United Nations Scientific Committee on the Effects of Atomic Radiation

S O U R C E S , E F F E C T S A N D R I S K S O F I O N I Z I N G R A D I AT I O N

UNSCEAR 2013 Report
Volume I
REPORT TO THE GENERAL ASSEMBLYSCIENTIFIC ANNEX A:
Levels and effects of radiation exposure due to the nuclear accident
after the 2011 great east-Japan earthquake and tsunami

SOURCES, EFFECTS AND RISKSOF IONIZING RADIATION
United Nations Scientific Committee on the
Effects of Atomic Radiation
UNSCEAR 2013
Report to the General Assemblywith Scientific Annexes

VOLUME I
Scientific Annex A

UNITED NATIONSNew York, 2014

NOTE
The report of the Committee without its annexes appears as Official Records of theGeneral Assembly, Sixty-eighth Session, Supplement No. 46 and corrigendum (A/68/46
and Corr. 1). The report reproduced here includes the corrections of the corrigendum
and other editorial corrections.
The designations employed and the presentation of material in this publication do not
imply the expression of any opinion whatsoever on the part of the Secretariat of theUnited Nations concerning the legal status of any country, territory, city or area, or of its
authorities, or concerning the delimitation of its frontiers or boundaries.
The country names used in this document are, in most cases, those that were in use at thetime the data were collected or the text prepared. In other cases, however, the names
have been updated, where this was possible and appropriate, to reflect political changes.
The attachments cited in this annex are electronically available for download fromhttp://www.unscear.org/unscear/en/publications/2013_1_Attachments.html

UNITED NATIONS PUBLICATION
Sales No. E.14.IX.1
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CONTENTS
Page

VOLUME I:
Report of the United Nations Scientific Committee on the Effects of Atomic Radiation
to the General Assembly .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .

1

Scientific Annexes
Annex A.	 Levels and effects of radiation exposure due to the nuclear accident
after the 2011 great east-Japan earthquake and tsunami.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .

VOLUME II:
Scientific findings on effects of radiation exposure of children
Annex B.	 Effects of radiation exposure of children

iii

19

Report of the United Nations Scientific Committee on the
Effects of Atomic Radiation to the General AssemblyContents
ChapterPage

I.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

II.

Deliberations of the United Nations Scientific Committee on the Effects of Atomic Radiation
at its sixtieth session . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2A.

Completed evaluations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

B.

Present programme of work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

1.

III.

Radiation exposures from electricity generation and an updated methodology for
estimating human exposures due to radioactive discharges . . . . . . . . . . . . . . . . . . . .

3

2.

Biological effects from selected internal emitters . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

3.

Epidemiology of low-dose-rate exposures of the public to natural and artificial
environmental sources of radiation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

4.

Development of an evaluation of medical exposures . . . . . . . . . . . . . . . . . . . . . . . . .

3

5.

Outreach activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4C.

Strategic plan for 2014-2019 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

D.

Future programme of work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5E.

Administrative issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5

Scientific findings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

A.

Levels and effects of radiation exposure due to the nuclear accident after the 2011 greateast-Japan earthquake and tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

1.

The accident and the release of radioactive material into the environment . . . . . . .

6

2.

Dose assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7

3.

Health implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

4.

Radiation exposures and effects on non-human biota . . . . . . . . . . . . . . . . . . . . . . . . .

11

Effects of radiation exposure on children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12Members of national delegations attending the fifty-eighth to sixtieth sessions of the United
Nations Scientific Committee on the Effects of Atomic Radiation . . . . . . . . . . . . . . . . . . . . . .

15

Scientific staff and consultants cooperating with the United Nations Scientific Committee on
the Effects of Atomic Radiation in the preparation of its scientific report for 2013 . . . . . . . . .

17

B.
Appendices
I.
II.

v

REPORT TO THE GENERAL ASSEMBLY

Chapter I
Introduction
1.
Since the establishment of the United Nations Scientific Committee on
the Effects of Atomic Radiation by the General Assembly in its resolution
913 (X) of 3 December 1955, the mandate of the Committee has been toundertake broad assessments of the sources of ionizing radiation and its
effects on human health and the environment.1 In pursuit of its mandate, theCommittee thoroughly reviews and evaluates global and regional exposuresto radiation. The Committee also evaluates evidence of radiation-induced
health effects in exposed groups and advances in the understanding of thebiological mechanisms by which radiation-induced effects on human healthor on non-human biota can occur. Those assessments provide the scientificfoundation used, inter alia, by the relevant agencies of the United Nations
system in formulating international standards for the protection of thegeneral public and workers against ionizing radiation;2 those standards, inturn, are linked to important legal and regulatory instruments.
2.
Exposure to ionizing radiation arises from naturally occurring sources(such as from outer space and radon gas emanating from rocks in the Earth)and from sources with an artificial origin (such as medical diagnostic andtherapeutic procedures; radioactive material resulting from nuclear weapons
testing; energy generation, including by means of nuclear power; unplanned
events such as the nuclear power plant accidents at Chernobyl in 1986 andfollowing the great east-Japan earthquake and tsunami of March 2011; andworkplaces where exposure to artificial or naturally occurring sources ofradiation may be increased).

__________________
1 The

United Nations Scientific Committee on the Effects of Atomic Radiation wasestablished by the General Assembly at its tenth session, in 1955. Its terms of reference
are set out in resolution 913 (X). The Committee was originally composed of thefollowing Member States: Argentina, Australia, Belgium, Brazil, Canada,
Czechoslovakia (later succeeded by Slovakia), Egypt, France, India, Japan, Mexico,
Sweden, Union of Soviet Socialist Republics (later succeeded by the RussianFederation), United Kingdom of Great Britain and Northern Ireland and United Statesof America. The membership of the Committee was subsequently enlarged by the
Assembly in its resolution 3154 C (XXVIII) of 14 December 1973 to include theFederal Republic of Germany (later succeeded by Germany), Indonesia, Peru, Poland
and the Sudan. By its resolution 41/62 B of 3 December 1986, the Assembly increased
the membership of the Committee to a maximum of 21 members and invited China tobecome a member. In its resolution 66/70 of 9 December 2011, the Assembly further
enlarged the membership of the Committee to 27 and invited Belarus, Finland, Pakistan,
the Republic of Korea, Spain and Ukraine to become members.
2 For example, the international basic safety standards for protection against ionizing
radiation and for the safety of radiation sources, currently co-sponsored by theInternational Labour Organization, the Food and Agriculture Organization of the United
Nations (FAO), the World Health Organization (WHO), the International Atomic
Energy Agency (IAEA), the Nuclear Energy Agency of the Organization for Economic
Cooperation and Development and the Pan American Health Organization.

12 UNSCEAR 2013 REPORT

Chapter II
Deliberations of the United Nations Scientific Committee on the
Effects of Atomic Radiation at its sixtieth session
3.
The Scientific Committee held its sixtieth session in Vienna from 27 to
31 May 2013.3 Carl-Magnus Larsson (Australia), Emil Bédi (Slovakia) andYoshiharu Yonekura (Japan) served as Chair, Vice-Chair and Rapporteur,
respectively. The Committee took note of General Assembly resolution
67/112 on the effects of atomic radiation.

A.

Completed evaluations
4.
The Committee discussed in detail two substantive scientificdocuments. The principal findings of those two documents are summarized
in a scientific report (see chap. III below) and, together with the two detailed
scientific annexes that underpin the findings, will be published separately inthe usual manner, after comments from the Committee have been addressed.
The first document reported the results of an assessment of the levels
5.
and effects of radiation exposure due to the nuclear accident after the 2011
great east-Japan earthquake and tsunami. The General Assembly, in its
resolution 66/70, had endorsed the Committee’s decision at its fifty-eighth
session to conduct that assessment. The Committee acknowledged that it had
been a major undertaking that had required efforts well beyond the resources
normally available to the Committee and its secretariat. Over 80 experts
from 18 countries and 5 international organizations had been involved in thework, constituting a major contribution in kind, and prepared material for theCommittee’s scrutiny at its sixtieth session. The experts had collected andreviewed data and information, and defined methodologies and processes for
ensuring the quality of the data and for their use. Germany, Sweden and
Switzerland had made financial contributions to the general trust fund tosupport the work of the Committee in this regard. An expert (offered by theGovernment of Japan under a non-reimbursable loan arrangement) had been
assisting the secretariat in Vienna.
There were many sources of data: (a) specific datasets in electronic
6.
formats and supplementary information requested of the Government ofJapan and other authenticated Japanese sources; (b) results of measurements
and evaluations made by other United Nations Member States; (c) datasets
made available by international organizations, including the Preparatory
Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization(CTBTO), the Food and Agriculture Organization of the United Nations(FAO), the International Atomic Energy Agency (IAEA), the World HealthOrganization (WHO) and the World Meteorological Organization; (d)information and independent analyses published in peer-reviewed scientificjournals; and (e) measurements made by non-governmental organizations.

__________________
3 The sixtieth session of the Committee was also attended by observers for FAO, WHO,the International Agency for Research on Cancer, the World MeteorologicalOrganization (WMO), IAEA, the Preparatory Commission for the Comprehensive
Nuclear-Test-Ban Treaty Organization (CTBTO), the European Commission, theInternational Commission on Radiological Protection, and the International
Commission on Radiation Units and Measurements.

REPORT TO THE GENERAL ASSEMBLY

37.
The Committee also discussed a substantive scientific document that
represented an extensive review of the effects of exposure to ionizing
radiation during childhood. The Committee had decided at its fifty-seventhsession (16-20 August 2010), in deliberations on its future programme ofwork, that it should undertake to address radiation risks for and effects onchildren, to help clarify how those risks and effects were different forchildren and adults. The delegation of the United States of America had led
the preparation of detailed technical documents on this subject, which had
been discussed at the fifty-eighth (23-27 May 2011) and fifty-ninth sessions(23-27 May 2012).

B.

Present programme of work

1.

Radiation exposures from electricity generation and an updated methodology
for estimating human exposures due to radioactive discharges
8.
The Committee discussed two progress reports, one on an evaluation ofradiation exposures from electricity generation and the other on updating theCommittee’s methodology for estimating human exposures due toradioactive discharges into the environment. The Committee noted that thereview and update of the existing methodology was well advanced. It notedthat electronic spreadsheets were being developed that would implement themethodology for use in conducting the assessment of radiation exposures of
populations from various types of electricity generation. The Committee
anticipated that both documents would be ready for final scrutiny at its sixtyfirst session.

2.

Biological effects from selected internal emitters
9.
The Committee discussed progress on evaluations of the biologicaleffects of exposure to selected internal emitters, addressing two specificradionuclides: tritium and uranium. It considered that further work wasneeded, but envisaged that the two components might be ready for detailed
discussion at the Committee’s sixty-first session.

3.

Epidemiology of low-dose-rate exposures of the public to natural and artificial
environmental sources of radiation
10. The Committee discussed progress on an evaluation of epidemiologicalstudies of low-dose-rate exposures of the public to naturally occurring andartificial environmental sources of radiation. The Committee acknowledgedthat the work was progressing but envisaged that it might not be completed
before the sixty-second session.

4.

Development of an evaluation of medical exposures
11. The Committee took note of a progress report by the secretariat on
developing an evaluation of medical exposures. Because (a) exposures ofpatients undergoing medical procedures represented the most significant
source of artificial exposure to ionizing radiation, (b) technology andpractices in this area were changing rapidly and (c) this was a thematic
priority of the Committee’s strategic plan (2009-2013), the Committee hadrequested the secretariat to prepare a detailed plan for a report on thissubject. It had also requested the secretariat to initiate the Committee’s next
Global Survey of Medical Radiation Usage and Exposures and to foster close
cooperation with other relevant international organizations (such as IAEA

4 UNSCEAR 2013 REPORTand WHO), as appropriate. A web-based questionnaire on medical exposures
had been developed and was being tested. The secretariat planned to initiate
the survey during 2013 and to obtain feedback from the Committee at its
sixty-first session on preliminary findings, with a view to completing theevaluation thereafter.
12. The Committee suggested that the General Assembly might (a)encourage Member States, the relevant organizations of the United Nations
system and other pertinent organizations to provide further relevant data
about doses, effects and risks from various sources of radiation, which would
help greatly in the preparation of future reports of the Committee to the
Assembly; and (b) encourage IAEA, WHO and other relevant organizations
to further collaborate with the Committee’s secretariat to establish andcoordinate the arrangements for the periodic collection and exchange of dataon radiation exposures of the general public, workers and, in particular,
patients.
5.

Outreach activities
13. The Committee took note of progress reports by the secretariat onoutreach activities, in particular plans for the dissemination of theCommittee’s report on the levels and effects of radiation exposure due to the
nuclear accident after the 2011 great east-Japan earthquake and tsunami. It
took note of the progress that the secretariat had made in enhancing the
public website of the Committee, developing leaflets and posters andupdating a booklet to explain in plain language the findings of its recent
reports.

C.

Strategic plan for 2014-2019
14. The Committee discussed a strategic plan to provide vision anddirection for all its activities during the period 2014-2019, to facilitate
results-based programming by the secretariat, to help foster the managementof sufficient, assured and predictable resources and to improve planning andcoordination among the various parties involved.
15. The Committee considered that its strategic objective for the period
2014-2019 was to increase awareness and deepen under-standing among
decision makers, the scientific community and civil society with regard tolevels of exposure to ionizing radiation and the related health andenvironmental effects as a sound basis for informed decision-making onradiation-related issues.
16. The Committee identified its thematic priorities for the period: (a) the
global impact of energy production (including follow-up of the radiologicalconsequences of the 2011 accident at the Fukushima Daiichi nuclear power
station) and of the rapidly expanding use of ionizing radiation in medical
diagnosis and treatment; and (b) radiation effects at low doses and low dose
rates.
17. Further strategic shifts were envisaged in order to better meet the needsof Member States, including: (a) further streamlining the Committee’sscientific evaluation processes to complete both wide-ranging summary
reports on the levels and effects of radiation exposure and preparing special
reports that respond to emerging issues as the need arises; (b) further using
intersessional expert groups to develop assessment methodologies, conduct

REPORT TO THE GENERAL ASSEMBLY

evaluations and maintain surveillance on emerging issues; (c) developing
networks of experts, scientific focal points in Member States and centres of
excellence to facilitate access to expertise; (d) further enhancing mechanisms
for data collection, analysis and dissemination; and (e) further raisingawareness and improving dissemination of the Committee’s findings inreadily understandable formats for decision makers and the public.

D.

Future programme of work
18. At its previous session, the Committee had decided that the work toassess the levels of exposure and radiation risks resulting from the nuclear
accident following the great east-Japan earthquake and tsunami of March2011 and to complete an extensive review of the effects of radiation
exposure on children should take priority over other evaluations andactivities that had been initiated as part of the present programme of work.
Because those two studies were to be completed and published during thefollowing months, the Committee, in discussions about its future programmeof work, agreed to focus on completing other outstanding evaluations that
had been delayed owing to the unexpected work resulting from the accident
at the Fukushima Daiichi nuclear power station, and not to introduce further
new topics at this stage.

E.

Administrative issues
19. The Committee welcomed developments in streamlining procedures for
publishing the Committee’s reports as sales publications. Nevertheless theCommittee suggested that the General Assembly might request the United
Nations Secretariat to continue to streamline the procedures, recognizing
that, while maintaining quality, the timeliness of their publication isparamount to fulfil the expected accomplishments approved in the
programme budget, and expecting that the report ought to be publishedwithin the same year in which it is approved.
20. The Committee recognized that, because of the need to maintain theintensity of its work and particularly to improve dissemination of its
findings, voluntary contributions to the general trust fund established by the
Executive Director of the United Nations Environment Programme toreceive and manage voluntary contributions to support the work of theCommittee would be beneficial. The Committee suggested that the General
Assembly might encourage Member States to consider making voluntary
contributions to the general trust fund for this purpose or to makecontributions in kind.
21. The Committee agreed to hold its sixty-first session in Vienna from26 to 30 May 2014.

5

6 UNSCEAR 2013 REPORT

Chapter III
Scientific findings
22. Two scientific annexes (published separately) provide the rationale forthe conclusions expressed in the present chapter.

A.

Levels and effects of radiation exposure due to the nuclear
accident after the 2011 great east-Japan earthquake andtsunami1.

The accident and the release of radioactive material into the environment
23. On 11 March 2011, at 14.46 local time, a 9.0-magnitude earthquake
occurred near Honshu, Japan, creating a devastating tsunami that left a trail
of death and destruction in its wake. The earthquake and subsequenttsunami, which flooded over 500 square kilometres of land, resulted in theloss of more than 20,000 lives and destroyed property, infrastructure andnatural resources. They also led to the worst civil nuclear disaster since theone at Chernobyl in 1986. The loss of off-site and on-site electrical powerand compromised safety systems at the Fukushima Daiichi nuclear power
station led to severe core damage to three of the six nuclear reactors on thesite; this resulted in the release, over a prolonged period, of very large
amounts of radioactive material into the environment.
24. As an immediate response, the Government of Japan recommended theevacuation of about 78,000 people living within a 20-km radius of the power
plant and the sheltering in their own homes of about 62,000 other people
living between 20 and 30 km from the plant. Later, in April 2011, theGovernment recommended the evacuation of about 10,000 more people
living farther to the north-west of the plant (referred to as the deliberate
evacuation area), because of the high levels of radioactive material on the
ground. The evacuations greatly reduced (by up to a factor of 10) the levelsof exposure that would otherwise have been received by those living in thoseareas. However, the evacuations themselves also had repercussions for thepeople involved, including a number of evacuation-related deaths and thesubsequent impact on mental and social well-being (for example, because
evacuees were separated from their homes and familiar surroundings, andmany lost their livelihoods).
25. The information reviewed by the Committee implies atmosphericreleases of iodine-131 and caesium-137 (two of the more significant
radionuclides from the perspective of exposures to people and theenvironment) in the ranges of 100 to 500 petabecquerels (PBq) and 6 to
20 PBq, respectively; for its further work, the Committee used estimates thatlie within those ranges. These estimates are lower, indicatively, by a factor of
about 10 and 5, respectively, than corresponding estimates of atmosphericreleases resulting from the Chernobyl accident. Winds transported a large
portion of the atmospheric releases to the Pacific Ocean. In addition, liquid
releases were discharged directly into the surrounding sea. The directdischarges amounted to perhaps 10 and 50 per cent of the corresponding
atmospheric discharges for iodine-131 and caesium-137, respectively; lowlevel releases into the ocean were still ongoing in May 2013.

REPORT TO THE GENERAL ASSEMBLY

2.

Dose assessment
26. Iodine-131 (with a short half-life of 8 days) and caesium-137 (with amuch longer half-life of 30 years) were found to be the two most importantradionuclides for dose assessment. For those two radionuclides, the affected
tissues and the time span of the exposure were quite different. Iodine-131
tended to accumulate in the thyroid gland for a few weeks after the releaseand delivered a dose primarily to that organ. Caesium-137 was deposited on
the ground; it delivers a dose to the whole body over many years following
the release.
27. The Committee has made estimates of the radiation exposures ofvarious categories of people, namely: members of the public exposed as aresult of the release of radioactive material into the environment;
occupationally exposed workers employed at the Fukushima Daiichi nuclear
power station at the time of the accident and those subsequently involved in
on-site recovery operations; and emergency personnel involved in on-site
and/or off-site activities. Where practicable, the Committee based its
evaluations on results of individual monitoring. Occupationally exposed
workers and emergency personnel were generally monitored for exposure tosources of radiation external to the body (external exposures) and for
exposures from intakes of radioactive materials into the body (internal
exposures) where these may have been significant.
28. At the time the Committee’s evaluation began, few direct
measurements of internal exposures were available for members of the
public. These were insufficient for the Committee to estimate doses for theareas in Japan most affected by the accident. Therefore, the Committee had
to rely on the use of various models to estimate doses on the basis ofmeasured, or predicted, levels of radioactive material in the environment andtheir transfer through the environment to humans (for example, the figure
illustrates the pattern — derived from measurements — of caesium-137
deposition in the areas of Japan most affected as a result of the accident). Of
necessity, modelling had to be used to forecast potential doses in the future.

7

8 UNSCEAR 2013 REPORT

FigureDeposition of caesium-137 on the ground in the Fukushima Prefecture andneighbouring prefectures based on measurement data adjusted to 14 June 2011
This map is derived by interpolating between measurements; its aim is
to portray the overall pattern of deposition levels and extent rather than toindicate precise demarcation areas.

Miyagi

Yamagata
38°N

Niigata

Fukushima-Daiichi
nuclear power
stationFukushima

37°N

Gunma

Tochigi
IbarakiNote: The boundaries and names shown and the designations used on this map
do not imply official endorsement or acceptance by the United Nations.
Source: Norwegian Radiation Protection Authority.

140°E
Density of caesium-137 deposition on the ground(kilobecquerels per square metre)

141°E
0

10

20

30

40

50 km

>1000
100 - 1000
10 - 100<10

29. The estimated effective doses resulting from the accident at the
Fukushima Daiichi nuclear power station can be put in perspective bycomparing them with those received from exposures to radiation sources ofnatural origin (such as cosmic rays and naturally occurring radioactive
material in food, air, water and other parts of the environment). The Japanesepeople receive an effective dose of radiation from naturally occurringsources of, on average, about 2.1 millisieverts (mSv) annually and a total of
about 170 mSv over their lifetimes. The Committee’s latest estimate for the
global average annual exposure to naturally occurring sources of radiation is
2.4 mSv and ranges between about 1 and 13 mSv, while sizeable populationgroups receive 10 to 20 mSv annually.4 Absorbed doses to individual organs
are expressed in milligrays (mGy). The average annual absorbed dose to thethyroid from naturally occurring sources of radiation is typically of the orderof 1 mGy.
__________________
4 Official Records of the General Assembly, Sixty-third Session, Supplement No. 46(A/63/46), table 1.

REPORT TO THE GENERAL ASSEMBLY(a)

Members of the public
30. The districts with the highest average estimated doses for members of
the public were within the 20-km evacuation zone and the deliberate
evacuation area. For adults, the effective dose estimated to have been
received before and during the evacuation was, on average, less than 10 mSv
and about half of that level for those evacuated early on 12 March 2011. The
corresponding estimated average absorbed dose to the thyroid was up to
about 35 mGy. For 1-year-old infants, the effective dose was estimated to beabout twice that for adults and the dose to the thyroid was estimated to be up
to about 80 mGy, as much as one half of which arose from the ingestion ofradioactivity in food. However, there was considerable variation between
individuals around this value, depending on their location and what foodthey consumed.
31. Adults living in the city of Fukushima were estimated to have received,on average, an effective dose of about 4 mSv in the first year following theaccident; estimated doses for 1-year-old infants were about twice as high.
Those living in other districts within the Fukushima Prefecture and inneighbouring prefectures were estimated to have received comparable or
lower doses; even lower doses were estimated to have been received
elsewhere in Japan. Lifetime effective doses (resulting from the accident)
that, on average, could be received by those continuing to live in the
Fukushima Prefecture have been estimated to be just over 10 mSv; thisestimate assumes that no remediation measures will be taken to reduce dosesin the future and, therefore, may be an overestimate. The most importantsource contributing to these estimated doses was external radiation from
deposited radioactive material.
32. Doses higher or lower than the average values above can be estimatedfor people with habits or behaviour significantly different from the average,
and/or for those living in areas where the levels of radioactive material wereor are significantly different from the average for a particular district orprefecture. Within a district the individual doses related to inhalation andexposure to external radiation typically range from about one third of theaverage up to three times the average. Larger doses cannot be totally
discounted for some individuals — in particular, if they consumed certain
locally produced foodstuffs in the aftermath of the accident despite
governmental advice or continued living in evacuation areas for an extended
period. Some infants may have received thyroid doses of 100 mGy or more.
33. Some information on internal doses, based on direct measurements ofradioactivity in people, was available shortly after the accident, but more
information became available after the Committee completed its dose
estimations. Collectively, these measurements of radioactive content of the
thyroid and of the whole body indicated doses due to internal exposure lower
than those estimated by the Committee, by a factor of about 3 to 5 forthyroid doses and up to about 10 for whole-body doses. Thus, the Committee
considers that its dose estimates may overestimate actual exposures.
34. Radiation exposures in neighbouring countries and the rest of the world
resulting from the accident were far below those received in Japan; effective
doses were less than 0.01 mSv, and thyroid doses were less than 0.01 mGy;these levels would be of no consequence for the health of individuals.

910 UNSCEAR 2013 REPORT(b)

Fukushima Daiichi nuclear power station workers, emergency
personnel, municipal workers and volunteers
35. By the end of October 2012, about 25,000 workers had been involved
in mitigation and other activities at the Fukushima Daiichi nuclear power
station site; about 15 per cent of them were employed directly by the plant
operator (Tokyo Electric Power Company (TEPCO)), while the rest were
employed by contractors or subcontractors. According to their records, theaverage effective dose of the 25,000 workers over the first 19 months after
the accident was about 12 mSv. About 35 per cent of the workforce received
total doses of more than 10 mSv over that period, while 0.7 per cent of theworkforce received doses of more than 100 mSv.
36. The Committee examined the data on internal exposure for 12 of themost exposed workers and confirmed that they had received absorbed doses
to the thyroid in the range of 2 to 12 Gy, mostly from inhalation of iodine131. The Committee also found reasonable agreement between its
independent assessments of effective dose from internal exposure and thosereported by TEPCO for those workers for whom there were measurable
levels of iodine-131 in the body. No account was taken of the potential
contribution from intakes of shorter-lived isotopes of iodine, in particulariodine-133; as a result, the assessed doses from internal exposure could havebeen underestimated by about 20 per cent. For many workers, because of thelong delay before monitoring, iodine-131 was not detected in their thyroids;
for those workers the internal doses estimated by TEPCO and its contractors
are uncertain.
37. Apart from those groups, in vivo monitoring of 8,380 personnel
affiliated with the United States Department of Defense was carried out
between 11 March 2011 and 31 August 2011. About 3 per cent of thosemonitored had measurable activity levels with a maximum effective dose of
0.4 mSv and a maximum absorbed dose to the thyroid of 6.5 mGy.

3.

Health implications
38. No radiation-related deaths or acute diseases have been observed
among the workers and general public exposed to radiation from theaccident.
39. The doses to the general public, both those incurred during the firstyear and estimated for their lifetimes, are generally low or very low. No
discernible increased incidence of radiation-related health effects are
expected among exposed members of the public or their descendants. The
most important health effect is on mental and social well-being, related tothe enormous impact of the earthquake, tsunami and nuclear accident, andthe fear and stigma related to the perceived risk of exposure to ionizing
radiation. Effects such as depression and post-traumatic stress symptoms
have already been reported. Estimation of the occurrence and severity ofsuch health effects are outside the Committee’s remit.
40. For adults in Fukushima Prefecture, the Committee estimates average
lifetime effective doses to be of the order of 10 mSv or less, and first-yeardoses to be one third to one half of that. While risk models by inference
suggest increased cancer risk, cancers induced by radiation are
indistinguishable at present from other cancers. Thus, a discernible increasein cancer incidence in this population that could be attributed to radiation
exposure from the accident is not expected. An increased risk of thyroid

REPORT TO THE GENERAL ASSEMBLY

cancer in particular can be inferred for infants and children. The number of
infants that may have received thyroid doses of 100 mGy is not known withconfidence; cases exceeding the norm are estimated by model calculations
only, and in practice they are difficult to verify by measurement.
41. For the 12 workers whose exposure data were scrutinized by theCommittee and who were estimated to have received absorbed doses to thethyroid from iodine-131 intake alone in the range of 2 to 12 Gy, an increased
risk of developing thyroid cancer and other thyroid disorders can be inferred.
More than 160 additional workers received effective doses currently
estimated to be over 100 mSv, predominantly from external exposures.
Among this group, an increased risk of cancer would be expected in the
future. However, any increased incidence of cancer in this group is expected
to be indiscernible because of the difficulty of confirming such a small
incidence against the normal statistical fluctuations in cancer incidence.
Workers exposed to doses above 100 mSv will be specially examined,
including through annual examinations of the thyroid, stomach, large
intestine and lungs for potential late radiation-related health effects.
42. In June 2011, a health survey of the local population (the Fukushima
Health Management Survey) was initiated. The survey, which began in
October 2011 and is planned to continue for 30 years, covers all 2.05 million
people living in Fukushima Prefecture at the time of the earthquake andreactor accident. It includes a thyroid ultrasound survey of 360,000 children
aged up to 18 years at the time of the accident, using modern high-efficiency
ultrasonography, which increases the ability to detect small abnormalities.
Increased rates of detection of nodules, cysts and cancers have been
observed during the first round of screening; however, these are to be
expected in view of the high detection efficiency. Data from similar
screening protocols in areas not affected by the accident imply that theapparent increased rates of detection among children in Fukushima
Prefecture are unrelated to radiation exposure.
4.

Radiation exposures and effects on non-human biota
43. Exposures of selected non-human biota in the natural environment
were also estimated. The doses and associated effects of radiation on nonhuman biota following the accident were evaluated against the Committee’s
previous evaluations of such effects.5 Exposures of both marine andterrestrial non-human biota following the accident were, in general, too low
for acute effects to be observed, though there may have been some
exceptions because of local variability:(a) Effects on non-human biota in the marine environment would be
confined to areas close to where highly radioactive water was released into
the ocean;(b) Continued changes in biomarkers for certain terrestrial organisms,
in particular mammals, cannot be ruled out, but their significance forpopulation integrity of those organisms is unclear. Any radiation effects
would be restricted to a limited area where the deposition of radioactive
material was greatest; beyond that area, the potential for effects on biota is
insignificant.

__________________
5 See Official Records of the General Assembly, Fifty-first Session, Supplement No. 46(A/51/46), and Sixty-third Session, Supplement No. 46 (A/63/46).

11

12 UNSCEAR 2013 REPORT

44. While it was not within the scope of the Committee’s evaluation, it isimportant to note that the effects of the protective actions and any
remediation conducted to reduce human exposure have a significant impact
on, inter alia, environmental goods and services, resources used inagriculture, forestry, fisheries and tourism, and amenities used in spiritual,cultural and recreational activities.

B.

Effects of radiation exposure of children
45. Epidemiological studies reported in the literature vary with regard to
the specific age groups they consider. For the purposes of the Committee’s
evaluation of the effects of radiation exposure on children, the term
“children”, in contrast to “adults”, included those exposed as infants,
children and adolescents. The evaluation did not specifically address effects
of in utero exposure to radiation because such information is contained inother comprehensive reports. The evaluation also did not address the many
beneficial uses of radiation exposure for children, such as in medical
diagnosis and therapy, which are outside the mandate of the Committee.
46. Sources of exposure to children that are of particular interest include
accidental exposures, and specific regions with enhanced levels of natural
background radiation, as well as diagnostic and therapeutic procedures. The
data reviewed by the Committee were derived from studies covering a wide
range of doses, variable dose rates, whole and partial body exposure andchildren of different ages. The effects described in the annex are often very
specific to a given exposure scenario.
47. At its sixtieth session the Committee considered the effects of radiation
exposure of children and reached the following conclusions:(a) For a given radiation dose, children are generally at more risk oftumour induction than are adults. Cancers potentially induced by exposure toionizing radiation at young ages may occur within a few years, but also
decades later. In its report on its fifty-fourth session, the Committee statedthat estimates of lifetime cancer risk for those exposed as children wereuncertain and might be a factor of 2 to 3 times as high as estimates for a
population exposed at all ages.6 That conclusion was based on a lifetime risk
projection model combining the risks of all tumour types together;(b) The Committee has reviewed evolving scientific material andnotes that radiogenic tumour incidence in children is more variable than in
adults and depends on the tumour type, age and gender. The term “radiation
sensitivity” with regard to cancer induction refers to the rate of radiogenic
tumour induction. The Committee reviewed 23 different cancer types.
Broadly, for about 25 per cent of these cancer types, including leukaemia andthyroid, skin, breast and brain cancer, children were clearly moreradiosensitive. For some of these types, depending on the circumstances, therisks can be considerably higher for children than for adults. Some of thesecancer types are highly relevant for evaluating the radiological consequencesof accidents and of some medical procedures;(c) For about 15 per cent of the cancer types (e.g. colon cancer),children appear to have about the same radiosensitivity as adults. For about__________________
6 Official Records of the General Assembly, Sixty-first Session, Supplement No. 46 andcorrigendum (A/61/46 and Corr.1) paras. 21-22.

REPORT TO THE GENERAL ASSEMBLY

10 per cent of cancer types (e.g. lung cancer), children appear less sensitive
to external radiation exposure than adults. For about 20 per cent of cancer
types (e.g. oesophagus cancer), the data are too weak to draw a conclusion
regarding any differences in risk. Finally, for about 30 per cent of cancer
types (e.g. Hodgkin’s disease and prostate, rectum and uterus cancer), there
is only a weak relationship or none at all between radiation exposure andrisk at any age of exposure;(d) At present, projections of lifetime risk for specific cancer types
following exposure at young ages are statistically insufficient. Estimatescurrently do not adequately capture the known variations, and additional
studies are needed;(e) For direct effects that occur after high (either acute or
fractionated) doses (so-called deterministic health effects), the differences inoutcome between exposure in childhood and in adulthood are complex andcan be explained by the interaction of different tissues and mechanisms.
These effects may be seen after radiation therapy or following highexposures in accidents. The difference between the radiation sensitivity ofchildren and that of adults for deterministic effects in a specific organ isoften not the same as the difference for cancer induction. There are someinstances in which childhood exposure poses more risk than adulthood
exposure (e.g. risk of cognitive defects, cataracts and thyroid nodules). There
are other instances where the risk appears to be about the same (e.g. risk ofneuroendocrine abnormalities), and there are a few instances wherechildren’s tissues are more resistant (e.g. lungs and ovaries);(f) Because of all the above considerations, the Committee
recommends that generalizations on the risks of effects of radiation exposure
during childhood should be avoided. Attention should be directed to
specifics of the exposure, age at exposure, absorbed dose to certain tissues
and the particular effects of interest;(g) There have been many studies of possible heritable effects
following radiation exposure; such studies were reviewed by the Committee
in 2001. It has been generally concluded that no heritable effects in humans
due to radiation exposure have been explicitly identified (specifically instudies of offspring of survivors of the atomic bombings). Over the past
decade, there have been additional studies that have focused on survivors ofchildhood and adolescent cancer following radiotherapy, where gonadal
doses are often very high. There is essentially no evidence of an increase inchromosomal instability, minisatellite mutations, transgenerational genomic
instability, change in sex ratio of offspring, congenital anomalies orincreased cancer risk in the offspring of parents exposed to radiation. One
reason for this is the large fluctuation in the spontaneous incidence of theseeffects;(h) Health effects and risks are dependent on a number of physicalfactors. Because children have smaller body diameters and there is lessshielding by overlying tissues, the dose to their internal organs will be larger
than for an adult for a given external exposure. Because they are also shorter
than adults, children may receive a higher dose from radioactivity distributedin and deposited on the ground. These factors are important when
considering doses to populations in some areas with high levels ofradionuclides in and on the ground. In diagnostic medical exposure, children
may receive significantly higher doses than adults for the same examination

13

14 UNSCEAR 2013 REPORT

if the technical parameters for delivering the dose are not specifically
adapted;(i) Regarding internal exposure, because of the smaller size of
infants and children, and thus because their organs are closer together,radionuclides concentrated in one organ irradiate other organs of children’sbodies more than occurs in adults. There are also many other age-related
factors involving metabolism and physiology that make a substantial
difference in dose at different ages. Several radionuclides are of particularconcern regarding internal exposure of children. Accidents involving
releases of radioactive iodines (for example, in a nuclear power plant
accident) can be significant sources of exposure of the thyroid gland, andthus have the potential to induce thyroid cancer. For a given intake, the doseto the thyroid for infants is eight or nine as large as that for adults. For
intakes of caesium-137, there is very little difference in dose between
children and adults. Internal exposure of children also occurs in the medical
use of radionuclides. The spectrum of procedures normally performed onchildren is different from that performed on adults. Potentially higher doses
in children are offset in practice by the use of a lower amount ofadministered radioactive material.
48. The Committee recognizes that continued research is needed to identify
the full scope and expression of the differences in effects, mechanisms andrisk from exposure to ionizing radiation for children and for adults. This isnecessary because for a number of studies (such as of the atomic bombing
survivors, children exposed to radioiodine after the Chernobyl accident andthose who have had computed tomography scans), the lifetime results remain
incomplete. Future long-term studies following childhood exposure will facesignificant difficulties owing to unlinked health records, administrative andpolitical barriers and ethical and privacy considerations.
49. Important areas of future research and work also include evaluation ofpotential radiation effects for children: (a) in areas of high natural
background exposure; (b) after high-dose medical procedures involving
interventional fluoroscopy; and (c) after cancer radiotherapy (including
evaluation of potential interactions with other therapies). The Committee has
identified the following areas for future research as well: development of
databases on radiation doses for children who can be tracked in the longterm; and evaluation of effects following whole and partial irradiation ofjuvenile organs. Studies at the molecular, cellular, tissue and juvenile animallevel are potentially informative.

REPORT TO THE GENERAL ASSEMBLY

15

Appendix I
Members of national delegations attending the fifty-eighth to
sixtieth sessions of the United Nations Scientific Committee on
the Effects of Atomic Radiation
Argentina

A. J. González (Representative), A. Canoba, M. di Giorgio

Australia

C. M. Larsson (Representative), C. Baggoley, G. Hirth,
S. B. Solomon, R. Tinker

BelarusJ. Kenigsberg (Representative), A. Stazharau, V. Ternov

Belgium

H. Vanmarcke (Representative), S. Baatout, H. Bijwaard,
H. Bosmans, G. Eggermont, H. Engels, F. Jamar,
L. Mullenders, H. Slaper, P. Smeesters, A. Wambersie,
P. Willems

BrazilJ. Hunt (Representative), D. R. Melo (Representative),
M. Nogueira Martins (Representative), M. C. Lourenço,
L. Holanda Sadler Veiga

CanadaC. Purvis (Representative), B. Pieterson (Representative),
N. E. Gentner (Representative), D. Boreham, K. Bundy,
D. B. Chambers, J. Chen, S. Hamlat, R. Lane, C. Lavoie,
E. Waller

China

Pan Z. (Representative), Chen Y., Du Y., Gao H., Liu J.,
Liu S., Pan S., Su X., Sun Q., Wang Y., Yang H., Zhang W.,
Zhu M.

Egypt

T. S. El-Din Ahmed (Representative), M.A.M. Gomaa(Representative)

Finland

S. Salomaa (Representative), A. Auvinen, E. Salminen

FranceL. Lebaron-Jacobs (Representative), A. Rannou(Representative), E. Ansoborlo, M. Bourguignon,
J.-R. Jourdain, F. Ménétrier, M. Tirmarche

Germany

W. Weiss (Representative), A. A. Friedl, K. Gehrcke,
P. Jacob, T. Jung, G. Kirchner, J. Kopp, R. Michel,
W. U. Müller

India

K. B. Sainis (Representative), B. Das, P. C. Kesavan,
Y. S. Mayya, K. S. Pradeepkumar

Indonesia

S. Widodo (Representative), Z. Alatas, G. B. Prajogi,
G. Witono, B. Zulkarnaen

Japan

Y. Yonekura (Representative), S. Akiba, T. Aono, N. Ban,
M. Chino, K. Kodama, M. Kowatari, M. Nakano, O. Niwa,
K. Ozasa, S. Saigusa, G. Suzuki, T. Takahashi, Y. Yamada,
H. Yamagishi

MexicoJ. Aguirre Gómez (Representative)

Pakistan

M. Ali (Representative), Z. A. Baig

Peru

A. Lachos Dávila (Representative), B. M. García Gutiérrez

16 UNSCEAR 2013 REPORT

PolandM. Waligórski (Representative), L. Dobrzyński, M. Janiak,
M. Kruszewski

Republic of Korea

K.-W. Cho (Representative), S. H. Na (Representative),
K.-H. Do, D.-K. Keum, J.-I. Kim, J. K. Lee, S. Y. Nam

RussianFederation

M. Kiselev (Representative), A. Akleyev, R. Alexakhin,
T. Azizova, V. Ivanov, N. Koshurnikova, A. Koterov,
I. Kryshev, B. Lobach, O. Pavlovskiy, A. Rachkov,
S. Romanov, A. Sazhin, S. Shinkarev

Slovakia

E. Bédi (Representative), M. Chorváth, Ž. Kantová,
K. Petrová, L. Tomášek, I. ZachariášováSpain

M. J. Muñoz González (Representative), M. T. Macías
Domínguez, B. Robles Atienza, E. Vañó Carruana

Sudan

M.A.H. Eltayeb (Representative), I. Salih Mohamed Musa
(Representative), E.A.E. Ali (Representative)

SwedenL. Hubbard (Representative), L. Moberg (Representative),
A. Almén, L. Gedda, J. Johansson Barck-Holst

UkraineD. Bazyka (Representative)

United Kingdomof Great Britain
and Northern
Ireland

J. Harrison (Representative), J. Cooper (Representative),
S. Bouffler, J. Simmonds, R. Wakeford

United States ofAmerica

F. A. Mettler Jr. (Representative), L. R. Anspaugh,
J. D. Boice Jr., N. H. Harley, E. V. Holahan Jr.,R. J. Preston

REPORT TO THE GENERAL ASSEMBLY

Appendix II
Scientific staff and consultants cooperating with the United
Nations Scientific Committee on the Effects of Atomic Radiationin the preparation of its scientific report for 2013
G. N. Kelly
V. Golikov
L. S. Constine
H. D. Nagel
D. Nosske
R. Shore

Secretariat of the United Nations Scientific Committee on the
Effects of Atomic Radiation
M. J. Crick
F. Shannoun
H. Yasuda (seconded)17

Corrigendum to Sales No. E.14.IX.1

18 May 2016

Sources, Effects and Risks of Ionizing Radiation: United
Nations Scientific Committee on the Effects of Atomic
Radiation 2013 Report
Volume I
Annex A (Levels and effects of radiation exposure due to the nuclear accident
after the 2011 great east-Japan earthquake and tsunami)Corrigendum
1.

Page 239, table D14

For the title of the subcolumn headed “5-10” under the column headed“TEPCO”, for 5-10 read 5-20
For the title of the subcolumn headed “5-10” under the column headed“Contractor”, for 5-10 read 5-20

V.16-02908 (E)*1602908*

ANNEX A
LEVELS AND EFFECTS OF RADIATION EXPOSURE
DUE TO THE NUCLEAR ACCIDENT
AFTER THE 2011 GREAT EAST-JAPAN
EARTHQUAKE AND TSUNAMI

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

CONTENTS
I.

21

page

INTRODUCTION................................................................................................................................... 25

II. CHRONOLOGY OF THE ACCIDENT................................................................................................ 28
A. Accident progression ................................................................................................................ 28
B. Release to the environment.................................................................................................... 35
C. Actions taken relevant to public exposure........................................................................ 36
D. Actions taken relevant to occupational exposure.......................................................... 38
III. RADIONUCLIDE RELEASES, DISPERSION AND DEPOSITION................................................ 39
A. Radionuclide releases ............................................................................................................... 39
1. Release to the atmosphere.............................................................................................. 39
2. Release to the marine environment............................................................................. 41
3. Summary of releases to the environment.................................................................. 42
B. Dispersion and deposition in the environment .............................................................. 43
1. Atmosphere and terrestrial environment .................................................................. 43
2. Marine environment .......................................................................................................... 46
IV. ASSESSMENT OF DOSES TO THE PUBLIC ................................................................................... 46
A. Exposure pathways.................................................................................................................... 47
B. Data for dose assessment ........................................................................................................ 48
C. Overview of methodology for assessing public exposures......................................... 50
D. Results of dose estimation ...................................................................................................... 52
1. Doses in the first year to members of the public not evacuated....................... 53
2. Doses to evacuees............................................................................................................... 57
3. Estimation of doses in Japan for exposure over future years.............................. 58
4. Estimation of doses in other countries........................................................................ 60
E. Uncertainties ................................................................................................................................ 60
F. Comparison with direct measurements and other assessments .............................. 62
1. Direct measurements of radionuclides in people ................................................... 62
2. Other assessments.............................................................................................................. 62

22 UNSCEAR 2013 REPORT

V. ASSESSMENT OF DOSES TO WORKERS ....................................................................................... 63
A. Introduction.................................................................................................................................. 63
B. Conditions affecting doses and health............................................................................... 64
C. Actions taken to protect workers from radiation............................................................ 65
D. Reported doses............................................................................................................................ 66
E. Evaluation of monitoring and dosimetry........................................................................... 69
1. Internal exposure ................................................................................................................ 70
2. External exposure................................................................................................................ 70
F. Evaluation of assessment of internal exposure ............................................................... 71
VI. HEALTH IMPLICATIONS .................................................................................................................... 74
A. General considerations............................................................................................................. 74
B. Health implications for the public ........................................................................................ 77
1. Observed health effects.................................................................................................... 77
2. Estimated health risks........................................................................................................ 77
3. Health screening.................................................................................................................. 79
C. Health implications for workers engaged in emergency work.................................. 80
1. Observed health effects.................................................................................................... 80
2. Estimated health risks........................................................................................................ 80
3. Health screening.................................................................................................................. 81
VII. ASSESSMENT OF DOSES AND EFFECTS FOR NON-HUMAN BIOTA ................................... 82
A. Introduction.................................................................................................................................. 82
B. Exposure and effects ................................................................................................................. 82
1. Terrestrial ecosystems ....................................................................................................... 82
2. Aquatic ecosystems............................................................................................................ 84
VIII. SUMMARY AND CONCLUSIONS .................................................................................................... 84
A. Basis for dose estimates ........................................................................................................... 85
B. Public exposures ......................................................................................................................... 86
C. Worker exposures....................................................................................................................... 87
D. Health implications for the public and for workers........................................................ 88
1. Public health implications................................................................................................ 89
2. Health implications for workers..................................................................................... 90
E. Radiation exposures and effects on non-human biota ................................................ 90
F. Future scientific research needs............................................................................................ 91

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

23

ACKNOWLEDGEMENTS............................................................................................................................ 93
APPENDIX A. DATA COMPILATION..................................................................................................... 95
APPENDIX B. RADIONUCLIDE RELEASES, DISPERSION AND DEPOSITION..........................109
APPENDIX C. ASSESSMENT OF DOSES TO THE PUBLIC .............................................................159
APPENDIX D. ASSESSMENT OF DOSES TO WORKERS ................................................................211
APPENDIX E. HEALTH IMPLICATIONS FOR THE PUBLIC AND WORKERS .............................245
APPENDIX F. ASSESSMENT OF DOSES AND EFFECTS FOR NON-HUMAN BIOTA ............267
GLOSSARY...................................................................................................................................................285
REFERENCES...............................................................................................................................................289

The attachments cited in this annex are electronically available for download fromhttp://www.unscear.org/unscear/en/publications/2013_1_Attachments.html

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

25

I. INTRODUCTION
1.
On 11 March 2011 at 14:46 local time, a 9.0 magnitude earthquake occurred near Honshu, Japanproducing a devastating tsunami (“the great east-Japan earthquake and tsunami”) that endangered
people, property, infrastructure and natural resources. The tsunami flooded over 500 square kilometresof land, and the earthquake and tsunami together resulted in an estimated 18,703 fatalities, 2,674
persons missing, and 6,220 persons injured as of 1 September 2013 [M21]. More than 250,000
buildings were destroyed or partially destroyed, and at least another 750,000 were partially damaged;
22,000 fishing boats were destroyed and over 200 square kilometres of farmland were so damaged bysalt water inundation that they could not be cultivated for two or more years.
2.
The natural disaster also led to severe damage to the Fukushima Daiichi Nuclear Power Station(FDNPS). A large amount of radioactive material was released to the atmosphere and to the sea. At theend of 2013, more than 100,000 people were still displaced due to the accident, releases ofradionuclides to the marine environment were still ongoing and workers on site were faced withcomplex problems related to removal of fuel from the spent fuel pools and management of damaged
reactor cores. Recovery operations in the areas most affected by the accident as well as efforts on
remediation of land and decommissioning of the damaged site will continue over decades and will
warrant monitoring of levels of exposure 1 and the health implications, on site and off site, overextended periods.
3.
At its fifty-eighth session in May 2011, the Scientific Committee decided to carry out, once
sufficient information was available, an assessment of the levels of exposure and radiation risks
attributable to the nuclear power plant accident following the great east-Japan earthquake and tsunami
of March 2011. The General Assembly subsequently endorsed that decision in its resolution 66/70.
4.
Many data were available regarding the radiation levels and deposition densities of radioactive
material in every prefecture in Japan, the concentrations in foodstuffs, and public and worker exposure.
Many of these data were provided by official government agencies in Japan; many were published inpeer-reviewed scientific journals. Twenty-five Member States of the United Nations other than Japan
officially provided information in response to the Committee’s request for data to support its
assessment. Additional data were made available by other international organizations, including the
Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), theFood and Agricultural Organization of the United Nations (FAO), the International Atomic Energy
Agency (IAEA), the World Health Organization (WHO), and the World Meteorological Organization(WMO). The Committee also considered data made available by several non-governmentalorganizations. All data were evaluated to determine their suitability for the assessment. Information on
the data collection process, the assessment methodologies, and quality assurance procedures can befound in appendix A; data and methodologies used for the assessment are issued as attachments to thisannex and its appendices. The Committee formally agreed to rely principally on data available andliterature published before the end of September 2012. However, in finalizing this scientific annex, theCommittee took into account where appropriate and practicable any significant new information that
became available after that date up until the end of 2013. Limited uncertainty/sensitivity studies were1
In this report, exposure is used in the general sense to express the act, condition or degree of being subject to irradiation, and notin the sense of a physical quantity.

