Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Togawa, Orihiko; Okura, Takehisa; Kimura, Masanori; Nagai, Haruyasu
JAEA-Review 2021-021, 61 Pages, 2021/11
JAEA-Review-2021-021.pdf:3.72MB
Triggered by the Fukushima Daiichi Nuclear Power Station accident, there have been a lot of arguments among various situations and levels about utilization of atmospheric dispersion models for a nuclear emergency preparedness and response. Most of these arguments, however, were alternative and extreme discussions on whether predictions by computational models could be applied or not for protective measures in a nuclear emergency, and it was hard to say that these arguments were politely conducted, based on scientific verification in an emergency response. It was known, on the other hand, that there were not a few potential users of atmospheric dispersion models and/or calculation results by the models within the Japan Atomic Energy Agency (JAEA) and outside. However, they seemed to have a lack of understanding and a misunderstanding on proper use of different kinds of atmospheric dispersion models. This report compares an outline of models and calculation method in atmospheric dispersion models for a nuclear emergency preparedness and response, with a central focus on the models which have been developed and used in the JAEA. Examples of calculations by these models are also described in the report. This report aims at contributing to future consideration and activities for potential users of atmospheric dispersion models within the JAEA and outside.
Nakano, Masanao; Hosomi, Kenji; Nishimura, Shusaku; Matsubara, Natsumi; Okura, Takehisa; Kuramochi, Akihiko; Kawasaki, Masatsugu; Takeuchi, Erina; Fujii, Yutaka*; Jinno, Tsukasa*; et al.
Hoken Butsuri (Internet), 55(2), p.102 - 109, 2020/06
After the Fukushima-Daiichi Nuclear Power Station (1F) Accident in March 2011, the increase was significantly observed in a part of the result of the environmental radiation monitoring in Ibaraki prefecture. "The review meeting of the environmental effect from 1F accident" was established to discuss technically the fluctuation of monitoring data. The review meeting collected the monitoring data from the four nuclear operators, and discussed a fluctuating trend, 
Cs/
Cs activity ratio, and so on. In this report, the results of the dose rate and Cs in fallout, surface soil, flatfish and seabed sediment are introduced. Also the problem solving in the review meeting is introduced.
Hirouchi, Jun; Okura, Takehisa; Satoh, Daiki
Nihon Genshiryoku Gakkai-Shi ATOMO
, 59(3), p.152 - 155, 2017/03
no abstracts in English
Okura, Takehisa; Oishi, Tetsuya; Taki, Mitsumasa; Shibanuma, Yukio; Kikuchi, Masamitsu; Akino, Hitoshi; Kikuta, Yasuaki; Kawasaki, Masatsugu; Saegusa, Jun; Tsutsumi, Masahiro; et al.
JAEA-Data/Code 2012-010, 37 Pages, 2012/05
JAEA-Data-Code-2012-010.pdf:2.28MB
Due to the accident at Fukushima Daiichi Nuclear Power Plant caused by the 2011 off the Pacific coast of Tohoku Earthquake occurred at 11th March 2011, the emergency environmental radiation monitoring was conducted at Nuclear Science Research Institute, Japan Atomic Energy Agency (JAEA). This report provides the monitoring results of ambient 
-ray dose rate and atmospheric radioactivity concentration until the beginning of June 2011. Some anthropogenic radionuclides such as Cs-134, Cs-137, I-131, I-132, Te-132, Xe-133 and others were detected from air samples. The atmospheric radioactivity concentrations varied with some peaks corresponded with that of ambient -ray dose rate after 15th March 2011. Composition of each peak showed various characteristic. Internal exposure caused by inhalation was estimated from the observed atmospheric radioactivity.
Fujita, Hiroki; Nagaoka, Mika; Kono, Takahiko; Takeyasu, Masanori; Kawasaki, Masatsugu; Okura, Takehisa; Tsujimura, Norio; Sumiya, Shuichi; Momose, Takumaro; Furuta, Sadaaki
Proceedings of 13th International Congress of the International Radiation Protection Association (IRPA-13) (Internet), 7 Pages, 2012/05
The nuclear accident at Fukushima Dai-ichi Nuclear Power Station of Tokyo Electric Power Co. (TEPCO) was caused by the Tohoku District-off the Pacific Ocean Earthquake. Various kinds of radionuclides were released from the power station right after the accident occurred and then reached our laboratories. Therefore, environmental monitoring was reinforced by observation of air absorbed dose rate, periodic collection of airborne dust, precipitation. The collected samples were used to determine radioactivity of ray emitters by High pure Germanium semiconductor detector. Moreover, rainwater and humidity were collected to do the usual routine monitoring. In some samples, 
Sr, 
I, Cs and Cs were detected with radioactivity released from the Fukushima station. In other samples such as seawater, seabed soil and etc., similar radionuclides were detected including the influence of the accident.
