RADIATION DOSE OF WORKERS ENGAGED IN
DECONTAMINATION OF ENVIRONMENTAFTER FUKUSHIMA-DAIICHI ACCIDENT
Tsubasa Ogawa1, Tetsuro Ueno1, Tomohiro Asano1and Atsuo Ito1
1
Radiation Effects Association, 1-9-16 kaji-cho, Chiyoda-ku, Tokyo, 101-0044, Japane-mail: ogawa@rea.or.jp
The Great East Japan Earthquake and Tsunami on March 11, 2011 was followed by FukushimaDaiichi Accident, which released Cs-134, Cs-137 and I-131 into the atmosphere resulting incontamination of environments including soil, woods, waters and houses. The government
issued evacuation orders in the contaminated areas with estimated exposure doses to Fukushimaresidents above 20 mSv/y. In order to facilitate lifting the orders and promoting
decontamination, the goverement enacted the Act on Special Measures Concerning theHandling of Radioactive Pollution, which was executed in January, 2012. The radiation dosesof workers engaged in decontamination of environment were registered through the contractors
in the radiation dose registration system at Radiation Dose Registration Center (RADREC) ofRadiation Effects Association. The purpose of this study is to report radiation doses received
by decontamination workers, with comparing doses received by workers in nuclear facilities
including nuclear power plants in Japan.
As of May 31, 2018, 420 primary contractors joined the RADREC registration framework andradiation dose of 464,283 workers are accumulated in the RADREC database, allowing the useof statistics on dose distribution of decontamination workers. Transitions of radiation dose ofdecontamination workers, average radiation dose and maximum dose registered during 20122017 are given in Figure. The number of decontamination workers has increased from 2012 to2015, then decreased from 2016 to 2017, because the operation in the special decontamination
areas was mostly completed by the end of March 2017. Compared with the nuclear workers,
the number of workers and the average radiation dose are low for decontamination workers.
The radiation dose registry system for decontamination workers has been successfully
established and statistics are available.

45,00040,00035,00030,00025,00020,00015,00010,0005,000
0Average Dose(mSv)

Maximum Dose(mSv)

40,37736,046

34,611
13.9

25,025
20,564
11,05810.4

6.7

0.50.50.7

2012

2013

2014

Year

7.8

7.8

8.0

0.6

0.50.3

2015

2016

2017

16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0

Dose(mSv)

Number of Workers

Number of Workers

Fig. Transitions of number of decontaminatoin workers, average dose and maximum dose

RADIATION DOSE OF WORKERS ENGAGED IN DECONTAMINATION OF ENVIRONMENTAFTER FUKUSHIMA-DAIICHI ACCIDENT
Tsubasa Ogawa, Tetsuro Ueno, Tomohiro Asano and Atsuo Ito
Radiation Dose Registration Center, Radiation Effects Association, Tokyo, Japan

Background :The Great East Japan Earthquake and Tsunami on March 11, 2011 was followed by Fukushima-Daiichi Accident, which released Cs-134,Cs-137 and I-131 into the atmosphere resulting in contamination of environments including soil, woods, waters and houses. Thegovernment issued evacuation orders in the contaminated areas with estimated exposure doses to Fukushima residents above 20 mSv/y.
In order to facilitate lifting the orders and promoting decontamination, the goverement enacted the Act on Special Measures Concerning
the Handling of Radioactive Pollution, which was executed in January, 2012. The decontamination based on the Act on Special Measures
has completed as of March 2018, except for the “Areas where Returning is Difficult (ARD)”. The construction of the Interim Storage
Facility for removed soil and the reconstruction of the ARD are in progress.
Great East Japan Earthquake and Tsunami

Decontamination based on the “Act on Special Measures”

Reference : Ministry of the Environment

Materials and Methods :Transitions of ambient dose rate within 80 km radius

The radiation doses of workers engaged in decontamination ofenvironment were registered through the contractors in theradiation dose registration system at Radiation DoseRegistration Center (RADREC) of Radiation Effects
Association. As of August 31, 2018, 422 primary contractors
joined the RADREC registration framework and radiation doseof 478,770 workers are accumulated in the RADREC database,allowing the use of statistics on dose distribution ofdecontamination workers.
Reference : Ministry of the Environment

Radiation Dose Registration System for Decontamination Worker

Transitions of number of decontamination workers, average doseand maximum dose

Results :••Transitions of radiation dose of decontamination workers, averageradiation dose and maximum dose registered during 2012-2017 aregiven in right Figure. The number of decontamination workers has
increased from 2012 to 2015, then decreased from 2016 to 2017,
because the operation in the special decontamination areas was
mostly completed by the end of March 2017.
Compared with the nuclear workers, the number of workers andthe average radiation dose are low for decontamination workers asgiven in right table.

Conclusion :Comparison of Doses for Decontamination and Nuclear Worker

Number of Workers
Mean Dose (mSv)
Maximum Dose (mSv)
Collective Dose (man-mSv)

Decontamination
WorkerJan.-Dec., 2017

Nuclear Worker
Apr.,2009 –Mar.,2010

25,0250.3
8.0
7,622.8

75,9881.1
2383,932•

The radiation dose registry for decontamination workers has been successfully established.

•For preserving the proper implementation of radiation protection prescribed in the regulations, contractors need to monitor the trendof dose distribution and provide administrative measures, if necessary, for the safety of employees. The radiation dose registration
system for decontamination workers operated by the RADREC provides essential information for radiation safety of workers, aswell as for nuclear workers.