26 UNSCEAR 2013 REPORT

conducted, as appropriate, to underpin the Committee’s qualitative statements of its confidence in its
conclusions.
5.
The Committee received a great deal of assistance and cooperation from many scientists andinstitutes in carrying out this evaluation. A team of more than 80 scientific experts was formed from
specialists offered by 18 countries, supplemented by a few individuals with relevant expertise notoffered by countries but whose experience was deemed important for the work. All experts wererequired to declare any potential conflicts of interest. The secretariat and officers of the Committee
reviewed these declarations, and affirmed that there were no conflicts of interest for the work in which
the experts were engaged. Five international organizations were also involved in the work. The
scientists were organized into various expert groups and overseen by a Coordination Expert Group,
chaired by W. Weiss (Germany). Each expert group had a leader, an adviser from Japan, a rapporteur,lead and contributing writers, and commentators (see the composition in the acknowledgements section
at the end of the main text of this annex). The Government of Japan appointed Y. Yonekura as ascientific focal point for the work. The experts collected and reviewed data and information, defined
methodologies and processes for ensuring the quality of the data was fit for purpose, evaluatedpublished literature, drafted material, conducted detailed radiation dose 2 assessments and evaluated thehealth implications as well as the implications for non-human biota in the environment. Many of theexperts were also assisted in their work by supplementary support staff in their national institutes. An
expert offered by the Government of Japan assisted the secretariat in Vienna.
6.
The secretariat provided support to the technical work, inter alia, by convening in Vienna three
All-Expert Meetings of the scientists, fostering cooperation and collaboration between the expert groupleaders through online meetings every two weeks, providing an online platform for sharing andmanaging data and information among the experts, liaising with governments and other internationalorganizations. Most of the work was conducted remotely using electronic communication means andtools. Many experts participated as individuals in workshops, conferences and meetings held at theinternational level, often in Japan. The secretariat organized only one technical visit in the name of theCommittee in order to clarify information by direct interaction with those involved in preparing it. The
Governments of Germany, Sweden and Switzerland made financial contributions to the general trust
fund to support the work of the Committee in these regards.
7.
The Coordination Expert Group planned and coordinated the work, and presented draft reports tothe fifty-ninth session of the Scientific Committee in May 2012, and to the sixtieth session in May
2013. The Committee under the chairmanship of C-M. Larsson (Australia) scrutinized the draft reports,
discussed methodologies, the quality of the data and interim results of the evaluation. The Coordination
Expert Group adapted its work according to the direction provided by the Committee. Delegations to
the Committee provided comments on the draft report after the fifty-ninth session and two times after
the draft report to the sixtieth session, before final endorsement for publication. To obtain additionaldata, the secretariat of the Committee and the expert groups also maintained frequent and extensive
contacts through advisers in Japan and discussed with them the interpretation and evaluation of results.
2

Dose is a measure of the energy deposited by radiation in a target, and is expressed by the fundamental dosimetric quantity,
absorbed dose (usually to an organ) in units of grays (Gy), equal to 1 joule per kilogramme. The Committee uses this quantity to
express scientific relationships between the absorbed dose and risk of health effect. However, the Committee has also used aquantity that was strictly derived for radiation protection purposes and that is the most commonly used indicator of potential
biological effects from radiation exposure, effective dose in units of sieverts (Sv). This quantity allows for the fact that different
kinds of radiation have different biological effects for the same amount of energy deposited and the fact that tissues also react
differently. As a reference for subsequent comparisons, the annual average per caput background dose to the Japanese populationfrom naturally occurring sources of radiation is about 2.1 mSv. Over a lifetime of say 80 years this would correspond to about
170 mSv on average.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

27

These contacts proved essential to the conduct of the project and they are here collectively recognizedwith appreciation.
8.
The aim of this scientific annex is to evaluate information, mainly from 2011 and 2012, on thelevels of radiation exposure due to the nuclear accident, and the associated effects and risk to humanhealth and the effects on non-human biota. The annex presents estimates of radiation doses anddiscusses implications for health for different population groups inside Japan, and to a lesser degree insome neighbouring countries, using data and information available to the Committee, and against the
backdrop of the Committee’s previous scientific assessments of effects of radiation on health and theenvironment from all sources, including accidents. The annex identifies gaps in knowledge for possible
future follow-up and research. The annex does not identify lessons or address policy issues with respect
to human rights 3, public health protection, environmental protection, radiation protection, emergency
preparedness and response, accident management, nuclear safety, and related issues; it does not intend
to provide advice to local governments, the Government of Japan or to national and international
bodies.
9.
The scientific annex comprises a main text with 8 chapters and 6 specialized appendices,supported by 28 electronic attachments. Chapter I introduces the aim, background, scope and method ofworking. Appendix A discusses the compilation of data used by the Committee for its work, and its
approaches to quality assurance.
10. Chapter II briefly summarizes the chronology of the accident including the accident progression at
FDNPS, how and when radioactive materials were released to the atmosphere and to the ocean, andwhat measures were taken to protect workers and members of the public from exposure to ionizing
radiation.
11. Chapter III describes the releases of radionuclides into the atmosphere and the Pacific Ocean andhow estimates have been made of time-dependent radionuclide concentrations in the surface air, on the
ground, and in seawater and sediments, locally, regionally and globally. Appendix B and threeelectronic attachments provide technical underpinning and more details related to chapter III.
12. Chapter IV describes the Committee’s assessment of doses to the public for the first year after theaccident for 20-year-old adults, 10-year-old children and 1-year-old infants. Projections were also madeof doses to be received over the first 10 years and up to age 80 years. The assessment was based on
measurement data as far as possible. Models were used, with realistic assumptions, to provide an
objective evaluation of the situation. Protective actions taken during the first year were considered andthe doses averted by them were estimated. Appendix C and 21 electronic attachments provide technicalunderpinning and more details related to chapter IV.
13. Chapter V describes the Committee’s evaluation of doses for workers involved in the emergency
response and in clean-up operations during the period between 11 March 2011 and 31 October 2012.
Reports of dose distributions for workers by time and exposure pathway are reviewed, summarized andtheir reliability assessed. Appendix D and one electronic attachment provide technical underpinningand more details related to chapter V.
3
The Committee took note of the report of the Special Rapporteur on the right of everyone to the enjoyment of the highest
attainable standard of physical and mental health, Anand Grover, Official Records of the General Assembly, Human Rights
Council, Twenty-third session (A/HRC/23/41/Add.3).

28 UNSCEAR 2013 REPORT

14. Chapter VI discusses the health implications of exposure to radionuclides released from FDNPS.
A review of other published health risk assessments are included, and current and future health surveys
are discussed. Appendix E provides technical underpinning and more details for chapter VI.
15. Chapter VII describes the Committee’s evaluation of doses and effects for non-human biota
inhabiting the terrestrial and aquatic (freshwater and marine) ecosystems. Appendix F and threeelectronic attachments provide technical underpinning and more details related to chapter VII.
16. Chapter VIII provides a summary and conclusions. The Committee envisages returning to thissubject in the future to report on the levels of radiation exposure and associated effects and risks as
information becomes clearer. In this regard, chapter VIII also briefly identifies some current researchneeds for better understanding the implications of the FDNPS accident for human health and for theenvironment.
17. A glossary is provided to explain some of the technical terms used throughout the report.
Numerical estimates are generally quoted to two significant figures (and sometimes more in theelectronic attachments). This enables better comparison between values, however the values themselves
are normally associated with considerable uncertainty and this degree of precision should not be
inferred.

II. CHRONOLOGY OF THE ACCIDENT

A. Accident progression
18. The Fukushima Daiichi Nuclear Power Station (FDNPS) of the Tokyo Electric Power Company(TEPCO) lies in Fukushima Prefecture of the Tōhoku region in Japan. It is located about 230 km northeast of Tokyo. The east side of FDNPS faces the Pacific Ocean (figure I). The total power generating
capacity of the six reactors on site was 4.7 gigawatts of electricity.
19. On 11 March 2011, an earthquake of magnitude 9.0 occurred along the Japan Trench at 14:46
Japan Standard Time (JST). The earthquake and the following tsunami triggered a severe nuclear
accident at FDNPS. On 12 April 2011, the Nuclear Industrial and Safety Agency (NISA) 4 in Japandeclared the accident at level 7 (“Severe Accident”) on the International Nuclear Event Scale (INES). A
timeline of the events that followed the earthquake and tsunami is provided in table 1.
4

In September 2012, NISA and the Nuclear Safety Commission were unified to form the Nuclear Regulation Authority (NRA).

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

29

Figure I. Layout of the Fukushima Daiichi Nuclear Power Station, including location of the automatic
monitoring posts [T12]30 UNSCEAR 2013 REPORT

Table 1. Timeline of events following the earthquake and tsunami
All times are JST

Date

Reactor2011-03-11

Environment

PublicWorkers

14:46, EARTHQUAKE
Scram in Units 1, 2 and 3
of TEPCO’s FDNPSa
Loss of external
electricity

15:35, MAJOR TSUNAMI
15:37, loss of allelectricity, except DC on
Unit 3

16:40, MEXTb
activated SPEEDIc
and started making
daily predictions ofconcentrations in air
and deposition
densities for unit
release ofradioactive material

Around 20:00, possible
start of damage toreactor core andpressure vessel in Unit 1

20:50, evacuation
within 2 km ordered
21:23, evacuation
within 3 km ordered
21:23, shelteringfrom 3 km to 10 km
ordered2011-03-12

02:45, strong likelihoodof reactor pressure
vessel failure in Unit 1
15:36, reactor buildingof Unit 1 damaged byhydrogen explosion

Ambient dose
equivalent rate 5 near
main gate of FDNPS:
04:00, about 0.1 μSv/h
04:50, 1 μSv/h
10:30, 390 μSv/h
Emergency monitoring
teams of Fukushima
Prefecture and JAEAd
started to measureambient dose rates andairborne dust, including
iodine within 20-km
radius05:44, evacuation
within 10 km

18:25, evacuation
within 20 km
orderedScreening began ofresidents at refuges
using Geiger–Müller
survey meters

Some workers
remained in themain control room
for several days
following the
explosions at Units 1
and 3. Presumed tohave inhaledradioactive material(mainly radioiodine)
because they lacked
protective
equipment (e.g. facemasks)

5
Portable or fixed equipment for area monitoring took measurements of the dosimetric quantity, H*(10), ambient dose equivalentrate, expressed in units of microsieverts per hour (μSv/h) or millisieverts per hour (mSv/h). In this report, the unqualified term
“dose rate” refers to “ambient dose equivalent rate”.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Date
2011-03-13

ReactorEnvironment

Public02:42, high pressure
coolant injection in
Unit 3 ceased

11:01, reactor buildingof Unit 3 damaged byhydrogen explosion

Emergency dose
limit for emergency
workers raised from
100 mSv to 250 mSvf

12:30, failure of reactor
core isolation coolingsystem in Unit 2
By 18:22, indications
that core in Unit 2
completely uncovered
Around 21:18, failure ofreactor pressure vessel
in Unit 2
2011-03-15

Between 06:00 and
06:12, hydrogen
explosion occurred at
Unit 4 from backflow ofgases vented from
Unit 3; peak dose rate
about 0.6 mSv/h at siteboundary
From around 07:38,
major discharge ofradioactive material
from Unit 2

09:00, maximum dose
rate of about 12 mSv/hrecorded near the maingate

11:00, Sheltering inplace between
20-km and 30-km
radius ordered
Evacuation fromwithin 20 km of
FDNPS completed.
Off-site centre in
Okuma Town
evacuated

2011-03-16

2011-03-17

Workers
Potassium iodide
tablets provided for
emergency workers
at FDNPS

Around 06:30 to 09:10,
likely damage to reactor
pressure vessel in Unit 3
2011-03-14

31

Monitoring of food anddrinking water started

Guidance on taking
stable iodine whenevacuating fromwithin 20 km of
FDNPS was issued.
Stable iodine nottaken because
evacuation alreadycompleted
Instructions firstissued on
restrictions on
distribution offoodstuffs

32 UNSCEAR 2013 REPORT

Date
2011-03-18

ReactorEnvironment

MHLWe advised
against drinking tap
water if levels
exceeded 300 Bq/kg
of radioiodine and
200 Bq/kg ofradiocaesium
Marine monitoring
startedRestrictions begin
on consumption offoodstuffs. Tokyo
Municipal Water
Authority urges
residents to usebottled water for
infant formula

2011-03-24

Ban on tap water
lifted by Tokyo
Metropolitan
Government

2011-03-26

Radiationmeasurements
made of the
thyroids of 1,080
children living in
Kawamata Town,
Iitate Village andIwaki City (until
30 March)

2011-03-30

Re-configuration of
the restricted areas
and otherevacuation areas
decided by theGovernment

2011-04-01

Highly-contaminated water unintentionallyreleased to the Pacific Ocean (until 2011-04-06)

2011-04-04

Weakly-contaminated water deliberately
discharged to the Pacific Ocean (until 2011-04-10)

2011-04-22

Workers

Monitoring of airborne
dust, soil anddeposition started

2011-03-19

2011-03-23

Public“Deliberate
evacuation areas"and “evacuationprepared area incase of emergency”
establishedContamination offeet of threeworkers confirmed;
caused by stepping
into puddles ofcontaminated water
wearing low-cut
shoesANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Date
2011-05-10

ReactorEnvironment

Workers

Moderately-contaminated water unintentionallyreleased to the Pacific Ocean (until 2011-05-11)

2011-06-30

2011-07-19

Public33“Specific spots
recommended forevacuation” were
specified in Date
City
Step 1 of the Roadmap to Recovery (i.e. dose rates steadily in decline etc.) attainedg

2011-09-30“Evacuationprepared area incase of emergency”
was terminated2011-12-16

Step 2 of the Roadmap to Recovery (i.e. cold shutdown state, releases under control etc.) attainedg

2012-03-31

Dose assessments(due to internal andexternal exposure)completed for about
21,000 workers

aFukushima Daiichi Nuclear Power Station of the Tokyo Electric Power Company.

b

Ministry of Education, Culture, Sports, Science and Technology.

cSystem for Prediction of Environmental Emergency Dose Information.

dJapan Atomic Energy Agency.

e

Ministry of Health, Labour and Welfare.

fExpressed in effective dose, the “emergency dose limit” in Japan corresponds to an ICRP “reference level” (see section V.A).

The increase in the emergency dose limit was repealed on 1 November 2011 for new workers and on 16 December 2011 for mostemergency workers registered before 31 October (footnote g).
g

Roadmap towards settlement of the accident at FDNPS, TEPCO. Step 2 completion report (2011), Nuclear Emergency

Response Headquarters [N6]. This triggered the repealing of the emergency dose limit (footnote f).

20. When the earthquake occurred, Units 1–3 of FDNPS were in normal operation; Units 4–6 were
undergoing periodic maintenance and refuelling operations, with Unit 4 being completely defuelled. As
designed, the emergency shutdown feature, or scram 6, went into operation at Units 1–3 immediately
after seismic activity started. The seismic tremors damaged electricity transmission facilities inside andoutside the site of FDNPS, resulting in total loss of off-site electricity. However, the emergency diesel
generators automatically activated, as designed, to provide backup power for the reactor coolingsystems and other plant safety systems.
21. The earthquake caused a tsunami to hit the Japanese coastline. A major wave arrived at FDNPS at
15:35 JST with an estimated maximum wave height of about 15 m, much higher than the 6 m seawall
and above the elevation of approximately 10 m where key buildings were constructed. The tsunami
damaged or destroyed the emergency diesel generators, the seawater cooling pumps, the electric wiring
system and the DC power supply for Units 1, 2 and 4, resulting in the loss of all on-site power, except
for Unit 6 that was supplied with electricity from an air-cooled emergency diesel generator. In short,
Units 1, 2 and 4 lost all power; Unit 3 lost all AC power, and later lost DC power before dawn of
6
A scram is a safety feature that triggers immediate shutting down of a nuclear reactor, usually by rapid insertion of control rods,
either automatically or manually by the reactor operator. Also known as a “reactor trip”.

34 UNSCEAR 2013 REPORT

13 March 2011. Unit 5 lost all AC power. Damage caused directly by the earthquake is still unclear andis yet to be fully quantified by further analyses.
22. The tsunami damaged more than just the power supply. It also destroyed or washed away
vehicles, heavy machinery, oil tanks, and gravel. It destroyed buildings, equipment, installations andother infrastructure generally. Seawater from the tsunami inundated a large portion of FDNPS. Afterthe water retreated, debris was scattered all over the site, hindering movement. Recovery tasks were
further interrupted as workers reacted to the intermittent and significant aftershocks and successive
tsunami waves. The loss of electricity deactivated monitoring equipment and the control functions in
the central control room. Lighting and communications were also affected. Decisions and responses tothe accident had to be made, on the spot, by operational staff at the site, without valid tools andmanuals.
23. Cooling the reactors, and monitoring whether the measures taken had any effect, was heavily
dependent on electricity, which was not available. The difficulties in accessing the control rooms andthe debris littering the site further hindered the provision of alternative power supplies and means ofcooling (e.g. by water injection using fire trucks).
24. With no cooling to remove heat generated by the radioactive material in the reactor core, damage
to the core may have begun at Unit 1 on 11 March. Injection pumps (driven by steam generated by thereactors) were used to provide cooling water to the reactors on Units 2 and 3, but these pumps
eventually stopped working, and all cooling to the reactors was lost until fire engines were used torestore water injection. Without adequate cooling, pressure inside the reactor vessels increased, and was
relieved to some degree for Units 2 and 3 by venting through the safety relief valves. In addition, wateror steam in direct contact with the over-heated fuel assemblies reacted with the zirconium of the fuelcladding to produce hydrogen gas. This hydrogen then accumulated in the upper portion of the reactor
buildings (secondary containment) and ignited, producing explosions in the Unit 1 and Unit 3 reactor
buildings on 12 and 14 March, respectively. Hydrogen generated in Unit 3 seems to have migrated into
the Unit 4 reactor building, resulting in a subsequent explosion and damage there on 15 March. Severe
damage, including meltdown, occurred in the cores of the three reactors (Units 1, 2 and 3). In all threeunits, melted fuel fell to and subsequently penetrated the bottom of the reactor pressure vessels,
resulting in molten-fuel–concrete interactions beneath the pressure vessels that further increased thepressure within the containments [T17]. As of December 2013, the fuel was covered by injected water
which, depending on the integrity of the containment, may be a source of release of radionuclides to thesurrounding area.
25. The core damage including melting of the overheated fuel assemblies resulted in the release of themore volatile fission products into the reactor vessels. Operations to reduce pressure in, or possibly
leaks from, the reactor vessels resulted in releases of volatile radionuclides into the containment vessel,
the reactor buildings and the outside environment. These volatile radionuclides were not only ingaseous form (such as noble gases and gaseous iodine), but some were also in aerosol form, although asignificant fraction of the aerosols was trapped in the water in the reactor containment and in theturbine buildings. Several tens of per cent of the inventories of the more volatile elements (i.e.
hydrogen/tritium, iodine and caesium) in the cores of the three damaged reactors have been found[N15] in stagnant water, mainly in the basements of the turbine and reactor buildings but also insurrounding areas. Less volatile elements (e.g. strontium, barium and lanthanum) were also found but at
levels that were between about one and ten per cent of those for the more volatile elements in terms of
their relative inventories. The processes of the underground liquid-phase releases are still uncertain andyet to be clarified in further analyses.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

35

26. As well as the overheated fuel in the reactors, there was also concern about cooling of fuelassemblies that had been removed from the reactors and stored under water in spent fuel pools prior to
the earthquake and tsunami. Unit 4 was in a periodic inspection on 11 March and all fuel assemblies
had been removed from the reactor into the Unit 4 spent fuel pool. With the loss of electricity, theability to replenish the water and maintain the temperature of these storage pools was also lost. Concern
was to a large extent focused on the storage pool of Unit 4 because the reactor building in which thestorage pool was located had suffered significant damage owing to the explosion on 15 March and also
because it contained the entire core of the defuelled reactor and spent fuel from previous defuelling.
However, because a large amount of water was supplied to the spent fuel pool of Unit 4 early on,
Japanese officials considered the water level in the pool to have been sufficiently high do not believethat the stored fuel assemblies did not sustain any significant damage [N7].
27. As of 16 December 2011, the Government of Japan announced that conditions equivalent to acold shutdown state 7 had been achieved at FDNPS [I5].
28. It is clear, from the experience of the accidents at the Chernobyl and Three Mile Island nuclear
power plants, that the next several years will provide more information on the factors contributing to
the accident’s progression. In particular, it is critical to quantify the liquid-phase release and dispersion
that would have occurred underground following core meltdown.

B. Release to the environment
29. As a result of the earthquake and tsunami, the fixed automatic radiation monitoring posts aroundthe boundary of FDNPS (MP 1−8, shown in figure I) were disabled, so measurements could only bemade with mobile monitoring equipment, until three temporary automatic posts were established on
29 March and the fixed monitoring posts restored in early April. Dose rates measured at several
locations around FDNPS increased drastically during the period from 12 March to beyond 20 March,
indicating significant releases of radioactive material to the environment [T9] (see figure II). Dose rates
higher than 10 Sv/h were measured for short periods of time at some locations [N6]. Further discussion
on the nature of the releases, how they varied over time and the resulting dispersion of released material
in the environment is provided in chapter III and in appendix B.
30. On 2 April 2011, workers discovered that highly-contaminated water had accumulated in a trenchoutside of Unit 2 and that the water was flowing from the trench into the ocean. The outflow was
stopped on 6 April. There were several other, smaller scale releases of radioactive material into theocean, including the deliberate discharge of low-level radioactive water being stored in tanks to create
storage capacity for the highly-contaminated water from the trench. These releases and their dispersion
in the marine environment are discussed further in chapter III and appendix B.
7Defined by TEPCO and the Nuclear Emergency Response Headquarters (NERHQ) as the state where the coolant watertemperatures of Units 1–3 were less than 100ºC, the pressure inside the reactor vessels was the same as the outside air pressure,and where any further releases would not result in an annual effective dose greater than 1 mSv at the site boundary.

36 UNSCEAR 2013 REPORT

Figure II. Dose rates on the Fukushima Daiichi Nuclear Power Station site
View is looking inland, westwards from the ocean. The buildings of Unit 1 (on the far right) and of Units 3 and 4 (on the left ofcentre and far left) have been destroyed by explosion. The building of Unit 2 (right of centre) remains intact. Measurements ofambient dose equivalent rate (mSv/h) were made in surveys conducted 15:00–18:00 JST on 20 March, 11:00–14:00 JST on 22
March and 11:30–12:30 JST on 23 March 2011
(Photo: Courtesy of Air photo service Co. Ltd., Myoko, Japan)

C. Actions taken relevant to public exposure
31. The Japanese authorities decided on a number of measures to protect the public, including
immediate and late (“deliberate”) evacuation, sheltering in homes, restricting distribution andconsumption of contaminated foodstuffs (milk, vegetables, grains, meat, fish, etc.) and water, andinstructions to take stable iodine 8. These actions were supported by radiation contamination surveys ofpeople and places (see table 1).
32. At 20:50 JST on 11 March 2011, the Governor of Fukushima Prefecture issued instructions toevacuate settlements within 2 km of FDNPS (Futaba Town and Okuma Town). Shortly afterwards (at21:23 JST), the Director-General of the Nuclear Emergency Response Headquarters (NERHQ) ordered
the evacuation of residents and others within 3 km of FDNPS and the sheltering indoors of all residents
and others within 10 km. At 05:44 JST the next morning, the people within 10 km were then ordered tobe evacuated. At 18:25 JST that same day (12 March), the evacuation radius was expanded to 20 km(an area of approximately 600 km2). Following the hydrogen explosion between about 06:00 and
06:12 JST on 15 March, an instruction was issued ordering all people living between 20 km and 30 km
from FDNPS to shelter indoors. In addition, on 16 March, an instruction was issued that anyone still
remaining within 20 km of FDNPS should take stable iodine. This instruction was not implemented,
because the area was considered to have already been evacuated (although the number of people who
8
If stable iodine (as potassium iodide or iodate, usually in a tablet form) is taken in the appropriate dosage and within theappropriate timescale, it can help prevent uptake into the thyroid gland of radioactive iodine released from nuclear accidents(“thyroid blocking”).

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

37

did not immediately follow the instructions to evacuate is uncertain). At the time of the earthquake,about 78,000 people were living within what became the 20-km evacuation zone and about 62,000 were
living between 20 km and 30 km from FDNPS [N8].
33. Monitoring of food and drinking water by Japanese and prefectural governments began on
16 March 2011. Selected foodstuffs (milk, vegetables, grains, meat, fish, and so on) containing
radioactive material that exceeded the provisional regulation values, as recommended on 17 March2011 by the Ministry of Health, Labour and Welfare (MHLW) of Japan, were prohibited from
distribution on 21 March 2011 and from consumption on 23 March 2011.
34. On 25 March, the residents in the area between 20-km and 30-km radius of the site, who had been
sheltering since 15 March, were advised by the Government of Japan to begin voluntary evacuation andinstructed to be prepared to evacuate depending on future developments at FDNPS. This instruction
was terminated on 30 September [N8]. In addition, environmental monitoring revealed that there wereareas where radioactive material had been deposited at high levels even outside of the 20-km
evacuation zone. Deposition densities of 131I and 137Cs were estimated from samples of soil collected by
IAEA teams at distances from 32 km to 58 km in the north to north-west direction from FDNPS
between 18 and 26 March 2011. Average values of deposition density for 131I ranged from 0.2 to
25 MBq/m2 and for 137Cs from 0.02 to 3.7 MBq/m2 with the highest values located near Iitate Village.
On the basis of these measurements, IAEA advised the Government of Japan to carefully assess thesituation in that region [I3]. On 22 April, “deliberate evacuation areas” were established for specificareas beyond the 20-km zone where the effective dose might exceed 20 mSv within a year [N8]. Most
residents of these areas were then evacuated between April and June. Figure III shows the extent of allof these areas as of 3 August 2011 [N7].
Figure III. Areas subject to measures to protect the public (as of 3 August 2011) [N7]
All times are JST

38 UNSCEAR 2013 REPORT

35. On 16 June 2011, the Government announced the concept of “specific spots recommended forevacuation” for localized areas more than 20 km away from FDNPS and outside the deliberate
evacuation areas. These were areas where the estimated effective dose might exceed 20 mSv over the
first year after the accident because of radioactive material deposited on the ground; they weredelineated based on environmental monitoring conducted by the Ministry of Education, Culture, Sports,
Science and Technology (MEXT). The local municipalities notified potentially affected residents andprovided them with information on their options for relocating or remaining, and on methods tomitigate future radiation exposures. Such designations were announced for Date City on 30 June 2011,
for Minamisoma City on 21 July and 3 August, and for Kawauchi Village on 3 August. On
25 November, additional locations were established in Date City and Minamisoma City [N7].
36. On 12 March 2011, staff of the Nuclear Emergency Response Headquarters (NERHQ) of
Fukushima Prefecture started surveying residents, including those who were evacuated, forcontamination of skin and clothing using Geiger–Müller survey meters. Screening criteria were
40 Bq/cm2 from beta/gamma contamination (corresponding to 13,000 cpm) for decontamination by
wiping, and 100,000 cpm for decontamination of the surface of the body. Most of the 195,354 people
checked between 12 March and 31 May did not require any decontamination [N8]. Between 26 and 30
March, staff of NERHQ conducted radiation surveys using hand-held sodium iodide (NaI) monitors of
the thyroid glands of 1,080 children aged 0 to 15 years living in Kawamata Town, Iitate Village andIwaki City. None of the surveyed children exceeded the established screening level corresponding to anabsorbed dose to the thyroid due to internal exposure from 131I of 100 mGy for a 1-year-old infant [N8].

D. Actions taken relevant to occupational exposure
37. On 14 March 2011, the pre-existing “emergency dose limit” for occupationally-exposed workers(“radiation workers” 9) in Japan performing emergency work was raised from 100 mSv to 250 mSv
effective dose by a special ministerial order, for the purposes of dealing with the particular
circumstances of the accident [I9, N6]. On 1 November 2011, this “emergency dose limit” was reduced
to 100 mSv for new workers.
38. Initially, there was a shortage of personal dosimeters and other essential equipment on site. Overthe first few weeks, successive measures were implemented to prevent external and internal exposure 10
to radiation. The distribution of potassium iodide tablets to FDNPS workers engaged in emergency
work was initiated on 13 March for those who were under 40 years of age and others who requested it.
Subsequently, physical barriers were introduced between different areas, working time in designatedareas was limited, and a coordination centre was established. Workers were issued with tight-fitting
full-face respirators (to minimize inhalation of radioactive particles and gases), and protective overalls,
gloves, safety shoes, cotton hats and helmets (to minimize contamination of body surfaces).
9

In Japan, the term “radiation worker” applies to personnel engaging in radiation work in a controlled area, such as in the
installation, operation, utilization or maintenance of nuclear reactors, or in the transport, storage, disposal or removal of nuclearfuel material or nuclear-fuel-contaminated material.
10
External and internal exposure are exposures from sources outside and inside the body, respectively.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

39

III. RADIONUCLIDE RELEASES, DISPERSION AND DEPOSITION
39. Events in the progression of the accident at FDNPS, summarized in chapter II above, led toreleases of radioactive material to the environment. Estimates of the amounts and temporal pattern ofthese releases, both to the atmosphere and to the marine environment, are described in detail inappendix B and summarized in this chapter. These estimates were made for two purposes:(a) To indicate the amounts of radioactive material released to the environment;(b) To be used, in combination with models (e.g. for atmospheric and marine dispersion), to infer
the dispersion and deposition of radionuclides at locations in the environment where either data
were not available or measurements can no longer be made.
40. Knowledge of the spatial and temporal distribution of released radioactive material in theenvironment (e.g. concentrations of radionuclides in air, deposition densities of radionuclides on the
ground, and concentrations of radionuclides in seawater and sediments) is a prerequisite for estimating
the radiation exposure of members of the public (see chapter IV) and for assessing the exposures andeffects in the environment (see chapter VII). Measurements of radiation levels or radioactive material in
the environment provide, in general, a reliable basis for estimating doses. The available measurements
and their origins are summarized in appendix A. Where measurements were not available, theCommittee has relied on estimates, and this chapter describes the nature of the estimates made forassessing doses.

A. Radionuclide releases
1.

Release to the atmosphere

41. Radioactive material was released from FDNPS over an extended period. The pattern of release
was complex, both temporally and spatially. Significant releases began on 12 March and the rate ofrelease varied considerably in magnitude over the following week, with marked increases associatedwith particular events at each unit (e.g. hydrogen explosions, venting, and leakage from the reactors andtheir containment systems). After the first week, the rates of release gradually declined, albeit withsome fluctuations over more limited periods. By the beginning of April, the release rates had fallen to athousandth or less of the release rates that occurred during the first week of the accident, although thesemuch lower release rates persisted for many weeks. The releases occurred from different locations, atdifferent heights and with quite different characteristics, all of which affected their subsequentdispersion in, and deposition from, the atmosphere.
42. Numerous estimates have been published of the magnitude, time profile and nature of the releaseof radionuclides (commonly referred to as the “source term”) from FDNPS; in general, their quality has
improved over time as more information has become available. Two distinct approaches have beentaken to derive such estimates, based on:(a) Detailed simulations of the progression of the accident at FDNPS;(b) “Inverse” or “reverse” modelling using measurements of levels of radiation or radioactive
material in the environment.
Both approaches have their limitations and are associated with much uncertainty.

40 UNSCEAR 2013 REPORT

43. In general, the published estimates of the “total” releases were broadly consistent, given theirinherent uncertainties and the fact that, strictly, many were not directly comparable; some estimates
were of the total release, while others were of releases over a limited period of time or only included
that fraction of the release partly or wholly dispersed over the Japanese land mass. The estimates of the“total” release of 131I fell within the range of about 100 to about 500 PBq 11 and those of 137Cs generally
in the range 6–20 PBq 12 (with some estimates that had been based on more limited information ranging
up to 40 PBq). These ranges comprised about 2-8% of the total inventory of 131I and about 1–3% of thetotal inventory of 137Cs in the three operating reactors (Units 1–3) at the time of the accident. For
perspective, the estimated releases (based on the averages of published estimates) of these radionuclides
from FDNPS were about 10% and 20% for 131I and 137Cs, respectively of those estimated for the
Chernobyl accident. Further details are given in appendix B.
44. Numerous estimates have also been made of the temporal pattern of the rate of material released,in particular for 131I and 137Cs. Notwithstanding the broad agreement between the various publishedestimates of the total amounts of radioactive material released, there were large differences in thetemporal patterns of release rates and in the extent to which they correlate with events on site.
45. The Committee has carefully assessed the numerous published estimates of the source term,
including the temporal patterns of the release rates. For its purposes, the Committee had to specify asource term to provide a sound basis for estimating levels of radioactive material in the terrestrial
environment where no measurements existed; these levels were an essential input to the subsequentestimation of doses to the public (see chapter IV below). Estimates based on reverse or inverse
modelling, as opposed to simulation of accident progression, were clearly preferable in this context
because they were derived from, and the models were already optimized to fit, measurements ofradioactive material in the environment. Having considered a number of options, the Committee chose
to use the source term estimated by Terada et al. [T19], which was selected from among those that had
been derived on the basis of reverse or inverse modelling 13 . The total releases of 131I and 137Cs
estimated by Terada et al. were 120 and 8.8 PBq, respectively, and were both at the lower end of theranges of published values (see above). There were indications that they may have underestimated thetotal amounts of these radionuclides released, perhaps by a factor of up to about two, because ofassumptions made about releases dispersed over the ocean. However, for reasons outlined above anddetailed in appendix B, they provided a sound basis for the purposes of estimating the levels ofradioactive material in the terrestrial environment where measurements did not exist.
46. Terada et al. estimated the release rates of 131I and 137Cs as a function of time. These two
radionuclides, together with 134Cs, made by far the largest contribution to the exposure of the public.
Other radionuclides that could have contributed significantly were also included in the source term andcomprise other radioisotopes of iodine and caesium, 132Te and 133Xe. The release rate pattern for theother radionuclides was derived in general by considering the amounts of these radionuclides relative to
131
I or 137Cs in the estimated inventories of the three reactors and their relative levels in environmental
measurements. A large number of radioisotopes of other elements would also have been released, with
their relative amounts determined by their volatility. For example, the volatilities of strontium, bariumand plutonium are much lower than those of iodine and caesium; consequently, their releases were
11

The activity released or measured in a sample represents the number of radioactive decays per unit time and its unit is thebecquerel (Bq). One becquerel is defined as one decay per second. One gigabecquerel (GBq) is equal to 109 becquerels; one
terabecquerel (TBq) is equal to 1012 becquerels; and one petabecquerel (PBq) is equal to 1015 becquerels.
12
The release of 134Cs was comparable with that of 137Cs.
13
This was chosen in preference to a later refinement by Kobayashi et al. [K18] that considered measurements of radioactive
material in the Pacific Ocean in addition to those over the Japanese land mass. If the Committee had adopted the Kobayashi et al.
source term, it would have overestimated the levels of radioactive material in the terrestrial environment, which would have been
inconsistent with its intent to make a realistic assessment of radiation exposure.

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41

relatively much lower. This was confirmed by measurements of their levels in the environment 14. This
contrasts markedly with the Chernobyl accident, where much larger fractions of the less volatileelements (e.g. strontium and plutonium) were released directly to the atmosphere. The total releaseassumed by the Committee of each of the radionuclides included in the source term is given in table 2.
The temporal pattern of the release of these radionuclides is shown in table B5, figure B-I andfigure B-XVI of appendix B.
Table 2. The total release of radionuclides to the atmosphere assumed by the Committee for the
purposes of estimating levels of radionuclides in the environment where no measurements existed
or measurements could no longer be madeThe values represent the sum of the activity released to the atmosphere whenever that occurredRadionuclide132

2.

Total release (PBq)

Radionuclide

Total release (PBq)

29

133

I

120

134

Cs

9.0

132

I

29

136

Cs

1.8

133

I

9.6

137

Cs

8.8

Te

131

Xe

7 300

Release to the marine environment

47. Radioactive material from FDNPS entered the marine environment directly and indirectly. Direct
release into the ocean is at least known to have resulted from leakage of highly-contaminated waterfrom a trench outside Unit 2 (discovered on 2 April 2011), and the deliberate discharge of weaklycontaminated water from storage tanks; the latter were emptied to create capacity for the storage ofhighly-contaminated water remaining in the trench (see chapter II). Further direct releases occurred
subsequently (for example, in May and December, 2011) but, in general, these were small comparedwith those that occurred in the first month after the accident. Radioactive material entered the ocean
indirectly via two routes: (a) most importantly, from the deposition onto the ocean surface of material
released to the atmosphere and dispersed over the ocean; and (b) from run-off into rivers of material
deposited over the land mass and transported downstream into the ocean.
48. At the end of 2013, releases of radionuclides to the marine environment continued to be reported[T18], apparently emanating largely from contaminated groundwater on the FDNPS site. As describedin chapter II, the sources of stagnant water mainly in the basement of the turbine and reactor buildings[N15] were contained to varying extents in the respective buildings. However, they are likely to be oneof the major contributors to the continuing releases of radionuclides to the groundwater. Monitoring
results published by the Nuclear Regulation Authority [N21]indicate that these continuing release rates
during 2013 were at a level much lower than the major releases that occurred in the immediate
aftermath of the accident. Furthermore, measures were being taken to attempt to control them (e.g. thebuilding of a containment wall between the FDNPS site and the ocean). It was considered that thosereleases were unlikely to significantly affect the Committee’s assessment of doses to the public.
However, continued monitoring and assessment of the implications of the releases is warranted.
14
The release of each of three radionuclides, 238Pu, 239Pu and 240Pu, has been estimated to be about 1 GBq [Z5]. Their contribution
to exposure of the public would have been insignificant.

42 UNSCEAR 2013 REPORT

49. Various estimates have been published of the total amounts of the more radiologically-significant
radionuclides reaching the ocean by each route, and of the pattern of release over time. The estimates of
direct releases to the ocean were made from measured levels of radionuclides in seawater. From a
review of the published estimates, the Committee considered that the total direct release of 137Cs to theocean was likely to have fallen within a range of about 3 to 6 PBq; that of 131I was considered likely tohave been about three times higher. The temporal pattern of the direct releases to ocean has been
estimated by Kawamura et al. [K3], Tsumune et al. [T24] and Estournel et al. [E4]; the largest releases
were estimated to have occurred during the last week in March and the first week in April, with direct
releases continuing at much lower, and slowly declining, levels for many weeks thereafter.
50. The estimates of the indirect releases (principally the contribution due to deposition onto theocean of radionuclides released to atmosphere) were made by modelling the dispersion of material
released to the atmosphere and its deposition over the ocean. For a significant fraction of the period
when the atmospheric releases were largest (that is from 12 March until the beginning of April 2011),
the wind was blowing out to sea. Kobayashi et al. [K18] have estimated that about 50% and 60%,
respectively, of the total atmospheric releases of 131I and 137Cs were deposited over the ocean. The total
amounts that entered the northern Pacific Ocean by deposition from the atmosphere were estimated byvarious authors to have been about 5 to 8 PBq and 60 to 100 PBq for 137Cs and 131I, respectively. Only asmall percentage (about 5%) of these amounts, however, was estimated to have been deposited within aradius of 80 km from the FDNPS site.
51. Other radionuclides, in addition to 131I and 137Cs, were also released to the ocean, both directly
and indirectly. Radioisotopes of strontium, plutonium and other elements have been measured inseawater and/or in sediments. Estimates have been made by Povinec et al. [P12] of the direct release of90
Sr to the ocean and these range from about 0.04 to 1 PBq. The levels of radioisotopes of plutonium inseawater were generally below the limits of detection.

3.

Summary of releases to the environment

52. A summary of published estimates of the release to the environment of the more radiologicallysignificant radionuclides from FDNPS is given in table 3 (see appendix B for details). Consideration is
given to releases (a) to the atmosphere and (b) to the Pacific Ocean (both directly in liquid form andindirectly as deposits from the radionuclides released to the atmosphere). In general, the tabulated
values encompass the range of published releases; in some cases, the ranges of tabulated values are
smaller and exclude estimates that the Committee judged to be less reliable. All estimates of release areassociated with much uncertainty. The total inventory of each radionuclide in the three reactors at thetime of their shutdown is also indicated for perspective.

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43

Table 3. Summary of release estimates for the more significant radionuclides to the environment
from FDNPS
Given their uncertainties, values are quoted to just one significant figure

Release to theatmosphere (PBq)

DirectIndirectb

I

6 000

100 to 500c

about 10 to 20e

60 to 100g

Cs

700

6 to 20d

3 to 6f

131
137

Release to the ocean (PBq)

Inventory in Units 1 to 3 atreactor shutdowna (PBq)

Radionuclide

5 to 8ga

Values quoted to two significant figures.

b

Indirect releases comprise radionuclides initially released to the atmosphere and subsequently deposited onto the ocean surface.

cEncompasses the full range of estimates reviewed by the Committee (see table B2).

d

Encompasses the full range of estimates reviewed by the Committee apart from two (these two extended up to about 40 PBq but
were based on limited information and were less reliable) (see table B2).
eBased on very limited information indicating that the direct release of 131I was about 3 times greater than that of 137Cs (seetable B6).
f

Range of estimates derived from more reliable three-dimensional modelling; other estimates were larger, extending up to about
30 PBq, but were less reliable (see table B6).
g

Encompasses the range of (few) estimates reviewed by the Committee (see table B6).

53. Improvements in the estimation of the releases to both the atmosphere and the ocean can be
expected in future, in particular as more information becomes available on the progression of theaccident, greater use is made of measurements in the environment, and improved assessment methods
are implemented. This is an active area of research; notwithstanding these expected improvements,
significant uncertainties are likely to remain, in particular surrounding the temporal pattern of thereleases.

