United Nations Scientific Committee on the Effects of Atomic Radiation

ATTACHMENT A-20

ESTIMATES OF COLLECTIVE DOSE FOR THE
JAPANESE POPULATION RESULTING FROM THE
ACCIDENT AT THE FUKUSHIMA DAIICHI NUCLEAR
POWER STATIONUNSCEAR 2020/2021 Report, Annex B, Levels and effects of radiation exposuredue to the accident at the Fukushima Daiichi Nuclear Power Station: implicationsof information published since the UNSCEAR 2013 Report
Contents
This attachment describes the approaches that the Committee has used to estimate collective
doses to the population of Japan following the accident at the Fukushima Daiichi Nuclear Power
Station (FDNPS). Collective effective and thyroid doses have been estimated and aresummarized for each pathway of exposure, for different age groups in the population, and fordifferent geographical areas of Japan.
Notes
For consistency, doses in this attachment are quoted, in general, to two significant figures. Thisshould not be interpreted as an indication of their precision that is often much less.
The designations employed and the presentation of material in this publication do not imply theexpression of any opinion whatsoever on the part of the Secretariat of the United Nationsconcerning the legal status of any country, territory, city or area, or of its authorities, orconcerning the delimitation of its frontiers or boundaries.
Information on Uniform Resource Locators (URLs) and links to Internet sites contained in thepresent publication are provided for the convenience of the reader and are correct at the time ofissue. The United Nations takes no responsibility for the continued accuracy of that informationor for the content of any external website.
© United Nations, April 2022. All rights reserved, worldwide.
This publication has not been formally edited.

ANNEX B, ATTACHMENT A-20: ESTIMATES OF COLLECTIVE DOSE FOR THE JAPANESE POPULATION …

3CONTENTS
ESTIMATES OF COLLECTIVE DOSE................................................................................... 5REFERENCES ........................................................................................................................... 9ANNEX B, ATTACHMENT A-20: ESTIMATES OF COLLECTIVE DOSE FOR THE JAPANESE POPULATION …

5ESTIMATES OF COLLECTIVE DOSE
1.
Collective doses 1 have been assessed on the basis of a Japanese population of 128 million
people as determined in the 2010 census [MIC, 2011]. The distribution of this population amongdifferent age groups was: 7.4 million (5.8%) were aged 0–5 years; 11.7 million (9.1%) were aged
6–15 years; and the remainder, 108.9 million (85.1%) were above 16 years old and considered
to be adults. The total population and its age distribution were assumed to remain constant overthe periods for which collective doses were estimated, 2 namely 1 and 80 years after the accident
at FDNPS.
2.
For pathways of exposure that depend on the location of those exposed (i.e., externalradiation from, and inhalation of, airborne radionuclides and external radiation fromradionuclides deposited on the ground), collective doses were estimated as follows:− For Fukushima Prefecture, 3 the collective doses were estimated as the sum, over allmunicipalities and the three age groups, of the product of the weighted mean dose for agiven age group in a given municipality and the number of people within that age group;− For those municipalities that were partly evacuated (e.g., Minamisoma City), anadjustment was made to take this into account;− For all evacuated residents of Fukushima Prefecture, the collective doses were estimatedas the sum, over all evacuation scenarios and the three age groups, of the product of theweighted mean dose for a given age group in a given evacuation scenario and the numberof evacuees within that age group;− For other prefectures in Japan, the collective doses were estimated as the sum, over allother prefectures and the three age groups, of the product of the weighted mean dose fora given age group for a given prefecture and the number of people within that age group.
3.
The approaches used to estimate individual doses from external radiation from, andinhalation of, airborne radionuclides and external radiation from radionuclides deposited on theground are described in attachments A-1 and A-10, respectively, for municipalities of Fukushima
Prefecture and other prefectures; the individual doses are tabulated in attachments A-13, A-14,
A-18 and A-19.
4.
Exposure from ingestion of food depends more on the location of agricultural production
and how it is subsequently distributed and marketed within Japan, rather than the location of thepopulation, per se. A different approach was, therefore, adopted for assessing the collective dosefrom this pathway. The collective dose from ingestion was estimated as the sum over all1The Committee has used the quantity, collective (effective) dose, for many years to compare the radiation exposures ofpopulations from different sources of ionizing radiation, or following different protection measures. The collective (effective)
dose is always estimated for a defined population over a specified period of time. It is the product of the mean effective dose toa specified population from a particular source, and the number of people in that population, integrated over a defined period oftime. Importantly, calculated doses are recommended only for comparative purposes and not for estimations related to healtheffects. Collective dose is not intended as a tool for epidemiological risk assessment. Moreover, the aggregation of very low
individual doses over extended time periods is inappropriate for use in risk projections and, in particular, the calculation ofnumbers of cancer deaths from collective doses based on individual doses that are well within the variation in backgroundexposure should be avoided.
2 In this report, the Committee has used the terms collective effective dose and collective absorbed dose to the thyroid anddescribed them as being for different time periods. This follows the approach used in the UNSCEAR 2013 Report. Strictly, thecorrect terms are collective effective dose commitment and collective absorbed dose commitment to the thyroid (for the timeintegrated quantity), and the descriptions should make clear that the dose commitment (time-integrated) has been truncated at
the different time periods. The Committee has retained the same terms as used in the UNSCEAR 2013 Report for ease ofcomparison with that report and for simplicity, while recognizing that it is not strictly correct.
3 As well as particular municipalities in Group 3 prefectures, namely Ibaraki, Miyagi, Tochigi and Yamagata Prefectures.

