Presented at ICRP International Conference on Recovery After Nuclear Accidents,
Radiological Lessons from Fukushima and Beyond, 1-4 December, 2020

Radiation Dose of Workers Engaged inDecontamination of Environment
December, 2020
Tsubasa OGAWA, Tetsuro UENO, Tomohiro ASANO, Akira SUZUKI and Atsuo ITORadiation Effects Association, Tokyo, JAPANContents• Establishment of Radiation Dose Registration System for
Decontamination and Related Workers• Statistics on Radiation Dose for Work Categories inside
Special Decontamination Area
• Comparison of Radiation Doses for Decontamination andNuclear Workers• Conclusions1

Decontamination and related works after Great East Japan
Earthquake and Tsunami• The Great East Japan Earthquake and Tsunami on March 11, 2011 was followed by Fukushima-Daiichi
Accident, which released radioactive materials, mainly Cs-134 and Cs-137, into the atmosphere resulting
in contamination of environments including soil, woods, waters and houses.
• The government enacted the“Act on Special Measures
Concerning the Handling ofRadioactive Pollution” inJanuary, 2012, in order topromote decontamination ofthe environment to facilitate
the lifting of the evacuation
order.
• The decontamination andrelated works are still inprogress in the restricted
area, especially in theSpecial Decontamination
Area and Difficult-to-ReturnZone.
2Establishment of Radiation Dose Registration System for
Decontamination and Related Workers• The radiation dose registration system was emerged to prevent scattering andloss of radiation dose records, when the decontamination of the environment
was initiated.
• The Radiation Dose Registration Center (RADREC) of the Radiation Effects
Association has been operating a radiation dose registration system fornuclear workers since 1977. So the radiation dose registration system fordecontamination and related workers was initiated in November 2013.
• In March 2015, the RADREC started operation of database system for doserecords of decontamination and related workers.
• The system was established ;to centralize radiation dose records, especially for subcontract workers changing
jobs/projects frequently
to manage radiation dose records both nuclear and decontamination related workers
to collectively respond inquiry on past dose recordsto prevent loss of dose records

3Work Categories and Registration Items• The registration items for the RADREC database depend on the work categories.
• Category I

 For the works inside special decontamination area and waste disposal, basically quarterly registration andfollowing items are required considering the work in relatively high radiation dose rate.

• Category II

 On the other hand, works outside special decontamination area, registration after works are requiredconsidering the work in relatively low radiation dose rate.
Work Category

Category I Decontamination and Related Work insideSpecial Decontamination Area
 Disposal of Specified Waste
Category II Decontamination and Related Work outside
Special Decontamination Area including
Intensive Contamination Survey AreaRegistration ItemsIssuance of Radiation Passbook for each worker
Periodical Registration (Quarterly) of Radiation DoseRegistration of Radiation Dose and Health Records after Work
Past Dose Records Inquiry

 Registration of Radiation Dose and Health Records after Work

4

Radiation Dose Registration Systemfor Decontamination and Related Workers
 Personal ID and Radiation Passbook are common with nuclear registration system.
 Registration and Inquiry of radiation dose can be done by on-line for primary contractors.
 Radiation dose for nuclear and decontamination can be cross referenced, as workers may go both.
Ministry of theEnvironment

RADREC(3)Application for Joining Registration System

Primary Contractor

Employer(1)Application for Issuanceof Radiation Passbook(4)Registration of Work Project
Registration of Radiation Dose
Registration of Statutory Records
Inquiry of Past Dose Records(Related Contractor)

Decontamination
WorkerInstitutions for Issuance ofRadiation Passbook

Decontamination
Worker DatabaseCrossreference(2)Issuance of Personal ID
Nuclear WorkerDatabase

Inquiry of Personal Records5

Number of Workers, Average Dose and Maximum Dose• As of November 1st, 2020, approximately 120 primary contractors of 750 recovery projects joined theRADREC registration framework and radiation dose of approximately 100,000 decontamination related
workers are accumulated in the database, allowing the statistics on radiation dose. Even if the subcontract
workers changed jobs/projects frequently, the radiation dose were aggregated by personal ID.
• Transitions of radiation dose of decontamination workers, average radiation dose and maximum dose
registered during 2012-2019 are given in Figure. The registered data are mainly workers in the special
decontamination area.
Maximum Dose(mSv)
40,37740,00035,00034,61113.9