B. Dispersion and deposition in the environment
1.

Atmosphere and terrestrial environment

54. The fate of radioactive material released to the atmosphere during the accident at FDNPS wasdetermined by the meteorological conditions pertaining at the time and the physical characteristics ofeach release, such as its height and whether it was in gaseous or particulate form. These conditions,which varied considerably during the period of releases, determined where the material was dispersed
and the rate at which it was diluted in and deposited from the atmosphere. The releases that largely
determined the levels and patterns of radionuclides on the Japanese land mass occurred on 12, 14–16,
and 20–23 March. The meteorological features that determined their fate were as follows:(a) Material initially released on 12 March went towards the Pacific Ocean, but the release in theafternoon of 12 March, in particular resulting from the hydrogen explosion in Unit 1 initiallyspread northwards along the eastern coast of the main island with significant dry deposition(particulate matter that settles on the ground), and later shifted to a north-north-easterly direction,over the coastal area of Miyagi;

44 UNSCEAR 2013 REPORT(b) Material released from late at night on 14 March moved towards the south, depositing along
the south-eastern coastal area of Fukushima Prefecture and the north-eastern area of Ibaraki
Prefecture (see figure IV) on the morning of 15 March; this material was further dispersed andresulted in dry deposition of radionuclides in the prefectures of Tokyo, Saitama and Kanagawa,albeit at reduced levels. By the afternoon of 15 March, this dispersing material encounteredprecipitation, which resulted in enhanced levels of wet deposition (brought to the ground with rain
and snow) in areas of the prefectures of Gunma, Tochigi and Fukushima. A further major releaseoccurred in the morning of 15 March; this material moved towards the south then progressively tothe north-west, leading to significant wet and dry deposition of radionuclides north-west of FDNPS;(c) Material released during the period 20 to 23 March was dispersed over parts of the Japanese
territory encountering rainfall on occasions and resulting in wet deposition, for example in areas ofthe prefectures of Iwate, Miyagi, Ibaraki and Chiba.
Figure IV. Location of Fukushima Daiichi Nuclear Power Station (FDNPS) and surrounding
prefectures

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45

55. The prolonged and varying releases, and the fluctuating meteorological conditions theyencountered, resulted in specific patterns of dispersion (see figures B-VIII to B-XIII in appendix B) for
each of the more significant release episodes.
56. Dose-rate measurements from automatic stations within Japan were the most abundant data
available for the course of the accident, although in Fukushima Prefecture many of the automatic
monitoring posts were inoperative and thus measurements there came mostly from portable dose-ratemonitors. In addition, extensive surveys were made of radionuclides deposited on the ground and insoils following the accident, and also of dose rates due to deposited material. The more notable were
the ground-based and airborne surveys carried out by the Ministry of Education, Culture, Sports,
Science and Technology (MEXT) and the Ministry of Agriculture, Forestry and Fisheries (MAFF), andthe airborne survey carried out by the United States Department of Energy (see appendix A).
Measurements of concentrations of radionuclides in air over Japan while the release was happening
were much more limited, in particular, in the early stages of the accident and in the areas devastated by
the tsunami.
57. Measurements of radionuclides in Japan were largely focused on 131I, 134Cs and 137Cs. Limited
data were also available for other radionuclides, such as 132Te, 129mTe, 132I and 133I, both measurementsof concentrations in the air and measurements of deposition density on the ground. Measurements of
89
Sr, 90Sr, 238Pu and 239+240Pu were also reported from a small fraction (fewer than 5%) of the sampling
points, generally in locations within Fukushima Prefecture. The levels of 238Pu and 239+240Pu depositedon the ground were very low and mostly below detection limits. The levels of 89Sr and 90Sr deposited on
the ground were significantly lower than those of 137Cs and these radionuclides were therefore notincluded in the Committee’s estimation of doses to the public. The available measurements are
discussed further in appendices B and C. The CTBTO network measured a broader range ofradionuclides, including 133Xe, but many of these were not significant radiologically.
58. The dispersion and deposition of released material has been modelled by many groups, including
Terada et al. [T19], WMO [W18], and the French Institute for Radiation and Nuclear Safety [I33], witha view, inter alia, to determining how well they could replicate the measured levels in the environment.
All were able to replicate the broad pattern of deposition density of 137Cs over the Japanese land mass.
At specific locations, the model estimates are generally within a factor of 10 (higher or lower) of themeasured levels (see appendix B) but sometimes better. Notwithstanding these limitations, suchanalyses are the only means available for inferring levels of radionuclides in the environment where nomeasurements exist and/or can no longer be made.
59. Members of a WMO Task Team made estimates of the levels of radionuclides in the environment,
based on the source term adopted by the Committee (see section III.A above) and modelling thedispersion of radionuclides in the atmosphere. The approach used and the resulting estimates are
summarized in appendix B, including comparisons of the estimates with measured levels. The
Committee used the modelled estimates to assess doses to members of the public when measured levelsin the environment were not available (see appendices B and C). Doses estimated in this manner are
inevitably more uncertain than those estimated directly from measurements in the environment. To
provide insight into their robustness and nature of the uncertainty, the estimated levels of radionuclides
in the environment were compared for alternative dispersion models, meteorology and an
independently derived source term.

46 UNSCEAR 2013 REPORT

2.

Marine environment

60. Extensive measurements were made of concentrations of 131I, 134Cs, 137Cs and other radionuclides
in seawater and sediments, as well as in fish and other marine biota. TEPCO made daily measurementsfrom 21 March of samples taken from close to the discharge outlets to the north and south of the
FDNPS site, from locations to the north and south along the shore and at 3 km, 8 km and 15 km
offshore. MEXT made measurements along a line of locations 30 km offshore, and independent
researchers made measurements in the waters off the coast of Japan (e.g. [B25, H7]).
61. The results of these measurements are summarized in appendix B and appendix F. They indicate
peak concentrations in seawater in the vicinity of the FDNPS site at the end of March and at locations
further away in early April. Measured concentrations in seawater subsequently fell steadily and, by
August 2011, radioiodine was undetectable and radiocaesium concentrations were around or below thelimit of detection even at the discharge outfalls from the site. The more limited number ofmeasurements of concentrations of other radionuclides in seawater, including 89Sr and 90Sr, generally
showed a similar pattern, but with concentrations less than 1−10% of those of 137Cs. The exception
concerned concentrations of 89Sr and 90Sr measured in December 2011 following an accidental leakageof treated water from which radiocaesium had been removed. The elevated concentrations ofradioisotopes of strontium were temporary and had fallen below those of 137Cs again by January 2012.
62. Low concentrations of radiocaesium detected in samples of seawater taken off the coast of
Fukushima Prefecture and across the northern Pacific Ocean indicate an easterly movement of thereleased radioactive material at a rate close to 80 mm/s [A12]. Measurements have also been made ofradionuclide concentrations in seabed sediments. These measurements were again focused on 131I, 134Cs
and 137Cs, but some were also of radioisotopes of strontium, plutonium and americium. Measurements
by TEPCO showed a maximum concentration of 137Cs in sediments of the order of 100,000 Bq/kg dryweight within the port of FDNPS, although measured levels were generally many orders of magnitude
lower. Measured concentrations in sediment have not fallen as rapidly over time as measured
concentrations in seawater. Further details are given in appendix B.
63. These measurements have been used by several authors (e.g. [E4, K3, P3, T13, T24]) to estimate
the total direct release to the sea, and/or to predict the subsequent dispersion of radionuclides in the
Pacific Ocean. Model estimates were generally able to reproduce the measurement data well. Material
entering from the atmosphere was dispersed and deposited onto the ocean surface over a wide area. On
the other hand, for radionuclides released directly, the models suggest that the released radionuclides
initially moved southwards along the coast for around 200 km in a relatively confined plume, in
response to winds from the north, and then, away from the coast in an eastward direction with greater
dispersion and dilution in response to the Kuroshio current (see figures B-XXI and B-XXII in
appendix B). The results of the models generally indicate that, in the most affected areas, material
deposited from the atmosphere contributed more to levels in the ocean before about 26 March, but that,after that date, the greater contribution came from direct releases into the ocean.

IV. ASSESSMENT OF DOSES TO THE PUBLIC
64. This chapter sets out how the knowledge about the distribution of radioactive material in theenvironment discussed in chapter III was used to estimate doses to the public in Japan and presents asummary of the doses estimated. The Committee’s aim was to make realistic estimates of doses and, tothat end, its main focus was on estimating doses to defined groups of individuals considered to be
representative of the different subsets of the Japanese population. Estimates were made for 20-year-old

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47

adults, 10-year-old children and 1-year-old infants. The main dosimetric endpoints were the absorbed
dose to selected critical organs (in grays, Gy), most importantly the thyroid but also the red bonemarrow and female breast, and the effective dose 15 (in sieverts, Sv). Projections were also made for
effective doses and absorbed doses to the thyroid, and for collective effective doses, over the first
10 years after the accident and until an attained age of exposed individuals of 80 years.

A. Exposure pathways
65. For releases of radioactive material to the atmosphere, there are several routes by which people
can be exposed (figure V). Firstly, as the released material moves through the atmosphere asradioactive plumes into an area where people are living, they can be exposed (a) externally to radiationfrom radioactive material in the passing plumes, and (b) internally as a result of inhaling radioactive
material from the plumes. Once the material released to the atmosphere has passed, people willcontinue to be exposed to any radioactive material deposited on to the ground. They will be exposed
externally from this deposited material and internally as a result of its transfer into food and drink thatis subsequently ingested. Deposited material can also be resuspended into the air and inhaled but, forthe more significant radionuclides released from FDNPS (that is 131I, 134Cs and 137Cs), this route of
exposure is of less significance [I1, J7]. Radionuclides that are incorporated into the body via either theinhalation or ingestion pathways remain in the body for varying lengths of time, depending on their
physical and biological half-lives.
Figure V. Exposure pathways from releases of radioactive material to the environment

15

The effective doses estimated were the sum of the effective doses from external exposure received during the period of interestand the committed effective doses from intakes of radionuclides by ingestion and inhalation during the same period. The effective
dose includes a contribution that derives from a weighted absorbed dose to the thyroid.

48 UNSCEAR 2013 REPORT

66. For direct or indirect releases of radioactive material into the sea, people can be exposed
externally from radionuclides in the sea or in sea sediments. However, doses through these pathways
are not expected to make significant contributions to overall exposure. People can also be exposedinternally through transfer of radioactive material into seafood that is then consumed; this pathway wasconsidered in the Committee’s assessment of internal exposure.

B. Data for dose assessment
67. Measurements of radionuclides in people provide a direct source of information on their internal
exposures. Two main sets of such data were available to the Committee: the first from measurements of
131
I in the thyroid, particularly of children; and the second from whole-body monitoring of 134Cs and137
Cs. Such measurements only indicate the internal exposures from the radionuclides present in the
person at the time of monitoring. The measurements covered only a limited number of people andlocations, and were insufficient to estimate directly the internal exposure of people in either Fukushima
Prefecture or the rest of Japan. Therefore the Committee’s estimates of internal exposure were based on
measurements of radioactive material in the environment, combined with models describing how
people were exposed to this material.
68. Appendix A catalogues the extensive body of data available that were considered by theCommittee as input to its assessment, and outlines the processes it used to ensure that the data quality
was sufficient for its assessment. Measurements had largely focused on the radionuclides 131I, 134Cs and137
Cs, because these were the most significant contributors to exposures. The radionuclide 131I waslargely responsible for determining absorbed doses to the thyroid, which were delivered over a
relatively short period after the accident (via inhalation and ingestion of radioiodines, specifically 131I,
132
I and 133I). The radionuclides 137Cs and, to a lesser extent 134Cs, are responsible for the continuing
longer term exposure of the population, in particular from radioactive material deposited on the ground.
Although the main source of data was the official information provided by the Japanese authorities,
data from other sources were also used, including data provided by other Member States (such as thoseobtained by personnel of the United States of America in Japan), and other published information, suchas those obtained by IAEA field teams. The Committee made extensive checks to determine whether
the measurements had been carried out using established methodologies that assured quality and wereappropriate. The measurements were used in one of two ways: (a) as direct input into the dose
assessment; or (b) as a check on the validity of the assessment.
69. In Japan, extensive measurements have been made of the levels of various radionuclides
deposited on the ground. These included measurements made at ground level, and surveys using
instruments carried on aircraft flying over the affected areas. These measurements were used by theCommittee as the preferred basis for estimating external exposures of the public from depositedmaterial. Where no information was available about the levels of radionuclides deposited on the ground(generally only in the evacuated areas in the weeks following the accident), the Committee relied on
estimates derived from the source term and simulations of the transport of radioactive material throughthe atmosphere using “atmospheric transport, dispersion and deposition models” (ATDM) referred to inchapter III and further outlined in appendix B.
70. Because measurements of concentrations of radionuclides in the air were insufficient for its
assessment, the Committee had to estimate values. Such estimates were also obtained from the source
term and simulating the transport of radioactive material through the atmosphere using ATDM.
However, these estimates have large uncertainties at specific times and locations, not only because of

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49

incomplete knowledge about the quantities of radionuclides released and how these varied over timeand location, but also because of uncertainties in the models used to simulate the subsequent dispersionof the released material in the atmosphere. In view of these uncertainties, the Committee chose to use
the measurements of deposition density to adjust the estimates of concentrations in the air from the
ATDM analysis.
71. While the estimates of radionuclide concentrations in air and of radionuclides deposited on the
ground provided by the source term and ATDM analyses at any specific location are uncertain, the ratioof these two estimates is much less so. In particular, the ratios are relatively insensitive to theuncertainties in the source term. The main factors influencing the uncertainties in these ratios wereuncertainties in the assumed parameters describing wet and dry deposition. The Committee usedlocation-dependent ratios, derived from the ATDM analyses, to infer time-integrated concentrations ofradionuclides in air from measured deposition density of radionuclides on the ground. It used these
inferred concentrations to assess the exposures from radionuclides in air in all regions of Japan except
in the evacuated areas.
72. For areas that were evacuated during the early stages (days to a few weeks) of the accident, only alimited number of measurements of radionuclide concentrations in air and deposited on the groundwere made during the periods of evacuation. Therefore, the Committee relied on estimates of thesequantities—over the period of the evacuation—from the source term and the ATDM analyses as thebasis for estimating doses to the populations who had undergone precautionary evacuation anddeliberate evacuation. This method was also used to estimate concentrations in air of radionuclides,
including 133Xe, which were not deposited on the ground.
73. A considerable amount of information was available on levels of radionuclides in a wide range offoodstuffs, including marine foods, and in drinking water (see appendix A). The Committee used data
for marketed foods, thereby implicitly taking account of restrictions on the supply of foodstuffs withconcentrations of radionuclides in excess of the prescribed limits (see table C4 in appendix C). The
Committee used these data (from the “FAO/IAEA food database”) as the primary basis for its
assessment of exposures from ingestion of radionuclides in food and drink in the first year. The
assessment was based on the mean concentrations of radionuclides measured in groups of foods (a) in
Fukushima Prefecture, (b) in the five neighbouring or nearby prefectures considered together, and (c) in
the rest of Japan. Data were insufficient for the first months following the accident to allow theCommittee to adopt a finer spatial resolution. Moreover, in Japan, most people obtain their food fromsupermarkets where foods are sourced from the whole of the country, so using mean concentrations
over wide areas was considered appropriate for the Committee’s purposes. In Japan, significant
amounts of some foods are imported from elsewhere in the world, and this was allowed for in theassessment.
74. The Japanese authorities provided the Committee with the results of measurements they had madeof radionuclides in drinking water. Levels were elevated for a limited period. The Committee estimateddoses based on these measurements, taking account of any restrictions introduced.
75. The Committee relied on information on levels of radioactive material in food and drink toestimate the exposure from ingestion in the first year after the accident. To estimate future levels of
exposure from ingestion, the Committee used models to assess concentrations of radionuclides infoodstuffs from the available measurements of deposition density of radionuclides on the ground.
Information was obtained on the agricultural practices in Japan, such as the times when different crops
are planted and harvested, crop yields and any Japanese-specific data on the transfer of radionuclides tospecific foods. These data were then used to modify a version of the FARMLAND model [B21] for
estimating the transfer of radionuclides through terrestrial foodchains. The results of modelling the50 UNSCEAR 2013 REPORT

dispersion of radionuclides in the sea off Fukushima Prefecture by Nakano and Povinec [N3] were used
to estimate possible exposures beyond the first year from ingestion of marine foods (see appendix C).
76. As outlined in chapter II, the Japanese authorities implemented a number of urgent measures toprotect the public. Approximately 85,000 residents within the 20-km evacuation area around the
FDNPS site, and some nearby areas, were evacuated as a precautionary measure between 11 and
15 March, and consequently most were not present in those areas when the major radionuclide
deposition occurred. “Deliberate evacuation”, based on environmental measurements, was undertaken
between March and June for about 10,000 residents of several settlements beyond the 20-km area.
These were settlements to the north-west of the FDNPS site where substantial deposition ofradionuclides took place following the major releases. The total number of evacuees was ~118,000,
which includes evacuees who had been living outside the 30-km radius and people evacuated forreasons other than the nuclear emergency situation. In addition, restrictions were introduced on
foodstuffs: food and drink containing more than prescribed concentrations of radioactive material wereprohibited from sale. The Committee took these protective measures into account in its assessment.
77. The Japanese authorities also issued directives with regard to protective measures other thanevacuation and food restrictions. These included directives to members of the public in the area
20-30 km from the FDNPS site who were advised to shelter in place during the main releases, as well
as directives to some members of the public to take stable iodine. However, precise information was
limited on how and when, and for which settlements these measures were implemented. Thus, theCommittee was not able to take these other protective measures into account in its estimation of doses
to the public.
78. In some of the more affected parts of Fukushima Prefecture (e.g. evacuated areas where theforecasted annual dose would have exceeded 20 mSv), large land remediation programmes have been
implemented and these have the potential to reduce future exposures of the public residing in theaffected areas. Experimental studies and tests of technologies for decontamination of inhabited areas,
and of countermeasures in agriculture and in forestry, were started in mid-2011. Detailed information
about the scale and efficiency of the implemented land remediation actions was not available at the timeof this assessment, and thus the Committee did not take into account the possible reduction in exposurelevels due to any remedial measures.

C. Overview of methodology for assessing public exposures
79. In order to estimate doses to the members of the public in Japan, the Committee focused on fourgroups of geographical areas (table 4).
80. For the same exposure, the doses vary according to the age at the time of exposure. Therefore, theCommittee considered three main age groups as at the time of the releases: adults, children and infants.
For the estimation of doses, 20-year-old adults were chosen to represent all adults, 10-year-old children
to represent all children older than 5 years old, and 1-year-old infants to represent all infants younger
than 5 years old. The Committee did not explicitly estimate doses to the foetus or breast-fed infants
because they would have been similar to those to other age groups for both external and internalradiation exposure (see appendix C). For example, doses to the foetus and breast-fed infant due toexternal exposure would have been approximately the same as those to adults and 1-year-old infants,
respectively. The Committee focused on estimating the accumulated exposures in the first year
following the accident (these would generally be higher than annual exposures in subsequent years).

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51

However, it also estimated accumulated exposures over the first 10 years after the accident, and up to
the age of 80 years, taking into account the ageing of the three age groups over those periods.
Table 4. Delineation and spatial resolution adopted for each group of geographical areas
Group

Areas
a

Spatial resolution for public dose assessmentb

1

Settlements in Fukushima Prefecture where
people were evacuated in the days to months
after the accident

Representative locations were used for eachsettlement identified in 18 evacuation scenarios

2

Districtsc of Fukushima Prefecture notevacuated

District level for external and inhalation pathways,
based on the estimates for each of the 1-km-gridpoints, averaged over the district
Prefecture level for ingestion pathway

3

4

Selected prefectures in eastern Japan thatwere neighbouring (prefectures of Miyagi,
Tochigi, Gunma and Ibaraki) or nearby(prefectures of Iwate and Chiba) to Fukushima
Prefecture

District level for external and inhalation pathways,
based on the estimates for each of the 1-km-gridpoints, averaged over the district

All remaining prefectures of Japan

Prefecture level for external and inhalation pathways

Estimated dose due to ingestion for Iwate Prefecturesame as for Group 4; for other five prefectures was
based on average for the five prefectures

Average for rest of Japan for ingestion pathway
aSettlements: This term is used in this report to represent an evacuation scenario. There were 18 evacuation scenarios thatcovered 12 districts of Fukushima Prefecture. Some of these districts were associated with more than one evacuation scenario so
the term “settlement” was selected to be representative of localized areas within a district that were considered in evacuation
scenarios.
b

Prefecture: Japan comprises 47 prefectures. In Japanese the word “prefecture” is used for translating references to an
administrative district, ken (県). Figures IV, VI and VII show the prefectures close to Fukushima Prefecture and those further
afield.
cDistrict: Each prefecture of Japan is divided into districts (or shi or gun in Japanese). This is a local administrative unit; thedistricts are used primarily in the Japanese addressing system to identify the relevant geographical areas and collections of
nearby towns and villages.

81. The models used to estimate doses due to external exposure to deposited radioactive material are
well established (for example, the Committee used similar models for its assessment of radiation doses
from the Chernobyl accident [U12]). They take into account processes such as radioactive decay,
removal of radionuclides from surfaces through weathering, and the movement of radionuclides
through the soil, as well as the shielding effects of buildings when people are indoors. The Committee
considered a number of different types of building (and hence degrees of shielding) and different
amounts of time spent indoors. In Fukushima Prefecture and the Group 3 prefectures, the majority ofhouses were of wooden construction, and the Committee therefore presented its dose estimates forpeople living in wooden houses.
82. Doses due to inhalation of radionuclides in the air were assessed using standard, internationallyrecognized models and data [I12, I15, I25]. An age-dependent breathing rate was used to estimate thequantities of the radionuclides in the air which entered the body, and the normalized dose resulting
from unit of inhaled activity of each radionuclide (known as the dose coefficient) was then used toestimate the dose received.
83. Similarly, doses due to ingestion of radionuclides in food and drinking water were estimated fromradionuclide concentrations in food, using age-dependent intake rates for different types of foodstuffs

52 UNSCEAR 2013 REPORT

and dose coefficients for unit of ingested activity of each radionuclide [I25]. For assessing doses inJapan due to ingestion in the first year, the Committee primarily used the measurement data in the
FAO/IAEA food database (see appendix A). However, in order to estimate doses due to ingestion
beyond the first year, the Committee had to use modelling approaches. The Ministry of Health, Labourand Welfare (MHLW) in Japan conducted surveys of the per caput consumption of particular foods,
and its data were used by the Committee. The most extensive data available were for adults, but there
were also data for infants and children.
84. For those who had been evacuated (Group 1), the Committee estimated exposures prior to andduring their evacuation and for the remainder of the year at the evacuation destination. The estimation
was based on the concentrations of radionuclides in the air and deposition densities on the ground in theareas from which people had been evacuated (as estimated from the source term and the ATDM
analyses), and knowledge of the movements of the evacuees during this period (obtained from a survey
conducted within Fukushima Prefecture [A5]; this survey identified 18 evacuation scenarios, which are
discussed in detail in appendix C). Estimates of the effective doses due to external exposure that would
have been received by the adult residents of evacuated settlements if they were to have returned to theirhomes and regular lifestyle were also assessed for the period March 2012 to March 2015 assuming noenvironmental remediation. These estimates provide an upper bound on the effective doses to thesecommunities in the future.
85. The Committee could not exclude the possibility that individuals may have remained in or gained
access to the 20-km evacuation zone during and after passage of the radioactive plumes. The
Committee estimated the doses to the evacuees, and the doses that they would have received if they had
not been evacuated (this can be used as an estimate of doses to those persons who might have stayed in
the zone, and as an upper bound for any individual who might have gained access to the zone). Fromthese two sets of estimates, the Committee also estimated the doses averted by evacuation.
86. The Committee also estimated the collective effective dose and the collective absorbed dose to thethyroid to the population of Japan. These estimates were based on the age and social composition of the
population of Japan and the population distribution by district and prefecture taken from the Japan 2010
Census (see table A1, appendix A). The collective doses were estimated for populations living inFukushima Prefecture and the other prefectures of Japan.
87. The Committee did not undertake a comprehensive assessment to estimate doses to members of
the public in the rest of the world. The assessment of doses for countries other than Japan was based ona review of estimates published in the literature, including the results of the WHO preliminary exposure
assessment [W11], supported by the extensive measurements and dose assessments carried out by
Member States of the United Nations.

D. Results of dose estimation
88. The Committee produced an extensive set of estimates of effective doses and absorbed doses toparticular organs for the public in Japan, which is presented in more detail in appendix C.

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53

Doses in the first year to members of the public not evacuated89. Table 5 summarizes the estimated district- or prefecture-average effective doses and absorbed
doses to the thyroid for the first year following the accident for adults, 10-year olds and 1-year olds
living in areas of Japan that were not evacuated. Doses were summed over the three main exposure
pathways (external exposure, and internal exposure due to inhalation and due to ingestion).
Table 5. Estimated district- or prefecture-average effective doses and absorbed doses to the thyroidfor the first year following the accident for typical residents of Japan that were not evacuated
The doses are in addition to the background doses due to natural sources of radiation. The values were the ranges of the
district-average doses for the Group 2 and Group 3 prefectures and the prefecture-average doses for the Group 4 prefectures.
These estimates were intended to be characteristic of the average dose received by people living at different locations anddo not reflect the range of doses received by individuals within the population at these locations. They may overestimate
actual average doses because of assumptions made where data were inadequate (see sections E and F of this chapter)

Effective dose (mSv)

Absorbed dose to the thyroid (mGy)

Residential area
Adults10-year old

1-year old

Adults10-year old

1-year oldGroup 2 - Fukushima
Prefecture

1.0–4.3

1.2–5.9

2.0–7.5

7.8–17

15–31

33–52

Group 3 prefectures b

0.2–1.4

0.2–2.0

0.3–2.5

0.6–5.1

1.3–9.1

2.7–15

Group 4c - rest of Japan

0.1–0.3

0.1–0.4

0.2–0.5

0.5–0.9

1.2–1.8

2.6–3.3aaGroup 2 - Members of the public living in the non-evacuated districts of Fukushima Prefecture.

bGroup 3 - Members of the public living in the prefectures of Miyagi, Gunma, Tochigi, Ibaraki, Chiba and Iwate.

cGroup 4 - Members of the public living in the remaining prefectures of Japan.

90. Effective doses. Figure VI shows a map illustrating district-average effective doses in the first year
to adults living in districts of Fukushima Prefecture that were not evacuated (Group 2) and in someGroup 3 prefectures. Absorbed doses to the thyroid (all ages) and effective doses to 10-year-old
children and 1-year-old infants show a similar geographical pattern that reflects the deposition densityof radionuclides in the different areas (see appendix C).
91. The relative contribution of each exposure pathway varied from location to location reflecting thelevels and composition of radionuclides in the environment and in foods. In the areas of higher
deposition density, the greater contribution to effective dose was from external exposure to depositedmaterial. The relative contribution to effective dose in the first year for Fukushima Prefecture due toingestion of food varied. This was because effective doses due to ingestion reflected concentrations ofradionuclides averaged over much larger areas than effective doses from other routes. In areas of Japan
far away from the FDNPS site, effective doses due to ingestion predominated for most prefectures.

54 UNSCEAR 2013 REPORT

Figure VI. Estimated district-average effective doses in the first year following the accident to adults
living in districts of Fukushima Prefecture and some districts of Group 3 prefectures that were notevacuated
The effective doses include contributions from all relevant pathways and radionuclides

92. Within Fukushima Prefecture, the districts that partly fall within the 20-km evacuation zone
(Minamisoma City) and those with high ground deposition density (Fukushima City, Nihonmatsu City,
Koori Town, Otama Village, Koriyama City, Motomiya City and Date City) had the highest estimatedeffective doses to individuals who were not evacuated, with the district-average effective doses toadults in the range 2.5 to 4.3 mSv in the first year. In those districts, the contribution of external dosefrom deposited radionuclides to effective dose was dominant. Average effective doses in the first year
for 1-year-old infants were estimated to be up to twice those for adults.
93. For the districts of the Group 3 prefectures (Chiba, Gunma, Ibaraki, Iwate, Miyagi and Tochigi),
the district-average effective doses to adults were in the range 0.2 to 1.4 mSv for the first year,
including 0.2 mSv from ingestion of food in the prefectures of Chiba, Gunma, Ibaraki, Miyagi andTochigi. In Iwate Prefecture, the effective dose due to ingestion of food was 0.1 mSv, the same as forthe remainder of Japan. The prefecture-average effective dose to adults for the prefectures in the

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55

remainder of Japan was in the range 0.1 to 0.3 mSv for the first year, with ingestion contributing
0.1 mSv and generally being the dominant pathway.
94. Figure VII shows the prefecture-average effective dose in the first year for 1-year-old infants in
the rest of Japan (the Group 4 prefectures). Prefecture-average doses for other prefectures were lower
than those for Fukushima Prefecture and are considerably lower for the more distant prefectures, where
the effective dose estimates were less than the normal variations in background effective doses due tonatural sources of radiation.
Figure VII. Estimated prefecture-average effective doses in the first year following the accident to1-year-old infants
The effective doses include contributions from all relevant pathways and radionuclides. The main map shows the prefectureaverage effective doses. The average dose for Fukushima Prefecture includes only districts that were not evacuated. The inset
map shows the district-average effective doses for the districts of Fukushima Prefecture that were not evacuated

95. Absorbed doses to organs. For districts of Fukushima Prefecture that were not evacuated(Group 2), the highest estimated absorbed doses to the thyroid in the first year were to individuals
living in Iwaki City and Fukushima City. The highest district-average absorbed dose to the thyroid of a

56 UNSCEAR 2013 REPORT

1-year-old infant in the first year was estimated to be about 50 mGy for Iwaki City (see table 5).
Approximately one third of this dose was due to inhalation and two thirds due to ingestion. The
estimated doses to the thyroid for adults in the first year were about 30% of those for 1-year-old infants.
These doses were mostly received over the first few weeks after the accident. The average absorbed
doses to the red bone marrow and the female breast in the first year for the districts within Fukushima
Prefecture that were not evacuated were estimated to be less than 6 mGy for all age groups.
96. For Group 3 prefectures (Chiba, Gunma, Ibaraki, Iwate, Miyagi and Tochigi), the district-averageabsorbed doses to the thyroid of infants in the first year were estimated to be in the range of 3 to
15 mGy. Ingestion was the dominant exposure pathway; the contribution of the inhalation pathway
ranged from a few per cent to about thirty per cent. The district-average absorbed doses to the red bonemarrow and the female breast in the first year were estimated to be less than 2 mGy for all age groups.
For the remainder of the 40 prefectures of Japan, the prefecture-average absorbed doses to the thyroidof infants in the first year were estimated to have been about 3 mGy, with between 75% and 100% of
the dose from the ingestion of food.
97. All of these estimated doses are representative of the average doses to the populations in therespective districts for Group 2 and Group 3 prefectures and in the respective prefectures for Group 4.
There would have been variation about these averages for particular individuals depending on factors
such as what foods they consumed and where they were located relative to the dispersion of thereleased radioactive material. Individuals may also have taken personal protective measures that theCommittee did not consider.
98. The Committee also undertook some indicative analyses of the likely variability in the doses due
to external exposure and due to internal exposure from inhalation within a district. These indicated thatwithin each district there was marked spatial variability in both the measured radionuclide deposition
densities and the 131I concentrations in air. The variability was such that the estimates of both theeffective doses and the absorbed doses to the thyroid from inhalation could be from 30−50% of the
district-average dose up to about two to three times higher than the district-average dose.
99. For external exposure from deposited material, a further factor affecting variability in the dose
estimates was the shielding effect of building materials. The main results presented were for people
living in wooden houses which are the most common in Fukushima Prefecture. But, for people living in
concrete multi-storey apartments or wooden plastered houses, their doses would be about 25% or 50%,
respectively, of those estimated.
100. There was also significant variability in measured levels of radionuclides in different foodstuffs
depending on where they were grown, the amount of radioactive material deposited on the ground, as
well as local factors such as the time of planting of the crop and the soil type. A key factor was where
people obtained their food; the majority of people in Japan use supermarkets, and so the approach used
to assess doses for the first year—based on mean concentrations in foodstuffs in Fukushima Prefecture,
in five of the six Group 3 prefectures (excluding Iwate), and in the rest of Japan—was consideredappropriate for the purpose of this assessment.
101. The transfer of radionuclides to foods is very dependent on the time of year that a release occurs.
The accident at FDNPS occurred in March when only few crops were being grown and animals werebeing given stored feed. This led to lower concentrations in foodstuffs than would have been the case if
the accident had happened later in the year (as was the case for the Chernobyl accident in 1986). The
Committee could not exclude the possibility that some individuals, particularly those in the deliberate
evacuation areas, might have consumed locally-grown food or have collected mushrooms or wild
plants, or caught or hunted local fish and game with high concentrations of radionuclides before theirANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

57

evacuation. Such food habits have the potential to increase the estimates of effective dose fromingestion for these individuals by up to perhaps a factor of 10, however there is no evidence of suchhigher doses in the extensive sets of in vivo whole body measurements of the general public. Also,
because of the time of year of the accident there was limited locally-grown food and many people inJapan took measures to reduce their intake of radionuclides in food by avoiding fresh produce oranything that might have come from Fukushima Prefecture. For these people doses due to ingestion
would have been significantly lower than those estimated by the Committee [S2].

2.

Doses to evacuees

102. Doses in the first year to people evacuated from Group 1 areas (Futaba, Hirono, Namie, Naraha,
Okuma, Tomioka, Iitate, Kawamata, Minamisoma, Tamura, Kawauchi and Katsurao) were estimated as
the sum of doses received before and during evacuation, and doses received during the remainder of theyear at the location to which they were evacuated. The estimated settlement-average effective doses andabsorbed doses to the thyroid are summarized in table 6.
Table 6. Estimated settlement-average effective doses and absorbed doses to the thyroid forevacuees for the first year following the accident
The doses are in addition to the background doses due to natural sources of radiation. The values were the ranges of thesettlement-average doses for the evacuation scenarios. These estimates of dose were intended to be characteristic of theaverage dose received by people evacuated from each settlement and do not reflect the range of doses received byindividuals among the population of the evacuated settlement. They may overestimate actual average doses because ofassumptions made where data were inadequate (see sections E and F of this chapter)

Age group

Precautionary evacuated settlementsa
Before andduringevacuation

At theevacuation
destination

First year
total

Deliberately evacuated settlementsb
Before andduringevacuation

At theevacuation
destination

First year
total

EFFECTIVE DOSE (mSv)
Adults

0–2.2

0.2–4.3

1.1–5.7

2.7–8.5

0.8–3.3

4.8–9.3

Child, 10-year old

0–1.8

0.3–5.9

1.3–7.3

3.4–9.1

1.1–4.5

5.4–10Infant, 1-year old

0–3.3

0.3–7.5

1.6–9.3

4.2–12

1.1–5.6

7.1–13

ABSORBED DOSE TO THE THYROID (mGy)aAdults0–23

0.8–16

7.2–34

15–28

1–8

16–35

Child, 10-year old

0–37

1.5–29

12–58

25–45

1.1–14

27–58

Infant, 1-year old

0–46

3–49

15–82c

45–63

2–27

47–83cPrecautionary evacuation refers to the evacuation of settlements that was instructed between the 12 and 15 March 2011 as anurgent protective action to prevent high exposure. The dose assessment considered evacuation scenarios 1−12 (see appendix C)
for towns of Futaba, Okuma, Tomioka, Naraha and Hirono, and parts of the cities of Minamisoma, Namie and Tamura andvillages of Kawauchi and Katsurao.
bDeliberate evacuation refers to evacuation of settlements (based upon environmental measurements) that was instructed

between late March and June 2011. The dose assessment considered evacuation scenarios 13−18 (see appendix C) for Iitate
Village and parts of Minamisoma City, the towns of Namie and Kawamata, and of Katsurao Village.
c

These absorbed doses to the thyroid were principally due to internal exposure from inhalation during the passage of theairborne radioactive material through the affected areas before and during evacuation in the early days of the accident and fromingestion over the subsequent period.

58 UNSCEAR 2013 REPORT103. The settlement-average effective doses in the first year ranged from a few millisieverts to about
ten millisieverts or slightly above for all age groups and both evacuation scenarios. The corresponding
settlement-average absorbed doses to the thyroid in the first year ranged up to about 35 mGy for adults
and up to about 80 mGy for 1-year-old infants. For the precautionary evacuated settlements thesettlement-average absorbed doses to the red bone marrow and the female breast in the first year were
estimated to be in the range of 0.6 to 7 mGy and for the deliberately evacuated settlements thesettlement-average doses were in the range of 4 to 10 mGy for all age groups.
104. The Committee estimated that the evacuation of settlements within the 20-km zone averted
effective doses to adults of up to about 50 mSv and absorbed doses to the thyroid of 1-year-old infantsof up to about 750 mGy (see tables C11 and C12 of appendix C).

3.

Estimation of doses in Japan for exposure over future years

105. The Committee also estimated district-average and prefecture-average doses accumulated over the
first 10 years after the accident, and accumulated up to the age of 80 years. These are presented intable 7 only for residents of districts who were not evacuated. Children who had been infants (1-yearold) at the time of the accident had the highest estimated effective doses, followed by 10-year-old
children and then adults. The differences in the estimated effective doses among these age groups were
not large, being less than a factor of two. Estimates of the effective doses due to external exposure thatwould be received by adult residents of evacuated settlements if they were to return to their homes andregular lifestyle (not accounting for any environmental remediation) are discussed in appendix C (seetable C19).
106. Generally, the district-average or prefecture-average effective doses that would be incurred overthe first 10 years were estimated to be up to twice the effective doses in the first year, and the lifetime
effective doses were up to three times higher, assuming there was no remediation. The Committee did
not consider the effects of remediation measures in its dose assessment, because the effectiveness of thedifferent measures being applied in Japan had not yet been established. However, estimates of theeffective doses that would be received by those who were evacuated if they were to return to theirhomes and regular lifestyle without any environmental remediation provide an upper bound on thedoses that might be received in the future. For the evacuated location with the highest deposition
density, the settlement-average effective dose for adults from external exposure was estimated to be
12 mSv for the period March 2012 to March 2013, falling to 5 mSv for the period March 2014 toMarch 2015. The lifetime absorbed dose to the thyroid was estimated to be less than 50% higher than
the absorbed dose to the thyroid in the first year. This is because most of the absorbed dose to thethyroid in the first year is due to 131I (delivered over a relatively short period), while in subsequent years
the dose is due to 134Cs and 137Cs (see appendix C).

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Table 7. Estimated district- or prefecture-average effective doses to adults, 10-year-old children and1-year-old infants (as of 2011) over the first year, first 10 years and up to the age 80 years
The estimated doses are in addition to the background effective doses due to natural sources of radiation. The values are theranges of the district-average effective doses for the Group 2 and Group 3 prefectures and the prefecture-average effective
doses for the Group 4 prefectures. These estimates of effective dose were intended to be characteristic of the average
received by people living at different locations and do not reflect the range of effective doses received by individuals among
the population at these locations. They may overestimate actual average effective doses because of assumptions madewhere data were inadequate (see sections E and F of this chapter)

District- or prefecture-average effective dose (mSv)
Age group

Geographical area of Japanas of 2011

Group 3b prefectures

Group 2

Group 4c – rest of Japana

Fukushima Prefecture

1 YEAR EXPOSURE
Adult

1.0–4.3

0.2–1.4

0.1–0.3

Child, 10-year old

1.2–5.9

0.2–2.0

0.1–0.4

Infant, 1-year old

2.0–7.5

0.3–2.5

0.2–0.5

10 YEAR EXPOSURE
Adult

1.1–8.3

0.2–2.8

0.1–0.5

Child, 10-year old

1.3–12

0.3–4.0

0.1–0.6

Infant, 1-year old

2.1–14

0.3–6.4

0.2–0.9

LIFETIME EXPOSURE
Adult

1.1–11

0.2–4.0

0.1–0.6

Child, 10-year old

1.4–16

0.3–5.5

0.1–0.8

Infant, 1-year old

2.1–18

0.4–6.4

0.2–0.9aGroup 2 - Members of the public living in the non-evacuated districts of Fukushima Prefecture.

bGroup 3 - Members of the public living in the prefectures of Miyagi, Gunma, Tochigi, Ibaraki, Chiba and Iwate. The prefecturesof Chiba, Gunma, Ibaraki, Miyagi, and Tochigi were grouped together to calculate the effective dose from ingestion in these
prefectures. For Iwate Prefecture the effective dose from ingestion was assumed to be the same as that for the rest of Japan.
cGroup 4 - Members of the public living in the remaining prefectures of Japan.

107. To provide some perspective on the overall exposure of the Japanese population from theaccident, the Committee also estimated collective effective doses and collective absorbed doses to thethyroid for the Japanese public. The resulting collective effective dose and collective absorbed dose to
the thyroid for the first year, for the first 10 years and over a lifetime are given in table 8. The main
contributors to the collective effective dose were the long-term exposure pathways of external exposure
from 134Cs and 137Cs deposited on the ground and internal exposure from ingestion of the sameradionuclides in foods. The major contributor to the collective absorbed dose to the thyroid in the firstyear was internal exposure due to inhalation and ingestion of 131I.

60 UNSCEAR 2013 REPORT

Table 8. Estimated collective effective dose and collective absorbed dose to the thyroid for the
population of Japan (approximately 128 million in 2010)
Exposure duration
Dose category
Over first year

Over ten years

Up to age 80 years

Collective effective dose(thousand man-sieverts)

18

36

48

Collective absorbed dose to the thyroid(thousand man-grays)

82

100

112

108. These estimates of the collective doses to the population of Japan due to the FDNPS accident canbe compared with estimates for populations of European countries exposed to radiation following the1986 Chernobyl accident in the former Soviet Union. The collective effective dose and collective
absorbed dose to the thyroid estimated by the Committee for a 20-year period (1986–2005) from theresults of both environmental and human measurements were about 360,000 16 man Sv and2,300,000 man Gy, respectively. Taking account of continuing lifelong exposure, those values would be
about 400,000 man Sv and 2,400,000 man Gy, respectively. The collective effective dose to the
population of Japan due to a lifetime exposure following the FDNPS accident is approximately 10–15%
of the corresponding value for European populations exposed to radiation following the Chernobyl
accident. Correspondingly, the collective absorbed dose to the thyroid was approximately 5% of that
due to the Chernobyl accident.

4.

Estimation of doses in other countries

109. The Committee’s assessment of doses to the public in countries neighbouring Japan and in therest of the world was based on a review of estimates published in the literature, including the results of
the WHO preliminary exposure assessment [W11], supported by the extensive measurements and dose
assessments carried out by Member States (appendix C). Based on an analysis of this body of
information, the Committee concluded that the average effective doses to populations living outside
Japan due to the accident were less than 0.01 mSv in the first year.

E. Uncertainties
110. There are uncertainties associated with the results of any assessment of this type because ofincomplete knowledge and information, and the assumptions that were made. The main sources of
uncertainty are discussed in detail in appendix C, but some important factors are outlined below.
111. The estimates of dose due to external exposure were largely based on measured levels ofradionuclides deposited on the ground. The uncertainties associated with individual measurements of137
Cs and 134Cs were relatively small, but those for 131I were larger because of the significant amount ofradioactive decay that occurred before the measurements were made. There were also uncertainties in
how well the measurements represented the spatial distribution of radionuclides for each district orprefecture when estimating district-average doses. For Fukushima Prefecture, there were extensive
16

About 260,000 man Sv without the contribution of the thyroid dose [U12].

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measurements with adequate spatial coverage, and the district-average doses estimated for specificdistricts were considered to be accurate within a factor of two. For the Group 4 prefectures, there werecomparatively fewer measurements, and the uncertainties in the prefecture-average doses were likely to
be larger.
112. Another source of uncertainty stemmed from the incomplete knowledge of the release rates ofradionuclides over time and the weather conditions during the releases. The results of the ATDM
analyses had large uncertainties when used to estimate doses at a specific location. Althoughmeasurements of concentrations of radionuclides in the environment were used to assess dose wherever
possible, some estimates were made using the assumed pattern of release of radionuclides and theoutput of the ATDM analyses. The estimates of doses due to inhalation and external exposure for thecommunities evacuated in March, before and during the evacuation, were based on the estimates of
release rates and ATDM analyses directly. The settlement-average effective doses and absorbed doses
to organs for these population groups may be over- or underestimated by a factor of up to typically four
to five because of uncertainties in the ATDM results for specific locations and times.
113. An additional factor that affected the estimation of absorbed dose to the thyroid due to inhalation
was the ratio of particulate to gaseous forms of 131I in the air. The atmospheric measurement data werelimited and available mostly at substantial distances from the release site. For Fukushima Prefecture,
where the absorbed doses to the thyroid could have been more significant, there were no measurement
data for the relative amounts of particulate and gaseous forms of 131I in air: the value of this ratio was
obtained from the ATDM results assuming that equal amounts of iodine were released in particulate
and gaseous forms. The estimated value for this ratio has an uncertainty of up to about a factor of two
over the periods of the principal exposures.
114. There was an uncertainty associated with the doses derived from the measurements ofradionuclides in foodstuffs (appendix C), and this was difficult to quantify. Foodstuffs were notsampled randomly, because the authorities gave priority to identifying foods with the highest
concentrations. It was therefore likely that the values of average concentrations used by the Committee
were overestimates, particularly for the first months after the accident when there were relatively few
measurements. Many measurement results were less than the detection limits and were assumed by theCommittee to have a fixed value at the detection limit; this also led to some overestimation of the doses
to people due to ingestion. Changes in the pattern of food distribution and consumption were anothersource of uncertainty. If it had been assumed that only 25% of food consumed in Fukushima Prefecture
was from the prefecture, then the estimated effective doses from ingestion for the first year would havebeen 30% of the Committee’s estimates.
115. Standard models were used to determine effective doses and absorbed doses to relevant organs
following intakes of radionuclides into the body. These were based on a standard-sized person withparticular metabolic characteristics. The Japanese diet is relatively high in stable iodine. This could
have resulted in less transfer of radioiodine to the thyroid than implied by the standard model, and thus
in slightly lower doses from this source. However the overall effect would have been small whencompared to other uncertainties associated with the dose assessment (see appendix C).

62 UNSCEAR 2013 REPORTF. Comparison with direct measurements and other assessments
1.

Direct measurements of radionuclides in people

116. Available measurements of radionuclides in people provided a direct source of information on
exposures of members of the public. There were two main sets of data: (a) measurements of 131I in the
thyroid, particularly of children; and (b) whole-body monitoring results for 134Cs and 137Cs. These
measurements provided one means of checking the validity of the dose assessment conducted by theCommittee.
117. There is likely some overestimation introduced by the methodology adopted by the Committee toestimate absorbed doses to the thyroid for the evacuees (e.g. in the assumptions on protective measuresowing to lack of information, and in dosimetric factors). Thyroid monitoring was carried out by local
authorities on 1,080 children aged between 1 and 15 years in Iwaki City, Kawamata Town and Iitate
Village over the period from 26 to 30 March 2011 using hand-held dose-rate instruments [K13]. The
absorbed doses to the thyroid from internal exposure were calculated assuming exposure wascontinuous over the period 12 to 24 March 2011. The results of the Committee’s analysis of themeasurement data for 10-year-old children and 1-year-old infants were consistent with the assessmentby the Japanese authorities. (In its analysis the Committee assumed a single exposure on the 15 March
2011.) The Committee’s estimates of settlement-average absorbed doses to the thyroid from internal
exposure were up to about five times higher than the corresponding values derived from direct
monitoring of this group. Thyroid monitoring results were also reported for measurements made on
62 evacuees between 12 and 16 April 2011 [T20]. The settlement averages for absorbed dose to thethyroid from internal exposure estimated by the Committee were up to four times higher than thoseestimated by Tokonami et al. (see appendix C).
118. As part of the Health Examination for Citizens in Fukushima Prefecture, whole-body counting of
more than 106,000 residents of Fukushima Prefecture and neighbouring prefectures was conducted up
to December 2012 [H5, M24]. Momose et al. [M24] reported that, for the period from July 2011 toJanuary 2012, the presence of 134Cs and 137Cs in the body could be detected in 20% of the 10,000
evacuees examined. Hayano et al. [H5] reported that, for the period from October 2011 to February
2012, the presence of 134Cs and 137Cs in the body could be detected in 12% of the 33,000 residents ofFukushima Prefecture and neighbouring prefectures examined. By March–November 2012, this
proportion had fallen to 1%. The estimates of average effective dose due to internal exposure based onthese large monitoring programmes are discussed in appendix C and were substantially lower thanthose estimated by the Committee from the inhalation and ingestion of 134Cs and 137Cs.