6ANNEX B, ATTACHMENT A-20: ESTIMATES OF COLLECTIVE DOSE FOR THE JAPANESE POPULATION …

prefectures of the products of the average individual dose from ingestion within a given
prefecture and the population of that prefecture. The estimation of individual doses fromingestion is described in attachments A-2 and A-3.
5.
For Fukushima Prefecture the average individual dose from ingestion was estimated basedon Murakami and Oki [Murakami and Oki, 2014] (see attachments A-2 and A-3) and that in
subsequent years on the basis of market surveys and duplicate-diet studies and a model developed
by Smith et al. [Smith et al., 2017] for estimating long-term doses in Japan from deposited caesium
radionuclides (see attachment A-3).
6.
For other prefectures, the average individual doses from ingestion were estimated basedon measured levels of radionuclides in food in a given prefecture relative to those in Fukushima
Prefecture – with the prefecture average individual dose scaled accordingly. Doses in the firstyear after the accident were based on an analysis in the UNSCEAR 2013 Report [UNSCEAR,2014] of an extensive database of measurements of food sampled in 2011 from food markets allover Japan. For ingestion of 131I, for Group 3 prefectures, the average dose ratio was 0.27 andfor all other prefectures 0.075. For ingestion of caesium radionuclides over the first year,
corresponding ratios were 0.23 and 0.143, respectively 4 [UNSCEAR, 2014]. Doses insubsequent years for ingestion of caesium radionuclides were estimated from market survey andduplicate-diet studies carried out in a number of prefectures and the model of Smith et al. [Smithet al., 2017]. For Group 3 prefectures, the average ratio was 0.75 and for all other prefectures theaverage ratio was 0.33 (see attachment A-3).
7.
Collective doses to the Japanese population are summarized by exposure pathway,
prefecture group and age group for the first year after the accident at FDNPS in table A-20.1 andfor 80 years after the accident in table A-20.2.

4

See appendix C and attachment C-15 of the UNSCEAR 2013 Report [UNSCEAR, 2014].

Table A-20.1. Collective doses to the Japanese population in the first year after the accident at the Fukushima Daiichi Nuclear Power Station aInhalation

Ingestion

External doseAlla

Collective absorbed dose to thyroid(man Gy)

