; Takigawa, Masayuki*; Hayami, Hiroshi*; et al.

NIRS-M-252, p.127 - 135, 2013/03

We estimated the release rates and total amounts of $$^{131}$$I and $$^{137}$$Cs discharged into the atmosphere from March 12 to April 5, 2011. The applied method is a reverse estimation by coupling environmental monitoring data with atmospheric dispersion simulations under the assumption of unit release rate (1 Bq/h). It calculates release rates of radionuclides (Bq/h) by dividing measured air concentrations of $$^{131}$$I and $$^{137}$$Cs into calculated ones at sampling points. The estimated temporal variation of releases indicates that the significant release, over 10$$^{15}$$ Bq/h of $$^{131}$$I, occurred on March 15, following to relatively small releases, 10$$^{13}$$ $$sim$$ 10$$^{14}$$ Bq/h, but the release rates from March 16 are estimated to be rather constant on the order 10$$^{14}$$ Bq/h until March 24. The release rates have decreased with small day-to-day variations to the order of 10$$^{11}$$ $$sim$$ 10$$^{12}$$ Bq/h of $$^{131}$$I on the beginning of April. The estimated source term was examined on the point of the time trend, total releases and the ground depositions of $$^{137}$$Cs by using different atmospheric dispersion models with above source term and compared them with observed $$^{137}$$Cs deposition distribution. These examinations showed that the estimated source term was reasonably accurate during the period when the plume flowed over land in Japan.

Journal Articles

Estimation of $$^{222}$$Rn flux and its effect on the atmospheric $$^{222}$$Rn concentration at Hachijo-jima island, Japan

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Iida, Takao*

Hoken Butsuri, 45(3), p.270 - 277, 2010/09

Measurements of $$^{222}$$Rn flux from the ground and $$^{226}$$Ra content in soil were made on Hachijo-jima, which is a solitary island in the Pacific about 200 km to the south of the main island of Japan, to evaluate effect of locally exhaled $$^{222}$$Rn to the surface air concentration of $$^{222}$$Rn measured on this island. Averages of $$^{222}$$Rn flux and $$^{226}$$Ra content in dry soil were 0.88 mBq m$$^{-2}$$ s$$^{-1}$$ and 6.8 Bq kg$$^{-1}$$ at Hachijo-jima and 9.7 mBq m$$^{-2}$$ s$$^{-1}$$ and 23.2 Bq kg$$^{-1}$$ at Nagoya, respectively. The low level $$^{226}$$Ra content in soil is one of main causes for the small $$^{222}$$Rn flux at the island. With this $$^{222}$$Rn flux, the contribution of locally exhaled $$^{222}$$Rn from the island was estimated by a simple model to occur at concentration of 0.035 to 0.072 Bq m$$^{-3}$$ (relative contribution is 4 to 12%) under typical nocturnal condition. Under diurnal condition effect is lower than that of nocturnal condition. This local $$^{222}$$Rn component is negligible as compared with concentration of long-range transported $$^{222}$$Rn of 0.5 to 3 Bq m$$^{-3}$$.

Journal Articles

Monitoring network of atmospheric Radon-222 concentration in East Asia and backward trajectory analysis of Radon-222 concentration trend at a small solitary island on Pacific Ocean

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Guo, Q.*; Tojima, Yasunori*; Iida, Takao*

Proceedings of 3rd Asian and Oceanic Congress on Radiation Protection (AOCRP-3) (CD-ROM), 3 Pages, 2010/05

Monitoring network of $$^{222}$$Rn concentration in air which was measured in Beijing, Nagoya, Hegura-jima, Hachijo-jima and Hateruma-jima, as a tracer for long-range transport in East Asia was established. At inland sites, Beijing and Nagoya, high concentrations $$^{222}$$Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, $$^{222}$$Rn concentrations level was very low. Seasonal variations of the $$^{222}$$Rn concentration show that $$^{222}$$Rn concentration was the lowest in the summer and the highest in the winter. Diurnal variations were measured at inland sites. At marine sites several-day-cycle variations were measured. It was pointed out by this study that the several-day-cycle variations at Hachijo-jima were dependent on synoptic-scale atmospheric disturbance. Backward trajectory analysis of the relationship between atmospheric $$^{222}$$Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric $$^{222}$$Rn at Hachijo-jima has much to do with transport pathway of air.