2.

Other assessments

119. A number of published scientific papers and reports contain various dose assessments formembers of the public. A preliminary dose estimation [W11] and related health risk assessment [W12]were carried out for WHO based on data available to September 2011. The results obtained in theCommittee’s assessment (using more realistic assumptions and more comprehensive and recent data,
particularly for the evacuated areas) and the doses estimated in the WHO studies were essentiallyconsistent; in general the ranges of estimates presented by WHO (see appendix C) encompassed theresults of the Committee’s assessment, but were higher for some of the evacuated settlements. Takahara
et al. [T3] also assessed the doses to adults in Fukushima Prefecture using a probabilistic approach.

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Where similar assumptions were made, the results were broadly consistent with those obtained by theCommittee. The National Institute for Radiological Sciences (NIRS) in Japan has assessed effective
doses due to external exposure to those evacuated. The NIRS assessment used a similar methodology tothat used by the Committee but a different atmospheric dispersion model. Estimated doses weregenerally consistent with those of the Committee’s assessment.

V. ASSESSMENT OF DOSES TO WORKERS

A. Introduction
120. The effective dose limit for workers given in the Japanese regulations is 100 mSv over a period of
5 years, with a maximum of 50 mSv in a single year; however, for female workers the effective dose
limit is 5 mSv in any three-month period. An effective dose reference level (in Japan termed“emergency dose limit”, which is used hereafter in this report) of 100 mSv was adopted immediately
after the accident [I9] for those workers dealing with the emergency. However, on 14 March 2011, after
further assessment of the conditions at the FDNPS site, the emergency dose limit was increased by theauthorities to an effective dose of 250 mSv, for all exposures received during the emergency period (i.e.
up to 16 December 2011). This increase was to enable essential mitigation activities to be carried out
while maintaining the protection of workers. TEPCO adopted a lower emergency dose limit of 200 mSv(effective dose) to ensure compliance with the level set by authorities [I6].
121. The exposure of workers to radiation decreased with time following the accident due toradioactive decay and the decline in the amounts of radioactive material being released from thedamaged reactors. The Ministry of Health, Labour and Welfare reinstated the pre-existing emergency
dose limit of 100 mSv (effective dose) on 16 December 2011 [T16, W1] following the cold shutdownof reactors in Units 1, 2 and 3.
122. Before the accident, a few thousand occupationally-exposed workers were employed at the site.
This number increased dramatically following the accident with almost 25,000 occupationally-exposed
workers having been involved in recovery and related operations by October 2012. The majority ofthese (about 21,000) were employed by contractors of TEPCO. TEPCO workers were mainly involvedin plant operation, recording of data and supervision of construction activities. Contractors’ workers
were mainly involved in work of restoration and construction of facilities; some of them also supported
TEPCO workers in stabilizing the nuclear reactors and managing the discharges of radioactive
materials.
123. In addition, a few hundred workers from the emergency services were deployed on the site of
FDNPS; these included fire-fighters (260), police (13) and personnel of the Self-Defense Force 17 (168).
Of these, 84 Self-Defense Force personnel were engaged in the on-site operations discharging water forcooling from helicopters and the remaining workers were engaged in similar activities on the ground. In
17

When disasters such as natural disasters occur in any part of the country, the Self-Defense Force works in collaboration withmunicipal governments, engaging in, for example, search and rescue operations, offering medical treatment, supplying water, andtransporting personnel and goods. Over 100,000 personnel of the Self-Defense Force were dispatched for relief operations ingeneral after the 2011 great east-Japan earthquake and tsunami.

64 UNSCEAR 2013 REPORT

addition, tens of thousands of fire-fighters, police and Self-Defense Force personnel were engaged inemergency response activities off-site.
124. By the end of December 2011, about 350 municipal employees of the Prefectural Office ofFukushima Prefecture had been involved in emergency operations within the restricted area (the 20-km
evacuation zone). Their main activities included monitoring of environmental radiation levels,
evaluating the damage caused by the disaster, restoring power supplies and radiation monitors,
protecting pets, capturing and slaughtering livestock, on-site inspecting at FDNPS and coordinating andcollaborating with relevant organizations. A further 34,000 or so municipal workers were involved withnumerous and diverse emergency activities within the area designated for evacuation [Y7].
125. The United States Department of Defense (DoD) and the United States National Nuclear Security
Administration (DOE/NNSA) provided about 24,000 personnel in support of the Japanese government
in the aftermath of the earthquake, tsunami and the reactor accident. United States personnel generally
remained outside the restricted area. They conducted environmental radiation measurements andsupported humanitarian missions (e.g. restoring the operational capability of Sendai airport, whichallowed air transport of humanitarian relief supplies including food, fuel and clothing).

B. Conditions affecting doses and health126. Following the accident, TEPCO and other organizations worked in and around the FDNPS site tobring the nuclear reactors under control and to reduce the release of radioactive material [I29]. In theearly phase of the accident (days to first few weeks), the first priority was to mitigate the radiologicalconsequences and further progression of the accident, in particular restoring the cooling system by reestablishing electrical power (achieved on 26 March 2011) [I6]. Reactor stabilization and water
decontamination became the next priority.
127. The earthquake and tsunami caused widespread destruction of many buildings, roads, tanks andother aspects of the infrastructure on the FDNPS site. The operators were faced with a catastrophic
emergency, with a more or less complete and prolonged loss of electrical power, reactor control or
instrumentation, and with little hope of immediate outside assistance. Communications systems bothwithin and external to the site were severely affected, although the TEPCO in-house communications
network between the site and headquarters was mostly intact [I6].
128. The response required exceptional dedication by workers on-site and elsewhere. Immediately
after the tsunami, approximately 400 workers (about 130 operators and 270 maintenance personnel)
were available for recovery operations [I29]. They had to work exceptionally long hours in very
adverse conditions (i.e. loss of almost all power supplies; dark, wet and cold conditions; lack of proper
equipment including compressed air and other services; loss of all safety systems including
instrumentation and control) to secure the safety of the six reactors, the six nuclear fuel storage pools, acommon fuel storage pool and the dry cask storage facilities. Some workers had lost their homes andfamilies as a result of the earthquake and/or tsunami, yet continued to work. Many workers slept onsite, on the floor, and, because of food shortages, were only provided with minimal nutrition [I29].
They continued to work despite high personal risk from the successive aftershocks (i.e. very high dose
rates and levels of contamination at various locations on site), and the damage to the reactors following
the hydrogen explosions [I6].
129. Hazards at the site varied as mitigation measures were put in place. Four major hazards wereidentified for the workers: radiation, heat, stress, and machine operation including manual handling.

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Initially, high radiation levels were the most serious hazard as a result of the hydrogen explosions andthe continuing releases of radioactive material from the damaged reactors. From May to September
2011, heat exposure became an extremely important hazard. This was because of the hot summer
weather and workers having to work outdoors wearing double-layer Tyvek protective overalls and fullface respirators (these inhibited cooling by evaporation). They were also at risk of injury from machine
operation, manual clean-up of the rubble, and stabilizing the nuclear reactor for cold shutdown [W1].
Many workers were exposed to multiple stressors, both work-related and personal; the latter weremainly a result of the evacuation of their families from within the 20-km zone where they had
previously lived, the loss of family members and their homes due to the earthquake and tsunami;
TEPCO workers also suffered public harassment and discrimination [I29, S8, W1].

C. Actions taken to protect workers from radiation
130. Initial capabilities for monitoring radiological conditions effectively, both on-site and off-site,were severely hampered. Few on-site monitoring systems remained following the tsunami. Most
electronic personal dosimeters, computer systems for activating and recording dose from these devices,and many portable survey instruments were lost in the flooding. Installed radiation monitors, essential
for monitoring core, containment, and spent fuel pool conditions, were also lost when the tsunami
flooded the electrical distribution equipment [I29]. It was not possible to gather information on accessto controlled areas or on personal dose data. The loss of individual monitoring capabilities resulted in
the need for emergency responders to share electronic personal dosimeters, with only one worker in ateam wearing a dosimeter for many missions, and workers having to log their individual doses
manually [I6].
131. Inside FDNPS, the main earthquake-proof building was reconfigured as a direct command centre
for operations and had some rooms for workers to stay overnight. This building was equipped with ahigh-quality purified-air ventilation system to control the ingress of airborne radioactive material [W1].
However, the high surface and airborne levels of radioactive material around the site combined withdamage to the entry of the command centre led to the centre becoming contaminated at an early stage in
the accident. The build-up of contamination within the command centre was not recognized until air
samples taken in the building were first analysed on 24 March 2011. As a result, controls were not inplace prior to this time, during which some workers were exposed internally to radioactive material
taken into the body by inhalation [I29].
132. The operator gradually improved on-site radiological monitoring. From 1 April 2011, personal
dosimeters were provided to every worker. Dose rates were measured in different areas of the plant andcomprehensive radiation maps of the site became available and were updated on a regular basis. These
were used to optimize the protection of workers, for example, through the establishment of clear
physical barriers between different areas, and the prevention of unauthorized entry to those areas withhigher risk. Individual daily working time in designated controlled areas was limited to a maximum of
2 hours. Gradually, special tools were introduced to support work in areas with the highest radiationlevels, such as robots and other unmanned equipment [I6].
133. A coordination centre was established at J-Village, a soccer training facility located 20 km to thesouth of FDNPS to manage and oversee radiation protection of all personnel entering the restricted area
and the facility. To protect workers from internal exposure (that is, from inhaling radioactive particles
and gases), the centre provided around 2,000 workers daily with tight-fitting full-face respirators withfilters that could provide 99.97% filtering efficiency against airborne particles. To avoid contamination

66 UNSCEAR 2013 REPORT

that might otherwise be inadvertently ingested and lead to internal exposure, and to minimize skin
exposure, workers wore double-layer (to guard against tears during operations) Tyvek protective
overalls, gloves (inner cotton and double outer rubber gloves), safety shoes covered by vinyl shoes, anda cotton hat. A safety helmet was also issued, depending on the nature of the operations. All personal
protective equipment once used was stored in a restricted area. A Geiger-Müller survey meter was usedat the J-Village gate to measure any contamination on individuals leaving the area [W1].
134. Medical countermeasures included the use of stable iodine for thyroid blocking8. Potassium iodide
tablets were prescribed to workers from 13 March 2011 onwards in accordance with previously defined
criteria, and subject to them being interviewed by a physician regarding iodine hypersensitivity and any
pre-existing thyroid condition [W1, W10]. Approximately 17,500 potassium iodide tablets (50 mg)
were distributed to about 2,000 workers involved in the emergency response, including TEPCO
workers, contractors’ workers, fire-fighters, policemen and Self-Defense Force personnel (seeappendix E for further information).

D. Reported doses
135. Results of the analyses of doses to workers are summarized below. More details of these analyses
are presented in appendix D. In order to judge the extent to which the individual doses reported inJapan provided an accurate and reliable measure of the doses actually incurred, the Committee adopted
a two-stage approach: first, it reviewed the methodologies used in Japan for assessing doses; andsecond, it made independent dose assessments for defined groups of workers, and compared resultswith those reported. Nevertheless the assessments were necessarily based on information provided by
TEPCO, contracting companies and Japanese authorities, because it was clearly not possible to verify
the conditions on site at the times of exposure.
136. TEPCO published regular press releases describing the status of dose evaluations foroccupationally-exposed workers at FDNPS. Up to the end of October 2012, a total of 24,832 workers
were reported to have been involved in mitigation and other activities on the site and were
occupationally exposed to radiation; of these, about 15% were employed by TEPCO, with theremainder employed by contractors and subcontractors. Tables presenting the numbers of workers with
reported doses 18 in specified dose bands for each month since the accident up to October 2011 havebeen published [T8] (see tables D1, D2 and D3 in appendix D). These tables show that the highest
doses resulted mainly from intakes of radioactive material, and that effective doses 19 due to monthly
intakes were observed in March 2011 to be in excess of 100 mSv. The exposure of workers to radiation
decreased over time due to radioactive decay and the decreases in the amounts of radioactive material
being released from the damaged reactors. From May 2011 onwards, none of the exposed workers
received more than 50 mSv effective dose in a month (from both external and internal exposure).
137. After November 2011, TEPCO presented the data in terms of cumulative totals for the number ofworkers in each dose band; the data published in November 2012 are reproduced in table D4 inappendix D [T16] and are illustrated in figure VIIIa. The data indicate that 34% of the workforce
received cumulative doses greater than 10 mSv, and that 0.7% of the workforce (corresponding to
173 individuals, mainly TEPCO workers) received cumulative doses greater than 100 mSv. Six TEPCO
18
19

Unless otherwise indicated, all references to “dose” in section V refer to the quantity “effective dose”.
Effective doses due to internal exposure for workers are calculated as the 50-year committed effective dose.

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workers received cumulative doses greater than 250 mSv. TEPCO has published data only on effective
doses, although results for absorbed doses to the thyroid have been published elsewhere [K27].
Figure VIIIa. Numbers of occupationally exposed FDNPS workers with effective doses in eachcumulative dose band for the periods in which they worked between 11 March 2011 and31 October 2012
The effective doses include contributions from external and internal exposure138. Additional information on doses due to internal and external exposure up to April 2012 for 21,776
workers was provided to the Committee (see appendix D). The highest reported effective dose was
679 mSv for the TEPCO worker who also had received the highest reported committed effective dose
due to internal exposure (590 mSv). The highest reported effective dose due to external exposure was
199 mSv for a contractor’s worker who had a reported effective dose that totalled 238 mSv. The
distribution of the doses within the workforce is illustrated in figure VIIIb. The median value (i.e. thedose below—or above—which is received by half of the workforce) of the distribution is about 5 mSv
with 6 extreme values greater than 250 mSv. The distribution of doses is skewed or asymmetric (i.e.
there is an increased frequency of higher values) but is not well represented by a log-normal
distribution.
139. The exposure of female workers received particular attention because of the more restrictive
standards applied to them. Nineteen women who had worked at FDNPS before the accident (five ofwhom were not occupationally exposed) received an effective dose of more than 1 mSv following theaccident; the two highest doses as a result of the accident were assessed to have been 7 mSv and18 mSv [O3]. Their doses were, with one exception, less than those of the average dose received byoccupationally-exposed workers involved in emergency working conditions. Female workers were notallowed to enter the FDNPS plant after the accident [W1].

68 UNSCEAR 2013 REPORT

Figure VIIIb. Distribution of log-transformed effective doses received by occupationally-exposed
FDNPS workers in each cumulative dose band for the periods in which they worked between
11 March 2011 and 30 April 2012
The effective doses include contributions from external and internal exposure. The red curve is the probability density of anormal distribution, with parameters μ = 1.3 and σ = 1.9 estimated among workers with non-zero doses; * represents workers
with effective doses recorded as zero (n = 352)

140. Data on reported doses due to internal and external exposure for 249 of the 260 fire-fighters werealso provided to the Committee by the Government of Japan. In vivo measurements of 131I in their
thyroids were performed in the period September–November 2011 and were all reported to be below
the minimum detectable activity 20 (38 Bq for 131I). This was to be expected given the delay inperforming measurements. Whole-body measurements of radiocaesium were below or close to theminimum detectable activities (320 Bq for 134Cs and 570 Bq for 137Cs). The assessed doses due tointernal exposure were reported to be less than 1 mSv for all these workers, who worked from18 March 2011 to 25 March 2011. The maximum value of the reported doses from external exposure
was 29.8 mSv. Unfortunately, in the absence of data from in vivo thyroid monitoring in the early stagesof the accident, no reliable estimates could be made of the doses due to intakes of radioiodine. Byanalogy with the assessed doses due to internal exposure for on-site workers, who may have beenworking in similar locations in the early stages of the accident, the effective doses due to intakes ofradioiodine by fire-fighters could have been significantly higher than those from intakes of the longerlived radionuclides (i.e. radiocaesium) that were detected during whole-body monitoring.
20

The minimum detectable activity represents the smallest activity of a radionuclide that can be detected with 95% confidence.

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141. Table 9 presents data on reported effective doses due to external exposure for (a) 147 of the 168
on-site Self-Defense Force personnel and (b) 8,458 off-site Self-Defense Force personnel that havebeen provided to the Committee by the Government of Japan. None of the Self-Defense Forcepersonnel was exposed to an effective dose due to external exposure that was greater than 100 mSv.
Doses due to internal exposure were also provided for eight on-site and four off-site workers: theassessed committed effective doses were reported to be less than 0.2 mSv for seven workers and equal
to 3.8 mSv for one on-site worker.
Table 9. Effective doses due to external exposure reported for the Self-Defense Force personnel
The data refer to the period 11 March 2011 to 31 August 2011

Number of workers in dose band
Location<10 mSv

10–20 mSv

20–50 mSv

50–100 mSv

On-site

132

3

8

4

Off-site

8 453

5

–

–

142. The Government of Japan provided data to the Committee on reported doses due to internal andexternal exposure for 13 policemen who were present on the site on 17 March 2011. The reported doses
due to external exposure were less than 10 mSv and the assessed committed effective doses due tointernal exposure were less than 0.1 mSv for all of the 13 policemen (see appendix D for further
information). The Committee recognized that many municipal workers were involved in various
response activities (such as support for evacuation, and conducting monitoring for contamination ofpeople and commodities), but information on their exposures was insufficient for the Committee toestimate their doses.
143. The Committee had insufficient information on beta irradiation to make an informed assessmentof doses to the eye lens of workers.
144. In vivo monitoring of 8,380 United States Department of Defense-affiliated personnel was carriedout between 11 March 2011 and 31 August 2011 to assess their doses due to internal exposure. About
3% of those monitored had detectable activity within their bodies with a maximum committed effective
dose of 0.4 mSv and a maximum committed absorbed dose to the thyroid of 6.5 mGy.

E. Evaluation of monitoring and dosimetry
145. One of the aims of the Committee’s work was to judge the extent to which the individual doses
reported in Japan provided a true and reliable measure of the doses actually incurred, and therefore theextent to which the reported doses could support a reliable assessment of potential effects on health. A
two-stage approach was adopted. First, the methodologies for assessing doses used in Japan werereviewed. The results are described in appendix D and summarized in this subsection. Second,
independent assessments of doses due to internal exposure were made for defined groups of workers,
and comparisons made with the doses reported in Japan for these workers; the results are summarized
in subsection F below.

70 UNSCEAR 2013 REPORT

1.

Internal exposure146. Initial in vivo measurements on the workers who were responding to the emergency were madewith simple whole-body monitoring equipment at Onahama, 55 km south of the FDNPS site. Thisequipment was not capable of performing measurements of radioactive material in the thyroid, and was
subject to relatively high environmental background levels because of its location. Where an assessed
effective dose due to radionuclide intake was over 20 mSv, the worker was additionally monitored at
the Japan Atomic Energy Agency (JAEA), with the results provided to TEPCO for dose assessment.
Where an assessed effective dose (due to both external and internal exposure combined) was in excessof the emergency dose limit (250 mSv), the National Institute of Radiological Sciences in Japan (NIRS)
additionally monitored the worker and further assessed intake and associated dose due to internal
exposure. For some of these cases, TEPCO staff then made a re-assessment of the dose. For mostworkers, results were reported only for 131I, 134Cs and 137Cs. For some of the workers with higher
effective doses, results were also reported for 136Cs and 129mTe, but the contribution to effective dosefrom these radionuclides was small. Data on their exposures to other short-lived radionuclides such as132
Te, 132I, 133I and 133Xe were lacking. A limited amount of in vitro monitoring of urine samples was
performed, but the results were not used for formal dose reporting.
147. Detailed information on the in vivo monitoring systems used was provided to the Committee,
specifically: (a) information on the in vivo measurement systems used at Onahama by TEPCO, and also
those used by JAEA and NIRS; (b) information on the calibration phantoms used for in vivo
measurements by JAEA; and (c) comprehensive data related to calibration and quality control of invivo measurements made both by JAEA at its own laboratories, and by JAEA and TEPCO at Onahama.
The information was sufficient to judge that the measurement systems, calibration phantoms andmethods, and quality control procedures were adequate for conducting in vivo measurements during aradiation emergency. In addition, assessments of dose from internal exposure for TEPCO workers were
performed either by TEPCO or (for a few cases with high exposures) by NIRS, using the software
packages MONDAL [N12] and IMBA [B12] respectively. Both software packages were qualityassured, and the Committee judged them appropriate for assessing intakes of internally-incorporated
radionuclides and the corresponding committed effective doses and absorbed doses to workers due tointernal exposure. More details on this information and of its evaluation by the Committee arepresented in appendix D.

2.

External exposure148. The Committee received information for TEPCO and contractors’ workers on the types ofindividual dosimeter used, the technical standards and calibration methods used, and the system used
for allocating electronic personal dosimeters to individuals during March 2011 when the availability ofthese dosimeters was limited. However, it did not receive similar information for emergency service
workers, for example, policemen, fire-fighters, and Self-Defense Force personnel.
149. The information provided, and the results of the Committee’s evaluation of it, are presented inappendix D. In summary, the instrumentation, technical standards and calibration methods used appear
to meet generally-accepted requirements for individual monitoring. Conclusions over the reliability of
the reported doses due to external exposure need some qualification, however, because of the use ofshared personal dosimeters during March 2011. According to TEPCO, the Automatic Personal
Dosimeter System was inoperable and 5,000 dosimeters could not be used during this period. For the
first few days, only 320 dosimeters were available. This meant that the initial emergency responders
had to share dosimeters, with only one worker in a team wearing a dosimeter for many missions, andANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

71

workers had to log individual doses manually [T11]. Conditions were developed setting out when it wasappropriate for dosimeters to be shared (appendix D). As long as these conditions were consistently
met, the results of the measurements made with the shared dosimeters should have provided anadequate basis for the assessment of dose due to external exposure.

F. Evaluation of assessment of internal exposure150. The Committee performed its own assessments of the doses due to internal exposure for selected
workers, and compared the results with the doses reported in Japan for these workers. Several assessors
were involved in evaluating the cases, each using his/her own established procedures and expert
judgement to make decisions on issues such as choice of monitoring data and the values of parameters
to be used in biokinetic models.
151. Doses received by workers with the highest exposures were of particular interest for theassessment of potential effects on health. Assessments were therefore performed for 12 workers 21 withthe highest reported internal exposures (committed effective doses higher than 100 mSv), with the aimof judging the reliability of the doses reported for these workers. While the assessment and recording of
external exposure resulted from a direct reading of the information provided by electronic personal
dosimeters, internal exposure assessments relied on expert judgment and assumptions related to the
exposure conditions as well as the use of biokinetic models and complex software. Thus, theuncertainty and potential for differing estimates between experts of internal exposure was greater thanthose associated with the estimation of external exposure.
152. The 12 workers with the highest internal exposures for whom the Committee conductedassessments were all TEPCO workers; measurements had all been performed at the same (or similar)
facilities and the methods of internal exposure assessment had also been similar. On the other hand, themuch larger number of workers with lower assessed internal exposures had different types of
employment status (e.g. TEPCO, contractor, subcontractor and emergency service workers), and boththe type of facilities used for measurements of radionuclide activities and the method used to assessinternal exposure could have depended on the level of the internal exposure. The reliability of theinternal exposure assessments for these groups of workers was evaluated by performing independentinternal exposure assessments for samples of workers randomly selected from the various groups. In
total, 42 workers were randomly selected, of whom 21 were TEPCO workers and 21 were
contractors 22. In addition, 13 workers from the emergency services (understood to be all from the police
force) were selected. The assessments and comparisons are described in detail in appendix D andsummarized below.
21
Following the Committee’s independent assessment of internal exposure for the 12 most exposed workers, the relevantJapanese organizations reviewed their estimates of doses due to internal exposure in July 2013; this resulted in the identificationof one further TEPCO worker with a committed effective dose greater than 100 mSv (i.e. there were then 13 workers in total witheffective doses due to internal exposure in excess of 100 mSv). The Committee did not make an independent assessment of thedose due to internal exposure for this thirteenth individual owing to the late acquisition of this information.
22
Following the Committee’s independent assessment of internal exposure for the random sample of 21 contractor workers,
TEPCO carried out a re-assessment in July 2013 of the doses due to internal exposure to these workers based on new information
provided by the contractor companies. The Committee was not able to update its assessment of internal exposure for this sample
of workers because of the late acquisition of this information (i.e. after the Committee’s assessment had been completed). The
implications of changes in the internal exposure assessments by TEPCO are addressed in appendix D—in general, they do notaffect the broad conclusions previously reached and presented in this section.

72 UNSCEAR 2013 REPORT153. Comparisons between the results of the Committee’s independent assessments of internal
exposure for twelve workers21 with the highest doses and those formally reported by the Japanese
authorities are shown in figure IX. These assessments were all based on in vivo measurements ofradionuclide activities in the whole body and 131I activities in the thyroid. Appendix D gives moredetailed results, including the contribution from 131I intakes to effective dose and to the absorbed doseto the thyroid (tables D9, D10, D11). The effective dose—and contributions due to internal and external
exposure—for these workers can be found in tables D5, D6 and D7 in appendix D.
Figure IX. Assessed committed effective doses for occupationally-exposed workers with the highest
internal exposures
The committed effective doses are from internal exposure only and from all measured radionuclides

154. The following conclusions were drawn for the 12 workers with the highest internal exposures forwhom the Committee conducted assessments:(a) For quality assurance purposes, all five assessors conducted an internal exposure assessment
for worker A, and good agreement was found. The other eleven cases were reviewed by at least
two assessors and again good agreement was found;(b) There was good agreement between the Committee’s own internal exposure assessments forthe twelve workers and the assessments reported in Japan;(c) For all 12 workers, the Committee concluded that the effective dose due to internal exposure
from the measured radionuclides arose almost completely from the contribution of 131I in the
thyroid (on average, 99%);(d) The largest assessed committed absorbed dose to the thyroid due to internal exposure was forworker A. The Committee’s assessments of absorbed dose to the thyroid due to internal exposure
from the measured radionuclides for this worker range from 9.7 to 12.6 Gy (with an average valueof 12 Gy), depending on assumptions made in the simulation, including the timing of main intakesof 131I;

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73(e) For most of the workers, in vivo monitoring of 131I in the thyroid did not start until mid- tolate-May, although for three workers (workers A and B, with the highest internal exposures, andworker F, with the highest external exposure), it started in mid-April. This delay in starting
monitoring increased the uncertainty in the dose assessments;(f) The delay in starting in vivo monitoring of the thyroid meant that shorter-lived radionuclides,
such as 132Te and 133I, were not detected. Indicatively, the additional contribution to effective dose
due to internal exposure from the intakes of these short-lived radionuclides by those workers onsite in the first few days of the accident may have been in the order of 20% relative to thecontribution from 131I; this contribution is likely to have varied considerably between individuals.
Owing to these factors and other uncertainties, further work is needed to fully characterize
occupational exposures during the very early stages of the accident;(g) The absence of adequate data from urine monitoring means that it was not possible to confirm
the reliability of doses assessed from the measurements of activity in the thyroid using results
obtained independently with a different bioassay monitoring method.
155. The results of the Committee’s internal exposure assessments for the 55 workers with lower
internal exposures, and comparisons with values reported by the Japanese authorities, are presented anddiscussed in appendix D. The following conclusions were drawn:(a) Reasonable agreement was found between the Committee’s independent internal exposure
assessments and the assessments reported by TEPCO for those workers for whom a positive
measurement of 131I in the body was made;(b) For all of the workers with assessed committed effective doses due to internal exposure above
0.1 mSv, the committed absorbed dose to the thyroid resulting from 131I intake made the dominant
contribution to the effective dose (on average, 98%);(c) Overall, the internal exposure assessments made by TEPCO for its workers were suitable forthe assessment of effects on health. The reliability of assessments reported by TEPCO for those of
its workers where a positive measurement of 131I in the body was made could be confirmed. On theother hand, the reliability of assessments reported by TEPCO for those of its workers for whom 131I
was not detected in the body could not be confirmed. Neither of the methods available to estimate
131
I intake in these circumstances provided a reliable estimate of true intake, and the resulting
internal exposure estimates could have been subject to a high degree of uncertainty. Although
workers in this category could have comprised about 40% of the total, they were, in general, more
likely to have received lower committed effective doses due to internal exposure than the overall
average;(d) Evidence from this investigation indicates that estimates of dose due to internal exposure
reported by contractors for their workers were less than about 50% of those of the Committee foreight cases out of the nineteen where a comparison could be made. For the other eleven cases, theCommittee’s dose estimates were broadly in agreement with those of TEPCO’s initial alternative
assessments (which were not normally reported). Based on the comparative assessments carriedout, the Committee was unable to confirm the reliability of the internal exposure assessments
reported by contractors for their workers 23;
23

After this conclusion was drawn by the Committee, doses due to internal exposure for contractors’ workers were reassessed inJapan [M18], and the Committee understands that at least some of the discrepancies were resolved. Further work would be
required to determine whether the reliability of the contractors’ assessments could be confirmed; this would require a detailed
analysis of the reassessments.

74 UNSCEAR 2013 REPORT(e) Effective doses due to internal exposure for the police appear to have been very low, in the
microsievert range;(f) Effective doses due to internal exposures reported for emergency service workers (e.g. firefighters and Self-Defense Force personnel) were all below 1 mSv with one exception (3.8 mSv).
The Committee was unable, however, to confirm the reliability of these reported exposures because
it lacked sufficient detailed information to enable it to carry out independent assessments.

VI. HEALTH IMPLICATIONS
156. The Committee has provided a commentary on the immediate and long-term health implicationsof exposures to ionizing radiation resulting from the FDNPS accident based on the Committee’sinterpretation of information on the exposures and their consequences (see appendix E).

A. General considerations
157. Decades of clinical experience, and evidence from animal and laboratory experiments andepidemiological studies of human populations underpin the current understanding of the health effectsof radiation exposure. Part of the mandate of the Committee has been to undertake broad reviews of theeffects of ionizing radiation exposure on human health, most recently reported in [U7, U9, U10, U12,
U13, U16]. The Committee has applied this pre-existing knowledge and understanding to the estimatesof doses to the public (chapter IV and appendix C) and workers (chapter V and appendix D) in its
assessment of the health implications of the FDNPS accident.
158. As stated in chapter IV, there were uncertainties associated with the estimates of district averagesof effective doses for the public. Local variability in deposition density and between members of the
exposed population contribute to a distribution of estimated effective doses around the average,
indicatively between 30–50% of the average and two to three times higher than the average. Thus, insome cases sizeable population groups may have been exposed to doses at the higher end of this
distribution.
159. Generally and in the absence of better available information, assumptions were made that would
have tended to overestimate the doses to members of the public. This may particularly have been thecase for estimating doses due to ingestion of radionuclides and not being able to take account ofprotective measures because of lack of information on their degree of implementation. Some direct invivo measurements of activity in the thyroid (a particularly important factor for those exposed as
children or infants when considering the risk of thyroid cancer later in life) and whole-body counting
also indicated that the Committee’s estimates were somewhat higher than the doses implied by thesemeasurements. Nevertheless, it cannot be excluded that some individuals incurred doses somewhat
higher than those estimated by the Committee.
160. For workers, uncertainties were mainly related to exposures in the early phase of the accident. At
that time, monitoring was impaired by the shortage of dosimeters, and thyroid monitoring was not
performed until later.

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75

161. In 2012, WHO published a preliminary dose estimation that had used information available up to
September 2011 [W11]. The Committee’s estimates of doses were based on a considerably expanded
database and were generally within the dose ranges estimated by WHO. In March 2013, WHOpublished a health risk assessment [W12] based on its preliminary dose estimation. The Committee’s
assumptions underpinning its estimates of health implications are generally well aligned with those of
WHO (see appendix E).
162. The Committee also drew on the experiences and direct observations of health effects in theaftermath of the Chernobyl accident. It was clear that the radiation exposures of the public and workers,
as well as the number of individuals exposed to higher doses, following the FDNPS accident wereconsiderably lower than following the Chernobyl accident.
163. Health, in its broad definition used by WHO, concerns physical, mental, and social well-being andis not just characterized by the absence of disease. It is clear from both the Chernobyl accident [U12]and from the FDNPS accident that nuclear accidents of such magnitudes and the associated protective
measures tend to lead to distress and anxiety from, among other things, disruption of life, and loss ofhomes and livelihoods; the distress and anxiety can have major impact on mental and social well-being.
Evaluating such effects is not part of the Committee’s mandate; however, they were important forunderstanding the broader health implications and the Committee refers to them as appropriate toprovide context for its assessment of the health implications directly related to radiation exposure.
164. Traditionally, health effects associated with radiation exposure have been classified in two
categories:(a) Deterministic effects occur after high doses of radiation normally delivered over a short periodof time, which kill large numbers of cells leading to possible tissue damage, major effects on bodyfunction, and even death. The effects include acute radiation syndrome, skin burns, loss of hair,
hypothyroidism, and developmental damage to an unborn child. Most deterministic effects occur
shortly after exposure (although some can appear later in life) above dose thresholds specific foreach exposed tissue. The pattern of symptoms for most of these effects is usually so specific thattrained medical professionals can diagnose a deterministic effect of irradiation. The ICRP has
introduced the term, “tissue reaction”, which encompasses deterministic effects, circulatory diseaseand cataracts [I26].
(b) Stochastic effects. Exposure to radiation can also induce non-lethal changes to cell
constituents. Unrepaired or misrepaired abnormal cells escaping the body’s immune defence maylead to hereditary effects in future offspring or, after a period known as the “latency”, to thedevelopment of effects such as cancer. At present, there is no way of distinguishing by observationor testing whether or not a specific stochastic effect has been caused by radiation exposure. Thus, if
the disease occurs in an individual, it is not possible to conclude unequivocally that it was causedby radiation. However, stochastic effects can manifest as an increased incidence of disease in a
population, and the incidence after irradiation tends to increase with increasing dose. From this it ispossible to infer an increased risk of stochastic effects in an exposed population.
165. When considering health implications, it is important to distinguish between those diseases thathave already been observed from those that may occur in the future. In this context, particularly when
considering stochastic effects over a lifetime, it is important to recognize different ways of expressing
the risk of future disease, including:(a) Lifetime risk of a disease is the probability that it occurs from a given point of time (e.g. at
exposure) until the end of life, and can be expressed variously. For example, a 1 in 10 risk of

76 UNSCEAR 2013 REPORT

developing a disease can also be expressed as a 10% or 0.1 risk. The “lifetime baseline risk” refers
to the probability of a disease occurring over a lifetime without exposure additional to thebackground from natural sources of radiation; and “lifetime risk due to exposure” 24 to theadditional probability of a disease occurring over a lifetime due to additional radiation exposure.
(b) Relative risk 25 is used to compare the disease risk in two different groups of people, and is theratio of the risk to each group. For example, the risk of a particular disease occurring in an exposedgroup could be say 20% higher than that in a non-exposed group, then the relative risk would be
1.2. If the lifetime baseline risk of a particular disease in the non-exposed group were 1 in 200,
then the lifetime risk in the exposed group would be higher by 20%, i.e. 1/200 × 1.2 = 1.2 in 200 or
1 in 167.
166. Studies can quantify with some confidence values of relative risk that are high enough toovercome the normal variability in cancer statistics (the ability to achieve this depends among otherthings on whether a large enough group of people are exposed to high enough doses). In such cases theCommittee has confidence to make risk assessments based on direct evidence. If the relative risks are
not high enough, then the Committee draws an inference about the risks and estimates their value fromthe existing knowledge and understanding on the relationship between radiation exposure and healtheffect in question. For example, an increased incidence of hereditary effects has not been reliably
demonstrated in humans for any level of exposure, and is not expected to be possible to demonstrate
among the general public or workers following the accident at FDNPS, although risk estimates havebeen made to take them into account based on animal studies. Such estimates are based on expert
judgement rather than direct evidence. While direct evidence mean that risks cannot have been grossly
underestimated, the underlying assumptions and variability make risk estimates at low doses highly
uncertain and of low predictive value, as well as potentially misleading.
167. In this chapter, the Committee has estimated values of the risk due to exposure for members ofvarious exposed groups. Where the estimated risk of the disease is sufficiently large in a large enoughpopulation, compared to the normal statistical variability in the baseline incidence of the disease in that
population, an increased incidence due to irradiation may be “discernible” in disease statistics andepidemiological studies. Conversely, when risks may be inferred on the basis of existing knowledge,
but the level of inferred risk is low and/or the number of people exposed is small, the Committee has
used the phrase “no discernible increase” to express the idea that currently available methods would
most likely not be able to demonstrate an increased incidence in the future disease statistics due toirradiation. This does not equate to absence of risk or rule out the possibility of excess cases of disease
due to irradiation, nor the possibility of detection of a biomarker for certain types of cancer in certain
subgroups being identified in the future that can be associated with radiation exposure; moreover, it is
not intended to disregard the suffering associated with any such cases should they occur.
24
The more technical term “lifetime attributable risk” was used in the WHO report [W12] and in other technical reports of theCommittee.
25
Another expression is the “excess relative risk”, the proportional increase in risk for the exposed group over the unexposedgroup.

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77

B. Health implications for the public
1.

Observed health effects

168. The Committee’s understanding of the exposures is that they fell well below the thresholds fordeterministic effects. This was consistent with no acute health effects (i.e. acute radiation syndrome orother deterministic effects) having been reported that could have been attributed to radiation exposure.
169. The Committee did not assess non-radiation-related health effects, which vary in their symptoms
and degree of severity. For example, more than 50 hospitalized patients were reported to have diedeither during or soon after evacuation, probably because of hypothermia, dehydration and deteriorationof underlying medical problems [T4]. Many people have been suffering from distress caused by theearthquake, tsunami and nuclear accident, and may also have been exposed to various hazards that havegiven rise to physical symptoms of disease.
170. Mental health problems and impaired social well-being were the major health impacts observed
following the accident. They were the results of understandable reactions to the enormous impacts ofthe earthquake, tsunami and nuclear accident, as well as fear and stigma associated with radiation
exposure. Psychological effects, such as depression and post-traumatic stress symptoms, among the
public have been observed [Y4, Y5] and may have serious health consequences.

2.

Estimated health risks

171. The lifetime baseline risk of solid cancer (i.e. the lifetime risk of solid cancer in the absence ofradiation exposure from the accident) in the general Japanese population is normally about 35% but
varies for individuals according to sex, lifestyle and other factors. The Committee previously estimatedthat a hypothetical acute absorbed dose to the whole body of 100 mGy for a typical population of Japan
would lead to an additional lifetime risk of solid cancers due to exposure of approximately 1.3%, i.e. a
relative risk of 36.3/35 = 1.04 [U9]. For exposures from the accident, the Committee estimated (seechapter IV and appendix C) both the settlement-average effective doses in the first year received byadult evacuees, and the district-average lifetime effective doses to adults living in the non-evacuatedand most affected districts of Fukushima Prefecture, to be up to about 10 mSv (tables 6 and 7). Higher
district-average effective doses, by a factor of about two, were estimated for children and infants.
Individual effective doses would have varied between perhaps 30−50% of this and two to three times
higher. While risk of cancer and hereditary effects at such doses can be inferred by assuming forexample a linear relationship between dose and risk, the inferred relative risk values are small (i.e. theinferred relative risk of solid cancer after an exposure to an effective dose of 10 mSv is approximately
35.13/35 = 1.004) when compared to the normal statistical variability of the baseline rates. A generalradiation-related increase in the incidence of health effects among the exposed population would not be
expected to be discernible over the baseline level.
172. While the lifetime cancer risks due to radiation exposure may not result in a discernible increasein disease incidence for the whole of the general population, the risks for some cancers and age groups
in principle might. Past experience provides an understanding of the organs, age groups and time
periods for which increased risk is more prone to become discernible as an increase in the incidence ofthe disease, and the Committee focused its attention on these. Moreover, for some organs, the relative

78 UNSCEAR 2013 REPORT

risk from exposure during infancy and childhood is considerably higher than during adulthood [U16].
Risk estimates for exposure were based on estimates of absorbed doses to those specific organs.
173. Thyroid cancer. The first-year average absorbed doses to the thyroid of adults were within a few
tens of milligrays (tables 5 and 6), for which the risk of thyroid cancer was considered low. The
Committee did not attempt to quantify the risk of thyroid cancer after such exposures during adulthood.
174. The baseline risk of developing thyroid cancer over the course of life is normally about 1 in 200
for 10-year-old children and 1-year-old infants in Japan [W12], although highly sensitive
ultrasonographic surveys could increase the rate of detection by several times. The Committee
previously estimated that, following a hypothetical absorbed dose to the thyroid of 200 mGy at 10 yearsof age, the risk was nearly doubled (i.e. a relative risk of 2 with estimates ranging from 1.15 to as muchas 4—see appendix E). However, most of the increased risk is associated with long times after
exposure; only about 10% of the lifetime risk is expressed during the first twenty years.
175. For exposures from the accident, the Committee used the methodologies outlined in appendix C
to estimate settlement-average absorbed doses to the thyroid of up to about 80 mGy for 1-year-old
infants who were evacuated (table 6). For infants who remained in the non-evacuated areas, districtaverage doses were up to about 50 mGy (table 5). The estimated doses would have varied considerably
between individuals (indicatively, from about 30–50% of the average to about two to three times higher
than the average). Direct in vivo measurements of radioiodine in the thyroid have indicated lower doses
than estimated in the Committee’s assessment (see paragraph 117). As explained in appendix E, mostof the absorbed doses to the thyroid were in a range for which an excess incidence of thyroid cancer has
not been observed in epidemiological studies. Nevertheless, doses towards the upper bounds of theranges could imply an increased risk for individuals that among sufficiently large population groups
might lead to discernible increases in the incidence of thyroid cancer due to the radiation exposure. The
WHO estimates of the relative risk of thyroid cancer due to radiation exposure from the accident [W12]
are consistent with the results of the Committee, assuming a linear dose–response relationship forabsorbed doses to the thyroid below several hundred milligrays. Information on dose distributions was
not sufficient for the Committee to draw firm conclusions as to whether any potential increased
incidence of thyroid cancer would be discernible among those exposed to higher thyroid doses during
infancy and childhood. The occurrence of a large number of radiation-induced thyroid cancers as wereobserved after the Chernobyl accident can be discounted because doses were substantially lower.
176. Leukaemia. The lifetime baseline incidence of leukaemia in Japan is about 1 in 200 or 0.5%, andfor childhood leukaemia around 1 in 1,500 or about 0.07% [I7]. The risk of leukaemia induced byirradiation has been assessed previously by the Committee for the general Japanese population [U9].
The lifetime risk due to exposure for children aged 0 to 9 years receiving an absorbed dose to the redbone marrow of 1 Gy was estimated to be in the range from 0.11% to 0.85%. After infants are exposed,
most of the risk of leukaemia would be expressed during childhood. For the FDNPS accident, theCommittee estimated absorbed doses to the red bone marrow of up to about 10 mGy in the first year forboth the settlement averages for infants who were evacuated and the district averages for infants in the
non-evacuated areas. The WHO estimates of the risks of leukaemia due to radiation exposure from theaccident [W12] are consistent with the previous general assessments of the Committee. Considering theexposures and risks, and the size of the exposed group, any increase in childhood leukaemia is notexpected to be discernible.
177. Breast cancer. The lifetime baseline risk of breast cancer among Japanese females is about 5.5%
[W12]. For a hypothetical exposure of the general female Japanese population with an absorbed dose to
the breast of 100 mGy, the Committee calculated previously a lifetime risk of breast cancer due to theirradiation of about 0.3% [U9]. The assessment of the difference in risk from childhood exposure

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79

compared to adult exposure depends on the model used [U16]. In some studies the breast cancer risk
after exposure as a child is a factor of three to five times higher than after exposure as an adult [U16].
The Committee estimated settlement-average absorbed doses to the breast of girls before and during theevacuation to be less than 10 mGy. The Committee does not expect that any radiation-induced increasein breast cancer incidence will be discernible.
178. Prenatal exposure. The prenatal exposure resulting from the accident at FDNPS is not expected toincrease the incidence of spontaneous abortion (miscarriages), perinatal mortality, congenital effects or
cognitive impairment. However, the Committee has previously estimated that absorbed doses in uteroof about 10 mGy may lead to an increased incidence of cancer during childhood, especially ofleukaemia (with a relative risk of 1.4) [U7]. It cannot be excluded that a small number of pregnant
women had absorbed doses to the uterus of about 20 mGy, perhaps doubling the risk of leukaemia for
their unborn children. However, the number of pregnant women involved was relatively small andchildhood cancer is a rare disease. Thus it is expected that any increase of the risk would not lead to adiscernible increase in the incidence of childhood leukaemia or other childhood cancers.

3.

Health screening

179. The Fukushima Health Management Survey [A4, Y4, Y5] was launched to “evaluate radiation
doses of citizens and [record] their health conditions, with the intention of utilizing the results forprevention, early detection and treatment of possible illness”. It includes a basic survey to estimate
external exposure to radiation of all 2 million residents of Fukushima Prefecture at the time of theaccident, a thyroid ultrasound examination of children, and for selected population groups a healthcheck, a mental health and lifestyle survey, and a pregnancy and birth survey. The investigation isplanned to continue for 30 years.
180. Thyroid ultrasound examinations were to be made for all individuals in Fukushima Prefecture
who were aged 18 years or younger on 11 March 2011 (about 360,000) and were expected to becompleted within 3 years (by March 2014). Thereafter, children would undergo thyroid examinations
every 2 years until age 20 and every 5 years thereafter [Y5]. By the end of July 2013, about 175,000
children living in Fukushima Prefecture had received thyroid examinations using modern, highly
sensitive ultrasound equipment [F3]. Thyroid nodules had been detected in about 1% of those surveyed
and thyroid cysts in about 40% of those surveyed. A survey, using similar equipment, of about 4,000
children and adolescents had also been made in the prefectures of Aomori, Yamanashi and Nagasaki[T5] which were largely unaffected by the accident; the observed prevalence of thyroid nodules andcysts there was even larger than that observed in Fukushima Prefecture. This indicates that the highdetection rate of nodules and cysts in all of these surveys is a consequence of the intensive screening
and the highly sensitive nature of the equipment being used, and not of additional radiation exposure
resulting from the accident.
181. The ongoing ultrasonography survey in Fukushima Prefecture is expected to detect relatively
large numbers of thyroid abnormalities, including a number of cancer cases, which would not normally
have been detected without such intensive screening [J8, W12]. Thyroid cancer is frequently detected at
autopsy even in subjects free of any clinical disease, and the survey would likely detect some of thesecancers. Surveys of thyroid cancer incidence in populations of areas unaffected by the accident would
provide useful input to estimates of the impact of such intensive screening.

