Simulation shows Iodine and Cesium may have reached 15 prefectures

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Radioactive iodine and cesium from the Fukushima No. 1 nuclear power plant likely spread across a wide area encompassing Tohoku, Kanto and parts of Chubu, according to a simulation by the National Institute for Environmental Studies.

The results of the study are expected to provide a basis for information used in decontamination efforts and other quake-related projects.

“The simulation data does not necessarily reflect actual measurements,” said Toshimasa Ohara, head of the institute’s Center for Regional Environmental Research. “We want the data to be used as reference figures and indicators of where to measure radiation levels, especially in areas where the results indicate high levels.”

Taking into account weather conditions, such as wind directions and rainfalls, Ohara estimated the amount of nuclear substances from the plant that had fallen on the ground and in nearby waters from March 11, when the Great East Japan Earthquake struck, until March 29, the date the radiation fallout was believed to have mostly eased off.

The results indicate the possibility that 13 percent of leaked iodine-131 and 22 percent of released cesium-137 fell on soil in 15 prefectures. Cesium-137 was estimated at high levels in spots scattered across a broad area, including Shizuoka, Nagano and Niigata prefectures.

In early May, the science ministry published the results of the System for Prediction of Environmental Emergency Dose Information (SPEEDI) to estimate the spread of radiation from the plant.

Many of SPEEDI’s radiation monitoring locations recorded values close to the ones estimated by Ohara’s simulation project. But the SPEEDI measurements were largely limited to an area close to the plant.

After radioactive cesium was detected in tea leaves in Shizuoka, Kanagawa and other prefectures, calls from the public intensified for assessments covering a much wider area.

The simulation map can be found on the National Institute for Environmental Studies’ website in Japanese at (http://bit.ly/qImVbY).

The radioactive material was released from the Tokyo Electric Power Co. Fukushima Daiichi Nuclear Power Station 
of the simulation results on the behavior of the atmosphere 
(News)

August 25, 2011 (Thursday)
Independent Administrative Institution National Institute for Environmental Studies 
Regional Center for Environmental Research
Director: Lee M. Ohara (029-850-2491)
Research and employee: Yu Morino (029-850-2544)


(Ministry of National Press Club, when meeting press release Tsukuba Science City)

National Institute for Environmental Research Group, in order to clarify the behavior of the atmosphere of radioactive materials released from TEPCO Fukushima Daiichi Nuclear Power Station accident due to the earthquake that occurred in eastern Japan, March 11, 2011 , Simulation of atmospheric deposition and advection-diffusion of the central region for Japan (Air Transport deposition simulation) was performed. As a result, the impact of radioactive material in addition to Fukushima, Yamagata and Miyagi, Iwate Prefecture, one and six Kanto, Shizuoka, Yamanashi, Nagano Prefecture, revealed that been over wide areas, such as Niigata directly below. In addition, the model analysis, 13% of the iodine-131 emitted by nuclear Fukushima Daiichi, and deposited in the land of Japan, 22 percent of the cesium-137 and the rest is either deposited in the ocean and is transported outside the computational domain model was estimated. This research, Geophysical Research Letters (American Geophysical Union publication) was published on August 11 with the electronic version of the Society for the employee magazine (* 1) .

Contents

The National Institute for Environmental Research Group, Tokyo Electric Power Co. Fukushima Daiichi Nuclear Power Station by accident due to the earthquake that occurred in eastern Japan, March 11, 2011 (the Fukushima Daiichi nuclear power plant) were released from radioactive material (iodine-131 and cesium-137) was conducted in Air Transport deposition simulation. The simulation is three-dimensional chemical transport model developed by the U.S. Environmental Protection Agency (CMAQ) to use to improve the area in Figure 1 (6km horizontal resolution), wet, dry deposition of radioactive material released in the advection-diffusion deposition (2)was calculated process. Chemical properties and physical properties of the radioactive material is an important element that determines the deposition rate, iodine-131 in this study is the 8:2 ratio of gas on purpose particle state and cesium-137 was assumed all particles on purpose. Change over time is the amount of radioactive material released by the estimation results of Japan Atomic Energy Agency (* 3) was used.

If the calculated amount of deposition, the results shown in Figure 2 for comparison with observational data deposition scheduled by the Ministry of Education. The collection is scheduled for deposition, the bulk sampler (* 4) because it uses a strict comparison with the amount of deposition can be calculated by the model in most of the observation point, wet deposition was estimated by the model The total amount deposited amount (weight = wet deposition + dry deposition) were consistent with the observations and the range of about one order of magnitude.