Rn flux and its effect on the atmospheric Rn concentration at Hachijo-jima island, JapanOkura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Iida, Takao*
Hoken Butsuri, 45(3), p.270 - 277, 2010/09
Measurements of Rn flux from the ground and 
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 Rn to the surface air concentration of Rn measured on this island. Averages of Rn flux and Ra content in dry soil were 0.88 mBq m
s
and 6.8 Bq kg at Hachijo-jima and 9.7 mBq m s and 23.2 Bq kg at Nagoya, respectively. The low level Ra content in soil is one of main causes for the small Rn flux at the island. With this Rn flux, the contribution of locally exhaled Rn from the island was estimated by a simple model to occur at concentration of 0.035 to 0.072 Bq m
(relative contribution is 4 to 12%) under typical nocturnal condition. Under diurnal condition effect is lower than that of nocturnal condition. This local Rn component is negligible as compared with concentration of long-range transported Rn of 0.5 to 3 Bq m.
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 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 Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, Rn concentrations level was very low. Seasonal variations of the Rn concentration show that 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 Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric Rn at Hachijo-jima has much to do with transport pathway of air.
Okura, Takehisa; Oishi, Tetsuya; Moriyama, Hirobumi; Miyagawa, Naoto
JAEA-Testing 2009-009, 46 Pages, 2010/03
JAEA-Testing-2009-009.pdf:7.13MB
The meteorological observation at Tokai site has conducted based on a "Guideline of meteorological statistics for the safety analysis of nuclear power reactor" (Nuclear Safety Commission on January 28, 1982; revised on March 29, 2001) at Nuclear Science Research Institute in JAEA. The meteorological field was changed in 2005. This report shows assessments of the effect on the change of the meteorological field on April 2005.
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 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 Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, Rn concentrations level was very low. Seasonal variations of the Rn concentration show that 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 Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric Rn at Hachijo-jima has much to do with transport pathway of air.
Rn) using electrostatic collection methodNakamura, Masahiko; Matsuda, Makoto; Nakanoya, Takamitsu; Kabumoto, Hiroshi; Kutsukake, Kenichi; Otokawa, Yoshinori; Asozu, Takuhiro; Ishii, Tetsuro; Asai, Masato; Okura, Takehisa
JAEA-Technology 2008-052, 17 Pages, 2008/07
JAEA-Technology-2008-052.pdf:1.0MB
Alpha rays (0.06 Bq/cm
) were detected on the first basement passage of the Tandem Accelerator Facility. We attempted to identify the alpha-emitting nuclide with surveying this area. We found a crack of concrete at the detected spot. We inferred that radon may seep out of the crack from several phenomena observed in the survey of this area. Furthermore, we identified all nuclides emitting rays at the crack as Naturally Occurring Radioactive Materials, (NORM: 
K, 
Bi, 
Ac and so on) by in-situ -ray measurement. Radon is not easy to be collected and detected by its nature of noble gas. We have developed a convenient electrostatic collection method: after collection of the radon decay product (
Po) using a Teflon sheet charged electrostatically, we have measured alpha rays and rays from this sheet. We concluded the leakage of radon from the soil caused a high counting-rate of alpha rays. The paper describes our survey works and identification procedures in detail.
Rn and its decay products coupled with a mesoscale meteorological model, 1; Model description and validationNishizawa, Masato; Nagai, Haruyasu; Chino, Masamichi; Moriizumi, Jun*; Yoshioka, Katsuhiro*; Okura, Takehisa; Yamazawa, Hiromi*; Iida, Takao*; Mukai, Hitoshi*; Tojima, Yasunori*; et al.
Journal of Nuclear Science and Technology, 44(11), p.1458 - 1466, 2007/11
Times Cited Count：4 Percentile：32.43(Nuclear Science & Technology)A three-dimensional Eulerian numerical model for Rn and its decay products coupled with a mesoscale meteorological model has been developed and applied to the reproduction of the daily and monthly variations of Rn concentration, the monthly variation of 
Pb deposition in Japan and the temporal variation of dose rate after the cold front passage in the coastal area of the Japan Sea for the verification of model capability. The results are as follows: (1) The model reproduced the monthly variation of surface Rn concentration in remote islands, but underestimated inland concentration due to coarse vertical resolution near the surface of the model. (2) The model reproduced the seasonal variation of the observed and the long-term yearly averaged Pb depositions as long as precipitations are predicted precisely. (3) The model reproduced the rise of dose rate in precipitation accompanied with the cold front passage. In particular, Rn decay products in melted snow and graupel contributed the rise of dose rate.