80 UNSCEAR 2013 REPORTC. Health implications for workers engaged in emergency work
1.

Observed health effects

182. No acute health effects (i.e. acute radiation syndrome or other deterministic effects) or deaths
have been observed among workers engaged in emergency work that could be attributed to radiation
exposure.
183. Three contractor workers were hospitalized in March 2011 after the skin of their feet and lower
legs were exposed to contaminated water in a turbine building. The Committee confirmed that the dose
estimates by TEPCO were far below the threshold for skin damage and they were released from
hospital after four days with no expectation of significant long-term harm.
184. In order to block the uptake of radioiodine into the thyroid, approximately 17,500 potassium
iodide tablets were administered to about 2,000 workers involved in emergency work [K11].
Approximately 230 workers received health check-ups because either (a) they took potassium iodide
tablets repeatedly for more than 14 days, or (b) they took more than 20 tablets. No side effects werereported by the workers, but changes to thyroid hormone levels were observed in eight workers. For
three cases, the changes were temporary; for the other four cases, the changes could not be attributed totaking potassium iodide tablets because the observed rate of hypothyroidism was comparable with thebaseline rate for a male population.
185. Initial observations have identified severe psychological effects among the FDNPS workers
engaged in emergency work [M8, S7, S8, W1]. These effects are attributable to a number of causes,
including distress and anxiety associated with the effects of the earthquake, the tsunami, very harshworking conditions, the loss of family members, separation from family, difficult living conditions
during emergency operations, worries about possible effects of radiation in the future anddiscrimination and stigma associated with being a radiation worker.

2.

Estimated health risks

186. Risks of future deterministic effects. Thirteen workers21 were estimated to have received absorbed
doses to the thyroid in the range of 2 to 12 Gy from inhalation of 131I, with an average dose of about
5 Gy. Given the magnitude and inherent uncertainties in these dose estimates, the Committee cannot
preclude the possibility of hypothyroidism in the more exposed workers; the likelihood of such effects
is, however, low. Risks for circulatory disease due to radiation exposure among the workers who weremost exposed is very low. The Committee had insufficient information on exposures of the eye lens ofworkers from beta radiation to reach an informed judgement on the risk of cataracts.
187. Cancer in general. For most workers (99.3% out of 24,832 as of 31 October 2012), the effective
doses were low (less than 100 mSv)—on average about 10 mSv. Even when taking account of somevariability and uncertainty in the estimates, the doses for the majority of the workers were below thoseat which there is reliable evidence from epidemiological studies of an increased cancer risk. While risk
models, by inference, suggest increased risks even for such doses, such risks would be low and no
discernible increase in health effects among this group of workers is expected that could be attributed totheir radiation exposure.

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81

188. The Committee took note of the estimates made by TEPCO that many workers received effective
doses of several tens of millisieverts and as of 31 October 2012, about 0.7% of workers (corresponding
to 173 individuals) had received effective doses of 100 mSv or more, with an average dose of about
140 mSv. Among this group, a small increased risk of cancer would be expected. Risk estimates would,
for this subgroup of exposed workers, correspond to about two to three additional cases of cancer in
addition to about seventy cancers that would occur spontaneously, given the baseline risk of about 40%;
however, such predictions are associated with significant uncertainties. While the cancer risk among
these workers remains a justified concern for the Japanese health authorities (see paragraph 191 below),
it is unlikely that such increased incidence of cancer due to irradiation would be discernible, because of
normal statistical variability of cancer incidence and other risk factors. However, special attention
needs to be paid to certain subgroups of the more highly exposed workers and specific cancers. Suchconclusions are drawn with regard to thyroid cancer and leukaemia below.
189. Thyroid cancer and leukaemia. The Committee took note of the estimates of TEPCO thatapproximately 2,000 workers had received absorbed doses to the thyroid exceeding 100 mGy. Evidence
for an elevated risk of thyroid cancer following exposures during adulthood in the range from 100 to
1,000 mGy remains to some degree equivocal (see appendix E). Nevertheless, the magnitude of any
inferred risk is such that any increase in the incidence of thyroid cancer within this group of workers
would likely not be discernible (i.e. any increase in incidence due to radiation exposure would be small
compared with statistical variability in the background incidence).
190. The risk of thyroid cancer is particularly enhanced for the group of thirteen workers who received
absorbed doses to the thyroid in the range of 2 to 12 Gy, although the numbers of workers exposed atsuch doses are likely too small to discern an increased incidence in thyroid cancer. Absorbed doses tothe red bone marrow, which is relevant for leukaemia risk, were estimated by the Committee for theseworkers to be up to about 100 mGy. Because of the small number of workers in this group, any increase
in incidence of cancers is not expected to be discernible.

3.

Health screening

191. In August 2011, the Japanese Ministry of Health, Labour and Welfare [M14] announced a “granddesign of a long-term health management of all the emergency operations workers at TEPCO’s No. 1
Fukushima Nuclear Power Plant”. A database was constructed containing exposure and health records
for workers involved with managing the emergency at, and the recovery of, the FDNPS site. Special
health examinations are to be given to workers with the highest exposures, including annual eye checkups (for lens opacity) and monitoring of the thyroid, stomach, large intestine and lung for cancer.
Ultrasonography surveys of these workers will, inevitably, result in increased detection of thyroid
cancer; the overwhelming majority of the cases detected are expected to have developed independentlyof radiation exposure.

82 UNSCEAR 2013 REPORTVII. ASSESSMENT OF DOSES AND EFFECTS FOR NON-HUMAN
BIOTA

A. Introduction
192. As for humans, any organism in the natural environment can be exposed both internally andexternally to radioactive substances in its habitat. The Committee assessed the consequences of such
exposures in its scientific annexes to the 1996 [U6] and 2008 [U12] Reports. The Committee concluded
that chronic dose rates of less than 100 µGy/h to the most highly-exposed individual organisms would
be unlikely to have significant effects for population integrity of most terrestrial communities, and thatmaximum dose rates of 400 µGy/h to any individual in aquatic populations of organisms would be
unlikely to have any detrimental effects at the population level [U12]. Other benchmark dose rates havebeen derived, mainly for guiding efforts to protect the environment [A10, G2, I22]; these are broadly
consistent with those provided by the Committee.
193. The Committee has examined the impact of the FDNPS accident on non-human biota inhabiting
terrestrial, freshwater and marine ecosystems. Its assessment was largely based upon measured data
provided to the Committee, other relevant reports, and published scientific papers. The radiation
exposures were considered in terms of the intermediate phase after the accident (approximately the firsttwo months) and the late phase (months to years). The areas considered in detail were some of the more
affected areas of Fukushima Prefecture and any neighbouring prefectures within approximately 100 kmof the FDNPS site, covering a land area of 7,000 km2 and extending to 30 km off the coast. Further
details of the methods used to estimate exposures dose estimation, the associated uncertainties andresults can be found in appendix F.

B. Exposure and effects
1.

Terrestrial ecosystems

194. An interpolated map of estimated weighted 26 absorbed dose rates from internal and external
exposure for a large mammal is provided in figure X.
195. From measured radionuclide concentrations in animals corresponding to the late phase of theaccident (June 2011), terrestrial mammals and birds were estimated to have been exposed to dose rates
between 1.2 and 2.2 µGy/h in areas encompassing most of the range of 137Cs deposition densities.
These dose rates are approximately one order of magnitude greater than those from naturally occurring
radionuclides in the environment [B5]. Dose rates of 300 µGy/h have been estimated for soil-dwellingorganisms in areas of high deposition density such as Okuma Town during the earlier intermediatephase. Inclusion of the very short-lived radionuclides, 132Te and 132I, indicates that dose rates may havebeen as high as 1 mGy/h (1,000 µGy/h) for some organisms over short periods (hours to days). While
26

Weighted to account for radiation quality (see paras. 122-129 of annex E to the UNSCEAR 2008 Report [U12]).

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83higher than the benchmark level of 100 µGy/h, these dose rates are unlikely to have resulted inobservable effects on populations; and any effects would have been transient in nature [U12].
Figure X. Map of interpolated estimates of weighted absorbed dose rates for a large mammal

196. For the late phase after the accident, a potential risk of effects on individuals of certain species,
especially mammals, may exist in areas of relatively high deposition density but observable population
effects for terrestrial biota are considered unlikely. Nonetheless, changes in biomarkers of various types
cannot be ruled out, especially in mammals [G5], and such effects may persist in the late phase forareas of highest deposition density.
197. A few field studies have reported effects in areas affected by FDNPS releases, such as decreases
in bird and insect populations [M22, M23] and morphological and genetic disturbances in butterflies[H6]. The relationship between exposure and effect has not been unequivocally established in thesestudies. Furthermore, the observations are not consistent with the Committee’s assessment and suggestthat further analysis is needed to establish whether radiation exposure was an important factor, among
many others, including the impact of the tsunami itself, in causing the environmental effects observed.

84 UNSCEAR 2013 REPORT

2.

Aquatic ecosystems

198. Freshwater ecosystem. Although dose rates calculated for freshwater fish were in some cases
more than an order of magnitude above the natural background level (see [H13]), they did not reachthreshold levels pertaining to chronic exposures above which observable effects in freshwater biota are
expected.
199. Marine ecosystem. For coastal locations where biological samples were available, dose rates in
the period 10 May 2011 to 12 August 2012 were low relative to the benchmarks. The highest dose
rates, from compiled arithmetic means of dose rates to all organism groups, were in the range of
0.10-0.25 µGy/h. Such levels were commensurate with background dose rates in the marine
environment [H13].
200. The highest dose rates were calculated from estimated concentrations in seawater for theintermediate phase of the accident (before 10 May 2011, when biological samples were not available),using a dynamic model for the northern drainage channel near the FDNPS site. For fish, the maximum
estimated dose rate occurred within the first month (approximately 140 µGy/h), and the accumulated
dose over 1 year was approximately 0.32 Gy. Maximum calculated exposures for macroalgae(exceeding 20 mGy/h) at the same location occurred at 23 days after the accident, but fell rapidly, with131
I being the dominant component. The accumulated dose for macroalgae over 1 year wasapproximately 7 Gy. Comparisons with reported benchmarks [G2, I22, U6] indicate that the calculated
doses, with the exception of the transient exposures for macroalgae at locations very close to thedischarge point, were substantially below those where observable effects on populations would be
expected.
201. As of August 2012, marine fish were still being found with radionuclide concentration levels
above the Japanese regulation value of 100 Bq/kg (fresh weight) for sale and human consumption[B24]. Although such a level may be of relevance to radiation protection of the public, thecorresponding dose rates for non-human biota are insignificant, falling far below any relevantbenchmarks.
202. The Committee concluded that the possibility of effects on non-human biota in both the terrestrial
and aquatic (freshwater and marine) environments was geographically constrained and that, in areas
outside of that considered by this assessment, the potential for effects on biota may be consideredinsignificant. The Committee also noted that releases to the marine environment were ongoing at theend of December 2013; this may warrant further follow-up of exposures and trends in the coming years.

VIII. SUMMARY AND CONCLUSIONS
203. In the afternoon of 11 March 2011 a magnitude 9.0 earthquake struck Japan. This was followed
within the hour by the first of a series of tsunami waves that hit the coast of the Tōhoku region ofnorthern Honshu. The natural disaster (referred to as “the 2011 great east-Japan earthquake andtsunami”) left devastation in its path, including the loss of 20,000 lives and damage to infrastructure,
economy and society. It also led to severe damage to the Fukushima Daiichi Nuclear Power Station(FDNPS), including core melt in the three reactors in operation at the time and large releases ofradioactive material to the atmosphere and the Pacific Ocean. The rapid accident progression at FDNPS
prompted “precautionary evacuation” (within days) of the population living close to the plant (mainly
within the 20-km zone) and subsequent “deliberate evacuation” (within weeks up to few months) ofpeople living further afield in areas where the deposition density of radioactive material were high.

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204. This scientific annex to the Committee’s report to the General Assembly records the results of theCommittee’s assessment of the levels of radiation exposure due to the nuclear accident at FDNPS, anddiscusses the implications for the health of people exposed and for non-human biota in theenvironment. The Committee considered the dispersion and deposition of radionuclides in theenvironment, public and worker exposures, health risks and effects, and exposures and effects in nonhuman biota; it also identified a number of issues requiring future research and study.
205. The Committee formally used data requested from the Government of Japan, published data, andother datasets available to it up to September 2012 (18 months after the accident); some more recent
information was taken into account when particularly relevant. The Committee notes that significant
challenges remain to remove spent and damaged fuel, to decommission the facility and to perform
remedial work on and off the FDNPS site. Releases of radioactive material to the Pacific Ocean are stillongoing at the time of publication of this report. Significant health surveys of the public and workers
are ongoing and will continue for many years. The Committee considers it will be appropriate to reevaluate the exposures and effects of radiation following the accident at FDNPS in due course. Thisapproach is consistent with the Committee’s several re-evaluations over more than two decades
following the Chernobyl accident [U4, U7, U8, U12].

A. Basis for dose estimates
206. The Committee reviewed existing estimates of atmospheric releases for 131I and 137Cs (the twomost significant radionuclides from the perspective of exposures of people and the environment); theserange generally from 100 to 500 petabecquerels (PBq) and from 6 to 20 PBq, respectively. The
averages of the published estimates are about 10% and 20%, respectively, of the corresponding
atmospheric releases estimated for the Chernobyl accident. On a number of occasions, themeteorological conditions were such that radioactive material released to the atmosphere was dispersed
over mainland Japan and radioactive material was deposited on the ground by means of (a) dry
deposition and (b) wet deposition with rain and snow. The main deposition occurred to the north-westof the FDNPS site, but significant deposition also occurred to the north, south and west of the FDNPS
site.
207. In general, the Committee relied on measured deposition as a basis for its estimates of doses due
to external exposure and doses due to inhalation. Doses due to ingestion were estimated mainly on thebasis of available information on concentrations of radionuclides in food and drink. In order to estimate
doses where measurement data were unavailable for the periods when exposures occurred (e.g. forprecautionary evacuated individuals from mainly the 20-km zone) or could no longer be obtained, theCommittee used an estimate of the source term, results from atmospheric transport, dispersion anddeposition modelling (ATDM) and knowledge of accident progression. For this purpose, the Committee
relied on a published source term, where the releases of the radiologically dominant radionuclides 131I
and 137Cs were 120 and 8.8 PBq, respectively. While at the lower end of the range of publishedestimates and possibly an underestimate of the total release, the Committee assessed this source term as
appropriate for estimating doses incurred as a result of dispersion over the land mass of Japan, i.e.
relevant for estimating doses to the Japanese population.
208. In contrast to the dose assessment for the public where it was possible to use a large number of
independent sources of relevant information (e.g. data on concentrations of radionuclides in theenvironment), the Committee had to rely on data provided by TEPCO, contractors and subcontractors
and the Japanese authorities for the assessment of doses to workers. Information on doses due to86 UNSCEAR 2013 REPORT

external and internal exposure for more than 20,000 workers (TEPCO workers, contractors andsubcontractors) at FDNPS was made available to the Committee. In addition, doses to other worker
categories irradiated during work to stabilize the reactors and prevent releases, as well as moregenerally during activities both on-site and off-site, were made available. This included doses incurred
by non-Japanese personnel involved, for example, in activities aimed at restoring essential
infrastructure that had been damaged by the earthquake and tsunami. Details of the methodology toestimate doses were supplied to the Committee, which enabled the Committee to assess whether the
methods were fit for purpose.

B. Public exposures
209. The Committee estimated exposure of the general public to ionizing radiation using the quantity
effective dose, expressed in millisieverts (mSv). The Committee also estimated organ-specific absorbed
doses, expressed in milligrays (mGy), to a number of organs. The estimates were made for 20-year-old
adults (representing all adults), 10-year-old children (representing all children older than 5-years old)and 1-year-old infants (representative of infants 0–5 years old). Measured deposition densities fordifferent locations within a district, which were used to calculate doses for non-evacuees, varied frombetween 30–50% of the district average, to two to three times the district average. For evacuees where
the dose estimates were based on the ATDM results, the values may have been under- or overestimatedby a factor of about four because of the choice of source term and ATDM. It is likely that someoverestimation has been introduced generally by the methodology used by the Committee (e.g. in theassumptions on protective measures). Comparison between the Committee’s estimates of doses due tointernal exposure and estimates based on a limited number of in vivo whole-body and thyroid
measurements that were conducted in a timely manner supports this view.
210. The Committee estimated effective doses for the first year following the accident for typicalresidents of evacuated settlements and for non-evacuated districts and prefectures of Japan (seetable 10). The average effective doses for adults in evacuated and non-evacuated areas of Fukushima
Prefecture, caused by the releases from FDNPS, range from a few up to about ten millisieverts. The
effective doses for 10-year-old children and 1-year-old infants were estimated to be about twice as high.
For neighbouring prefectures and for the rest of Japan, doses were lower. To provide context, theaverage effective dose received annually in Japan from natural background radiation is about 2.1 mSv.
211. Average absorbed doses to the thyroid among those most exposed ranged up about 35 mGy for
adults and up to about 80 mGy for a 1-year old (table 10). This is significantly higher than absorbed
doses to the thyroid from natural background radiation; the average annual absorbed dose to the thyroidfrom naturally occurring sources of radiation is typically of the order of 1 mGy. Absorbed doses to thethyroid were considerably lower in less affected areas of Japan.
212. The Committee estimated settlement-average absorbed doses to the red bone marrow of 1-yearold evacuees to be up to 10 mGy, and in the non-evacuated areas, district-average doses were estimatedto be up to about 6 mGy. For girls and women who had been evacuated, the settlement-averageabsorbed doses to the breast were estimated to be up to about 10 mGy for all age groups. Doses to the
foetus and breast-fed infants were not explicitly estimated but would have been approximately the sameas those to adults and 1-year-old infants, respectively.

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Table 10. Estimated district or prefecture-average effective doses and absorbed doses to the thyroidfor the first year following the accident for typical residents of evacuated settlements and nonevacuated areas of JapanThe doses are in addition to the background doses due to natural sources of radiation. The estimates were intended to be
characteristic of the average dose received by people living at different locations and do not reflect the range of doses
received by individuals within the population at these locations. They may overestimate actual average doses because ofassumptions made where data were inadequate (see sections E and F of chapter IV)

Effective dose(mSv)

Residential area

Adults1-year old

Absorbed dose to the thyroid(mGy)
Adults1-year old

EVACUATED SETTLEMENTS
Precautionary-evacuated settlements (townsof Futaba, Okuma, Tomioka, Naraha andHirono, and parts of cities of Minamisoma,
Namie and Tamura and villages of
Kawauchi and Katsurao)

1.1–5.7

1.6–9.3

7.2–3415–82

Deliberately-evacuated settlements (for Iitate
Village and parts of Minamisoma City, thetowns of Namie and Kawamata and of
Katsurao Village)

4.8–9.3

7.1–13

16–35

47–83

AREAS NOT EVACUATED
Non-evacuated districts of Fukushima
Prefecture

1.0–4.3

2.0–7.5

7.8–17

33–52

Prefectures of Miyagi, Gunma, Tochigi,
Ibaraki, Chiba and Iwate

0.2–1.4

0.3–2.5

0.6–5.1

2.7–15

Remaining prefectures of Japan

0.1–0.3

0.2–0.5

0.5–0.9

2.6–3.3

213. The Committee also projected district-average and prefecture-average doses for the three agegroups integrated over the first 10 years after the accident and up to an age of 80 years. Generally, thedistrict-average or prefecture-average effective doses that would be incurred over the first 10 years
were estimated to be up to twice the doses in the first year, and those incurred up to an attained age of
80 years are up to three times higher, if no remediation were to take place (such activities would reduce
exposures in the long term). To provide context, 80-year cumulative doses from background exposure
to natural sources of radiation in Japan are on the average about 170 mSv.
214. The evacuation of the population living within the 20-km zone considerably reduced doses to theevacuees. The Committee estimated that effective doses thus averted ranged up to 50 mSv for adults;
the absorbed doses to the thyroid of 1-year-old infants averted by evacuation ranged up to about
750 mGy.

C. Worker exposures
215. By the end of October 2012, about 25,000 workers had been involved in emergency work andother activities at the FDNPS site. The average effective dose to these workers over the first 19 months
after the accident was about 10 mSv. About 34% of the workforce received effective doses over this88 UNSCEAR 2013 REPORT

period above 10 mSv, while 0.7% of the workforce (corresponding to 173 individuals) received
effective doses more than 100 mSv; the maximum effective dose reported was 679 mSv.
216. The Committee conducted assessments of the doses due to internal exposure for twelve workers(out of a total of thirteen 27) who had committed effective doses due to internal exposure higher than
100 mSv, with the aim of judging the reliability of the doses reported for these workers. The Committee
confirmed that they had received absorbed doses to the thyroid due to inhalation of 131I in the range of
2 to 12 Gy.
217. Overall, the dose assessments made by TEPCO for its workers were suitable for the assessment ofeffects on health. The dose estimates were, however, associated with uncertainty, in particular for the
early phase of the accident (days to few weeks) where personal radiation monitors were scarce. In
addition, in vivo monitoring in general began too late to make reliable estimates of the contribution ofshorter-lived radionuclides such as 132Te and 133I. Further work is needed to fully characterize
occupational exposures during the very early stages of the accident.

D. Health implications for the public and for workers
218. No acute health effects (i.e. acute radiation syndrome or other deterministic effects) had been
observed among the workers and the general public that could be attributed to radiation exposure fromthe accident. The most important health effects observed so far among the general public and among
workers were considered to be on mental health and social well-being, relating to the enormous impactof the earthquake and tsunami, causing loss of family and friends and loss of livelihood andnecessitating evacuation; and the impacts of the nuclear accident, including not only further evacuationand loss of livelihood, but also fear and stigma related to real and perceived health risks associated withionizing radiation. Estimation of the occurrence and severity of such health effects is outside of theCommittee’s remit but information relevant to mental and social well-being remains important when
considering the total health impact of the accident at FDNPS.
219. Risks for stochastic health effects (such as cancer) are reasonably well quantified for doses thatare considerably larger than those estimated for the vast majority of the people (public and workers)
irradiated due to the accident at FDNPS. Where such estimated risks of disease are sufficiently large ina large enough exposed population, compared to the normal statistical variability in the baseline
incidence of the disease in that population, an increased incidence due to irradiation may be discernible
in the disease statistics. Conversely, when risks are small or may only be inferred on the basis ofexisting knowledge and risk models, and/or the number of people exposed is small, the Committee has
used the phrase “no discernible increase” to express the idea that currently available methods would
most likely not be able to demonstrate an increased incidence in disease statistics due to radiation
exposure. This does not rule out the possibility of future excess cases or disregard the suffering
associated with any such cases should they occur.
27
Following the Committee’s independent assessment of doses for the 12 most exposed workers, the relevant Japaneseorganizations reviewed their estimates of dose due to internal exposure in July 2013; this resulted in the identification of one
further TEPCO worker with a committed effective dose greater than 100 mSv (i.e. there were then 13 workers in total with doses
due to internal exposure in excess of 100 mSv). The Committee did not make an independent assessment of the dose due tointernal exposure for this thirteenth individual owing to the late acquisition of this information.

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1.

89

Public health implications

220. The average first-year effective doses to evacuees and to the population in the non-evacuatedareas most affected by the accident were estimated to be in the range from about 1 to 10 mSv for adults
and about twice as large for a 1-year old. Risk models, by inference, suggest a small increased risk ofcancer for such doses; however, any overall increase in disease incidence in the general population due
to radiation exposure from the accident would be too small to be observed against the lifetime baseline
risk for members of the Japanese population (which, for all solid cancers, is on the average 35%,
although this figure is subject to individual variation related to sex, lifestyle and other factors).
221. Notwithstanding the above, previous experience indicates that the relative risks for certain cancers
in certain population groups (notably following exposure as foetus, or during infancy and childhood)are higher than for the population average.
222. Thyroid cancer later in life following exposure to radioiodine during infancy and childhood is ofhigh relevance in this regard. For 1-year-old infants, settlement-average absorbed doses to the thyroid
among the population that underwent precautionary evacuation were estimated to be up to about
80 mGy. The uncertainties around the estimates of average doses based on the ATDM results suggestthat higher doses were possible; however, data from in vivo thyroid monitoring indicate that the
average absorbed doses to the thyroid may have been overestimated by up to a factor of five. Most of
the doses were in a range for which an excess incidence of thyroid cancer due to radiation exposure has
not been confirmed. However, absorbed doses to the thyroid towards the upper bounds could among
sufficiently large population groups lead to a discernible increase in the incidence of thyroid cancer.
Information on dose distributions was not sufficient for the Committee to draw firm conclusions as towhether any potential increased incidence of thyroid cancer would be discernible among those exposed
to higher thyroid doses during infancy and childhood. The occurrence of a large number of radiationinduced thyroid cancers in Fukushima Prefecture—such as occurred after the Chernobyl accident—canbe discounted, because absorbed doses to the thyroid after the FDNPS accident were substantiallylower than those after the Chernobyl accident.
223. For leukaemia, the Committee considered the risk to those exposed as foetuses during pregnancy,and during infancy and childhood. The Committee also considered risks of breast cancer, in particular
for those exposed at young ages. Based on assessed doses and available risk estimates, the Committee
does not expect discernible increases in the incidence of these diseases among those groups.
224. The Committee does not expect any increase in spontaneous abortion, miscarriages, perinatal
mortality, congenital effects or cognitive impairment resulting from exposure during pregnancy. In
addition, the Committee does not expect any discernible increase in heritable disease among thedescendants of those exposed from the accident at FDNPS.
225. The Fukushima Health Management Survey of about 2 million residents has been launched tomonitor the long-term health of residents of Fukushima Prefecture (including a pregnancy and birth
survey), to promote their future well-being, and to examine whether long-term low-dose-rate radiation
exposure has unexpected health effects. Thyroid ultrasound examinations are to be made for all
children in Fukushima Prefecture (about 360,000) who were aged 18 years or less on 11 March 2011
and are expected to be completed within 3 years (by March 2014). The ongoing ultrasonography survey
in Fukushima Prefecture has detected relatively large numbers of thyroid anomalies, corresponding tosimilar surveys in areas unaffected by the accident at FDNPS. The ongoing ultrasonography survey inFukushima Prefecture is expected to detect relatively large numbers of thyroid abnormalities (including
a number of cancer cases) that would not normally have been detected without such intensive

90 UNSCEAR 2013 REPORT

screening. Surveys of thyroid cancer incidence in populations of areas unaffected by the accident would
provide useful input to estimates of the impact of such intensive screening.

2.

Health implications for workers

226. For most of the about 25,000 workers (99.3% as of 31 October 2012) involved in emergency
work and other activities, the effective doses reported were less than 100 mSv, with an average of about
10 mSv. Risk models indicate low risks (but increasing with dose) for diseases due to radiation
exposure at such doses. For the 173 workers that were estimated to have received effective doses ofmore than 100 mSv (average about 140 mSv), predominantly due to external irradiation, risk estimatescorrespond to about two to three additional cases of cancer in addition to about seventy cancers thatwould occur spontaneously given the lifetime baseline risk for solid cancer of about 40%; however,such predictions are associated with significant uncertainties and any increased cancer incidence in thissmall group may not be discernible against the variability of cancer incidence. No increase in otherdisease is expected in this group of workers; note, however, that the Committee could not estimate therisk of cataract from exposure of the lens of the eye to beta radiation.
227. For the thirteen workers27 who were estimated to have received absorbed doses to the thyroidfrom 131I in the range of 2 to 12 Gy, an increased risk of developing thyroid cancer can be inferred.
However, the numbers exposed are likely too small to discern an increased incidence in thyroid cancer.
Given uncertainties in the estimated doses, the possibility of thyroid disorders (e.g. hypothyroidism) inthe most exposed workers cannot be totally precluded, but the likelihood of them occurring is low.
228. Workers who received effective doses greater than 100 mSv are being specially examined,
including annual examinations of the thyroid, stomach, large intestine and lungs for potential lateradiation-related health effects. Ultrasonography surveys and close medical surveillance of theseworkers would result in increased detection of thyroid cancer (and possibly cases of other cancers); theoverwhelming majority of the cases detected are expected to have developed independently of radiation
exposure.

E. Radiation exposures and effects on non-human biota
229. The doses and associated effects of radiation on non-human-biota following the accident were
evaluated by comparing with the Committee’s generic evaluations of such effects that were conducted
before the accident. Exposures of both marine and terrestrial non-human biota following the accident
were, in general, too low for acute effects to be observed, though there may have been some exceptions
because of local variability. In general:(a) Effects on non-human biota in the marine environment would be confined to areas close towhere highly radioactive water was released into the ocean;(b) Continued changes in biomarkers for certain terrestrial organisms, in particular mammals,cannot be ruled out but their significance for population integrity is unclear. Any radiation effects
would be constrained to a limited area where the deposition density of radioactive material was
greatest; beyond this area, the potential for effects on biota is insignificant.

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F. Future scientific research needs
230. Similar to the experience of the Chernobyl and Three Mile Island accidents, the next years anddecades will continue to provide more information on the factors contributing to the accident
progression, the releases to the environment, the resulting exposures to the public, workers and theenvironment, and the associated health risks. The Committee is aware that close to three years after theaccident, the collective effective doses to workers on site are inevitably increasing, radioactive water isleaking on the site, and groundwater is transporting radionuclides into the aquatic environment(although control measures are being put in place). Scientific research will be desirable to extend,
corroborate and increase confidence in the Committee’s evaluations. Some of the key priorities forscientific research are to:(a) Improve estimates of the amount and characteristics of releases to the atmosphere as a functionof time, based on better understanding of the accident progression, the weather conditions during
the releases and the use of model predictions to reconstruct the atmospheric transport, dispersion
and deposition patterns;(b) Continue to measure and improve the characterization of the leaks of radioactive water andreleases to the aquatic environment, including groundwater and ultimately the Pacific Ocean, overtime; and forecast and quantify the long-term transport and mixing of these releases and theconsequent exposures through aquatic pathways;(c) Continue to measure the dose rates due to external exposure to deposited material, forecast andtrack changes over time, and quantify the impact of environmental remediation programmes;(d) Better characterize distributions of doses to the public expressing variability between
individuals, using probabilistic approaches, available data and appropriate models (this would
include further consideration of individual behaviours, detection limits, sampling procedures andthe distributions of measurement results), and better quantify the uncertainties in the dose
estimation;(e) Further conduct in vivo measurements of radionuclides in people to support refinement in theestimation of doses and their distributions, and to estimate current and future levels of exposure;(f) Continue the ongoing health survey in Fukushima Prefecture; continue the ultrasonographic
survey of children in Fukushima Prefecture based on the current protocol; analyse and quantify the
impact of this screening on the apparent incidence rates of thyroid cancer in Fukushima Prefecture(surveys of thyroid cancer incidence in areas unaffected by the accident would be useful in thisregard); consider the feasibility of establishing a cohort for epidemiological study with members
whose individual doses could be adequately assessed;(g) Quantify the uncertainties in reported doses to workers considering the work histories ofindividual workers during the early days of the accident, the time-varying levels of radionuclides(including short-lived radionuclides) and ambient dose equivalent rates where they worked andrested, the reliability of dose estimates based on shared personal dosimeters, and the protective
measures taken by individual workers; estimate absorbed doses to the lens of the eye for workers
involved in on-site mitigation activities (and associated uncertainties) in order to assess the risk ofcataracts; conduct further investigations to assure the quality of the effective dose estimatesreported by contractors;

92 UNSCEAR 2013 REPORT(h) Consider establishing a tissue bank for (a) unexposed workers and (b) workers who had
effective doses greater than 100 mSv, and subsequently underwent surgery for possible use in
future investigations;(i) Measure and assess the environmental exposures typical for certain species of non-humanbiota; and further analyse whether radiation exposure was an important factor in causing
environmental effects that were reported in field studies but were inconsistent with theCommittee’s assessment.

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ACKNOWLEDGEMENTS
In approving this Report, the Committee wishes to acknowledge with gratitude the help of the experts
directly involved in conducting the evaluation, all the support staff in their institutes who assisted them,and the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization(CTBTO), the Food and Agricultural Organization of the United Nations (FAO), the International
Atomic Energy Agency (IAEA), the World Health Organization (WHO), and the World MeteorologicalOrganization (WMO) who provided access to relevant data and expertise. It would also like to draw
attention to and commend the spirit of collaboration and exchange of data and ideas between countries,
international organizations, laboratories and scientists, which greatly enhanced the outcome of thisstudy. The interpretations expressed remain those of the Committee and do not necessarily represent theviews of the experts, the United Nations or its Member States, or the other international organizations.

Coordination expert group
Chair: W. Weiss (Germany); Senior Adviser: Y. Yonekura (Japan)

Expert Group A (Data and quality assurance)
Group Leader: E.V. Holahan Jr. (United States); Lead Writers: A. Rannou (France),
D. de Souza Santos (Brazil); Contributing Writers: J. Johansson Barck-Holst (Sweden), M. Zähringer(Germany); Technical Adviser: M. Nakano (Japan); Commentators: P. Bérard (France), S.H. Na(Republic of Korea), T. Takahashi (Japan)

Expert Group B (Radionuclide releases and dispersion)
Group Leader: G. Kirchner 28 (Germany); Lead Writer: R. Draxler (United States); Contributing
Writers: P. Chen (WMO), D. da Costa Lauria (Brazil), C. Estournel (France), O. Isnard (France),
R. Períáñez (Spain), K.S. Suh (Republic of Korea); Technical Adviser: J. Sugimoto (Japan);Commentators: M. Chino (Japan), F. Gering (Germany), M.C. Hort (United Kingdom), G.-B. Lee(Republic of Korea), M. Monfort (France), M. Nikkinen (CTBTO), M. Zähringer (Germany)

Expert Group C (Pathways and exposure assessment: the public and the environment)Group Leader: S. Solomon (Australia); Lead Writers: M. Balonov (Russian Federation), J. Simmonds(United Kingdom), P. Strand (Norway); Contributing Writers: P. Bedwell (United Kingdom), J. Brown(Norway), G. Dercon (FAO), F. Gering (Germany), V. Golikov (Russian Federation), G. Hirth(Australia), P. Verger (WHO); Technical Adviser: N. Ban (Japan); Commentators: M. Aerts (Belgium),
T. Aono (Japan), M. Chartier (France), M. Dinovi (United States), S. Fesenko (IAEA), J. GarnierLaplace (France), S. Haywood (United Kingdom), T. Homma (Japan), A. Hosseini (Norway),
D.-K. Keum (Republic of Korea), V. Kliaus (Belarus), C.-M. Larsson (Australia), I. Naletoski (FAO),
J.M. de Oliveira Godoy (Brazil), G. Proehl (IAEA), C. Rääf (Sweden), K. Sakai (Japan), T. Sazykina(Russian Federation), J. Sherwood (United Kingdom), S. Shinkarev (Russian Federation),
J. Vives i Batlle (Belgium)
28

Until mid-2013, owing to a major change in career.

94 UNSCEAR 2013 REPORT

Expert Group D (Worker exposure and health effects)
Group Leader: J.-R. Jourdain (France); Lead Writers: G. Etherington (United Kingdom), R. Lane
(Canada), A. Wiley (United States); Contributing Writers: E. Salminen (Finland); Technical Adviser:
M. Akashi (Japan); Commentators: D. Bazyka (Ukraine), E. Blanchardon (France), J. Harrison(United Kingdom), L. Lebaron-Jacobs (France), J.K. Lee (Republic of Korea), Z. Luo (China),
D. Rabelo de Melo (Brazil), M. Rickard (Canada), S. Romanov (Russian Federation), S. Saigusa(Japan), B. Thériault (Canada)

Health implications task group (Health implications)Group Leader: P. Jacob (Germany); Lead Writers: J. Harrison (United Kingdom), L. Hubbard(Sweden), J. Kenigsberg (Belarus), R. Lane (Canada), W.-U. Mueller (Germany); Technical Adviser:
K. Kodama (Japan); Contributing Writers: L. Holanda Sadler Veiga (Brazil), V. Ivanov (RussianFederation), V. Krasnyuk (Russian Federation), Y.-K. Lim (Republic of Korea), F. Ménétrier (France)

Critical reviewers
L. Anspaugh (United States), P. Jacob (Germany)

Final quality assurance teamTeam Leader: C.-M. Larsson (Australia); Contributing Writers: M. Balonov (Russian Federation),
M. Chino (Japan), R. Draxler (United States), G. Etherington (United Kingdom), F. Gering (Germany),
O. Isnard (France), P. Jacob (Germany), J.-R. Jourdain (France), G.N. Kelly (United Kingdom),
S. Solomon (Australia), W. Weiss (Germany), M. Zähringer (Germany)

Other contributing experts
C. Blackburn (FAO/IAEA), J.D. Boice Jr. (United States), L. Brookmire (United States), D.H. Byron(FAO/IAEA), J. Carpenter (Australia), T. Charnock (United Kingdom), S. Field (United Kingdom),
H. Ishida (Japan), V. Kryuchkov (Russian Federation), K. Leuraud (France), Q. Liang (FAO/IAEA),
K. Mortimer (United Kingdom), M.-L. Nguyen (FAO/IAEA), S. Nielen (FAO/IAEA), B. Orr(Australia), M. del Rosario Perez (WHO), K. Sakamoto (Japan), J. Smith (United Kingdom),
A. Thomassin (France), R. Tinker (Australia), A. Ulses (IAEA), D. Urban (Australia), S. Watson(United Kingdom), J. Wellings (United Kingdom), Y. Yamada (Japan), I. Zvonova (RussianFederation)

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

95

APPENDIX A. DATA COMPILATIONI.

INTRODUCTION................................................................................................................................... 95

II. DATA COMPILATION AND QUALITY ASSURANCE .................................................................. 96
A. Submitted datasets.................................................................................................................... 96
B. Radionuclide releases and dispersion................................................................................. 97
C. Assessment of doses to the public....................................................................................... 98
D. Assessment of doses to workers ........................................................................................... 98
III. ACKNOWLEDGEMENTS TO PROVIDERS OF DATA ................................................................107

I. INTRODUCTION
A1. The Government of Japan and 25 other Member States of the United Nations responded to theCommittee’s request for information 29 and provided extensive datasets. The Preparatory Commission
for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), the Food and Agriculture
Organization of the United Nations (FAO), the International Atomic Energy Agency (IAEA), theWorld Health Organization (WHO) and the World Meteorological Organization (WMO) also madeavailable data, analysis and expertise.
A2. This appendix summarizes the data compiled by the Committee for its assessment. It outlines themain sources of data, how these data were compiled, the processes used by the Committee to assure
sufficient quality of the data for the purpose of the assessment, and the Committee’s views on thequality of the data. The data themselves are presented in electronic form as attachments.
A3. The Committee also drew upon other relevant information and analysis published in peerreviewed scientific journals or other publication formats as appropriate. This material and its
interpretation and use by the Committee is not summarized in this appendix, but is cited and addressed,
as appropriate in the relevant technical appendices that describe the Committee’s assessment in detail.
29

The Netherlands, although not requested, voluntarily submitted data to the secretariat.

96 UNSCEAR 2013 REPORT

II. DATA COMPILATION AND QUALITY ASSURANCE
A4. The Committee designated experts to be responsible for reviewing and analysing data, conducting
assessments and delivering quality-assured contributions to its main report and the supporting
appendices.
A5. A list of data requirements (confined to those data that were or could be available before the
10 March 2012) was submitted to the Government of Japan, other selected United Nations Member
States, and several international organizations. The Government of Japan and 25 other Member States
submitted information to the Committee in response. After reviewing these materials, the Committee
made requests for supplemental information or for clarification of information or datasets previously
submitted. Many Japanese ministries, commissions, agencies, prefectures, universities and nongovernmental organizations provided information and data. Organizations contributing information ordata to this assessment are acknowledged in section III of this appendix. The datasets provided to theCommittee through this process and used for the assessment are summarized in table A1. In this table,
datasets are classified as either primary or secondary: (a) primary denotes that the dataset was used toprovide direct input into the Committee’s analysis or calculations; and (b) secondary denotes that thedataset was used to cross-check and compare with the results of the Committee’s analysis or
calculations. Some datasets were classified as both primary and secondary; they were used to provide
input to one part of the Committee’s assessment and to cross-check another part.

A. Submitted datasets
A6. Datasets received upon request were uploaded together with their metadata (descriptive
information) into a restricted online workspace on an electronic collaboration platform. Some datasets
related to the measurements performed in workers were provided to the secretariat and a few authorized
experts on a confidential basis. These datasets were not shared generally nor are they published here,
because they contain medically-confidential information. Nevertheless they provided important anduseful insights to the experts conducting the analysis on behalf of the Committee.
A7. The Committee made arrangements for each dataset received to be reviewed for its relevance andscientific quality. If the originator of the dataset provided sufficient information and assurance on how
the data were collected, what protocols were followed, what technical specifications were implemented
to ensure that high quality and reliable data were obtained, and what quality control procedures were
performed, then no additional quality assessment by the Committee was deemed necessary. If theoriginator of the dataset did not or could not submit sufficient or accurate information to provide
assurance about the quality of their data, the Committee made arrangements for the dataset to undergo
additional scrutiny. For example, where it was possible, datasets were compared and cross-checkedwith datasets from other sources. Table A1 includes brief general comments on the quality of eachdataset. The criteria used to assess data quality varied across the datasets and no single set of criteria
could be applied to all of them. Only information that was deemed of acceptable quality and fit for the
purpose of the Committee’s assessment was used.

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97

B. Radionuclide releases and dispersion
A8. To assess the releases of radionuclides from the Fukushima Daiichi Nuclear Power Station(FDNPS) to the atmosphere and to the ocean, the Committee largely relied on analyses conducted byothers and published in the peer-reviewed literature. These analyses made use of environmental
measurements of ambient dose equivalent rates, of concentrations of radionuclides in the air, inseawater and sea sediments, and of deposition densities on the ground surface made during the releaseand afterwards. (These data were also used by the Committee both as primary and secondary datasets.)
The Committee reviewed these analyses, as well as other analyses that had been made publicly
available but had not been subject to peer review (e.g. some very early analyses published in press
releases), and came to a view about the ranges of likely releases of the radiologically significant
radionuclides generally considered in its assessment. The literature reviewed is cited in appendix B.
A9. To provide an input into the assessment of doses to the public and workers, the Committee
adopted one of the peer-reviewed estimates of the releases to atmosphere of the radionuclides 131I and137
Cs. To estimate releases of other radiologically significant radionuclides to atmosphere, theCommittee used (a) estimates of the inventories of radionuclides in each of the reactors of Units 1-3 of
FDNPS at the time of shutdown, provided by the Japan Atomic Energy Agency (JAEA), and(b) measurements in air samples made in Japan and global measurements of radionuclide
concentrations in air that it had requested from CTBTO.
A10. Measurements of radionuclide concentrations in air made within the International Monitoring
System of the CTBTO followed clear, documented, standardized protocols and were considered highquality data. However, the CTBTO monitoring system and procedures are tailored for detecting tracesof radioactive material from clandestine nuclear tests and were not per se appropriate for monitoring
comparatively high levels of radionuclides following a reactor accident. The data on radionuclide
concentrations in air received from CTBTO were thus reviewed internally under arrangements made by
the Committee taking into account detailed descriptions of sampling, measurement and analysis
methods applied by the CTBTO monitoring system.
A11. To gain an understanding of the transport and dispersion of radionuclides released to the ocean,
the Committee reviewed the data on measurements of radionuclides in seawater and in sea sediments
made by the Tokyo Electric Power Company (TEPCO) and by the Ministry of Education, Culture,
Sports, Science and Technology (MEXT), and the results of analysis and modelling carried out byothers and published in the peer-reviewed literature. To gain an understanding of the transport anddispersion of radionuclides released to the atmosphere and, in particular of the influence ofmeteorological data and analyses, the Committee received input from a task team of WMO. The task
team evaluated meteorological analyses by comparing measurements of concentrations of radionuclides
in air and of deposition densities of radionuclides deposited on the ground with calculations made foran assumed release using each participating organization’s own atmospheric transport and dispersion
model (ATDM) and meteorological analysis data fields available to it, supplemented by higher spatial
and temporal resolution fields provided by the Japan Meteorological Agency (JMA). The performanceof the model–meteorology combinations was evaluated using a number of statistical measures. Further
details can be found in a report on this work prepared by the task team [W17, W18]. On the basis of
this analysis, one of the better performing ATDM–meteorology combinations was used to provide
estimates of concentrations in air and deposition densities of radionuclides released to atmosphere fromFDNPS. These estimates were used to supplement the measurement data in assessing doses to the
public (see below and appendices B and C for further details).

98 UNSCEAR 2013 REPORTC. Assessment of doses to the public
A12. Data required for the assessment of doses to the public and non-human biota included: deposition
densities of radionuclides on the ground; radionuclide concentrations in air, soil, water (freshwater andmarine), drinking water, food, biota (vegetation, terrestrial biota, marine biota, and wildlife), andfreshwater and marine sediments; ambient dose equivalent rates; in vivo measurements of activity inthe human body (including whole body and thyroid); population demographics; foodstuff consumption;
occupancy factors; dose reduction factors (location factors); land use; background levels of ambient
dose equivalent rates and radionuclide concentrations in the environment; and information on protective
measures.
A13. During the review process most data were reformatted to be suitable for the dose assessment
calculations, for combination with other datasets, or for visualization in a range of Geographic
Information Systems (GIS-software). The visualization process enabled checking to ensure that data
points were valid, for example, that marine samples were correctly reported for marine locations. Some
datasets required conversion of units. All data reformatting or manipulation was checked by a second
person to ensure the integrity of the data was maintained and conversions were correct.
A14. For areas in Fukushima Prefecture where no measured data were available, the data from ATDM
were utilized. Modelled data were provided in Network Common Data Form (NetCDF), and a script
was developed to extract data into an Excel®-compatible format. Subsets of these data were thenextracted to match the MEXT spreadsheets (see appendix C). All data manipulations were crosschecked by a second person.
A15. Derived datasets were also produced during the quality assurance process. These included the
MEXT datasets on ground deposition density that were combined with population density data. The
procedures utilized to derive and check these datasets are detailed in appendix C and associatedattachments. After review, all datasets were cleared for use in the dose assessments using themethodologies described in appendices C and F. Subsequent checks and quality assurance of the results
produced from the assessments are generally described in these appendices and their attachments.

