Research and Development Relating to the Accident at the TEPCO's Fukushima Daiichi NPS

1-6Radiation Dose Map of Japan Using an Aircraft=Visually Grasping the Influence of the Accident=

Data logger

Air dose rate at 1 m above
ground level (ǴSv/h)
Converyed info the value
as of May 31.2012
㧨19.0 ‫ޓ‬
9.5 㧙 19.0
3.8 㧙 9.5
1.9 㧙 3.8
1.0 㧙 1.9
0.5 㧙 1.0
0.2 㧙 0.5
0.1 㧙 0.2
҇ 0.1 ‫ޓ‬

Detectors

Fig.1-11 Airborne radiation monitoring system
The airborne radiation monitoring system operates to save thedata that synchronizes the calculation rate of the large NaI
detector and positional information with the GPS every second.

The TEPCỎsFukushima
Daiichi NPS
A boundaryline of 80 km

Fig.1-12 Radiation dose map for the whole of Japan
We installed a large NaI detector on a plane, measured NaI
concentration at intervals of 3~5 km (or 1.8 km in the vicinityof the nuclear power plant), and converted the data collected
into dose rates at a height of 1 m above the ground. The
influence of the natural radiation is included in this map.
0 50 100200300400500km

Since the accident at the TEPCO s Fukushima Daiichi
NPS (1F), a method of environmental radiation monitoringthat can quickly measure large areas has been required. It isalso desirable for the results of this monitoring to bevisualized. We conducted monitoring of the radiation inconjunction with JAEA, using a plane (helicopter) to grasp
the full extent of the effects of the accident.
For this airborne radiation monitoring, we installed large
detectors for γ-rays (NaI detectors) on a helicopter andmeasured the count rate of γ-rays, which we synchronizedwith the location and altitude information collected by GPS(Fig.1-11). The survey was conducted at 3 km intervals ineastern Japan (1.8 km intervals in the vicinity of 1F and at
5 km intervals in western Japan and Hokkaido. The data wegathered in this manner were compared with the datameasured on the ground; then, we corrected for the influenceof factors such as altitude and converted the data into dose
rates at 1 m above ground level. We deducted backgroundnatural radionuclides based on an energy spectrum of thegamma beam that we measured at the same time; we werealso able to convert the dose rate into rates of radiocesium
deposition (Bq/m2).
The dose rate map is shown in Fig.1-12. Because
measurement days vary according to location, an equivalencemap (dose rate and radiocesium) was created as a result ofapplying decay correction to data from May 31, 2012. A highdose area was found to extend from 1F in the northwest towardTochigi and Gunma. In addition, a relatively high-dose area wasfound in southern Ibaraki and northern Miyagi. It is thought thatradioactive Cs released by 1F was deposited in these areas.
Conversely, relatively high doses were found in the central partof Chugoku District and Kyushu. However, these areas wereshown to have been influenced by the background radiation.
This map is available to the public on the homepage of the
Ministry of Education, Culture, Sports, Science and Technology(http://radioactivity.mext.go.jp/ja/contents/6000/5847/view.html).
This work was carried out under a contract with the
Ministry of Education, Culture, Sports, Science andTechnology of Japan (MEXT) in fiscal years 2011 and 2012.

ReferenceTorii, T., Sanada, Y. et al., Report of Investigation of Radionuclide Distribution using Aircraft for Surrounding Environmental Survey from Fukushima
Daiichi Nuclear Power Plant, JAEA-Technology 2012-036, 2012, 182p. (in Japanese).
JAEA R&D Review 201217