Kajimoto, Yoichi; Fujii, Katsutoshi; Tanimura, Yoshihiko; Yasu, Katsuji; Yamane, Kenji; Okura, Takehisa; Shimizu, Shigeru
no journal, ,
no abstracts in English
Onuma, Isamu; Kawasaki, Katsuya; Kowatari, Munehiko; Yasu, Katsuji; Okura, Takehisa; Kajimoto, Yoichi; Shimizu, Shigeru
no journal, ,
no abstracts in English
-ray dose rates in rain fall eventsOkura, Takehisa; Oishi, Tetsuya; Moriyama, Hirobumi; Miyagawa, Naoto
no journal, ,
no abstracts in English
-ray monitoringOkura, Takehisa; Oishi, Tetsuya; Miyauchi, Hideaki; Yoshitomi, Hiroshi; Tachibana, Haruo; Higashi, Daisuke; Suzuki, Akifumi*; Kobayashi, Ikuo*
no journal, ,
no abstracts in English
Oishi, Tetsuya; Kikuchi, Masamitsu; Takahashi, Kenichi; Okura, Takehisa; Akino, Hitoshi; Kawasaki, Masatsugu; Kikuta, Yasuaki; Saegusa, Jun; Shibanuma, Yukio; Yamamoto, Hideaki
no journal, ,
no abstracts in English
Taki, Mitsumasa; Okura, Takehisa; Oishi, Tetsuya
no journal, ,
no abstracts in English
Shinonaga, Taeko*; Markus, L.*; Okura, Takehisa
no journal, ,
The isotopic composition of uranium (U) in aerosol samples collected before and after the accident of the Fukushima Daiichi Nuclear Power Plant (FDI-NPP), occurred on March 11, 2011, was studied. The aerosol samples were collected on filters by an air sampling system in Tokai, Japan (at 120 km south-southwestern of the FDI-NPP). The U isotopic composition in each filter was analyzed by sector field inductively coupled plasma mass spectrometry (SF-ICPMS). The compositions of U in the samples collected after the accident show that non-natural U existed in the aerosol. The results of series measurements of radioactive materials before and after the accident indicate that the radioactive materials released from the FDI-NPP into the atmosphere were transported to the sampling station in Tokai, a place at 120 km distance from the FDI-NPP, within a day.
Okura, Takehisa; Feistenauer, P.*; Meisenberg, O.*; Shinonaga, Taeko*; Tschiersch, J.*
no journal, ,
The atmospheric radioactivity monitoring at Nuclear Science Research Institute, following the Fukushima accident was reviewed in this study. Comparison with measurement result of the filters at Helmholz Zentrum Muenchen (Germay) was made in order to discuss how to make an estimate of background under contaminated circumstance soon after the accident. Values of each other for samples with important level to estimate internal exposure was consistent; this points to that the adopted method to estimate background was appropriate. But some of samples with relative lower level were incompatible with each other. Penetration of radiocesium aerosols through HE-40TA was discussed with size distribution of radiocesium aerosols and characteristics of HE-40TA. Size distributions of radiocesium aerosols were evaluated experimentally, separated from HE-40TA and collected into a cascade impactor. The penetration was estimated by about 1% - 5%.
Okura, Takehisa; Meisenberg, O.*; Feistenauer, P.*; Shinonaga, Taeko*; Tschiersch, J.*
no journal, ,
Atmospheric radioactivity monitoring was made at Nuclear Science Research Institute, JAEA, following the Fukushima accident. Aerosol-bound radiocesium (Cs) was collected on paper filter (HE-40TA). In this study, to evaluate size distribution of the Cs, radioactive aerosols collected on HE-40TA was removed into distilled water, and then radioactive aerosols were extracted from the solution with a nebulizer and collected into a cascade impactor. The size distribution soon after the accident has one peak which is found around 0.3 
m. Corresponded temporal decreasing Cs concentration, the second peak which has median of 1-2 m was developed besides ca. 0.3-m-median peak at sites around field. The size distribution collected at a site in woods has only one peak after also significant decreasing of Cs concentration. It is presumed that the coarser-median peak was attributed to resuspended radioactivity, considered on the basis of distribution of radioactive aerosols on the filters observed with autoradiography and reference articles.