D. Assessment of doses to workers
A16. In contrast to the dose assessment for the public where it was possible to use a large number of
independent sources of relevant information, the Committee had to rely on data provided by TEPCO,
contractors and subcontractors and the Japanese authorities for the assessment of doses to workers. It
was necessary to judge the extent to which the individual doses reported in Japan provided an accurate
and reliable measure of the doses actually incurred. Moreover, it was not feasible for the Committee toreview or reassess the assessments of dose to each of the approximately 25,000 workers involved.
Therefore, the Committee adopted a two-stage approach: first, it reviewed the methodologies used inJapan for assessing doses; second, it made independent dose assessments for defined groups of workers,
and compared its estimates with the values reported in Japan for these workers. The starting point for
the Committee’s assessment was therefore to review data on the doses to FDNPS workers from internaland external exposure as reported by their employers.
A17. Following requests to the Government of Japan, TEPCO, JAEA and the Japanese National
Institute of Radiological Sciences (NIRS), provided detailed information to the Committee on
instruments, measurement systems, calibration phantoms and methodologies used for in vivo

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

99

monitoring, and on measurement data for selected workers (the dataset of reported doses was
supplemented by data in spreadsheet form on the individual monthly and cumulative doses frominternal and external exposures reported for 21,776 TEPCO and contractors’ workers up to April 2012).
A18. The Committee compared its estimates of doses, the doses estimated by NIRS and TEPCO, andthe doses reported formally. Appendix D gives more detailed results, including the contribution madeby intakes of 131I to the absorbed dose to the thyroid and to the effective dose.
A19. This comparative approach could not be used to validate reported results of external exposure
assessments because they were made from personal dosimeter readings which could not be
independently verified on an individual basis. Therefore, information provided by TEPCO on personal
dosimeters, technical standards, calibration methods and the system used for allocating personal
dosimeters to individuals (as described in appendix D) was reviewed and evaluated.

100

Dataset title
Measuredradioactivity in air

Dataset description

Data provider(s)UsageRemarks on source and quality assurance

Tabulated data from selected stations for the time period.
Measurements of particulate 95Nb, 99Mo, 110mAg, 113Sn, 129Te,
129m
Te, 132Te, 131I, 133I, 136Cs, 137Cs and 140Ba at 38 stations
between 15 March and 24 May 2011

Comprehensive
Nuclear-Test-Ban
Treaty Organization(CTBTO)Primary

Measuredradioactivity in air

Air filter samples over the period of 15 to 20 March 2011 from
NIES site, Tsukuba City, Ibaraki, double filter (quartz andactivated carbon filters), high-resolution Germanium
detector

KEK High Accelerator
Research
Organization,
National Institute forEnvironmental
Studies (NIES),
IbarakiPrimary

Datasets extracted from [K5]Input to source term
and its nuclide
composition

The Committee reviewed this dataset andconsidered it acceptable and fit for purpose

Measuredradioactivity in air

Measurement of particulate radionuclides (99mTc, 132Te, 129Te,
129m
Te, 131I,132I,133I, 134Cs, 136Cs, 137Cs), and gaseous (131I, 132I, 133I)
concentrations in air at JAEA site in Tokai-mura

Japan Atomic Energy
Agency (JAEA)

Primary

Data taken from [F7, O2]

Input to deriving
nuclide spectrum ofsource term, including
radioiodine and its
chemical speciation

The Committee reviewed this dataset andconsidered it acceptable and fit for purpose

Input to nuclide
spectrum and source
term

Officially provided by CTBTO as issued in its specific“Radionuclide Reviewed Reports”
The full CTBTO internal quality assurance systemapplied and this was also checked by theCommittee. The Committee deemed thesedatasets acceptable and fit for purpose. Data are
confidential. Data used by the Committee havebeen declassified (attachment B-1)

Secondary
Used to compare with
ATDM calculations
Measuredradioactivity in air

Data from high quality, continuous air sampling at the Yokota
Air Base, which provided measurements of daily
concentrations in air of 99Mo, 99mTc, 86Ru, 106Ru, 102Rh, 129Te,
129m
Te, 131mTe, 132Te, 130I, 131I, 132I, 133I, 134Cs, 136Cs, 137Cs and 140La
over the period 11 March 2011 to July 2011

United States Air
Force via UnitedStates Departmentof State

Secondary

Datasets extracted from [U17]

Input to source term
assessment and publicdose assessment

Subsequent quality checks and reformatting
conducted. The Committee reviewed this dataset
and considered it acceptable and fit for purpose

Measuredradioactivity in air

Measurements of daily concentrations in air of 99Mo, 99mTc,
129
Te, 129mTe, 131mTe, 132Te, 131I, 132I, 133I, 134Cs, 136Cs, 137Cs carriedout over the period 13 March 2011 to 10 April 2011 at
Setagaya, Tokyo

Tokyo Metropolitan
Government/ Bureau
of Industrial andLabour Affairs

Secondary

Summarized radionuclide sampling data accessedfrom [T21]

Input to public dose
assessment

The Committee reviewed this dataset andconsidered it acceptable and fit for purpose

UNSCEAR 2013 REPORT

Table A1. Datasets provided to the Committee that were used for the assessment

Dataset description

Data provider(s)Measured grounddeposition density
and ambient dose
equivalent rates

Ambient dose equivalent rates were measured and soil
samples collected from 6 June to 8 July 2011 for areas within
100 km from FDNPS. From FDNPS out to 80 km these were
undertaken on 2 km × 2 km grids. Between 80 km and100 km from FDNPS they were divided into 10 km × 10 km
grids. Ambient dose equivalent rates were measured at aheight of 1 m above the ground surface at one location ineach of these divided grids (nearly 2,200 locations in total),and soil samples were collected at five points at eachlocation. Around 11,000 soil samples were taken; deposition
densities of five gamma-emitting radionuclides (110mAg,
129m
Te, 131I, 134Cs and 137Cs) were measured using germanium
semiconductor detectors

Ministry of Education,
Culture, Sports,
Science andTechnology (MEXT)

Radiation was measured from 2 April 2011 to 9 May 2011,using large thallium-activated sodium iodide (NaI(Tl)) crystals
attached to a fixed-wing aircraft. Ground teams performed
measurements with High-Purity Germanium (HPGe)
detectors to determine the isotopic composition of thedeposited activity. This was used to project the time
evolution of dose rate from the deposits, and thecontribution of caesium isotopes to the dose rate as afunction of the deposition density. In order to combine thedata collected over the 5 weeks represented by the dataset,the projected dose rates and deposition densities were
calculated for the common date of 30 June 2011

United States
Department ofEnergy (USDOE) via
United States
Department of State3,422 measurements of 134Cs and 137Cs in cultivated soils in
15 prefectures in eastern Japan (Fukushima, Iwate, Miyagi,
Yamagata, Ibaraki, Tochigi, Gunma, Saitama, Chiba, Tokyo,
Kanagawa, Nigata, Yamanashi, Nagano and Shizuoka), basedon samples collected from 26 April 2011 to 3 February 2012.
The cultivated soil activities were adjusted to a reporting
date of 5 November 2011

Japanese Ministry ofAgriculture, Forestry
and Fisheries (MAFF)

Data from monitoring performed by IAEA teams in locations
between 20 km and 80 km from FDNPS and in Tokyo during
period 18 March 2011 to 18 April 2011. Data included
ambient dose equivalent rates, surface activity concentration,
activity concentrations in air and gamma spectra for selected
locations. Radionuclides detected included 99Mo, 99mTc, 129Te,
129m
Te, 131mTe, 132Te, 131I, 132I, 134Cs, 136Cs, 137Cs and 140La

IAEA

Measured grounddeposition density
and airborne
monitoring

Measured activity
concentrations in
soils

Measured grounddeposition
densities, ambient
dose rates,
concentrations in
air, in situ gamma
spectroscopy

Usage
Primary
Basis for dose
assessments for public
and non-human biota
in Fukushima
Prefecture
Secondary
Used to compare with
ATDM calculations

Primary
Input data for publicdose assessment
Secondary
Used to compare with
ATDM calculations

Remarks on source and quality assurance
JAEA conducted the survey with cooperation ofvarious universities and research institutes. MEXT
was responsible for the coordination of themeasurement data and assessment of validity[M12, M13]
The Committee reviewed this dataset andsupporting documentation and considered it
acceptable and fit for purpose (attachments C-1,
C-2, C-3, C-4, C-5, C-6 and C-7)

Dataset downloaded from the US Government
website [U17]Files downloaded in Google Earth™ KML formats andconverted to spreadsheet format for use by theCommittee
The Committee reviewed this dataset andconsidered it acceptable and fit for purpose(attachment C-7)

Primary

Officially provided by the Government of Japan

Input to public dose
assessment

The original datasets were supplied as pdf files, data
were converted and cross-checked to produce
data in spreadsheet format
The Committee reviewed this dataset andconsidered it acceptable and fit for purpose

Secondary

Officially provided by IAEA

Used for generalcomparison in the
public dose
assessment

The processes by which these samples were made,analysed and presented were reviewed by theCommittee. The Committee deemed thesedatasets acceptable and fit for purpose

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Dataset title

101

Monitored radiationdose rates

The Commission de Recherche et d’Information
Indépendantes sur la RADioactivité / Commission for
Independent Research and Information about RADiation(CRIIRAD) is a French non-governmental organization whose
teams carried out radiation measurements in Japan at theend of May 2011

CRIIRAD

Data comprising measurements of dose rate at more than
4,000,000 data points, collected using Geiger-Mueller tube
based radiation monitors

Safecast

Monitored radiationdose rates

Data provider(s)UsageSecondary
Used for generalcomparison in the
public dose
assessment
SecondaryComparison with resultsof public dose
assessment

Remarks on source and quality assurance
Data in the form of a CRIIRAD Communiqué were
downloaded from the CRIIRAD website [C9]The Committee did not review the quality of thesedata in detail

Safecast is a global community group providing a
web-based network for collecting, sharing anddisplaying radiation measurements using GeigerMueller tube based radiation monitors. Data
downloaded from the Safecast website [S1]The Committee did not review the quality of thesedata

Measured activity
concentrations inenvironmental
samples

The Association for Radioactivity Control in west France (ACRO)
measured radioactivity in environmental samples collected in
the prefectures of Fukushima and Miyagi over the period
March 2011 to June 2012

ACRO

Measured activity
concentrations indrinking water

Drinking water samples were first collected in Fukushima
Prefecture on 16 March 2011. Some districts did not begin
sampling until late March or early April 2011. Outside
Fukushima Prefecture data were only available for 131I, 134Cs
and 137Cs. Within Fukushima Prefecture 132I was also detected.
Data fields were translated into English by the Nuclear Safety
Commission Office prior to submission to the Committee

Measured activity
concentrations inmarine water andsediments

Data for 131I, 134Cs and 137Cs in water and sediments from marine
systems in the coastal region around FDNPS

Secondary

Data downloaded from the ACRO website [A3]Used for generalcomparison in the
public dose
assessment

The Committee did not review the quality of thesample collection methods; however, the samples
were analysed in laboratories that follow
internationally recognized procedures and quality
standards

Japanese Ministry of
Health, Labour andWelfare (MHLW)

Primary

Officially provided by the Government of Japan

Input to public dose
assessment

The Committee deemed this dataset acceptable andfit for purpose

TEPCO, JAEA, MEXT,JAMSTEC, MERI, FRA,
JCAC, NIRS, MOE,
Fukushima
Prefectural Fisheries
Experimental
Station, theUniversity of Fukui

Primary

Officially provided by a number of organizations
through the Government of Japan

Input to review ofmarine dispersion andto dose assessment for
non-human biota

The processes by which these samples were
sampled, analysed and presented were reviewed
by the Committee. A small number of anomalies insome of these datasets were identified, queriedand subsequently corrected prior to their use
The Committee deemed this dataset acceptable andfit for purpose

UNSCEAR 2013 REPORT

Dataset description

102

Dataset title

Dataset title

Dataset description

Data provider(s)Measured activity
concentrations infoodstuffs

A database has been compiled on radionuclide concentrations
in foodstuffs under the guidance of FAO/IAEA and incollaboration with MAFF and MHLW. This “FAO/IAEA food
database” includes over 500 types of foodstuffs sampled inall 47 prefectures

FAO/IAEA, MHLW and
MAFF

Usage
Primary
Input to public dose
assessment

Remarks on source and quality assurance
Data provided through the FAO/WHO International
Food Safety Authorities Network (INFOSAN) basedon information provided by MHLW and compiled
by FAO/IAEA
FAO/IAEA and MAFF/MHLW undertook an extensive
quality assurance process to produce this database(attachment C-8)
The Committee reviewed the quality assurance
process and considered the database acceptableand fit for purpose

Population data

Protective measures

Food intake

Japanese Ministry ofInternal Affairs andCommunications(MIC) / Statistics
BureauPrimary

Data downloaded from [M20].

Input to public dose
assessment

The Committee accepted this dataset as qualityassured by the Government of Japan and fit for
purposeData on typical occupancy factors for various population andage groups were derived from national survey data specificfor Japan and obtained from the official website

Japanese Ministry ofInternal Affairs andCommunications(MIC)

Primary

Data downloaded from [M19]

Input to public dose
assessment

The Committee accepted this dataset as qualityassured by the Government of Japan and fit for
purposeIn November 2011 the Fukushima Prefecture government
reported on a Health Management Survey that accounted forresidents’ activities over a four-month period from 11 March
to 11 July 2011. Based on the results of a questionnaire issued
to all residents, information was provided on 18 scenarios
representative of the movements of residents evacuatedfollowing the accident at FDNPS. Description of the status of
the protective measures in evacuated localities, including
information on food and drinking water restrictions and on
distribution of stable iodine tablets

Fukushima Prefecture
government,
Government ofJapan, National
Institute ofRadiological
Sciences in Japan(NIRS)

Primary

Officially provided by the Government of Japan

Input to public dose
assessment

The Committee accepted this dataset as qualityassured by the Government of Japan and fit for
purposeInformation on food consumption habits for various
population groups, age groups and food groups

MAFF, MHLW

Primary

Officially provided by the Government of Japan

Input to public dose
assessment

The Committee accepted this dataset as qualityassured by the Government of Japan and deemed
it fit for purpose. These data were provided inconfidence and are not publicly available

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Occupancy factors

Population data, including sex/age structure, urban and rural
population, distribution by professions, dwelling/settlement
type. The data from both the 2005 census (which provided
the grid for which the population data was mapped) and the2010 Japan census (which provided population information)
were utilized103

Dataset description

Data provider(s)Detailed data on agricultural production including major
planting and animal breeding habits in JapanMAFF

Measuredradioactivity in thehuman bodyResults of in vivo measurements of radionuclides in people, inparticular thyroid monitoring for 131I and whole-bodymonitoring for 134Cs and 137Cs

Measured activity
concentrations inmarine biota

Data for 131I, 134Cs and 137Cs in a range of marine biota from thecoastal area around FDNPS

Measured activity
concentrations inmedia infreshwater systems

Data for 131I, 134Cs and 137Cs in water and sediments from
freshwater systems in Fukushima Prefecture

Remarks on source and quality assurancePrimary

Officially provided by the Government of Japan

Input to public dose
assessment

The Committee accepted this dataset as qualityassured by the Government of Japan and deemed
it fit for purpose

Fukushima Prefecture
Health Survey

Secondary

Officially provided by the Government of Japan

Comparison with resultsof public dose
assessment

The Committee independently analysed themeasurements of radionuclides in people thatwere provided for use in the dose assessment anddeemed the datasets acceptable and fit for
purpose. Many of these results were subsequently
published in peer-reviewed journals and are cited
in appendix C

TEPCO, JAEA, MEXT,JAMSTEC, MERI, FRA,
JCAC, NIRS, MOE, theFukushima
Prefectural Inland
Water Fisheries
Experimental
Station, theUniversity of Fukui

Primary

Officially provided by a number of organizations
through the Government of Japan

MOE, NIRS and the
Fukushima
Prefectural Inland
Water Fisheries
Experimental Station

Primary

Officially provided by the Government of Japan

Input to dose
assessment for nonhuman biota

The processes by which these samples were
sampled, analysed and presented were reviewed
by the Committee. The datasets were very limited
in data quantity and some information aboutsampling was unavailable. Samples were however
analysed in laboratories that follow recognizedprocedures and quality standards

Input to dose
assessment for nonhuman biota

The processes by which these samples were
sampled, analysed and presented were reviewed
by the Committee. The Committee deemed thesedatasets acceptable and fit for purpose

The Committee deemed these datasets acceptableand fit for purpose
Measured activity interrestrial wildlife

Data for 131I, 134Cs and 137Cs in a range of terrestrial biota within
about 100 km of the FDNPS

Fukushima Prefecture
Nature Conservation
Division

Primary

Officially provided by the Government of Japan

Input to dose
assessment for nonhuman biota

The processes by which these samples were
sampled, analysed and presented were reviewed
by the Committee. The Committee deemed thisdataset acceptable and fit for purpose

UNSCEAR 2013 REPORT

Agricultural
production andproducts

Usage

104

Dataset title

Dataset description

Data provider(s)Measured activity inmarine biota andseawater

Data for 131I, 134Cs and 137Cs in a range of marine biota from thecoastal area around FDNPSGreenpeace

Dose information
recorded for
24,832 TEPCO andcontractors’
workers

Statistics on dose distribution for workers as of
31 October 2012; numbers of TEPCO and contractors’
workers for several dose bands

TEPCO

Monthly dose
information
recorded for
21,776 TEPCO andcontractors’
workers

Dataset provided the following information for 21,776 workers:
employer (TEPCO/contractors), age of the worker at end of
April 2012, monthly dose from external exposure fromMarch 2011 to April 2012, monthly dose from internal
exposure from March 2011 to April 2012, cumulative dosefrom external exposure, cumulative dose from internal
exposure, cumulative dose from March 2011 to April 2012

TEPCO

Usage

Remarks on source and quality assurance

Secondary

Data accessed from the Greenpeace website [G11]

Used to compare withresults of models indose assessment for
non-human biota

The Committee deemed these datasets acceptableand fit for purpose. The collection methods forsome of these samples were not always well
documented, however the samples were analysedin laboratories that followed internationallyrecognized procedures and quality standards

Primary
Used for analysis andpresentation of dose
distributions

The Committee checked the consistency of
information provided [T8], compared to
information provided in previous TEPCO press
releasesPrimary

Data provided by TEPCO to the Committee

Used for analysis andpresentation of dose
distributions,
identification of 12
workers with highest
internal exposure, andrandom selection of 42
workers for theCommittee’s own dose
assessment

An aim of the Committee’s assessment was to judge
the reliability of the doses to workers reported by
TEPCO and set out in this dataset

SecondaryFor selected workers,
used to compare withresults of Committee’s
own dose assessment

This dataset could not be made publicly available
because it contained personal confidential
information

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Dataset title

105

Data provider(s)Dose information for
the 12 workers withhighest internal
exposure

Dataset comprised for each of 12 workers: worker ID, age on
12 March 2012, height, weight, sex, working period(start/end), numeration of the measurement, date/place ofmeasurements, activity for 129mTe, 132Te, 131I, 132I, 134Cs, 136Cs and137
Cs, assumed date of intake, number of days between
assumed date of intake and date of measurement, retention
rate for 132Te, 131I, 132I, 134Cs and 137Cs, intake for132Te, 131I, 132I,
134
Cs and 137Cs, effective dose coefficient for 132Te, 131I, 132I, 134Cs
and 137Cs, committed effective dose due to 129mTe, 132Te, 131I,
132 134
I, Cs, 136Cs and 137Cs, effective dose from external andinternal exposure, organization which performed the dose
assessment (NIRS or TEPCO), body surface activity levels
measured on head, neck and hand and background value,
dose rate at neck surface and background value

NIRS and TEPCO

Dose information for
13 emergency
workers randomly
selected in thelower dose bands

Dataset comprised for each of 13 emergency workers: worker
ID, date of measurement, assumed date of intake, dose fromexternal exposure, activity of 131I measured for 5 minutes inthe thyroid, thyroid committed equivalent dose from 131I,
activity of 134Cs measured for 10 minutes in the whole body,
activity of 137Cs measured for 10 minutes in the whole body,whole body committed effective dose from 134Cs, whole bodycommitted effective dose from 137Cs, hypothesis considered
for the internal exposure assessment (type of intake, AMAD,
assumed day of intake, chemical type)

Dose information for
21 TEPCO workers
and 21 contractors’
workers randomly
selected in thelower dose bands

Information about
personal
dosimeters used
for monitoring
workers’ external
exposure

Usage

Remarks on source and quality assurancePrimary

Data provided by NIRS and TEPCO to the Committee

Used for theCommittee’s own dose
assessment

This dataset could not be made publicly available
because it contained personal confidential
information

National Police
Agency (NPA)

Primary

Data provided by NPA to the Committee

Used for theCommittee’s own dose
assessment

This dataset could not be made publicly available
because it contained personal confidential
information

Dataset comprised for each of 42 workers: worker ID, dose
range (0-5 mSv/5-10 mSv/20-100 mSv), company(TEPCO/contractors), age on 3 March 2012, sex, working
period (start/end), date/place of measurement, activity
measured for 132Te, 131I, 132I, 134Cs and 137Cs, assumed date ofintake, number of days between assumed date of intake anddate of measurement, intake for132Te, 131I, 132I, 134Cs and 137Cs
committed effective dose due to 132Te, 131I, 132I, 134Cs and 137Cs,
total committed effective dose

TEPCO

Primary

Data provided by TEPCO to the Committee

Used for theCommittee’s own dose
assessment

This dataset could not be made publicly available
because it contained personal confidential
information

Document containing detailed information on types of
personal dosimeter used, technical standards and calibration
methods used for both TEPCO and contractors’ workers

TEPCO

Primary

Data provided by TEPCO to the Committee arereported in tables D8 and D9 of appendix D

Used to assess thereliability of external
exposuremeasurements

UNSCEAR 2013 REPORT

Dataset description

106

Dataset title

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

III. ACKNOWLEDGEMENTS TO PROVIDERS OF DATA
Japan

Fire and Disaster Management Agency (FDMA)
Fukushima Medical University
Fukushima Prefecture Nature Conservation Division
Fukushima Prefectural Fisheries Experimental Station
Fukushima Prefectural Inland Water Fisheries Experimental Station
Fisheries Research Agency (FRA)
Geospatial Information Authority of Japan
Institute for Environmental Sciences
Japan Agency for Marine-Earth Science and Technology (JAMSTEC)Japan Atomic Energy Agency (JAEA)
Japan Chemical Analysis Center (JCAC)
Japan Coast Guard (JCG)
Japanese Meteorological Agency (JMA)
Japan Nuclear Energy Safety Organization (JNES)
Marine Ecology Research Institute (MERI)
Ministry of Agriculture, Forestry and Fisheries (MAFF)
Ministry of Defence (MOD)Ministry of Education, Culture, Sports, Science and Technology (MEXT)
Ministry of Economy, Trade and Industry (METI)
Ministry of Foreign Affairs (MOFA)
Ministry of Health, Labour and Welfare (MHLW)
Ministry of Internal Affairs and Communications (MIC)
Ministry of Land, Infrastructure, Transport and Tourism (MLIT)
Ministry of the Environment (MOE)
National Institute of Radiological Sciences (NIRS)National Police Agency (NPA)
Nuclear and Industrial Safety Agency (NISA) (former)
Nuclear Regulation Authority (NRA)
Nuclear Safety Commission (NSC) (former)
Radiation Effects Association
Radiation Council
Federation of Electric Power Companies of JapanTokyo Electric Power Company (TEPCO)
Tokyo University of Marine Science and Technology
University of Fukui
OTHER MEMBER STATES

Argentina

Nuclear Regulatory Authority

Australia

Australian Radiation Protection and Nuclear Safety Agency (ARPANSA)
Bureau of Meteorology

Belarus

Ministry of Natural Resources and Environmental Protection

Belgium

Federal Agency for Nuclear Control

BrazilInstitute for Radioprotection and Dosimetry
Nuclear and Energy Research Institute

CanadaCanadian Meteorological Centre (CMC)
Health Canada
Natural Resources Canada

107

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UNSCEAR 2013 REPORT

China

Ministry of Environmental Protection

Finland

Radiation and Nuclear Safety Authority (STUK)FranceInstitute for Radiological Protection and Nuclear Safety (IRSN)
Alternative Energies and Atomic Energy Commission (CEA)

Germany

Federal Office for Radiation Protection (BfS)

India

Bhabha Atomic Research Centre

Indonesia

Badan Tenaga Nuklir Nasional (BATAN)

Malaysia

Ministry of Health
Ministry of Science, Technology and Innovation

MexicoNational Commission for Nuclear Safety and Safeguards

Pakistan

Pakistan Nuclear Regulatory Authority

Philippines

Philippines Nuclear Research Institute

PolandNational Atomic Energy Agency (PAA)

Republic of Korea

Korea Meteorological Administration

Russian Federation

Federal Medical Biological Agency of Russia
Institute of Radiation Hygiene

Singapore

National Environmental Agency

Slovakia

Public Health Authority of the Slovak Republic

Spain

Nuclear Safety Council

SwedenLinköping University
Lund University
Swedish Defense Research Agency
Swedish Radiation Safety Authority
Swedish University of Agricultural Sciences
Swedish Women’s Voluntary Defense Organization

United Kingdom

Public Health England (PHE) (the former Health Protection Agency)
Met Office

United States of America

Department of Defense (DoD)
Department of Energy (DOE)
Environmental Protection Agency (EPA)
Food and Drug Administration (FDA)
National Oceanic and Atmospheric Administration (NOAA)
Nuclear Regulatory Commission (NRC)
INTERNATIONAL ORGANIZATIONSInternational
intergovernmentalorganizations

Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO)
Food and Agricultural Organization of the United Nations (FAO)
International Atomic Energy Agency (IAEA)
World Health Organization (WHO)World Meteorological Organization (WMO)

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

109

APPENDIX B. RADIONUCLIDE RELEASES, DISPERSION AND
DEPOSITIONI.

INTRODUCTION................................................................................................................................. 109

II. RADIONUCLIDE RELEASES ............................................................................................................ 110
A. Releases to atmosphere......................................................................................................... 110
B. Releases to the ocean ............................................................................................................. 126
III. TRANSPORT AND DISPERSION IN THE ATMOSPHERE ......................................................... 129
A. Meteorological conditions.................................................................................................... 129
B. Synthesis of observations...................................................................................................... 130
C. Atmospheric dispersion pattern......................................................................................... 134
D. Methodology and results of dispersion and deposition assessment.................... 137
E. Robustness of estimation of radionuclide levels in the environment
where no measurements are available ............................................................................ 142
IV. TRANSPORT AND DISPERSION IN THE OCEAN ...................................................................... 148
A. Synthesis of observations...................................................................................................... 148
B. Marine dispersion models and validity checks.............................................................. 151
C. Results of dispersion assessment ....................................................................................... 154

I. INTRODUCTION
B1. This appendix sets out the Committee’s evaluation of information on the releases of radionuclides
from the accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) to the atmosphere and tothe ocean and their subsequent dispersion in the environment (see chapter I of the main text of thescientific annex for the timescale of the evaluation).
B2. An overview of estimates of the radionuclide releases to the atmosphere and to the ocean, both of
the total amounts and the rates of release over time, is provided in section II. The meteorologicalconditions that prevailed during the period when the releases to the atmosphere were greatest(11-31 March) are described in section III; the influence of these conditions on how and where thereleased material was dispersed in, and deposited from, the atmosphere onto the Japanese land massand the ocean surface is illustrated. Based on these meteorological conditions and the time-dependent
releases to the atmosphere, estimates have been made—using atmospheric transport, dispersion anddeposition models (ATDM)—of the spatial and temporal distribution of radioactive material in theenvironment (that is, concentrations of radionuclides in air and deposited on the ground as a function of

110

UNSCEAR 2013 REPORTtime). This was done to estimate levels of radioactive material in the environment at places and times
for which measurements did not exist; these measured and estimated levels underpinned the assessmentof doses to the public described in appendix C. The dispersion of radioactive material released to theocean (directly or indirectly) is described in section IV.

II. RADIONUCLIDE RELEASES

A. Releases to atmosphere
B3. The accident at FDNPS resulted in the release of large amounts of radioactive material into theenvironment. A large number of fission and activation products were released from the molten fuel inthe reactors, generally as aerosols or in a gaseous form. Those that contributed most to the radiation
exposure of members of the public and workers were isotopes of iodine, caesium, tellurium and thenoble gases. The accident was classified by the Japanese Nuclear and Industrial Safety Agency (NISA)
at the highest level (level 7) on the International Nuclear Event Scale (INES). The main sequence of
events in each reactor that resulted in the release of radioactive material is summarized below.

1.

Accident sequence

B4. The earthquake that occurred off the eastern coast of Japan at 14:46 Japan Standard Time 30 (JST)on 11 March 2011 resulted in reactors in Units 1–3 of FDNPS shutting down automatically. The threeother reactors (Units 4–6) had already been shut down for routine outages and Unit 4 had been
completely de-fuelled. The earthquake damaged the power transmission grids from the Shin–
Fukushima electrical substation and FDNPS lost all connection with its off-site electricity supply. In
addition, the tsunami inundated the FDNPS site less than one hour later and flooded a number of
emergency safety systems, in particular the on-site power distribution system and the DC power supply
system. Units 1, 2 and 4 lost all of their power supplies. Unit 3 initially lost its AC power followed byloss of DC power during the night of 12−13 March. The tsunami also washed away vehicles, heavyequipment and oil tanks, ruined buildings, equipment and facilities, and devastated the site moregenerally. This exceptional situation resulted in the melting of the reactor cores of Units 1, 2 and 3 andthe substantial release of radioactive material into the atmosphere and the ocean.
B5. The main events that influenced the release of radioactive material from Units 1–3 of FDNPS (asset out in the July 2012 final report of the Investigation Committee on the Accident at the Fukushima
Nuclear Power Stations of Tokyo Electric Power Company [I9], and supplemented by the 2012 report
Fukushima Nuclear Accident Independent Investigation Commission of the National Diet of Japan[N2]) are summarized in table B1.
30

In this appendix, unless specifically stated otherwise, all dates and times are given in Japan Standard Time (JST).

Table B1. Summary of the main events that influenced the release of radioactive material from Units 1–3 of FDNPS [I9, N2]
All times are JST

Date (2011)

Unit 1

Unit 2

Unit 3

14:46 EARTHQUAKE

11 March

Automatic shutdown (Scram 31)
Loss of external AC electricity
Automatic activation of emergency diesel generators
14:52 Start of core cooling by isolation condenser (IC)14:50 Start of core cooling by Reactor Core Isolation Cooling(RCIC) system

15:05 Start of core cooling by Reactor Core Isolation Cooling(RCIC) system

15:37 Loss of all electricity
IC stopped operating following loss of all power~20:00 Possible start of damage to core and reactor pressure
vesselRCIC continued to operate for about 70 hours, but its
operation could not be controlled because of lack of DC
power

15:37 Loss of AC power
16:03 RCIC manually restarted; RCIC continued to operate forabout 21 hours; DC power enabled measuring instruments tofunction correctly~21:50 Radiation in reactor building reached levels forbuilding to be declared off-limits~22:00 Core likely to have been damaged to considerable
degree12 March

02:45 Strong likelihood of reactor pressure vessel failure
04:50 First indications of off-site release detected; ambient
dose equivalent rate at site boundary 1 μSv/h

Between ~04:20 and ~05:00 water source for RCIC switched tosuppression chamber
11:36 RCIC and water injection into reactor stopped

15:36 Explosion of hydrogen accumulated in reactor building;possible release of large amounts of radioactive material into
the atmosphere; dose rates at site boundary increased toaround 1 mSv/h
19:04 Fire trucks started to fill reactor with seawater

15:36 Explosion in Unit 1 caused blow-out panel in reactor
building to open

12:35 High pressure coolant injection (HPCI) system started
automatically and restored water level~19:00 HPCI operated below allowable operating range
20:36 Reactor water level measurement devices became
inoperable and water injection capacity of HPCI started to
become insufficient to maintain water level31

A scram is a safety feature that triggers immediate shutting down of a nuclear reactor, usually by rapid insertion of control rods, either automatically or manually by the reactor operator. Also known as a “reactor trip”.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

15:35 MAJOR TSUNAMI

111

Unit 1

Unit 2

02:42 HPCI manually stopped, because of concern about
possible damage, before confirming availability of alternative
diesel-driven fire-pump system; unsuccessful attempt torestart HPCI
~02:45 Unsuccessful attempt to reduce pressure in reactor
pressure vessel through safety relief valve~06:30 to ~09:10 Likely damage to reactor pressure vessel anddegradation of its containment function~08:45 Start of venting of primary containment vessel
09:25 Start of injection of fresh water
12:20 Water tank emptied; reactor water level dropped again
13:12 Seawater injection started, but occasionally interrupted,
and flow rate never sufficient to fully re-cover core

14 March

04:30 Started monitoring pressure of suppression chamber
09:00 Water injection functionality of RCIC started to degrade
12:30 RCIC failure and cessation of water injection into reactor~13:45 to ~18:10 Possible damage to primary containment
vessel
~16:34 Start of depressurization of reactor pressure vessel
through safety relief valve

11:01 Hydrogen explosion occurred in reactor building withpossible release of large amounts of radioactive material

16:30 Seawater injection restarted, but sometimes interrupted

by 18:22 Indications that core may have been completely
uncovered
19:57 Seawater injection started but disrupted several times~21:18 Failure of reactor pressure vessel containment
function
15 March
From ~07:38 Release of large amounts of radioactive
materials; peak dose rate at ~09:00 about 12,000 μSv/h at siteboundary
19:54 More seawater successfully injected into reactor;
continued in following days with varying degrees of successas reactor pressure varied~06:00 to ~06:12 Hydrogen explosion occurred at Unit 4 frombackflow of gases vented from Unit 3

UNSCEAR 2013 REPORT

13 March

Unit 3112

Date (2011)

Date (2011)
20 March

22 March

Unit 1

Unit 2Off-site power restored and Unit 1 progressively brought backunder control

Off-site power restored and Unit 2 progressively brought backunder control

Unit 3Off-site power restored and Unit 3 progressively brought backunder control

Note: Concerns were frequently expressed during the accident over the adequacy of the cooling of the spent fuel in the storage pool of Unit 4, in particular whether the fuel may have become uncovered (due to possible
earthquake damage), and thus overheated. Notwithstanding these concerns, there was no release of radioactive material to the atmosphere from the spent fuel pool. Furthermore, the hydrogen explosion which damaged
Unit 4 on 15 March was caused by the backflow of gases from the venting of Unit 3 (see above).

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...
113

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UNSCEAR 2013 REPORT

2.

Approaches to estimating the source term

B6. Estimates of the source term (that is the time-dependent release of radioactive material to theenvironment) were made for two main purposes:(a) To indicate the amounts of radioactive material released to the environment;(b) To be used, in combination with models (for example, for atmospheric and marine dispersion),as support for inferring the dispersion and deposition of radionuclides at locations in theenvironment where measurements were not available or could no longer be made.
Measured and estimated levels of radionuclides in the environment were used by the Committee toestimate exposure levels to members of the public (see appendix C).
B7. Estimates of the release of radioactive material to the atmosphere can be made using twocomplementary approaches: (a) based on analyses of how an accident progressed; and (b) based on
measurements of radioactive material in the environment and using reverse or inverse methods toreconstruct their transport through the atmosphere back to the source of the release. Both approaches
have their limitations and are associated with much uncertainty.
B8. The first approach, based on analyses of the progression of an accident, uses reactor simulation
codes, such as MELCOR [G4], ASTEC [C5] and MAAP [E3]. The main inputs to these computercodes are (a) the events that are either known or are postulated to have occurred during the progressionof the accident and (b) the characteristics of the reactors. The simulations are based on detailed
modelling of the different parts of the reactor and its systems, and address all the physical and chemical
phenomena involved in the course of a severe accident (for example, thermal-hydraulic conditions, thebehaviour of the fuel as temperatures rise when cooling is reduced or lost, the release of radionuclides
from the fuel into the reactor coolant as the fuel overheats, hydrogen production, the degradation of thereactor core as the fuel melts and how it interacts with the bottom of the reactor vessel, the retention ofradionuclides in the containment and their release to the environment through any leakage paths, and soon). These computer codes were developed for, and are used extensively in, reactor safety assessments,
in particular in relation to designing reactors to prevent and mitigate potential severe accidents. The
uncertainty associated with the use of these codes for estimating the release of radionuclides following
an actual accident is, however, much greater, not least because of the lack of specific information on
key plant parameters as the accident progresses, the need to make major assumptions about the timing
and nature of key events in the process, and the fact that the models still represent a considerable
simplification of reality. The Fukushima Nuclear Accident Independent Investigation Commission of
the National Diet of Japan [N2] expressed major reservations about the reliability of these methods,
both now and in the future, because of the major uncertainties about what exactly occurred in thedamaged reactors. The estimates so far published using these methods only considered releases during
the first few days of the accident; this limited their usefulness for the Committee’s purpose of
estimating exposures, where account needed to be taken of all significant releases.
B9. The second approach is based on measurements of radioactive material in the environment andthe use of reverse or inverse modelling:(a) Reverse modelling evaluates the rates of release of radionuclides by comparing measurementsof radioactive material or dose rates in the environment with estimates derived from simulations ofdispersion of radionuclides in the atmosphere. Atmospheric transport, dispersion and deposition

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

115

models (ATDM) are used to estimate levels in the environment for unit release of a radionuclide.
Each measurement location is considered independently and the estimate is compared with themeasurement; the release is adjusted empirically to fit the measured levels. Comparisons can bemade with a range of measurements of radionuclides in the environment, for example, timedependent concentrations in air and deposition densities on the ground, dose rates, and dust
samples. A weakness of this approach is that it does not take account of uncertainties or bias in themeasurements, the dispersion model and the meteorological data.
(b) Inverse modelling involves a similar, but mathematically more sophisticated, approach inwhich the (matrix) equation relating the measured values (of concentration or deposition density ofradionuclides, or dose rate) to the source term is solved by minimizing the function which includes
all of the sources of technical error that contribute to differences between calculated values(derived generally by ATDM) and measured values. Technical errors are therefore explicitly taken
into account.
B10. Estimates made using this second approach are also associated with much uncertainty; their
quality is influenced by the availability and quality of measurements of radiation or radioactive material
in the environment and of meteorological data of sufficient temporal and spatial resolution. The
complexity of a release (for example, marked variation in its magnitude and characteristics such as its
height, thermal energy, and chemical form with time) adds further to the uncertainty. In addition, where
the source term had been estimated by reverse or inverse modelling, it was inextricably linked to anddependent on the measurement data, the meteorology and the ATDM used in its derivation; if different
meteorology or ATDM had been used with the measurement data, then the resulting source term
estimate could have been different. Strictly, therefore, source term estimates derived in this way would
be best used to estimate environmental levels by employing the same meteorology and ATDM used intheir derivation. If used with different meteorology and ATDM to predict concentrations ofradionuclides in the environment, the fit with measurements could have been less good (at least at thosemeasurement points used for the reverse or inverse modelling). The extent to which this matters inpractice is the subject of ongoing scientific discussion.

3.

Source term estimates

B11. Numerous estimates have been published of the release of radioactive material from FDNPS;
these are summarized in table B2 in terms of the total release of two of the more radiologicallyimportant radionuclides, 131I and 137Cs. For each case, the method used and the date the estimate wasmade and/or the date of its publication are indicated. The earliest estimates were made in late March
2011, even while the accident was still progressing. Others followed in the subsequent months, withmany being further refined over time as more information became available (relating to both thedevelopment of the accident and measurements in the environment), and as methods improved. Thissubject remains an active area for research and investigation and further improvements can be expected.

116

Strictly, the various estimates of total release are not all directly comparablea

Total releasea (PBq)
Reference

Date of publication

131

I

137

Approach used

Comments

Cs

IRSN [I31]

22 March 201190

10

Accident progression

Based on limited information while the accident was still progressing. Estimates related totime period 12 to 22 March 2011

ZAMG [Z3]22 March 2011

400

33

Reverse modelling

Based on limited information while the accident was still progressing. Estimates related to
first 4 days of accident (12 to 15 March 2011 inclusive)

NISA [N13]12 April 2011

130

6

Accident progression

Estimates made for purposes of INES assessment of accident severity

NISA [N14]6 June 2011

160

15

Accident progression

Estimates related to time period 12 to 18 March 2011

Chino et al. [C6]

July 2011

150

13

Reverse modelling

Estimates for the period 12 to 31 March 2011 only. Based on limited data available at thetime. Subsequently refined by Katata et al. [K1] and Terada et al. [T19]NISAb

16 February 2012

150

8

Accident progression

Included releases only over a limited period–

37

Inverse modelling

Based solely on CTBTO measurements in the northern hemisphere. Guided by a first estimatebased on assumptions on the total release from the three reactors and from the spent fuelpool of Unit 4, analysed the accident sequence using MELCOR and on-site measurements ofdose rate. Appeared to be an overestimate compared with most other estimatescStohl et al. [S11]

1 March 2012

Winiarek et al. [W15]

9 March 2012

190–380

12Inverse modelling

Obtained similar results when using inverse modelling with and without a first estimate(used an IRSN-estimated source term as the first estimate). Source term estimate limited toreleases that were partly or wholly dispersed over Japanese land mass

TEPCO [T13, T15]

24 May 2012

≈500

≈10

Reverse modelling

Based on dose rates measured by monitoring vehicles on site and considered most unlikely
to be an underestimate. Estimates related to time period 12 to 31 March 2011

Terada et al. [T19]19 June 2012

120

9

Reverse modelling

Further refinement of Chino et al. [C6] and Katata et al. [K1]. Releases over the ocean
estimated by interpolation of those over the land

Mathieu et al. [M6]

June 2012

197

20.6

Forward and reverse
modelling

Based on dose-rate measurements on- and off-site using IRSN codes. Source term estimate
limited to releases that were partly or wholly dispersed over Japanese land mass

Katata et al. [K1]

July 2012

130

11

Reverse modelling

Refinement of Chino et al. [C6] using more extensive monitoring data during the early stagesof the accident. The releases tabulated were the sums of the estimates made by Katata et al.
for the period up to 17 March 2011 and by Chino et al. for the period after 17 March. For theperiod up to 17 March, Katata et al. estimated releases of 131I and 137Cs of 44 and 3.9 PBq,
respectively

Hoshi and Hirano [H9]17 September 2012

250–340

7.3–13

Accident progression

Estimates relate to period 11 to 17 March 2011

UNSCEAR 2013 REPORT

Table B2. Source terms estimated for the FDNPS accident

Total releasea (PBq)
ReferenceaDate of publication

131

I

137

Approach used

Comments

Cs

Achim et al. [A2]

September 2012

400

10

Reverse modelling

Based solely on CTBTO measurements in the northern hemisphere. Release of 131I inparticulate form estimated to be 100 PBq. Estimate of total release was more uncertain andrelied on assumptions about gas–particulate conversion of iodine

Kobayashi et al. [K18]15 March 2013

200

13

Reverse modelling

Further refinement of Terada et al. [T19] to provide a better estimate (i.e. not interpolated) ofradionuclides dispersed directly over the ocean. Coupled atmospheric and oceanic
dispersion simulations with observed concentrations of 134Cs in the Pacific Ocean

Saunier et al. [S3]25 November 2013d

106

15.5

Inverse modelling

Used an original approach (using IRSN codes) to inverse modelling based solely on dose-rate
measurements from 57 monitoring stations in Japan. Source term estimate limited toreleases that were partly or wholly dispersed over Japanese land mass

The various estimates of total release are not all directly comparable. Many of the estimates of total release do not actually represent the total and, where appropriate, this is indicated in the comments column. Somethese releases were estimated by interpolating between estimates of releases that were obtained by simulating dispersion over the Japanese land mass (i.e. where environmental measurements were made); in others thecomponent of the total release that was dispersed wholly or partially over the Japanese land mass was simply not included in the total; and in one case, environmental measurements made on land were supplemented
with measurements made in ocean water in order to estimate the total release.
b

Quoted in [T13, T15].

c

Published online as a discussion paper on 20 October 2011.

d

Published online as a discussion paper on 12 June 2013.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

estimates were for releases over prescribed time periods. Estimates based on reverse or inverse modelling used different approaches in estimating the releases that were dispersed wholly over the ocean: in some cases

117

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UNSCEAR 2013 REPORT

B12. Given their inherent uncertainties and the fact that not all of the estimates were directlycomparable (that is, some early estimates covered only the first days after the accident, whereas others
integrated the release over a much longer period; and some represented the total release to theatmosphere, whereas others represented only that fraction that was partly or wholly dispersed over theJapanese land mass—see table B2), the various estimates of the releases of the two principal
radionuclides spanned relatively small ranges. For 131I the estimates ranged from about 100 to 500 PBq;
for 137Cs they ranged, in general, from about 6 to 20 PBq (albeit with some estimates based on more
limited information ranging up to 40 PBq). For perspective, the releases of 131I and 137Cs following theChernobyl accident were estimated at 1,760 and 85 PBq, respectively [U12], that is about factors of
10 and 5 times higher than the averages of the estimates given in table B2 for the FDNPS accident.
B13. Much greater variation was, however, apparent in the estimated temporal patterns of release andthis is exemplified in figure B-I for three of the published estimates. While all three show peaks in theestimated release rate of 137Cs corresponding to the main events occurring at the three reactors, thesepeaks were assessed to have occurred at different times, to have been of different durations, and to havediffered in magnitude at particular times by more than a factor of ten.
Figure B-I. Three estimates of the pattern of release rates of 137Cs over time [S3, S11, T19]

B14. The various estimates have differing strengths and weaknesses reflecting when they were madeand the methods used. In general, the Committee preferred those made later because they were often
refinements of earlier estimates and/or had benefited from additional information. Further, theCommittee preferred estimates derived using inverse or reverse modelling, as opposed to those fromanalyses of accident progression for three reasons: (a) the former are judged to be more reliable being
based on measurements of radioactive material in the environment; (b) the Committee acknowledged
the major reservations expressed in the report by the Fukushima Nuclear Accident Independent

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

119

Investigation Commission of the National Diet of Japan [N2] on the reliability of estimates based on
accident progression; and (c) estimates based on accident progression only covered a limited period of
the release.
B15. For its purposes, the Committee had to select a source term that was best able to provide a soundbasis for estimating levels of radioactive material in the environment where no measurements existed;these levels were an essential input to the subsequent estimation of doses (see chapter IV of the main
annex A, and appendix C). Estimates based on reverse or inverse modelling, as opposed to simulationof accident progression, were clearly preferable in this context consequent upon them having been
derived from, and optimized to fit, measurements of radioactive material in the environment. The
Committee chose to use the source term estimated by Terada et al. [T19] from among those derived on
the basis of reverse or inverse modelling. This was the last but one refinement in a series of estimates
made by a group of Japanese scientists at JAEA [C6, K1]. It was chosen in preference to the latest
refinement by Kobayashi et al. [K18] that took account of measurements of radioactive material in the
Pacific Ocean in addition to those over the Japanese land mass; by contrast, Terada et al. had estimatedthe magnitude of releases dispersed wholly over the ocean by interpolation between releases for whichmeasurements were available over the Japanese land mass. Adoption of the Kobayashi et al. source
term by the Committee would, however, have resulted in an overestimation of the levels of radioactive
material in the terrestrial environment, which would have been inconsistent with the Committee’s intent
of making a realistic assessment. The Committee did not consider the source term estimated by Saunieret al. [S3] because it had not yet been published at the time the choice was made; it was, however,subsequently used to test the robustness of a number of assumptions made regarding the use of thesource term of Terada et al. together with ATDM simulations for estimating levels of radionuclides inthe environment (see section III.E of this appendix).
B16. The releases of 131I and 137Cs estimated by Terada et al. lay within the ranges of published source
terms in table B2, albeit at the lower ends. While they provided a sound basis for estimating the levelsof radioactive material in the terrestrial environment where measurements did not exist, there wereindications that they may have been underestimates of the total amounts of these radionuclides released,
perhaps by a factor of up to about two because of assumptions made about the magnitude of releases
dispersed wholly over the ocean (see table B2). For its purposes, the Committee had to specify a source
term to provide a sound basis for estimating levels of radioactive material in the terrestrial environment
where no measurements existed. With one exception (that is, for evacuees during the early stages of theaccident), the levels of radionuclides in the environment estimated on the basis of the assumed source
term and its subsequent dispersion in the atmosphere were not used in any absolute sense; rather, they
were used in a relative sense to scale measured deposition densities of radionuclides on the ground toinfer concentrations of radionuclides in the air. When used in this relative way, the scaling (and theinferred concentration in air) is relatively insensitive to plausible choices of the source term (seesection E of this appendix).
B17. Terada et al. provided estimates of the releases of 131I and 137Cs as a function of time. These two
radionuclides, together with 134Cs, make by far the largest contribution to the dose received by the
population. A large number of other radionuclides would also have been released in the accident andsome were measured in the environment; but very few were released in sufficient amounts to contributesignificantly to doses. Those that could have contributed significantly were incorporated by theCommittee into the source term used, and comprised other isotopes of iodine and caesium, 132Te and133
Xe.
B18. The significance of very short-lived radionuclides was greatly reduced by the delay between
reactor shutdown and when the first release occurred (around 14 hours). The fractional release andsignificance of isotopes of elements such as strontium, barium and plutonium was much lower than

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those of iodine and caesium because of their much lower volatilities; this has been confirmed bymeasurements in the environment [N18] 32.
B19. The releases of other isotopes of iodine and caesium were estimated from those of 131I and 137Cs
by scaling with the ratio of their respective inventories in the three reactor units at shutdown and taking
account of radioactive decay before the time of any release. This approach was justified because thebehaviour of all isotopes of iodine (and likewise all isotopes of caesium) was the same within a given
reactor and its containment system; consequently, their fractional releases (relative to their inventories
at any given time) were identical. The ratios of other isotopes of iodine and caesium [N16] for each of
the three units at the time of shutdown and for the three units taken as a whole are shown in table B3.
The ratios differed slightly between the three units reflecting the different operating histories of thereactors; average values were assumed to apply throughout the release period when estimating thereleases of these other radioisotopes. The ratio of 133I to 131I, corrected for radioactive decay back to thetime of reactor shutdown (14:46 on 11 March 2011 JST), was derived from measurements of air
samples taken between 14 and 20 March 2011 at various locations in Japan and also by the CTBTO
network (figure B-II); the measured ratios are broadly in accord with the 133I/131I ratio averaged over theinventory of the three reactors. Iodine isotopes were assumed to be released in equal amounts inparticulate and gaseous/elemental forms notwithstanding the wide variation over time in their relative
components in measurements (contribution of particulates varying, in general, within a range of about
20% to 70%) [F7, O2]; 132I produced by radioactive decay of the parent radionuclide 132Te was,however, assumed to be in particulate form only (that is, the form assumed for its parent).
Table B3. Ratios of the quantities of other radionuclides to those of 131I or 137Cs in the three reactors
at time of shutdown (14:46 on 11 March 2011 JST) [N16]Radionuclide ratio

Reactor unit
132 131

I/ I

133 131

Unit 1

1.47

2.10

9.7

0.94

0.27

Unit 2

1.47

2.09

13.2

1.08

0.32

Unit 3

1.47

2.10

14.0

1.05

0.34

Average ratio (Units 1−3)

1.47

2.10

12.4

1.03

0.31

I/ I

132

Te/137Cs

134

Cs/137Cs

136

Cs/137Cs

B20. For releases of isotopes of tellurium, however, there was no a priori reason why they should havebeen directly correlated with those of caesium or iodine; the chemistry, physical characteristics andbehaviour in the reactors of these three elements were all different and would have influenced both thetiming and magnitudes of their releases. Measured concentrations of 132Te in air samples, relative tothose of 137Cs, are shown in figures B-III and B-IV. Figure B-III includes measurements made in Japan
at different times by various research institutes; measurements from other sources were also available
but showed greater variability in the ratio, raising some additional questions about their reliability.
Figure B-IV contains measurements from the CTBTO network (see attachment B–1 for details); theline through the data is the ratio of the respective inventories of 132Te and 137Cs (corrected forradioactive decay to the time of shutdown). The measured 132Te/137Cs ratios varied considerably withtime and space, typically from a value of a few to a few tens (corrected for radioactive decay to the time
32

This situation differs markedly from that of the Chernobyl accident; less volatile elements (for example strontium andplutonium) were released, in relatively larger amounts, directly to the atmosphere as a result of the initial explosion and physicaldestruction of parts of the core. Such mechanisms did not occur in the accident at FDNPS, where the volatility of the elements,
and the extent to which they were retained within the containment by other mechanisms (for example the suppression pool), were
the principal determinants of the amounts released.