Prefecture/s
Adults

6–15 years

0–5 years

Total

Adults

6–15 years

0–5 years

Total

Group 1: Evacuated locations

250

39

33

320

16

2.4

1.9

21

Group 2: Fukushima b

2 400

430

320

3 200

120

2014150

Group 3: Some neighbouring c430

78

49560

25

4.3

3.2

32

Group 4: All others

1 200

230

180

1 700

38

139.260

All

4 300

800

600

5 700

200

3928

270

Group 1: Evacuated locations

96

23

21140

3.90.90.9

5.7Group 2: Fukushima b

720

170

130

1 000

60

9.1

6.376

Group 3: Some neighbouring c830

200

150

1 200

64

107.182Group 4: All others

3 400

780

590

4 700

400

50

31480

All

5 000

1 200

900

7 100

530

70

46640

Group 1: Evacuated locations

56

6.3

4.566

56

6.6

4.668

Group 2: Fukushima b

2 200260

190

2 700

2 200260

190

2 600

Group 3: Some neighbouring c

2 700

310

230

3 200

2 600

320

200

3 100

Group 4: All others

4 400

510

370

5 200

4 200

510

400

5 100

All

9 300

1 100790

11 000

9 000

1 100

800

11 000All

19 000

3 000

2 300

24 000

9 800

1 200

870

12 000All doses quoted to two significant figures but this should not be interpreted as a reflection of their precision.
Excluding evacuated locations.
cIbaraki, Miyagi, Tochigi and Yamagata Prefectures.
b

Collective effective dose(man Sv)

ANNEX B, ATTACHMENT A-20: ESTIMATES OF COLLECTIVE DOSE FOR THE JAPANESE POPULATION …

Exposure
pathway7

8

Table A-20.2. Collective doses to the Japanese population integrated to 80 years after the accident at the Fukushima Daiichi Nuclear Power Station aInhalation

IngestionExternal dose

Alla

Collective absorbed dose to thyroid(man Gy)

Prefecture/sAdults

6–15 years

0–5 years

TotalAdults

6–15 years

0–5 years

Total

Group 1: Evacuated locations

250

39

33

320

162.4

1.9

21

Group 2: Fukushima b

2 400

430

320

3 200

120

20

14150

Group 3: Some neighbouring c430

7849560

25

4.3

3.2

32

Group 4: All others

1 200

230

180

1 700

38

13

9.2

60

All

4 300

780

600

5 700

200

39

28270

Group 1: Evacuated locations

962321140

3.9

0.9

0.9

5.7

Group 2: Fukushima b750

170

130

1 100

84

117.4100

Group 3: Some neighbouring c

900

200

160

1 300

140

1510170

Group 4: All others

3 900

810

610

5 300

990

80

51

1 100

All

5 700

1 200910

7 800

1 200

110

69

1 400

Group 1: Evacuated locations

56

6.3

4.5

66

56

6.6

4.6

68

Group 2: Fukushima b

9 100

1 000

710

11 000

8 800

1 000

720

11 000Group 3: Some neighbouring c

10 000

1 100

780

12 000

9 700

1 100

800

12 000Group 4: All others

17 000

1 900

1 300

20 00017 000

1 900

1 400

20 000All

36 000

4 000

2 800

43 00035 000

4 000

2 900

42 000All b

46 0006 000

4 40057 000

37 000

4 100

3 000

44 000All doses quoted to two significant figures but this should not be interpreted as a reflection of their precision.
Excluding evacuated locations.
cIbaraki, Miyagi, Tochigi and Yamagata Prefectures.
b

Collective effective dose(man Sv)

ANNEX B, ATTACHMENT A-20: ESTIMATES OF COLLECTIVE DOSE FOR THE JAPANESE POPULATION …

Exposurepathway

ANNEX B, ATTACHMENT A-20: ESTIMATES OF COLLECTIVE DOSE FOR THE JAPANESE POPULATION …

9REFERENCES
MIC. Population census 2010. Ministry of Internal Affairs and Communications, Japan. [Internet]
Available from (https://www.e-stat.go.jp/en/stat-search/files?page=1&toukei=00200521&bunya_l=02&tstat=000001039448&cycle=0&result_page=1&cycle_facet=cycle)
on 27 February 2020.
Murakami, M. and T. Oki. Estimated dietary intake of radionuclides and health risks for thecitizens of Fukushima City, Tokyo, and Osaka after the 2011 nuclear accident. PLoS One
9(11): e112791 (2014).
Smith, J.T., K. Tagami and S. Uchida. Time trends in radiocaesium in the Japanese diet following
nuclear weapons testing and Chernobyl: Implications for long term contamination postFukushima. Sci Total Environ 601-602: 1466-1475 (2017).
UNSCEAR. Sources, Effects and Risks of Ionizing Radiation. Volume I: Report to the General
Assembly and Scientific Annex A. UNSCEAR 2013 Report. United Nations ScientificCommittee on the Effects of Atomic Radiation. United Nations sales publication
E.14.IX.1. United Nations, New York, 2014.