Journal Articles

Monitoring network of atmospheric Radon-222 concentration in East Asia and backward trajectory analysis of Radon-222 concentration trend at a small solitary island on Pacific Ocean

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Guo, Q.*; Tojima, Yasunori*; Iida, Takao*

Taiki Kankyo Gakkai-Shi, 44(1), p.42 - 51, 2009/01

Monitoring network of $$^{222}$$Rn concentration in air which was measured in Beijing, Nagoya, Hegura-jima, Hachijo-jima and Hateruma-jima, as a tracer for long-range transport in East Asia was established. At inland sites, Beijing and Nagoya, high concentrations $$^{222}$$Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, $$^{222}$$Rn concentrations level was very low. Seasonal variations of the $$^{222}$$Rn concentration show that $$^{222}$$Rn concentration was the lowest in the summer and the highest in the winter. Diurnal variations were measured at inland sites. At marine sites several-day-cycle variations were measured. It was pointed out by this study that the several-day-cycle variations at Hachijo-jima were dependent on synoptic-scale atmospheric disturbance. Backward trajectory analysis of the relationship between atmospheric $$^{222}$$Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric $$^{222}$$Rn at Hachijo-jima has much to do with transport pathway of air.

Oral presentation

Development of a compartment model for tritium transport in the environment and comparison with a detailed model

Ishida, Yamato*; Hirao, Shigekazu*; Moriizumi, Jun*; Yamazawa, Hiromi*; Atarashi-Andoh, Mariko

no journal, , 

no abstracts in English

Oral presentation

Model intercomparison study for atmospheric $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Plant Accident using identical input data

Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qu$'e$lo, D.*; et al.

no journal, , 

An intercomparison of atmospheric dispersion model targeting on the physical process of $$^{137}$$Cs released from the Fukushima Daiichi Nuclear Power Plant was conducted. Twelve atmospheric models participated in this project. To exclude the uncertainties of the model result due to the emission inventory and meteorological data, all models used the same emission and meteorological data. Concentration of $$^{137}$$Cs from the national suspended particle matter monitoring network and the deposition density by the aircraft were used for the comparison between results of the model and observation. Our analyses elucidated the figure of merit in space (FMS) of the model ensemble mean was improved from a previous model intercomparson about the accumulated deposition. The model ensemble mean captured approximately 36% of the observed high concentration. The inter-model spread of the capture rate was from 8% to 38%. It was originated from the difference in deposition and diffusion processes among the models.

Oral presentation

Model intercomparison project for $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Station Accident using identical meteorological data and source term

Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qu$'e$lo, D.*; et al.

no journal, , 

no abstracts in English

Oral presentation

Model intercomparison project for cesium ($$^{137}$$Cs) from the Fukushima Daiichi Nuclear Power Station Accident using identical meteorological data and source term

Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qu$'e$lo, D.*; et al.

no journal, , 

no abstracts in English

Oral presentation

Detailed intercomparison of atmospheric transport models using newly obtained concentration data of Cs-137 from the Fukushima Daiichi Nuclear Power Plant Accident

Yamazawa, Hiromi*; Sato, Yosuke*; Adachi, Shinichiro*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; et al.

no journal, , 

Cs-137 released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident was conducted by 12 models. The present study focuses on differences in the model results of atmospheric Cs-137 concentration of Plume 2, which traveled southward in the morning of 15 March, 2011, in the area 100 to 200 km downwind from FDNPP by using the concentration data recently evaluated from gamma radiation spectral data at monitoring stations (MS data) and those measured from the suspended particulate matter filters (SPM data). Comparison was made from the following aspects: (1) plume arrival time, (2) concentration level, (3) cross-wind surface concentration profile, (4) vertical concentration profile and (5) mass balance of Cs-137 activity including deposition processes. Additional analyses were made also for Plume 4, which traveled over the same area on 16 March under rainy condition.

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