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121

of shutdown). The data, however, were not sufficiently comprehensive or consistent to be used toestimate or model the time dependence of the release of 132Te. In the absence of such data, the releaseof 132Te relative to that of 137Cs was assumed to be fixed and determined from their respective
inventories in the three reactors at the time of shutdown, i.e. an average ratio of 12.4, as indicated intable B3. In broad terms this assumption was reasonable (see the comparisons between the lines anddata in figures B-III and B-IV); however, this led to under- and overestimates of the release of 132Te
during particular release episodes, which may have had implications for the contribution of thisradionuclide to estimated doses.
Figure B-II. Ratio of 133I to 131I in air samples taken between 14 and 20 March 2011 in Japan and by
the CTBTO network (corrected for radioactive decay to time of reactor shutdown, 14:46 on
11 March 2011 JST, see attachment B–1)
The dashed line corresponds to a ratio of 2.1, the average ratio of the respective inventories of the two isotopes in the threeunits at shutdown [K5, O2, T7]; see attachment B–1 for CTBTO data. For Takasaki pre-detection: the data from the CTBTO
station at Takasaki for the first 2 days when extraordinary preliminary signals were recorded; these data were considered to
be valid for checking radionuclide ratios only

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UNSCEAR 2013 REPORT

Figure B-III. Ratio of 132Te to 137Cs concentrations in air samples measured at various locations andtimes (JST) in JapanThe line represents how the ratio would vary as a function of time if the releases of 132Te and 137Cs had been in proportion totheir respective inventories in the three units [A9, F7, J6, K5, O2]

Figure B-IV. Comparison of measured concentrations of 132Te and 137Cs in air samples measured by
the CTBTO network (corrected for radioactive decay to the time of reactor shutdown, 14:46 on
11 March 2011 JST)See attachment B-1 for measurement data

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123

B21. For 133Xe, the temporal pattern of release estimated by the updated simulation of [H10] wasadopted together with the estimated inventory of this radionuclide in the three operating reactors takenfrom Nishihara et al. [N16]; this estimate was comparable with those of Le Petit et al. [L4] and Achim
et al. [A2]. The total release of each radionuclide in the source term adopted for the purposes of thisstudy is summarized in table B4; the time-dependent releases of the two most significant radionuclides,
131
I and 137Cs, are shown in figures B-I and B-XVI.
B22. While most of the radioactive material was released in the period up to 17 March, releases
continued for a considerable time thereafter. After the first week, the release rates gradually declined,
albeit with some fluctuations over more limited periods of time (see table B5 and figure B-I). By the
beginning of April, the rate of release had fallen to one thousandth or less of those during the first
week; these much lower release rates persisted for many weeks afterwards, but were insignificant
compared with what had gone before.
Table B4. Estimated total amounts of radiologically significant radionuclides released to atmosphere(based on [T19])
Total release to atmosphere (Bq)

Percentage of the inventory atreactor shutdown released (%)

2.85 × 1016

0.33

I

1.24 × 1017

2.1

132 a

16

0.32

I

15

9.56 × 10

0.07

Xe

7.32 × 1018

61

Cs

9.01 × 1015

1.3

136

Cs

15

1.77 × 10

0.81

137

Cs

8.83 × 1015

1.3Radionuclides
132

Te

131

I

133

133

134

a

2.85 × 10

Direct release of 132I was small compared to the ingrowth from radioactive decay of released 132Te.

124

Time period in 2011 (JST)

Release rate (Bq/h)
Duration (h)
132

131

132 a

I

133

4.0 × 1013

3.7 × 1013

4.0 × 1013

4.8 × 1013

6.6 × 1015

3.8 × 1012

1.1 × 1012

3.7 × 1012

6

1.7 × 1013

1.7 × 1013

1.7 × 1013

1.9 × 1013

7.6 × 1016

1.8 × 1012

5.1 × 1011

1.7 × 1012

12 March 16:00

0.5

3.0 × 1015

3.0 × 1015

3.0 × 1015

3.0 × 1015

1.2 × 1016

3.1 × 1014

8.9 × 1013

3.0 × 1014

12 March 16:00

13 March 23:00

31

7.3 × 1013

8.4 × 1013

7.3 × 1013

5.5 × 1013

1.2 × 1017

8.6 × 1012

2.4 × 1012

8.4 × 1012

12 March 23:00

14 March 11:00

12

2.6 × 1013

3.6 × 1013

2.6 × 1013

1.2 × 1013

5.8 × 1015

3.7 × 1012

9.8 × 1011

3.6 × 1012

14 March 11:00

14 March 11:30

0.5

2.0 × 1015

3.0 × 1015

2.0 × 1015

8.3 × 1014

6.4 × 1015

3.1 × 1014

8.1 × 1013

3.0 × 1014

14 March 11:30

14 March 21:30

10

1.5 × 1013

2.3 × 1013

1.5 × 1013

5.5 × 1012

6.1 × 1015

2.4 × 1012

6.1 × 1011

2.3 × 1012

14 March 21:30

15 March 00:00

2.5

7.9 × 1014

1.3 × 1015

7.9 × 1014

2.6 × 1014

6.6 × 1015

1.3 × 1014

3.4 × 1013

1.3 × 1014

15 March 00:00

15 March 07:00

7

2.3 × 1014

3.5 × 1014

2.3 × 1014

6.0 × 1013

1.1 × 1017

4.1 × 1013

1.0 × 1013

4.0 × 1013

15 March 07:00

15 March 10:00

3

1.7 × 1015

3.0 × 1015

1.7 × 1015

4.4 × 1014

1.9 × 1017

3.1 × 1014

7.7 × 1013

3.0 × 1014

15 March 10:00

15 March 13:00

3

4.3 × 1013

8.0 × 1013

4.3 × 1013

1.1 × 1013

1.1 × 1017

8.2 × 1012

2.0 × 1012

8.0 × 1012

15 March 13:00

15 March 17:00

4

2.1 × 1015

4.0 × 1015

2.1 × 1015

4.9 × 1014

2.1 × 1017

4.1 × 1014

1.1 × 1014

4.0 × 1014

15 March 17:00

17 March 06:00

37

1.3 × 1013

2.1 × 1014

1.3 × 1013

1.5 × 1013

1.3 × 1016

3.1 × 1012

7.3 × 1011

3.0 × 1012

17 March 06:00

19 March 15:00

57

2.9 × 1013

4.1 × 1014

2.9 × 1013

7.6 × 1012

1.0 × 1013

2.2 × 1012

1.0 × 1013

19 March 15:00

21 March 03:00

36

6.6 × 1013

3.8 × 1014

6.6 × 1013

1.7 × 1012

3.5 × 1013

6.8 × 1012

3.5 × 1013

21 March 03:00

21 March 21:00

18

2.1 × 1013

1.4 × 1014

2.1 × 1013

2.7 × 1011

1.4 × 1013

2.6 × 1012

1.4 × 1013

21 March 21:00

22 March 23:00

26

5.8 × 1012

4.1 × 1014

5.8 × 1012

4.1 × 1011

4.8 × 1012

8.3 × 1011

4.7 × 1012

22 March 23:00

24 March 00:00

25

8.7 × 1012

7.1 × 1014

8.7 × 1012

3.3 × 1011

9.0 × 1012

1.5 × 1012

8.9 × 1012

24 March 00:00

25 March 00:00

24

2.3 × 1012

1.9 × 1014

2.3 × 1012

4.3 × 1010

2.9 × 1012

4.6 × 1011

2.9 × 1012

25 March 00:00

26 March 11:00

35

7.5 × 1011

5.6 × 1013

7.5 × 1011

5.4 × 109

1.3 × 1012

1.9 × 1011

1.2 × 1012

26 March 11:00

28 March 10:00

47

7.3 × 1010

4.0 × 1012

7.3 × 1010

1.2 × 108

1.8 × 1011

2.4 × 1010

1.7 × 1011

28 March 10:00

29 March 21:00

35

1.4 × 1012

7.5 × 1012

1.4 × 1012

6.4 × 107

4.8 × 1012

5.8 × 1011

4.7 × 1012

29 March 21:00

30 March 11:00

14

2.1 × 1012

1.5 × 1013

2.1 × 1012

6.0 × 107

8.9 × 1012

1.0 × 1012

8.8 × 1012

30 March 11:00

31 March 00:00

13

2.9 × 1013

1.8 × 1014

2.9 × 1013

4.8 × 108

1.4 × 1014

1.6 × 1013

1.4 × 1014

Start

End

Te

12March 05:00

12 March 09:30

4.5

12 March 09:30

12 March 15:30

12 March 15:30

I

I

133

Xe

134

Cs

136

Cs

137

Cs

UNSCEAR 2013 REPORT

Table B5. Estimated release rates to atmosphere of potentially significant radionuclides (based on [T19])

Time period in 2011 (JST)

Release rate (Bq/h)
Duration (h)

Start

a

132

End

131

Te

132 a

I

11

133

I

13

133

I

11

Xe

7

134

136

Cs

137

Cs

12

Cs

11

31 March 00:00

31 March 22:00

228.0 × 10

2.4 × 10

8.0 × 10

3.9 × 10

4.6 × 10

5.0 × 10

4.5 × 1012

31 March 22:00

2 April 09:00

35

2.2 × 1011

1.8 × 1012

2.2 × 1011

1.3 × 106

1.7 × 1012

1.7 × 1011

1.6 × 1012

2 April 09:00

4 April 09:00

48

5.5 × 1010

1.8 × 1012

5.5 × 1010

3.9 × 105

5.9 × 1011

5.5 × 1010

5.8 × 1011

4 April 09:00

7 April 17:00

80

7.8 × 109

7.0 × 1011

7.8 × 109

2.6 × 104

1.4 × 1011

1.2 × 1010

1.4 × 1011

7 April 17:00

13 April 23:00

150

7.2 × 109

7.0 × 1011

7.2 × 109

1.4 × 103

3.5 × 1011

2.2 × 1010

3.5 × 1011

13 April 23:00

1 May 00:00

409

4.5 × 108

7.0 × 1011

4.5 × 108

6.2 × 100

1.7 × 1011

6.2 × 109

1.8 × 1011

Direct release rate of 132I is small compared to the ingrowth from radioactive decay of released 132Te.
ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...
125

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UNSCEAR 2013 REPORT

B. Releases to the ocean
B23. Radioactive material from FDNPS entered the marine environment directly and indirectly.


Direct release into the ocean was at least known to have resulted from leakage of highlycontaminated water from a trench outside Unit 2 (discovered on 2 April 2011), and thedeliberate discharge of weakly contaminated radioactive liquid waste from storage tanks; thelatter were emptied to create capacity for the storage of highly contaminated water remaining
in the trench (see section III below). Further releases occurred subsequently (for example in
May and December 2011) but, in general, these were insignificant compared with those that
occurred in the first month after the accident. In addition, groundwater, contaminated bynumerous sources of radioactive material on site (e.g. leaks from storage tanks, dispersal ofcontaminated reactor coolant, and deposition of radionuclides released to the atmosphere),
represents a continuing source of release to the ocean.

Radioactive material entered the ocean indirectly via two routes: (a) most importantly, fromthe deposition onto the ocean surface of material released to the atmosphere and dispersed over
the ocean; and (b) from run-off into rivers of material deposited over the land mass andtransported downstream into the ocean. This latter process would continue over an extended
period. Further releases could not be excluded in the future, either inadvertently (e.g. fromwater continuing to be released from the reactor buildings into groundwater) or as part of thewaste management strategy adopted in the remediation of the FDNPS site.

B24. At the end of 2013, releases of radionuclides to the marine environment continued to be reported[N19], apparently emanating from contaminated groundwater on the FDNPS site. Several tens of percent of the inventories of the more volatile elements (i.e. hydrogen/tritium, iodine and caesium) in the
cores of the three damaged reactors had been found in stagnant water, mainly in the basement of theturbine and reactor buildings but also in surrounding areas [N15]. Less volatile elements (e.g.
strontium, barium and lanthanum) had also been found but at levels that were between about a tenth toone hundredth of those for the more volatile elements in terms of their relative inventories. Monitoring
results published by the Nuclear Regulation Authority [N18] indicated that these continuing release
rates during 2013 were much lower than of the major releases that occurred in the immediate aftermathof the accident. Furthermore, measures were being taken to attempt to control them (e.g. the building ofa containment wall between the FDNPS site and the ocean). As at the end of 2013, it was consideredthat the ongoing releases were unlikely to significantly affect the Committee’s assessment of doses tothe public. However, continued monitoring and assessment of the implications of the releases were
warranted.
B25. Following the accident, numerous observations were carried out in the ocean in order to detect thepresence of radionuclides released from FDNPS and have continued ever since. The operator of thestation (TEPCO), the Japanese government agencies, and research laboratories from different countries(mainly Japan) collected and analysed numerous samples of water, suspended matter, sediment, andmarine organisms. These measurement data are described in detail in section IV below. They were usedby various authors to estimate the amounts of radionuclides released directly into the ocean. Theseestimates are summarized in table B6 together with estimates of the deposition on to the ocean surface
from material released to atmosphere.

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127

Table B6. Comparison of estimates of direct release to the ocean with those of deposition on theocean surface from the atmosphere
Source of estimate(Period considered in 2011)

Direct release to the ocean
(PBq)
131

137

TEPCO [T15](26 March–30 September)

11

3.6

Kawamura et al. [K3]
(12 March–30 April)

11a

4a

I

Tsumune et al. [T24](26 March–31 May)

3.5 ± 0.7

Bailly du Bois et al. [B2]
(26 March–18 July)

27 ± 15

Estournel et al. [E4]0.81b
4.1–4.5c
5.5 (upper bound)

Charette et al. [C4]

11–16

Kobayashi et al. [K18](12 March–1 May)
a

Cs

11

3.5d

Deposition on ocean surface from theatmosphere (PBq)
131

I

137

57

5

Cs

5.7–5.9(northern Pacific
Ocean)

99

7.6

21 March–30 April. b 1–6 April. c 12 March–30 June. d 26 March–30 June.

B26. Tsumune et al. [T24] indicated from an analysis of 131I/137Cs ratios that atmospheric inputs were
responsible for concentrations in seawater measured before 26 March 2011. Atmospheric inputs would
have been responsible for concentrations of 137Cs ranging from 100 to 1,000 Bq/L in the vicinity of
FDNPS, a few tens of becquerels per litre 10 km to the south and about 10 Bq/L at 30 km. It should be
noted that this is an approximation because atmospheric deposition was not isotropic around FDNPS.
The total amounts estimated by Kawamura et al. [K3] to have been deposited on the surface of thenorthern Pacific Ocean from the atmosphere were about 60 PBq and 5 PBq for 131I and 137Cs,
respectively. Estournel et al. [E4] estimated that about 6 PBq of 137Cs was deposited on the northern
Pacific Ocean; only a small percentage (about 5%) of this amount, however, was estimated to havebeen deposited within a radius of 80 km of FDNPS. Kobayashi et al. [K18] estimated the deposition of131
I and 137Cs to be about 99 PBq and 7.6 PBq, respectively; these estimates were derived from coupling
atmospheric and oceanic dispersion simulations with observed concentrations of 134Cs in seawatercollected from the Pacific Ocean.
B27. Several authors have used models of oceanic circulation and radionuclide dispersion in the ocean
to estimate the magnitude of direct releases of radionuclides into the ocean from FDNPS. Kawamura etal. [K3] used the information published by TEPCO of the leak detected from 1 to 6 April 2011 to
estimate this to be 4 PBq of 137Cs and 11 PBq of 131I. Tsumune et al. [T24] adjusted the release of 137Cs
in their model so that their estimate of average concentration between 26 March and 6 April fitted theaverage concentration measured at the southern outlet of FDNPS. This method resulted in a source term
estimate of 3.5 ± 0.7 PBq of 137Cs. The modelling work of Dietze and Kriest [D3] supported a source
term in the range 1-4 PBq, rather than the much higher estimate reported in Bailly du Bois et al. [B2];according to the analysis of Diest and Kriest [D3], the methodology used by Bailly du Bois et al. [B2]produced estimates of early releases (to mid-April) which were biased high and later releases (midApril to July) which were biased low, and therefore total estimates from extrapolating backwards intime would be too high. Estournel et al. [E4] used a model with a relatively high resolution near the
FDNPS site (600 m). The release of 137Cs was calculated daily using an inverse method, constrained by

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UNSCEAR 2013 REPORT

fitting to the observed concentrations at the two outlets of the plant. The total 137Cs release to the ocean
was estimated to be around 4.1–4.5 PBq. Estournel et al. adjusted this to a maximum value of 5.5 PBq
to account for the observed increase in concentration 30 km offshore in mid-April, which had not been
reproduced by the dispersion model (see section IV below). Charette et al. [C4] extrapolated theinventory of 134Cs in the ocean from June 2011 back to early April, the period of the peak release. They
thus estimated a value of 11 PBq for the direct release of 134Cs, and that of 137Cs could be assumed to be
the same.
B28. Both Kawamura et al. [K3] and Estournel et al. [E4] estimated the time distribution of the releases
to the ocean, and both showed a similar pattern that indicated direct releases to the ocean dominatedover inputs from deposition of radionuclides released to atmosphere from around the end of March2011 onwards. The release rates of 137Cs as estimated by Estournel et al. [E4] are shown in figure B-V;
they estimated that about 99% of the total direct release to ocean occurred before 22 April 2011.
Measurements of radionuclide concentrations in seawater were not available before 21 March. The
estimations by Estournel et al. for the period 11 March to 30 June assumed that concentrations inseawater before 21/23 March were the same as the first measured values.
Figure B-V. Estimated daily release of 137Cs into the ocean [E4]
(Red: deposition from the atmosphere on to the ocean surface integrated over the whole modelling domain; blue: direct
release calculated by inverse method)

B29. Other radionuclides were also released to the ocean, both directly and indirectly. Isotopes ofstrontium and plutonium have been measured in seawater and sediments. Povinec et al. [P12] studied
the measurements of concentrations of 89Sr and 90Sr in seawater. These generally showed strontium
concentrations during the main period of the direct release to be one to two orders of magnitude lower
than those of caesium. There was an exception to this general pattern around December 2011, when,
following an accidental leakage of treated water from which caesium had been removed, measured
concentrations of 89Sr and 90Sr, but not 137Cs, rose [P12]. The concentrations of 90Sr had fallen below
those of 137Cs again by January 2012. On the basis of different assumptions about the ratios of 90Sr to137
Cs and the range of estimates of total direct release of 137Cs to the ocean, Povinec et al. estimated a

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129

direct release of 90Sr of between 0.04 PBq and 6.5 PBq (although the latter was based on the highestimated release of 137Cs of 27 PBq by Bailly du Bois et al. [B2]).
B30. All of the estimates of releases to the ocean were associated with much uncertainty. In reviewing
these estimates, the Committee gave more weight to results based on three-dimensional modelling
taking into account the high variability of the dispersion, rather than to those derived with extrapolation
methods using constant dispersion rates. It concluded that the direct release to the ocean of 137Cs was
likely to have been in the range of about 3–6 PBq, with the direct release of 131I likely to be about threetimes higher. The direct release of 90Sr could be estimated to be in the range of about 0.04–1 PBq(based on ratios to the 137Cs release). The estimated direct releases of 137Cs (about 3-6 PBq) were of asimilar order of magnitude to the estimated deposition on to the ocean from releases to the atmosphere(about 5–8 PBq). For 131I, deposition on to the ocean from releases to atmosphere (about 60–100 PBq)
was estimated to be about 5–10 times higher than the direct releases. However, because the inputs from
deposition on to the ocean surface provided a diffuse source, whereas the direct releases were from a
localized source, direct releases accounted for most of the observed elevated concentrations in seawateraround FDNPS from 26 March onwards. The dispersion of radionuclides deposited from theatmosphere and released directly to the ocean is considered further in section IV below.

III. TRANSPORT AND DISPERSION IN THE ATMOSPHERE

A. Meteorological conditions
B31. The meteorological conditions observed during the key episodes in the release of radioactive
material to the atmosphere have been described by many authors [K15, K20, M25, S11, S12, W16].
From 9 to 11 March 2011, a weak low pressure trough over eastern Japan caused the appearance oflight rain until 12 March in the morning (JST). Then, a high pressure system moved eastward along thesouth coast of the main island from 12 to 13 March; the wind direction was from the south below 1 km,
and from the west above 1 km in altitude in the afternoon of 12 March, at the time when the hydrogen
explosion occurred in Unit 1. During the period 14 to 15 March, another weak low pressure troughmoved eastward off the southern coast of the main island, then moved toward the north-east whiledeveloping rapidly after 15 March. Some light rain was observed from 15 to 17 March in the morning
because of a weak low pressure system that moved north-eastward off the east coast. In particular, rain
was observed in Fukushima Prefecture during the night, from 15 March at 17:00 to 16 March at 04:00[K15], a time corresponding with significant releases of radioactive material to the atmosphere. The
low-level winds were from the south-west during the morning of 14 March, the time when a hydrogen
explosion occurred at Unit 3. The 950 hPa winds were from the west until 14 March, but changed to a
direction from north-north-east in the morning of 15 March, the time when significant releases occurredfrom Unit 2. During the period 18 to 19 March, a high pressure system dominated and winds weregenerally blowing from the west. A low pressure system was then observed passing over the mainisland from 20 to 22 March with moderate rain until 23 March in the Kanto area (Ibaraki, Chiba,
Tochigi, Saitama and in Tokyo).

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B. Synthesis of observations
B32. Dose-rate measurements provided a useful basis for estimating the source term by inverse or
reverse modelling (see section II.A above); furthermore, they provided a valuable basis for assessing
the quality of estimates made by atmospheric transport models of the dispersion of released material.
Most of the measured dose rates came from portable monitoring posts deployed by Fukushima
Prefecture during the accident. This was because many of the automatic monitoring posts in theprefecture did not operate during much of the period when the largest release occurred because ofdamage caused by the earthquake and tsunami. MEXT also published extensive dose-rate
measurements made in each prefecture [N18], and particularly in Fukushima Prefecture.
B33. There were also some automatic stations recording dose rates continuously during the course of
the accident. The spatial distribution of dose-rate stations in the vicinity of FDNPS is shown infigure B-VI.
Figure B-VI. Spatial distribution of dose-rate stations in the vicinity of FDNPS [F5]B34. Dose-rate measurements made at three locations, namely Fukushima, Minamisoma andKitaibaraki, are shown in figure B-VII.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Figure B-VII. Dose-rate measurements at Fukushima, Minamisoma and Kitaibaraki [F4, I8]

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UNSCEAR 2013 REPORT

B35. In comparison, very few extended or continuous measurements in Japan were made, or have been
published, of the concentration of radionuclides in air during the release period 33 . The few
measurements of particular interest, because they spanned the whole period of major releases,
comprised the following:Tokyo–Setagaya, located 250 km south-south-west of FDNPS;



Tsukuba (Ibaraki Prefecture), located about 170 km from FDNPS in the direction of Tokyo;

Takasaki (Gunma Prefecture) located 250 km south-west of FDNPS;

Tokai-mura (JAEA office) located 100 km south-south-west of FDNPS.

The monitoring stations at Tokyo, Tsukuba, Takasaki and Tokai-mura were, however, all located in the
Kanto area; consequently, their measurements were largely redundant; the exception is Takasaki where
measurements were also made of the concentrations in air of noble gases.
B36. However, numerous and extensive measurements of the deposition densities of radionuclides
were made. The United States Department of Energy measured deposition densities from aerial
monitoring with fixed-wing aircraft from 17 March 2011 [U17] and ground measurements (in situ
gamma spectrometry). MEXT subsequently, from June 2011, carried out a major campaign of aerial(helicopter) and ground measurements to cover the whole of the affected territory [N18]. The
deposition density of 137Cs on the ground surface is shown in figure B-VIII [N18].
33

Outside of Japan, numerous measurements were made of concentrations of radionuclides in air when the released material
passed overhead; these were used by many countries to assess doses to the public (see appendix C).

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Figure B-VIII. Measurement results of the airborne monitoring surveys conducted by MEXT
(deposition density of 137Cs) [N18]

133

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UNSCEAR 2013 REPORTC. Atmospheric dispersion pattern
B37. Several events during the course of the accident led to major releases of radionuclides to theatmosphere (see table B1). Four periods were of particular interest in this respect.
B38. Venting and the hydrogen explosions in Units 1 and 3, during the period 12 to 14 March, were theorigins of the initial and substantive releases of radioactive material to the atmosphere. The material
released from Unit 1 spread mainly northwards along the eastern coast of the main island, then towards
the north-east and east over the Pacific Ocean. This release was only detected by the Minamisoma
station (see figure B-VI), located on the coast, about 25 km from FDNPS. No rainfall was recorded
during this release episode. An increase in the dose rate during the night of 12 March was evident at the
Minamisoma station (see figure B-VII) followed by a rapid decrease; this was characteristic of thepassage of a radioactive plume in dry conditions. Simulations from one of the ATDMs used by a task
team of the World Meteorological Organization (WMO) (see next section) of the 131I concentration in
air on 12 and 13 March, following the releases from Unit 1 and then Unit 3, are illustrated infigure B-IX. Owing to westerly winds, this plume travelled mostly towards the Pacific Ocean and had
limited impact on the Japanese land mass.
B39. The material released from Unit 2 over the period 15 to 16 March was mainly due to the meltingof the core and a breach of the reactor containment; this material was dispersed over eastern Japanbecause of rapidly changing weather conditions. This release episode could be better characterized thanmany others because it was monitored by many stations. It was the major contributor to the depositionof radioactive material on the Japanese land mass. The release took place in two quite distinct periods:
firstly, during the night of 14 to 15 March; and, secondly, in the late morning and early afternoon of
15 March. From 00:00 to 05:00 JST on 15 March, the released material moved towards the south
without encountering rain. An increase in the dose rate during the morning of 15 March was evident at
the Kitaibaraki monitoring station (see figure B-VII). Radioactive material continued to be released
throughout the rest of the day; this material moved towards the south then progressively towards thenorth-west and then to the south again on 16 March; these changes were reflected in the dose rates
measured at the Kitaibaraki monitoring station (see figure B-VII) where two increases in the dose rate
were recorded during 16 March. After 17:00 on 15 March, rainfall occurred until early morning of
16 March and this resulted in major deposition of radioactive material onto the ground; this wasreflected in the large increase in the dose rate observed during the evening of 15 March at Fukushima(see figure B-VII). The relatively slow decrease in the dose rate at Fukushima is characteristic ofradioactive material passing over a monitoring station in wet conditions (i.e. rainfall); the radionuclides
deposited onto the ground by rain contribute to the dose rates measured by the monitoring station.
Figure B-X shows simulations of the 131I concentration in air at two times following the major releases
that occurred from Unit 2; the simulated concentrations also include contributions due to continuing
releases from Units 1 and 3.
B40. From the afternoon of 16 March onwards, subsequent releases, mainly from Units 2 and 3, spreadeasterly over the Pacific Ocean without any major impact for the Japanese territory. The simulated 131I
concentration in air during these releases is shown in figure B-XI.
B41. During the period from 20 to 23 March, releases from the three units were dispersed over theJapanese territory encountering rainfall on occasions. The simulated 131I concentrations in air at
particular times following these further releases from Units 1–3 are shown in figure B-XII.
B42. From 23 March, the release rates fell significantly and, compared with earlier releases, had
minimal impact on the Japanese territory. The chronological patterns of atmospheric dispersion are seen
as animations in attachments B-2 to B-3.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Figure B-IX. Simulated 131I concentration in air during the initial releases from Units 1 and 3

Figure B-X. Simulated 131I concentration in air following the major releases from Unit 2 to theatmosphere

135

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UNSCEAR 2013 REPORT

Figure B-XI. Simulated air concentration of 131I during subsequent releases from FDNPS

Figure B-XII. Simulated 131I concentration in air during the releases from FDNPS in the period
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137

D. Methodology and results of dispersion and depositionassessment
B43. The World Meteorological Organization (WMO) organized a task team to advise the Committee
on the use of meteorological analyses and data in estimating concentrations of released radionuclides inthe terrestrial environment using atmospheric transport and dispersion models (ATDM). The task teamapproached this by applying the meteorological data to ATDMs and comparing the results with theavailable measurement data. The task team consisted of participants from the Canadian MeteorologicalCentre (CMC), the United States National Oceanic and Atmospheric Administration (NOAA), theUnited Kingdom Met Office (UKMET), the Japan Meteorological Agency (JMA), and the Austrian
Zentralanstalt für Meteorologie und Geodynamik (ZAMG). Each of these participants used their
institute’s own models, each with its unique treatment of the meteorological input data, dispersion, anddeposition computations. Each participant also used the computed fields derived from meteorological
data analysis that were already available to them, as well as the higher spatial and temporal resolution
fields provided by JMA. The results provided a range of solutions because of variations in model
parameterizations and the meteorological analysis data. Further information on the meteorologicalanalyses and the models can be found in the task team’s final report [W18].
B44. Dispersion and deposition calculations for a unit source using each model–meteorology
combination were made available on a website [N17] for three generic species of material: (a) a gas
with no wet or dry scavenging (to represent noble gases such as 133Xe); (b) a gas with a relatively large
dry deposition velocity (0.01 m/s) and wet removal (to represent released iodine in a gaseous form);and (c) a particle with wet removal and a small dry deposition velocity (0.001 m/s) (to represent allother released radionuclides, including iodine in a particulate form). These could be used to estimate
concentrations in air and deposition densities of radionuclides on the ground for any postulated source
term subject to specifying the time dependence of release rates for each released radionuclide.
B45. In order to evaluate the performance of the various ATDM–meteorology combinations, the WMO
task team used a provisional source term estimate that had been developed prior to the Committee
making a formal choice on what to use for its dose assessment. The provisional source term differed ina number of respects from that finally adopted by the Committee, but was sufficiently similar not toprejudice the main findings relating to the performance of different ATDM–meteorology
combinations 34. The results for each ATDM–meteorology combination can be found in [W18] where
they were compared with the measurements of deposition densities of radionuclides and the more
limited measurements of concentrations in the air. The outcome of the evaluation was inconclusive withrespect to which ATDM–meteorology combination provided the best fit to the measured deposition
densities and concentrations of radionuclides in air: the best fit for deposition density was not the sameas that for concentration in air. To obtain better fits, the mean of the ten most representative ATDM–
meteorology combinations was computed and compared with the measurement data. Statistical analysis
showed that this “ensemble mean” provided a better fit than any individual ATDM–meteorology
combination for both deposition density and radionuclide concentration in air. The performance ofsome ATDM–meteorology combinations was, however, not dissimilar to that of the ensemble mean
[W18].
B46. In estimating the dispersion and deposition of radioactive material released from FDNPS, anumber of simplifying assumptions had to be made to configure the ATDM simulations. Most of these34
Since this work was completed, task team members carried out further analyses using the Terada et al. source term [T19] (thatis the source term adopted by the Committee for its assessment). The performance of the various ATDM–meteorology
combinations for this source can be found in [D4].

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UNSCEAR 2013 REPORT

concerned the characteristics of the source term as estimated by Terada et al. [T19] and were made as acompromise to accommodate the following potentially conflicting demands: (a) faithfully representing
the varying radionuclide release rates; (b) the spatial and temporal resolution of the available
meteorological data; and (c) the computational time and storage requirements of the subsequent
simulations made using the ATDM in the WMO work. The main simplifications were the following:(a) release rates were specified in three-hourly time intervals as opposed to the finer resolution given by
Terada et al. [T19] for particular release periods; (b) all releases were assumed to occur from, and be
uniformly distributed over, a column from the ground to a height of 100 m, rather than characterizing
the specific events leading to the releases (for example, hydrogen explosions and venting).
B47. For the assessment of exposures in the non-evacuated areas, the ATDM results were used toestimate the concentrations of radionuclides in air from measured deposition densities on the ground byscaling the measured deposition densities by the ratio of the concentration in air and deposition density
estimated by one or other ATDM–meteorology combination. Despite the better performance of theensemble mean (in terms of estimating measured levels in the terrestrial environment), the use of asingle ATDM was judged to be more appropriate for most of the Committee’s purposes.
B48. Estimates of the “bulk deposition velocity” for 137Cs at selected locations (that is the ratio of thedeposition density to the time integral of concentration in air) are given in table B7 for five of the best
performing ATDM–meteorology combinations of the ten combinations that constituted the ensemble
mean. The values for a given location varied within a range of about three to ten but, typically, by about
five. This variability provided an indication of the uncertainty associated with inferring concentrations
in air (and thus internal exposures via inhalation) from measured deposition densities. In general, thecontribution of inhalation to the total exposure from all pathways was small; consequently, variabilityof the magnitude indicated above was unlikely to have had much impact on the overall precision of
estimated doses.
Table B7. Comparison of “bulk deposition velocities” for 137Cs estimated by different ATDM–
meteorology combinations for selected locations
Bulk deposition velocity (mm/s) for 137Csa
Location/ModelNOAAGDASbUKMETMESOc

UKMETECMWFd

NOAAECMWFZAMGECMWF

AverageOkuma Towne

6.2

3.3

3.2

3.4

1.2

3.4

Iwaki City

6.8

3.2

6.1

7.6

8.8

6.4

Fukushima City

91

160

71

66

340

140

Iitate Villagee

48

52

250

200

130

140

e

48

24

240

87

80

97

Namie Towna

The bulk deposition velocity is the ratio of the estimated deposition density on the ground and the estimated integrated

radionuclide concentration in air; it was used to infer integrated concentrations in air from deposition density measurements for
estimating internal exposures from inhalation of radioactive material (see appendix C).
b

GDAS – Global Data Assimilation Systemc

MESO – Mesoscale Analysis provided by the Japan Meteorological Agency (JMA).

d

ECMWF – European Centre for Medium range Weather Forecasting.

eBulk deposition velocities were not used for assessing exposures in evacuated areas (Okuma Town, Namie Town and Iitate

Village were all evacuated).

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139

B49. Given this limited sensitivity, the choice of which ATDM–meteorology combination to use had
limited practical significance for the Committee’s assessment of doses. The Committee chose the
NOAA-GDAS ATDM–meteorology combination for the purposes of estimating ratios; this model was
one of the higher ranked combinations 35, indeed even more highly ranked than the ensemble mean fordeposition of 137Cs. Compared with the average ratios of the five combinations at particular locations,the use of the NOAA-GDAS combination led to inferred concentrations in air that were typically withina factor of two lower or higher.
B50. The 137Cs deposition pattern computed by NOAA-GDAS (figure B-XIII) was compared with themeasured deposition pattern. The modelling results reproduced the observed deposition pattern quite
well. The NOAA-GDAS calculations of the concentrations in air were compared to measured
concentrations in air at the JAEA sampling site [F7, O2] (figure B-XIV); the comparison was not as
good, capturing only three of the four main peaks and estimating the size of the peaks only within abouta factor of ten. While the modelling results were able to capture the general pattern of radionuclide
concentrations in the environment spatially and temporally, their ability to reproduce deposition density
or concentration in air accurately at any particular time or location may have had considerable
uncertainty; this is illustrated in figure B-XV where the NOAA-GDAS predictions are compared withthe corresponding measurement of 137Cs deposition density. The predictions showed little bias
compared to the measured deposition densities. However, the uncertainty for specific locations varied
by more than a factor of ten for the lowest deposition densities, but fell with higher deposition densities;
at the highest deposition densities, the model predictions underestimated those measured by a small
factor.
B51. The results of the ATDM simulations were used in a different way for estimating theconcentrations in air and deposition densities of radionuclides to which the early evacuees were
exposed. No data were available on the measured deposition densities before or during the evacuations;consequently, the method for estimating concentrations of radionuclides in air from deposition density
measurements and a ratio derived from ATDM simulations could not be used. Instead, the timedependent radionuclide concentrations in air and deposition densities estimated by the ATDM
simulations were used directly. For reasons of consistency with the estimation of radionuclide
concentrations in air for non-evacuees from the measured deposition densities, the NOAA-GDAS
combination was also used here for estimating concentrations in air (and deposition densities) to which
the early evacuees were assumed to be exposed. Given the inherent uncertainties in the estimates ofthese models for any given location, the choice of the NOAA-GDAS combination (relative to any other
ATDM–meteorology combination or an average of several) was unlikely to be of great practicalsignificance (see section E).
35
Ranked in terms of a complex statistical measure related to how well a model was able to replicate measured levels in theenvironment (see [W18]).

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UNSCEAR 2013 REPORT

Figure B-XIII. The calculated 137Cs deposition density using the NOAA-GDAS combination
The contours show the terrain elevation at 250 m intervals

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141

Figure B-XIV. The calculated 137Cs concentrations in air (red +) using the NOAA-GDAS combinationand measured data at Tokaimura, Ibaraki, Japan (black o) [F7, O2]

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UNSCEAR 2013 REPORT

Figure B-XV. Scatter plot comparing NOAA-GDAS estimates and measurements of 137Cs deposition
density

E. Robustness of estimation of radionuclide levels in theenvironment where no measurements are available
B52. The ATDM estimates of the concentrations of radionuclides in air and deposition densities on the
ground were associated with much uncertainty resulting from uncertainties in the source term and how
material was dispersed in and deposited from the atmosphere. A rigorous analysis of these uncertainties
was beyond the scope of this assessment. However, indications of the robustness of the estimates madein this assessment were made by conducting more limited scoping studies.
B53. For this purpose, separate estimates were made, using an independently derived and applied
source term–ATDM–meteorology combination (that was not part of the WMO group), of the main
quantities used to calculate doses to people; these quantities were time integrals (total and truncated) ofconcentrations of radionuclides in air and their deposition density on the ground, and ratios of these twoquantities used to infer concentrations in air from measured deposition densities.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

143

B54. The NOAA-GDAS ATDM results were compared with an IRSN ATDM–meteorology
combination, namely an IRSN–ECMWF model using the source term of Saunier et al. [S3], which wasderived using a different methodological approach, and measurements that were largely independent
from those used by Terada et al. [T19] (the source term adopted by the Committee). The main featuresof, or assumptions adopted in, the two source term–ATDM–meteorology combinations are summarizedin table B8. A comparison of the two source terms is also provided in figure B-XVI, where the timedependent releases of 131I are shown. A comparison of the time-dependent releases of 137Cs is given in
figure B-I, at least for the first few days when the releases were largest. Much greater temporal
resolution was apparent in the Saunier et al. source term estimate consequent upon it being derived
from numerous measurements of dose rate that were, in general, continuous throughout the release
period.
Table B8. Comparison of the main features and assumptions in the two source term–ATDM–
meteorology combinations
Characteristics of the source
term–ATDM–meteorology
combinations
Source term

Basis ofderivation

Terada–NOAA-GDAS

Saunier–IRSN-ECMWF

Reverse modelling of environmental
measurements (concentrations in air,deposition densities, dust samples, dose
rates)

Inverse modelling of generally
continuous dose-rate measurementsfrom 57 monitoring stations in Japan

Total releases: 131I, 120 PBq;
137
Cs, 8.8 PBq

Meteorology

Atmosphericdispersion
anddeposition

Total releases: 131I, 103 PBq;
137
Cs, 16 PBq

Releaseheights

Assumed spread uniformly over acolumn from ground to height 100 m

Assumed spread uniformly over acolumn from ground to height 160 m

Form ofreleaseAll nuclides released as particulates
apart from noble gases, and iodine(assumed half released as particulate
and half as elemental gaseous iodine)

Apart from noble gases, all nuclides
released as particulates

SourceNOAA global analysis [W18]

ECMWF [W18]Timeresolution

3 hourly

HourlySpatialresolution

0.5° latitude and longitude

0.125° latitude and longitude

Verticalresolution

56 layers; 10 within the lowest 1 km

11 layers between 0 and 3 400 m

ATDM model

HYSPLIT [D5]IdX [S3]−3

Dry
deposition

Particulates 10 m/s

Wet
deposition

Particulates in-cloud 4 × 104 L/L

Particulates 2 × 10−3 m/s

Elemental iodine 10−2 m/s

Particulates below-cloud 5 × 10−6 s−1
Gaseous iodine 0.08 M/a solubility[D6]

5 × 10−5p0
where p0 is the precipitation rate
(mm/h)

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UNSCEAR 2013 REPORT

Figure B-XVI. Comparison of the time-dependent releases of 131I estimated by Terada et al. [T19] andSaunier et al. [S3](a) Period of 12 to 17 March 2011(b) Period 17 to 27 March 2011 (Note: different vertical scale to that used in (a))

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

145

B55. Table B9 shows the “bulk deposition velocities” estimated by the Terada–NOAA-GDAS
combination and the Saunier–IRSN-ECMWF combination (referred to as “NOAA” and “IRSN” in thetable) at selected locations for 131I and 137Cs. In addition, the ratio of the IRSN and NOAA ratios arealso shown to indicate by how much the estimated concentrations in air (and thus the doses frominhalation) would have been different had the IRSN combination been used instead of the NOAA
combination.
Table B9. Comparison of “bulk deposition velocities” for 131I and 137Cs estimated by different source
term–ATDM–meteorology combinations for selected locations
131

Location/Model

NOAA (mm/s)

137

I

IRSN (mm/s)

Ratio
IRSN to NOAANOAA (mm/s)

Cs

IRSN (mm/s)

Ratio
IRSN to NOAA

48

28

0.58

DELIBERATE EVACUATION AREA
Iitate Village

28

42

1.5

NON-EVACUATED LOCATIONS
Iwaki City

8.5

5.6

0.65

6.8

4.9

0.71

Fukushima City

34

150

4.4

91

95

1.1

Note: The bulk deposition velocity is the ratio of radionuclide deposition density to the integrated concentration in air used toinfer concentrations in air from measured deposition densities on the ground and thus estimate internal exposure from inhalationof radioactive material.