30,00025,00020,56420,00015,00010,0005,000
011,058

6.7

0.5

0.5

2012

2013

Average Dose(mSv)
16
14

36,04630,807

10.4
7.8

7.8

25,025 24,415
9.6
8.0

12
10

9.3

86
4

0.7
2014

0.6
2015

0.5
2016

0.3

0.3

0.3

2017

2018

2019

Radiation Dose（mSv）

45,000
Number of Workers• The number ofdecontamination workers
increased up to 2015, thendecreased to 2017, because
the operations of whole area
decontamination werecompleted by the end ofMarch 2017.
• No workers received anannual dose greater than 20mSv. Recently, more than
90% of workers are lessthan 1 mSv.

Number of workers

206

Age Distribution of Workers• The workers engaged in the decontamination and related works are relatively high age, 50s-60s.

Number of Workers• The number of age 60-64 workers were maximum during 2012-2016, since 2017, the number of age 5559 workers became maximum.
6,5006,000
5,500
5,000
4,500
4,000
3,500
3,000
2,500
2,000
1,500
1,0005000

2012

2013

2014

2015

2016

Age2017

2018

2019

7

• Establishment of Radiation Dose Registration System forDecontamination and Related Workers• Statistics on Radiation Dose for Work Categories inside
Special Decontamination Area
• Comparison of Radiation Doses for Decontamination andNuclear Workers• Conclusions

8

Work Categories inside Special Decontamination Area
• Although the whole area decontamination in the Special Decontamination Area wascompleted by the end of March 2017, other related works are still in progress in therestricted area.
• In this presentation, workers are classified into five categories ; “Decontamination” includes ; whole area decontamination, land restoration in temporary storage site, demolition of houses in special
decontamination area

 “Waste disposal” includes ; treatment of specified waste less than 100,000 Bq/kg, minimizing the waste volume, incineration facilities

 “Interim storage” includes ; construction of soil separation and storage facilities, transportation of soil and waste from temporary storage
to interim storage facilities, processing and storage of soil and waste

 “Reconstruction/Revitalization” includes ; construction of specified reconstruction and revitalization base, demolition of houses and decontaminationin 6 municipalities (Futaba, Okuma, Namie, Tomioka, Iitate and Katsurao) “Others” includes ; radiation monitoring, management support for construction, consultants, road constructions• The categories above are classified using the titles of work projects registered in
the RADREC database.

9Number of Workers in Each Category• As the constructions of Interim
Storage Facilities and Specified
Reconstruction /Revitalization
Base are in operation, number ofthese workers are increasing
since 2015.
• In 2015, number of workers ofInterim Storage was approx. 2%,
but in 2019, approx. 50%

Waste Disposal
Reconstruction/Revitalization

45,0002,347

40,000

1,069
2,730

35,000

Number of Workers• As the whole area
decontamination in the Special
Decontamination Area wascompleted by the end of March
2017, number of decontamination
workers are decreasing.

Decontamination
Interim Storage
Other

1,935

815

30,000

2,097

263
3,389
3,274
1,608

489

25,00032,062

15,000

5,000
0

1,082

35,99530,40819,246

3,976

14,861

10,118

2012

1,859

3,261
12,057

2014

2015

2016

Remark : The workers engaged in multiple projects are accounted in each category.

2017

17,753

4,592
7,390

2013

6,613

7,193

1,347
177

20,00010,000

3,364

2018

4,167
3,866

2019

10

Collective Dose
• The collective dose of
decontamination workers wasdominant during 2012-2016.

Waste Disposal

Interim Storage

Reconstruction/Revitalization

Other

30,00025,000

Collective Dose (man-mSv)• After the whole area
decontamination wascompleted, the collective doseof construction of interim
storage and specifiedreconstruction/revitalizationbase are becoming significant.