Budget analysis model (Table 1), 13% of the iodine-131 emitted by nuclear Fukushima Daiichi, and deposited in the land of Japan, 22 percent of the cesium-137 and the rest is either deposited in the ocean outside the computational domain model was estimated to be transported. Iodine-131 is mainly present in the gas state, whereas the main dry deposition from the atmosphere to be deposited directly to the surface, cesium-137 is present as a pair of wet deposition of particles incorporated into clouds and then rain the estimated dominant.

Amount of deposits accumulated iodine-131 have been distributed radially around the primary Fukushima Daiichi As with the atmospheric concentrations, the amount of deposits accumulated cesium-137, by contrast, is estimated to be distributed to the hot spot unlike atmospheric concentration or (3). This reflects differences in deposition process, deposition of iodine-131 is a major dry deposition process is similar to the concentration and deposition shows the distribution of atmospheric deposition of cesium-137 is the main process is wet deposition is therefore an important determinant of spatial distribution of precipitation as well as the timing of atmospheric concentrations.

In the future, while improving the simulation accuracy by refining the deposition process, such as emission process is expected to be utilized in the study to elucidate the environmental fate of radioactive contamination in the area and no real understanding of the experimental data.

Figure 1.  The computational domain (the fill) and scheduled deposition measurement sites (red)
Figure 1.  The computational domain (the fill) and scheduled deposition measurement sites (red)
(Click on the image for a larger view.)
Figure 2.  30 days at March 18, 2011, the amount of fallout deposition was scheduled observation (horizontal axis) and model results (vertical axis) in comparison

Figure 2. 30 days at March 18, 2011, the amount of fallout deposition was scheduled observation (horizontal axis) and model results (vertical axis) for comparison. Wet deposition amount of the surplus, the total amount of blue deposition (wet + dry). The numbers correspond to the observation point in Figure 1.(Click on the image for a larger view.)

Table 1. 30 days at March 11, 2011, the balance of the radioactive material was estimated by the model (in Bq). Because the residual atmosphere in the area of ​​radioactive material were released calculation, the balance of the contribution rate does not match exactly.

Table 1.

(Click on the image for a larger view.)

* A positive sign in the release area is calculated, if negative, means the removal of runoff from the computational domain.

In the emission standards from the Fukushima Daiichi nuclear power plant **

Figure 3.  29 days at March 11, 2011, the amount of cesium-137 deposition and accumulation of iodine-131 calculated by the model (above) and the average concentration (below)
Figure 3. 29 days at March 11, 2011, the amount of cesium-137 deposition and accumulation of iodine-131 calculated by the model (above) and the average concentration (below)

(Click on the image for a larger view.)

■ Note Description

(* 1) Morino, Y., T. Ohara, and M. Nishizawa: Atmospheric behavior, deposition, and budget of radioactive materials from the Fukushima Daiichi nuclear power plant in March 2011, Geophys. Res. Lett., Doi: 10.1029 / 2011GL048689, in press.

(2) dry deposition, wet deposition: the former, particles and gases in the atmosphere, gravity and diffusion, and it drops to the ground surface such as by chemical forces. The latter, it drops to the ground or sea is captured in the rain and snow particles and gases.

(* 3) Chino, M., H. Nakayama, H. Nagai, H. Terada, G. Katata, and H. Yamazawa (2011), Preliminary Estimation of Release Amounts of 131I and 137Cs Accidentally Discharged from the Fukushima Daiichi Nuclear Power Plant into the Atmosphere, J Nucl Sci Technol, 48 (7), 1129-1134.

(* 4) Bulk sampler: A device to collect atmospheric fallout. Deposits have been collected in moist 100% efficiency, the efficiency of dry deposition is taken should be noted that it is not.

■ link-related data

Related Pages East National Institute of Environmental earthquakehttp://www.nies.go.jp/shinsai/index.html # title04 commentary Results – Research iodine 131 and cesium-137 concentrations in the atmosphere · iodine, the amount deposited, the amount of deposits accumulated Spatial (Video)

■ Contact

Regional Environmental Center, National Institute for Environmental Studies, IAA 
Lee M. Ohara TEL: 029-850-2491 
TEL Yu Morino: 029-850-2544

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