Decontamination

901
35

1,076
548
528

20,000
662
44
1,251

15,000387

806
110,00021,92921,75914,600

5,000

161

5,089
0

2012

543
330

1,233

593

2,555

119

4,807

5,963

2,822

10,135

3,824

2013

2014

2015

2016

804

2017

291

1,521

2018

209
572

2019

11

Average Dose

0.4
0.2

0.3

0.3

0.4
0.4

0.4
0.3

0.2

0.1
0.1

2014

0.1

2013

2018

2019

0.0

0.0

0.1
0.0

2012

0.2

0.2

0.3

0.4

0.5

0.5
0.5

0.5

0.6

0.6
0.5
0.1• The work of waste disposal includes
handling of waste less than 100,000
Bq/kg, and works outside special
decontamination area, average doses
are relatively low.

0.5

• The average doses for specified
reconstruction/revitalization basewere 0.2-0.7 mSv/y, relatively highbecause projects are implemented in“Difficult-to-Return Zone”

0.7• The work of interim storage includes
demolition of housings anddecontamination in the Special
Decontamination Area, average doses
were 0.3-0.5 mSv/y

Waste Disposal
Reconstruction/Revitalization

0.7

DecontaminationInterim Storage
Other

0.3

• The average doses for whole area
decontamination in 2012-2016 were0.5-0.7 mSv/y

2015

2016

2017

12

Maximum Dose
Decontamination
Interim Storage
Other2013

2014

2018

4.6
1.5

2.9
2.3

2.6

3.7
3.8

3.2
2.8
2.6

3.4

3.0

2017

0.6

0.3

2012

9.3

8.0

6.4
5.3

2016

1.6

• No workers received an annual
dose greater than 20 mSv

5.2

5.2
4.4
5.6
3.8

2015

2.6

4.4

6.4

6.7

7.8

9.6

10.4

• Maximum dose during 20122014 was due to decontaminationwork.
• Maximum dose since 2015 due
to interim storage workers,
especially managers of theprojects tend to stay longer ineach site.

Waste Disposal
Reconstruction/Revitalization

13.9• Maximum dose in 2012 fordecontamination worker included
radiation dose in 2011 by JAEA
Pilot Project.

2019

Remark : Because the decontamination worker of 5.2 mSv in 2015 engaged in multiple categories, it did not match with maximum
dose of 7.8 mSv in 2015 in page 6.
13

• Establishment of Radiation Dose Registration System for
Decontamination and Related Workers• Statistics on Radiation Dose for Work Categories inside
Special Decontamination Area
• Comparison of Radiation Doses for Decontamination andNuclear Workers• Conclusions

14

Comparison of Radiation Doses for Decontamination
and Nuclear Workers• Compared with the nuclear workers, the number of workers and thedoses are relatively low for decontamination.
Decontamination
Related Worker(Jan.-Dec., 2019)

Nuclear Worker(Apr.,2019 –Mar.,2020)*

Number of Workers

30,80763,638Average Dose (mSv)

0.3

0.6

Maximum Dose (mSv)

9.3

19.6

10,10336,174

Collective Dose (man-mSv)* Including radiation dose of workers engaged in Fukushima Daiichi decommissioning

15

Age of Workers• In the decontamination and related work, relatively higher age workers are employedcompared with nuclear worker.
10,000Decontamination in 2019

9,000

Nulcear in FY 2019

Number of Workers

8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0

Age16

• Establishment of Radiation Dose Registration System for
Decontamination and Related Workers• Statistics on Radiation Dose for Work Categories inside
Special Decontamination Area
• Comparison of Radiation Doses for Decontamination andNuclear Workers• Conclusions

17

Conclusions• The radiation dose registry for decontamination and related workers has beensuccessfully established.
• Although the whole area decontamination in the Special Decontamination Area
were completed by the end of March 2017, other related works are still in progress.
Especially, the construction and operation of interim storage facilities, constructionof specified reconstruction and revitalization base are becoming important.
• Compared with the nuclear workers, the number of workers and the doses ofdecontamination and related workers are relatively low.
• The radiation dose registration system operated by the RADREC provides
essential information for radiation safety of workers, as well as for nuclearworkers.
• The work of recovery responders within the restricted areas may change in thelong-term phase in the affected area after nuclear accident. The preparedness forthe dose registration system may be important for the recovery process.
18