B56. For 137Cs, the bulk deposition velocities estimated by the IRSN combination were, on average,
about 20% lower than those estimated by the NOAA; at specific locations, they ranged from about 10%
higher to a factor of about 1.5 lower, depending on the location. For the same value of measured
deposition density, these differences would have translated into inferred concentrations in air (and thus
doses from inhalation for the non-evacuated areas) ranging from about 10% lower to about a factor of
1.5 higher, depending on the location, compared with those estimated by the Committee using the
NOAA combination.
B57. For 131I, the bulk deposition velocities estimated by the IRSN combination ranged from about afactor of about 4 higher to a factor of about 30% lower—depending on the location—than thoseestimated by NOAA. These differences would have translated into inferred concentrations in air (andthus doses due to inhalation for the non-evacuated areas) ranging from about a factor of 30% higher toabout a factor of 4 lower, depending on the location; on average, they would have been about 40%
lower compared with those estimated by the Committee using the NOAA combination.
B58. The time integrals (truncated to when evacuation occurred) of the concentrations of 131I in air anddeposition densities estimated by the NOAA and the IRSN combinations are shown in table B10 at 14
selected locations and times relevant to the estimation of doses to early evacuees. The ratios oftruncated concentrations in air estimated by the IRSN and NOAA combinations (and likewise the ratiosof their respective estimates of deposition densities) are also shown in the table; the variation in theseratios was much greater than in the ratios of the two quantities (i.e. ratios of concentration in air anddeposition density, see table B9).
B59. For 9 of the 14 locations, the IRSN estimates for 131I concentration in air were within a factor of
two of those for NOAA, and, for most locations, the ratios varied between about 0.5 and 12 (ignoring
the value of zero for Futaba Town and 2,100 for Minamisoma City). For deposition, the IRSN estimates

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UNSCEAR 2013 REPORT

were within a factor of two of those for NOAA for 6 out of 14 locations, and for most locations (13 outof 14) the ratios varied between about 0.2 and 8 (ignoring the value of zero for Futaba Town). Thislevel of variability was not unexpected and was typical of the uncertainty associated with the use of
ATDM–meteorology combinations to estimate concentrations in air and deposition densities at specificlocations; this variability was further compounded by the use of different source terms in the two cases.
The implications of this variability for the estimation of doses to evacuees are further addressed inappendix C.

Table B10. Comparison of the time-integrated concentration of 131I in air and deposition density estimated by two combinations of source term, ATDM and meteorology
Location

Time period
From

NOAA
To

Time-integrated
concentration in air

IRSN
Deposition
density (Bq/m2)(Bq s/m3)

Time-integrated
concentration in air

Ratios (IRSN/NOAA)
Deposition
density (Bq/m2)

Time-integrated
concentration in air

Deposition density(Bq s/m3)

2011-03-12 11:00

2011-03-16 08:00

3.4 × 107

4.1 × 105

4.0 × 108

2.9 × 10611

7.0

Okuma Town

2011-03-11 21:23

2011-03-12 04:00

0

0

0

0

1

1

Kawamata
elementary
school

2011-03-12 08:00

2011-03-19 08:00

6.8 × 107

2.2 × 106

7.5 × 107

2.7 × 106

1.1

1.2

Futaba Town

2011-03-11 21:23

2011-03-12 21:00

8.4 × 107

5.6 × 105

0

0

0

0

Kawamata
elementary
school

2011-03-12 21:00

2011-03-19 17:00

6.8 × 107

2.2 × 106

7.5 × 107

2.7 × 106

1.1

1.2

Iwaki City

2011-03-12 13:00

2011-03-31 12:00

2.9 × 108

2.5 × 106

1.5 × 108

8.1 × 105

0.51

0.33

Iwaki City

2011-03-12 13:00

2011-03-16 15:00

2.2 × 108

1.2 × 106

1.1 × 108

2.5 × 105

0.50

0.21

8

6

6.8 × 108

1.7 × 106

3.1 × 10

0.75

0.46

Namie Town
Tsushima
activation centre

2011-03-12 15:00

2011-03-16 10:00

2.2 × 10

Tamura City,
Denso
Higashinihon

2011-03-12 08:00

2011-03-31 08:00

9.4 × 106

3.6 × 105

9.4 × 107

2.5 × 10610

6.9

Minamisoma City

2011-03-11 00:00

2011-03-15 10:00

1.3 × 105

9.3 × 105

2.7 × 108

5.7 × 105

2100

0.61

Date City office

2011-03-15 16:00

2011-03-31 11:00

1.8 × 107

3.1 × 105

1.9 × 107

2.1 × 106

1.1

6.8

Kawauchi Muraelementary
school

2011-03-13 11:00

2011-03-16 10:00

3.3 × 107

4.0 × 105

3.9 × 108

3.1 × 106

12

7.9

Namie Town
Tsushima
activation centre

2011-03-11 00:00

2011-03-23 14:00

2.8 × 108

7.4 × 106

1.8 × 108

3.9 × 106

0.64

0.53

Katsurao Village

2011-03-11 00:00

2011-03-21 12:00

2.4 × 108

5.5 × 106

2.4 × 108

4.0 × 106

0.99

0.74

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Kawauchi Village

147

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UNSCEAR 2013 REPORT

IV. TRANSPORT AND DISPERSION IN THE OCEAN

A. Synthesis of observations(a) In the water column
B60. Numerous observations of radionuclides were made in the northern Pacific Ocean over a wide
range of distances from FDNPS, beginning one week after the accident [B25, H7, M11, T6].
Measurements were also made in the Sea of Japan to assess the radionuclide concentrations on thewestern side of the archipelago. These data provided a relatively good understanding of the spatial andtemporal distribution in the ocean of 137Cs and 134Cs, the most radiologically significant radionuclides
released.
B61. Isotopes of other elements were also measured, including: 131I, which was measured at elevatedconcentrations but only over a limited time because of its relatively short half-life of 8 days; 129I, which
was detected near the Japanese coast; and 89Sr and 90Sr, which were detected near FDNPS in 2011 and2012 and, for 90Sr, over a larger area (30 to 600 km) in June 2011.

(b) Observations of 131I, 134Cs and 137Cs
B62. On 21 March 2011—within ten days of the first release of radionuclides from FDNPS—theoperator, TEPCO, began to conduct monitoring of seawater near one of the two outlets located on eitherside of the FDNPS port [T6]. Monitoring was also carried out inside the port. Three days later, themonitoring was extended to the second outlet. Monitoring for 131I, 134Cs and 137Cs was then conductedat points near each of these outlets twice daily. The results for 137Cs in seawater near FDNPS are shownin figure B-XVII [B23]. They indicated that concentrations of 137Cs increased to a first peak at
47,000 Bq/L on 31 March, followed by a second peak at 68,000 Bq/L on 7 April, before declining
rapidly to under 10,000 Bq/L by 9 April and generally below 200 Bq/L by the end of April. Thereafter,
the decrease was much slower. The ratio of the concentrations in seawater of 134Cs to those of 137Cs wasfound to be very close to 1. In 2012, concentrations of 137Cs measured near the two outlets were
between 1 and 10 Bq/L. Measurements of concentrations in the port during 2012 ranged between
10 and 100 Bq/L, indicating that some releases were continuing, possibly from residual leaks, fromunderground water sources, from run-off into rivers from deposits on land, or from desorption ofradionuclides from marine sediments.

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149

Figure B-XVII. Measured concentrations of 137Cs in seawater near the FDNPS site [B23]

B63. During the first days of monitoring, concentrations of 131I in seawater 20 to 30 times higher thanof 137Cs were measured, reflecting the relative importance of atmospheric deposition at this time.
Around 25 March, the ratio of the two radionuclides in the vicinity of FDNPS fell sharply to 10. Byaround mid-May, this ratio was close to 0.1, reflecting the comparatively short half-life of 131I.
B64. TEPCO also conducted monitoring in coastal waters further away from FDNPS [T6], andincreased the number of measurement stations over time. Two coastal stations south of FDNPS weremonitored daily: the first 11 km to the south at the Fukushima Daini Nuclear Power Station; and thesecond 16 km to the south at Iwasawa beach. TEPCO progressively added other sites, both along thecoast and on sections located 3 km, 8 km and 15 km offshore. In addition, MEXT [M11] performed
regular measurements at different stations on a section located 30 km from the coast.
B65. During the period characterized by large direct liquid releases (between 26 March and 8 April),dispersion of the released radionuclides away from FDNPS was relatively limited. Concentrations at themonitoring site 11 km to the south, where they were the next highest after the FDNPS outlets, wereapproximately 20 times lower [T6]. Moreover, concentrations fell even more rapidly with distance overthis period perpendicular to the shoreline. At 15 km offshore, concentrations were 100 times lower thanat FDNPS and, at 30 km offshore, they were about 1,000 times smaller. After 8 April, when theconcentrations measured in seawater at FDNPS peaked, concentrations at 30 km offshore increased
significantly for a few days suggesting a mechanism of seaward dispersion. From the middle of May,
samples collected 15 km offshore by TEPCO were most often below the relevant detection limit.
B66. Regarding the dispersion along the coast, a comparison of two sites to the north and to the south
located at the same distance from FDNPS [T6] indicated that the coast south of FDNPS would have

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UNSCEAR 2013 REPORT

been more affected than the northern coast. However, this indication should be treated with caution
because the northern coast was not monitored during the period of large direct releases.
B67. Various scientific cruises were made at distances farther from FDNPS between April and June
2011 [B25, H7]. In addition, ships voluntarily took measurements across the entire northern Pacific
Ocean at least up until March 2012 [A12]. The detection limits for these measurements were lower thanthose of the regular monitoring discussed above.
B68. One month after the accident, a scientific cruise aimed at measuring 134Cs and 137Cs wasorganized several hundred kilometres from the Japanese coast with an additional extension to about
2,000 km towards the north-east [H7]. The concentrations of 137Cs were found at up to 100 times higher
than the pre-accident levels. The ratio of these two caesium radionuclides was found to be close to one,indicating that the source was FDNPS. The presence of these radionuclides in the north-east and southeast directions at such a large distance from FDNPS so shortly after the accident indicated that theirpresence was mainly because of atmospheric inputs.
B69. In June 2011, a cruise conducted measurements with a relatively high spatial density between
30 and 600 km from the Japanese coast of radionuclide concentrations in the surface and subsurface
waters [B25]. The concentrations of 134Cs were highest near the coast. At 600 km offshore,concentrations at the surface reached 0.1–0.3 Bq/L. A clear finding of this sampling work was that theconcentrations to the south of the Kuroshio current were low, showing that this powerful current
formed a southern boundary for liquid releases from FDNPS.
B70. Finally, for the period from March 2011 to March 2012, other ships sampled the northern Pacific
Ocean between 20°N and 50°N [A12]. The results showed radiocaesium was moving towards the east
at a rate close to 80 mm/s. The main body of the radioactive plume reached longitude 180°E (more than
3,000 km from the station) in March 2012, one year after the accident, with a maximum concentrationof 10-2 Bq/L. This propagation was confined along the parallel of 40°N latitude.
B71. Generally, measurements where the detection limit was high (10 to 20 Bq/L) did not detectreleased radionuclides in seawater below the surface. More precise measurements with a lower
detection limit indicated that 134Cs concentrations decreased significantly with depth below the ocean
surface. In June 2011, released radiocaesium in a dissolved form apparently had not penetrated below
100–200 m from the ocean surface [B25].

(c) Other radionuclides
B72. Radiostrontium (89Sr and 90Sr) was detected in measurements made regularly over a year at
FDNPS [P12] and offshore during a cruise in June 2011 [C2]. At FDNPS, 90Sr concentrations were up
to 4 orders of magnitude higher than those that preceded the accident, but were generally at least oneorder of magnitude lower than those of 137Cs (except for the short period following the direct release to
the ocean in December 2011—see section II.B above). Further offshore, in June 2011, the ratio of theconcentration of 90Sr in seawater to that of 137Cs was about 0.02. This concentration ratio was muchhigher in seawater than in ground deposition, indicating direct liquid releases to the ocean were thedominant source, rather than deposition from the atmosphere.
B73. TEPCO [T6] and NRA [N20] conducted—and at the end of 2013 continue to conduct—seawater
monitoring; they detected the presence of plutonium radioisotopes in seawater samples, but levels werenear or below the detection limit.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

151(d) Concentrations of 134Cs and 137Cs in sediments
B74. Almost 1,000 samples of sediment from the surface (30 mm) of the seabed taken between the endof April 2011 and the end of 2012 off Fukushima Prefecture and neighbouring prefectures have been
analysed [M11]. The radionuclides most frequently detected were 134Cs and 137Cs. The highest
concentration of 137Cs, of the order of 105 Bq/kg in dry sediment, was measured in the port of the
FDNPS site. Levels decreased significantly with distance from the FDNPS site, with 137Csconcentrations generally lying between 10 and 1,000 Bq/kg in dry sediment, compared to values of
1 Bq/kg before the accident (see figure B-XVIII). The initial 134Cs/137Cs ratio was close to 1, in linewith ratios found in seawater. The higher concentrations were associated with fine sediments.
Measurements performed on the 30–100 mm layer showed significant concentrations that could haveresulted from bioturbation [O7]. The Committee considered how the distribution of 137Cs in sedimentdeveloped with time, but it was difficult to draw conclusions, owing to the high spatial heterogeneity ofconcentrations. However, it was clear that concentrations of 137Cs in sediment had changed much lessover time compared to concentrations in water (compare figures B-XVII and B-XVIII).
B75. The resuspension of fine sediments in coastal areas is a process that recurs when currents andwaves are sufficiently energetic. Transport of turbid layers generated by resuspension along the bottom
can then redistribute radionuclides for several years before they are permanently buried under new
layers of sediment. Moreover, sediment represents a source of radionuclides for marine species living
or feeding on the ocean floor.
Figure B-XVIII. Concentrations of 137Cs in sediment
Taken from [M11]. Higher values observed in the FDNPS port have not been plotted

B. Marine dispersion models and validity checks
B76. The numerous observations available enabled an understanding of some of the characteristics ofthe dispersion of released radionuclides in the marine environment. Modelling of dispersion could
supplement this understanding provided that models had been reasonably well-validated byobservations. To understand how this dispersion occurred at the regional level, the modelled surface
currents for the month of April 2011 are presented (as arrows) in figure B-XIX [E4]. This shows, inparticular, the influence of the Kuroshio current that transports warm and salty waters along the152

UNSCEAR 2013 REPORT

southern coast of Japan and then eastwards to the central Pacific Ocean north of the 35°N parallel. This
current flows from about one hundred kilometres south of FDNPS and creates a boundary between thewarm waters to the south and the cold waters to the north, into which the direct liquid releases ofradionuclides were made. Periáñez et al. [P3] conducted similar modelling studies.
B77. Off the coast of FDNPS, the continental shelf (where the water is less than about 200 m deep—
corresponding to the darker blue colours in figure B-XIX) is about 40 km wide. Currents on thecontinental shelf vary in response to forcing by the wind, tides and freshwater inputs from rivers. Wind
seems to be the main driver of the currents in this coastal region. The coast induces a blockage whichchannels the currents within the first few kilometres. When the wind is favourable for southwardtransport, surface water and associated contaminants can reach the Kuroshio current within a few days,
and then be dispersed eastwards towards the centre of the Pacific Ocean.
B78. To be confident in an analysis of the dispersion, the results of models had to be validated against
available observations. The results of different models mentioned in section II.B of this appendix [E4,K3, T24] and those from the analysis of Periáñez et al. [P3] (which incorporated a dynamic model ofthe interactions between seawater and sediments) were compared with observations at different points.
Masumoto et al. [M5] presented an intercomparison of the results of some of these models with others.
The models sometimes related to winds used to force the hydrodynamic models, to oceanic currents,
and to time series of concentrations at different points. Estournel et al. [E4], using the daily source term
discussed in section II.B above, simulated the 137Cs dispersion and then compared simulated andobserved concentrations at 13 sites along the coast and at 3, 8, 15 and 30 km offshore (see position in
the insert of figure B-XIX). The results are shown in figure B-XX. The variations of concentration withtime were generally well reproduced, apart from the early observed increase in concentrations at 30 km
offshore (discussed in section II.B of this appendix). This simulation was used to provide insight into
how direct releases to the ocean and deposition from the atmosphere were dispersed in the ocean.
Figure B-XIX. Surface current simulated for April 2011 superimposed on the sub-marine topography(from [E4])aa

The red dot indicates the Fukushima Daiichi Nuclear Power Station (FDNPS). The top left insert is a close-up around FDNPS

indicating the position of the points used to validate the dispersion model (see figure B-XX).

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

153

Figure B-XX. Comparison of 137Cs concentrations (Bq/L) observed (dots) and simulated (solid line) atdifferent points indicated in the frames (from [E4])a

154

a

UNSCEAR 2013 REPORT

See map on figure B-XIX for site locations. The red dashed line indicates the detection limit while vertical cyan dashed lines

indicate observations below the detection limit.

C. Results of dispersion assessment(a) Dispersion of direct releases to the ocean
B79. The wind blew mainly southwards during the first month after the accident, when the direct
releases from FDNPS to the ocean were highest. Such wind conditions produced transport to the south
and confinement against the coast (see figure B-XXI), owing to the Coriolis effect. This situation istypical of coastal downwelling. It is the origin of the high concentrations observed south of FDNPS (atFukushima Daini Nuclear Power Station and Iwasawa beach) [T6]. This southward transport then led toANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

155

an interaction between the coastal waters carrying the released radionuclides and the Kuroshio current,
and subsequently to an eastward transport.
B80. After mid-April, the wind blew mainly northwards inducing a northward and eastward surface
current. This situation was favourable to disperse radionuclides in the entire coastal area, including to
the north of FDNPS (see figure B-XXII). Radionuclide concentrations then decreased sharply near tothe coast, while they increased 30 km offshore. An analysis of observations of 137Cs and temperatureand salinity profiles at 30 km offshore in mid-April indicated that radiocaesium was associated with a
10–20 m thick low-salinity layer. The presence of this river-influenced coastal water pushed by thewind over denser oceanic water promoted the offshore transport of radionuclides, limited theirdispersion into the underlying waters and thereby increased the residence time of radionuclides insurface waters.
Figure B-XXI. Mean concentration of 137Cs in surface waters (Bq/L) during the first month after theaccident (from [E4])156

UNSCEAR 2013 REPORT

Figure B-XXII. Mean concentration of 137Cs in surface waters (Bq/L) in May 2011 (from [E4])aa

Note that the horizontal scale differs from the one used in figure B-XXI.

(b) Dispersion of radionuclides deposited from the atmosphere
B81. Radionuclides released to atmosphere were deposited on to the ocean over a wide region.
Deposition density was highest in the coastal area near FDNPS. According to different authors [E4,K3], the magnitude of the accumulated deposition density would have been of the order of 104 Bq/m2
close to the coast and around 102–103 Bq/m2 500 km away from FDNPS, depending on the winddirection at the time of the releases. Oceanic dispersion models have been used to simulate the fate ofthese deposits.
B82. The contribution to concentrations in surface waters due to these deposits from atmosphere wasmuch lower than that due to the direct releases into the ocean (except perhaps during the first days,
when direct releases were not detected). At large distances during the first month, atmosphericdeposition was responsible for the observed concentrations, which were low (less than 0.05 Bq/L at a
few hundred kilometres [E4]). These results were within an order of magnitude of the averageobservations reported by Honda et al. [H7], although some values around 0.3 Bq/L were measured in a
relatively small area.
B83. Regarding 131I, Kawamura et al. [K3] simulated concentrations along the coast south of FDNPS
that reached a few hundreds of becquerels per litre in March, decreasing offshore to about 10 Bq/L also
within March, and to 1 Bq/L in April.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

157(c) Long-term global transport
B84. Simulations of the 137Cs dispersion across the Pacific Ocean over the first 30 years after theaccident have been published [N3]. These simulations indicated that radionuclides released directly
would reach the Californian coast of the United States 4–5 years after the accident, but this timescale
was likely to have been overestimated because the low-resolution ocean model used in this study
underestimated the strength of currents. This has been confirmed by observations reported by Aoyama
et al. [A12] and discussed in section III.A of this appendix. However, the simulated concentrations for2012 were of the same order of magnitude as Aoyama’s observations. The model indicated that 137Cs
released directly from FDNPS would be distributed throughout the northern Pacific Ocean within ten
years of the accident at concentrations below 10-3 Bq/L; these are less than concentrations of 137Cs in
the Pacific Ocean of 1−2 × 10-3 Bq/L that existed before the accident [B25].

(d) Uptake onto, and release from, sediments
B85. Periáñez et al. modelled the interactions between seawater and sediments [P3] using a threedimensional advection/diffusion model with terms describing the adsorption/desorption reactions
between the deepest water layer and seabed sediments in a dynamic way using both one-step and twostep kinetic models. They estimated concentrations of 137Cs in seawater and sediment for comparison
with measurements. The model provided a fit to the measurements of 137Cs concentrations in surface
water similar to that illustrated in figure B-XX; it also was able to reproduce the general pattern of 137Csconcentrations measured in sediments. The authors estimated a half-time for the 137Cs content in thesediment of 167 days.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

159

APPENDIX C. ASSESSMENT OF DOSES TO THE PUBLICI.

INTRODUCTION................................................................................................................................. 161
A. Exposure pathways.................................................................................................................. 161
B. Data for dose assessment...................................................................................................... 162

II. METHODOLOGY ............................................................................................................................... 168
A. Regions considered for dose estimation ......................................................................... 168
B. Assessment of external exposure in non-evacuated areas....................................... 169
C. Assessment of doses in non-evacuated areas from inhalation ofradionuclides ............................................................................................................................. 173
D. Assessment of doses from ingestion of radionuclides ............................................... 174
E. Assessment of doses to residents of evacuated communities ................................ 177
F. Assessment of collective doses ........................................................................................... 179
III. RESULTS............................................................................................................................................... 180
A. Estimates of doses in Japan in the first year ................................................................... 180
B. Estimation of doses in Japan from exposure over future years............................... 193
C. Radiation exposure outside of Japan................................................................................ 195
D. Estimates of collective doses ............................................................................................... 199
IV. UNCERTAINTIES ................................................................................................................................ 200
A. Assessment of dose from external irradiation and inhalation ................................. 200
B. Assessment of dose from ingestion .................................................................................. 202
C. Future remediation and protective measures ............................................................... 205
V. COMPARISON WITH OTHER ASSESSMENTS............................................................................ 206
A. Direct measurements of radionuclides in people ........................................................ 206
B. WHO study.................................................................................................................................. 207
VI. CONCLUSIONS................................................................................................................................... 208

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161

I. INTRODUCTION
C1. This appendix provides more detailed information on the assessment of radiation exposures of the
public. Knowledge about the distribution of radioactive material in the environment was used to makeestimates of the doses to members of the public in Japan. This study also took account of thepreliminary dose estimation carried out by the World Health Organization (WHO) [W11] and the large
amount of information that had become available since the WHO preliminary dose estimation wascompleted. A review of relevant published scientific papers and information formed part of this study.
C2. The assessment considered the more important pathways by which people were exposed toradiation following the accident, with the main focus being on estimating exposures of individuals
considered to be representative (i.e. having typical habits, such as food intake and behaviour) of thedifferent subsets of the Japanese population. Three main age groups at the time of the releases wereconsidered: 20-year-old adults, 10-year-old children and 1-year-old infants. For some exposure
pathways, people were only exposed for a short period of time—during and just after the releases.
Other pathways can continue to cause exposure for many years into the future, albeit at rates that
reduce with time. The assessment, therefore, included exposures in the first year following the accident,
exposures integrated over the first 10 years and exposures up to age 80 years, taking into account theageing of the three age groups considered. An integration period of 80 years was used rather than the
70-year value that is standard for radiation protection; this was to reflect the longer lifespans common
in Japan. Particular attention was paid to the exposures of people living in the more affected areas of
Fukushima Prefecture and some neighbouring or nearby prefectures in eastern Japan. It is important torecognize that there was significant variability in the deposition density of radionuclides deposited on
soil across Japan and that very few measurements of radionuclides in air were made for the mostaffected areas following the accident.

A. Exposure pathways
C3. A broad range of radionuclides was released from Fukushima Daiichi Nuclear Power Station(FDNPS) over a prolonged period of time (see appendix B). The main endpoints of the Committee’s
dose assessment were the absorbed doses to selected critical organs (in grays, Gy), most importantly
the thyroid, but also the red bone marrow and female breast, and the effective doses (in sieverts, Sv).
The Committee focused on estimating absorbed doses to the thyroid because radioiodine, if ingested orinhaled, concentrates in the thyroid, and this is particularly important for infants and children. The
effective doses estimated in the Committee’s study were the sum of the effective doses due to external
exposure received over the period of interest and the committed effective doses due to internal
exposure from intakes of radionuclides by ingestion and inhalation over the same period.
C4. As detailed in appendix B, the major releases following the accident were to the atmosphere andthe ocean. The radionuclides in these releases subsequently moved through the environment. Figure C-I
illustrates the more important exposure pathways.

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UNSCEAR 2013 REPORT

Figure C-I. Exposure pathways following releases of radioactive material to the environment

C5. The major exposure pathways following the releases to atmosphere were:(a) External exposure from radionuclides in the radioactive plumes;(b) Internal exposure from inhalation of radionuclides in the radioactive plumes;(c) External exposure from radionuclides deposited on the ground;(d) Internal exposure from ingestion of radionuclides in food and water.
C6. The first two exposure pathways were only relevant during the passage of the radioactive plumes.
The third and fourth exposure pathways persist until the deposited radionuclides have decayed or been
removed by physico-chemical processes. Other possible exposure pathways, such as the inhalation ofresuspended radionuclides or exposure via contamination of the skin, were not major contributors to
exposure for the releases from FDNPS and were not considered further.
C7. For radionuclides released to the ocean or deposited onto the ocean from the atmosphere, transfer
to fish and other seafood that may be eaten by people is of particular importance. Other exposure
pathways could have resulted from radionuclides in sediments and sand (external irradiation plus
internal irradiation following inadvertent ingestion); however, these could only have been relevant forthe coast outside of the 20-km evacuation zone established around the FDNPS site because of therestrictions placed on public access. At this distance from the plant, they were not expected to besignificant contributors to human exposure, and were not included in the Committee’s assessment.

B. Data for dose assessment
C8. Appendix A catalogues the extensive body of data available as input to the assessment, and sets
out the processes that were used to ensure that the quality of the data was sufficient for the purposes of
the assessment. Measurements were largely focused on the radionuclides 131I, 134Cs and 137Cs, because
these were considered to be the most significant contributors to exposure. The radionuclide, 131I, largely
determined absorbed doses to the thyroid, which were delivered over a relatively short period after theaccident (via inhalation and ingestion). The radionuclides, 137Cs and, to a lesser extent, 134Cs, determine

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163

the continuing longer-term exposure of the population, in particular from radioactive material depositedon the ground. Only limited data were available for 133Xe, the radionuclide with the largest estimatedrelease of activity (see appendix B), because this is an unreactive (noble) gas which cannot be collectedby air filter sampling. (These data were obtained by the monitoring station of the Comprehensive
Nuclear-Test-Ban Treaty Organization (CTBTO) at Takasaki, Gunma Prefecture.) However, thecontribution of 133Xe to exposures was very small.
C9. In vivo measurements of radionuclides in people provide a direct source of information to assess
their internal exposures. Two main sets of data were available to the Committee: the first was frommeasurements of 131I in the thyroid, particularly of children; and the second was from whole-bodymonitoring for 134Cs and 137Cs. Such measurements can only indicate what activities of radionuclides
are in the person at the time of monitoring. The available measurements covered only a limited numberof people and locations and were insufficient to directly estimate internal exposure of people in either
Fukushima Prefecture or the remainder of Japan. Therefore, the estimates of internal exposure werebased on measurements of radioactive material in the environment, combined with models describing
how people were exposed to this material.
C10. The data were used in one of two ways in this study: either as direct input into the exposure
assessment, or to check the validity of the assessment. Data used as direct input included those from themeasurements of deposition density of radionuclides on the ground. The Committee used these data as
the primary basis for estimating external exposure. In addition, an extensive database of measurementsof activity concentrations of radionuclides in food in Japan was used for the estimation of doses fromingestion. The data used as a check on the dose assessment included the results of numerous dose-rate
measurements, a limited number of measurements of concentrations of radionuclides in air at particularlocations and times, and the limited number of in vivo measurements of radionuclides in people(whole-body and thyroid measurements). The Committee used the results from atmospheric transport,
dispersion and deposition modelling (ATDM) described in appendix B to supplement the available
measurements of the levels of radionuclides deposited on to the ground or in the air.

1.

Radiation measurements within Japan

C11. Although the main source of data was the official information provided by the Japanese
authorities, data from other sources were also used. These included data provided by Member States of
the United Nations (such as those obtained by personnel of the United States of America in Japan), andpublished information (such as that obtained by IAEA field teams [I6]). The Committee madeextensive checks to determine whether the measurements were consistent or not, and whether or notthey had been carried out using established methodologies whose quality had been assured.
C12. An extensive monitoring programme was conducted under the direction of the Japanese Ministryof Education, Culture, Sports, Science and Technology (MEXT) with the cooperation of the Japan
Atomic Energy Agency (JAEA), various universities and research institutes. The dataset of the initial
MEXT ground survey provided the most comprehensive measurements of deposition density
comprising approximately 2,200 results derived from measurements of soil samples conducted over theperiod from 6 June to 8 July 2011, in areas within a distance of 80 km of FDNPS. The dataset provided
information on ambient dose equivalent rates and deposition densities of the gamma-emitting
radionuclides, 110mAg, 129mTe, 131I, 134Cs and 137Cs, on soil. The higher values for deposition density
were found for sampling locations within the evacuated areas. The highest measured value for 137Cs
was 15 MBq/m2 for a location in Okuma Town, where the corresponding ambient dose rate at the timeof measurement was 55 μSv/h.
C13. The MEXT dataset also included the results of measurements of deposition density for 89Sr, 90Sr,
238
Pu and 239+240Pu on soil at a limited number (100) of the sampling points. The highest values ofdeposition density for 89Sr and 90Sr were 22,000 Bq/m2 and 5,700 Bq/m2, respectively, at locations

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UNSCEAR 2013 REPORT

within the 20-km evacuation zone. Only 6 samples gave measured values of 238Pu above the detection
limits; the highest value measured was 4 Bq/m2. The results of the measurements of 239+240Pu for 50%of the samples were below the detection limits; the highest value was 14 Bq/m2. The detailed
measurement results for the initial 2,200 measurements are provided in attachments C-1 to C-5 andmaps for all radionuclides measured are provided in attachment C-6.
C14. In late 2011, MEXT conducted an additional series of in situ measurements and/or soil sampling
and measurements of 134Cs and 137Cs in 11 prefectures of eastern Japan. The results of the later MEXT
survey were combined with the initial 2,200 measurements and provided the primary input data for theestimation of external exposure at district level within Fukushima Prefecture and the prefectures of
Miyagi, Tochigi, Gunma, Ibaraki, Iwate and Chiba. Concurrent with the MEXT surveys, the Japanese
Ministry of Agriculture, Forestry and Fisheries (MAFF) conducted measurements of 134Cs and 137Cs in
cultivated soils in 15 prefectures of eastern Japan from April 2011 to February 2012. The results ofthese surveys were also used in the assessment.
C15. For the Committee’s assessment of doses to the public, the measurement results of the groundsurvey were combined with data on the Japanese population. The Japanese Government divided Japan
into a grid for the purposes of reporting relevant geospatial information. The primary, first-order gridused 1 degree of longitude (east and west), and 40 minutes of latitude (north and south). The secondorder grid split each first-order grid cell into 8 by 8 cells, each corresponding to 0.125 degrees oflongitude and 0.083 degrees of latitude. The dimensions of these grid cells were approximately 10 km
by 10 km. A third-order grid was obtained by equally dividing the second-order grid cells into further
10 by 10 cells. The horizontal and vertical distances of the third-order grid cells were approximately
1 km by 1 km. Each of the results of the measurements made by MEXT was assigned to thecorresponding grid cell of approximately 1-km squares to allow combination with the population data.
C16. Once combined, the Committee produced dose rates and deposition densities of radionuclides foreach district covered by the surveys. A map of the deposition density of 137Cs in Fukushima Prefectureand some neighbouring prefectures, referenced to the 14 June 2011, is shown in figure C-II. The
derived measurement datasets are provided in attachment C-7.
C17. The United States Department of Energy (USDOE) performed airborne surveys in areas within adistance of 80 km of FDNPS. Data were collected from 2 April to 9 May 2011, with the reported dose
rates and deposition densities of 134Cs and 137Cs adjusted to 30 June 2011. This dataset was used torefine the interpretation of the ATDM results (appendix B), and to quantify the variability of thedeposition density within each district or prefecture. The measured values of dose rate and deposition
density from the USDOE airborne survey were averaged within each grid cell of approximately 1-km
squares and compared with the measurement data from the MEXT ground survey. Figure C-III shows
the deposition densities of 137Cs derived from the USDOE airborne survey for the eastern part of
Fukushima Prefecture, and indicates that the areas of highest deposition density were in an area to thenorth-west of FDNPS.

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Figure C-II. Deposition density of 137Cs averaged by district within Fukushima Prefecture and some
districts in neighbouring prefectures, based on data from the MEXT ground survey adjusted to
14 June 2011

Figure C-III. Deposition density of 137Cs in Fukushima Prefecture based on measurement data fromthe airborne radiometric surveys adjusted to 30 June 2011 [U17]C18. There was only limited information available on the concentrations of radionuclides in air
following the releases from FDNPS. The data provided by the Japanese Government and by the
USDOE are summarized in appendix A. There were insufficient data during the first weeks onconcentrations of 131I in air to provide direct estimates of the exposure from inhalation during thepassage of the radioactive plumes.

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C19. Measurements of 131I, 134Cs and 137Cs were made in a wide variety of foods in Japan following theaccident. Since March 2011, a database has been compiled on radionuclide concentrations in foodstuffs
under the guidance of the Food and Agriculture Organization of the United Nations (FAO) and theInternational Atomic Energy Agency (IAEA) in collaboration with the Japanese authorities, including
the MAFF and the Japanese Ministry of Health, Labour and Welfare (MHLW). This FAO/IAEA food
database includes data for over 500 types of foodstuffs sampled in all 47 prefectures in Japan. These
data were provided through the FAO/WHO International Food Safety Authorities Network(INFOSAN) based on information published or provided by MHLW and compiled by the Joint
FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. The FAO/IAEA food databasewas validated before use by the Committee as outlined in attachment C-8.
C20. Data on concentrations of radionuclides in drinking water were provided by MHLW. The firstsample of drinking water was collected in Fukushima Prefecture on 16 March 2011. Some districts did
not begin sampling water until late March or early April 2011. Outside of Fukushima Prefecture, data
were only available for 131I, 134Cs and 137Cs in drinking water. For districts within Fukushima
Prefecture, data were also available for 132I.

2.

Atmospheric transport, dispersion and deposition modelling for Japan

C21. Since there was much less information available on the concentrations of radionuclides in air, theexposures from the plume at specific times and locations were estimated from the assumed time
sequence of the release of the more significant radionuclides and their transport through the atmosphereusing NOAA–GDAS ATDM as described in appendix B. While the estimates of radionuclide
concentrations in air and deposition densities of radionuclides provided by the assumed source termand ATDM analyses at any specific location are uncertain, the ratios of these two estimates are muchless so. In particular, the ratios are relatively insensitive to the absolute magnitude and temporal patternof the estimated release of the radioactive material, which is associated with much uncertainty. The
main uncertainties in these ratios result from uncertainties in the parameters that describe wet and dry
deposition. The Committee used such location-dependent ratios, derived from the ATDM analyses, toinfer time-integrated radionuclide concentrations in air from the measured deposition densities ofradionuclides. It then used these inferred concentrations to assess the exposures from radionuclides in
air in all regions of Japan except in the evacuated areas.
C22. For the evacuated areas, where only a limited number of measurements of radionuclide
concentration in air and deposition density were made during the periods of the evacuations, theCommittee relied on estimates of these quantities provided by the assumed pattern of release of themore significant radionuclides and the ATDM analyses. The ATDM results provided the timedependent activity concentrations in air of the radionuclides, 132Te, 131I, 132I, 133I, 133Xe, 134Cs, 136Cs and137
Cs. While the ATDM results were based on the available source-term data and the NOAA–GDAS
model included detailed information on the meteorological conditions, there were significant
uncertainties in the ATDM results for specific locations and times (see appendix B). The ATDM results
were also used in the calculation of dose from ingestion of radionuclides in future years to communities
within Fukushima Prefecture and elsewhere in Japan.
C23. The ATDM results were provided as points on a grid of 5-km squares and these values wereassigned to the corresponding cells of the measurement dataset of the MEXT ground survey. The
ATDM analyses provided estimates for both the particulate and the non-particulate forms of 131I.
Figure C-IV shows the estimated time-integrated concentrations of particulate 131I in air for the period
from 13 March to 1 April 2011, based on the ATDM analyses. The map of the ATDM results
demonstrates that a significant proportion of the releases of radionuclides to atmosphere were dispersed
over the ocean. The derived datasets and maps for 131I and 137Cs from the ATDM analyses are provided
in attachments C-9 to C-10.

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Figure C-IV. Time-integrated (13 March–1 April 2011) concentration of particulate 131I in air overJapan based on the results from the NOAA–GDAS atmospheric transport, dispersion and deposition
modelling analyses (appendix B)

3.

Radiation measurements outside of Japan

C24. Twenty-five Member States of the United Nations provided, on request, relevant data directly to
the Committee (Argentina, Australia, Belarus, Belgium, Brazil, Canada, China, Finland, France,
Germany, India, Indonesia, Malaysia, Mexico, Pakistan, the Philippines, Poland, the Republic ofKorea, the Russian Federation, Slovakia, Singapore, Spain, Sweden, the United Kingdom of GreatBritain and Northern Ireland, and the United States of America). The data included information on:radionuclides detected in air samples, and in imported and locally produced foods; in vivo (such as
whole-body counting and thyroid measurements) and in vitro (such as urine analyses) measurements ofcitizens of these States who were in Japan at the time of the accident; and analyses of environmental
samples. A summary of the data provided is given in attachment C-11.
C25. A number of publications reported radionuclide concentrations in air, rainwater, soils, plants anddairy products, and deposition densities. These cover locations within south-east Asia [K10, K12, L13],
the Russian Federation [B14], North America [B10, B15, D1, M2, S10, W8, Y3], Europe [B1, B3, B7,
B11, C1, C7, C8, E5, I30, K21, L9, L14, M3, M4, P4, P7, P9, P10, P13, T22], the Arctic [P1] and Cuba
[A8].
C26. Detection of 131I, 134Cs and 137Cs in air samples was reported in most of these publications,peaking from late March to early April 2011. Across the European monitoring network, rising levels ofthese radionuclides were recorded up to 30 March 2011 for western and central Europe, and up to
3 April 2011 for eastern Europe. In general terms, the levels were extremely low and by the end of
April 2011, measurements of particulate 131I were again below the limit of detection. A summary of thedata is provided in [M4].

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4.

Protective actions

C27. Extensive measures were put in place by the Japanese authorities to protect people from theradioactive releases [A6]. These included the initial evacuation over the period 11–15 March 2011 out
to a distance of 20 km from the site, and the implementation of the so-called “deliberate evacuationarea” (from 22 April 2011). Further evacuation was carried out, based on environmental measurements,
in districts to the north-west of FDNPS between March and June 2011. For its assessment, theCommittee took account of when and where these protective measures were implemented. In
November 2011, the government of Fukushima Prefecture reported the results of a questionnaire issued
to all residents of Fukushima Prefecture regarding their activities over the four-month period from
11 March to 11 July 2011. Based on the results, 18 scenarios representative of the movements ofresidents evacuated following the accident at FDNPS were developed. These scenarios are discussed in
the next section. Additional information describing the status of the protective measures in theevacuated localities was provided by the Japanese Government.
C28. Early measurements made on samples of vegetables grown in the most affected area showed
concentrations of 131I above the provisional regulation values. Restrictions on food supplies wereintroduced from 17 March 2011. Many people took their own protective actions, in addition to thoserecommended by the authorities. For example, some people evacuated on their own accord, avoided
fresh foods or avoided foods produced in Fukushima Prefecture. The Committee only took into accountthe likely impact of the official protective actions. Nevertheless, it gave consideration to the effect thatdifferent dietary intakes would have made on individual exposures.
C29. The long-term process of remediation of contaminated areas, which has started, will reduce future
exposures from the deposited radionuclides and the transfer of radionuclides to food. The possible
impact is discussed in later sections of this appendix.

II. METHODOLOGY

A. Regions considered for dose estimation
C30. In order to estimate doses to the members of the public in Japan, the Committee focused on fourgroups of geographical areas (see figure C-V). Group 1 included settlements in Fukushima Prefecturefrom which members of the public were evacuated in the days to months after the accident according to18 evacuation scenarios, with each scenario applying to a settlement. Group 2 included all nonevacuated districts of Fukushima Prefecture. Group 3 included selected prefectures in eastern Japanthat were neighbouring (prefectures of Miyagi, Tochigi, Gunma and Ibaraki) or nearby (prefectures of
Iwate and Chiba) Fukushima Prefecture. Group 4 included all the remaining prefectures of Japan.
C31. The spatial resolution adopted for assessing the doses in each of these groups was dependent
on the available data. Estimates for Group 2 were made at the district level for the external exposure
and inhalation pathways and at the prefecture level for the ingestion pathway. The selection of
the six prefectures included in Group 3 was based on the number of measurements taken and themeasured levels of deposition density of 137Cs. Estimates of dose for Group 3 were made at the districtlevel for a number of districts for the external exposure and inhalation pathways. The dose fromingestion for five of the six prefectures was based on an average for the five prefectures. Iwate
Prefecture was the exception and the estimated average dose for this prefecture was the same asthat for Group 4. Doses for all Group 4 prefectures were assessed at prefecture level for the external
exposure and inhalation pathways, and on the basis of an average for the Group 4 prefectures
together for the ingestion pathway.

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169

Figure C-V. Geographic regions for estimation of doses to representative members of the public in
Japan

Group 1. Members of the public who were evacuated in the days to months after the accident, based on the 18 scenarios reported
by NIRS, were included in this group.
Group 2. Members of the public living in the non-evacuated districts of Fukushima Prefecture.
Group 3. Members of the public living in the prefectures of Miyagi, Gunma, Tochigi, Ibaraki, Chiba and Iwate.
Group 4. Members of the public living in the remaining prefectures of Japan.

C32. For this assessment, estimates of the radiation exposures of representative members of the publicwith typical habits were made using a number of different methods. The methodologies outlined in thissection are described in detail in attachments C-12 and C-13. The Committee did not explicitly estimate
doses to the foetus or breast-fed infants because they would have been similar to those to other age
groups for both external and internal radiation exposure. For example, doses to the foetus and breastfed infant due to external exposure would have been approximately the same as those to adults and1-year-old infants, respectively.
C33. The assessment of doses for countries outside of Japan was based on a review of estimatespublished in the literature, including the results of the WHO preliminary dose estimation, supported by
the extensive measurements, and dose assessments carried out by Member States of the United Nations.
The Committee did not undertake a comprehensive assessment based on a modelling approach toestimate doses to members of the public in the rest of the world.

B. Assessment of external exposure in non-evacuated areas
C34. External exposure was a major contributor to the doses to the public from the releases ofradionuclides into the environment (for example, see [W11]). There were two components of theexternal exposure: (a) exposure from radionuclides in the air; and (b) exposure from radionuclides

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UNSCEAR 2013 REPORT

deposited on the ground. The exposure from radionuclides in the air would have been relatively shortterm and only would have persisted while the radionuclides were present in the air, but the exposure
from deposited radionuclides would persist until they have decayed or been removed by physicochemical processes or remedial action.
C35. The measured ambient equivalent dose rates (or air kerma rates) included those from released
radionuclides (in the air and on the ground) and a background component from naturally occurringsources of radiation [U12]. It was not possible to directly use the measurements of dose rate owing to alack of detailed information about the background component and the contribution from particularradionuclides. For this reason, the dose rates as a function of time and location due to the depositedradionuclides were estimated from the measurements of the deposition densities of these radionuclides
on the ground. This also allowed for the estimation of dose rates into the future, with account being
taken of the radioactive decay and migration into the ground of each radionuclide.
C36. The assessment of absorbed dose to organs or effective dose from external exposure required
information on the gamma-radiation field, information relating to human behaviour in the radiation
field over time and conversion coefficients that relate the radiation field to absorbed or effective dose,
as appropriate. These conversion coefficients depend on the irradiation geometry and therefore whether
the radionuclides were in the air or deposited on the ground. For external exposure from depositedradionuclides, the kerma rate in air at a height of 1 m above the ground surface was used as thereference measure for the radiation field. Its value is influenced both by the deposition density ofradionuclides on the ground surface and by natural factors such as the initial attenuation of radiation in
soil, radioactive decay, migration of long-lived radionuclides into soil, and the presence of snow cover.
Account was taken of the change of these factors with time. So-called “location factors” were used toexpress the effects of these factors as the ratio of the dose rate in a given location to that in a reference
location. Occupancy factors were used to take account of the fraction of time spent by different groupsof people in different locations. The detailed methodology is provided in attachment C-12.

1.

External exposure from deposited material

C37. For the assessment of external exposures of people within the areas of Japan that were notevacuated, the main approach was to use the measurements of deposition density of radionuclides on
the ground. The measurement datasets are summarized in the previous section and appendix A. The
computational model (see [G6, G8, G9, J3]) consists of four submodels: (a) the estimation of the kerma
rate in free air at a reference site in the settlement; (b) the estimation of the location factors; (c) the
estimation of occupancy factors for different population groups at various types of locations; and (d)the estimation—for different population groups—of coefficients to convert kerma rate in air toabsorbed dose rate to the particular organ or effective dose rate. The models, parameters andassumptions are described in detail in the attachment C-12 and outlined below.
C38. The external exposure of members of the public depends on the amount of time spent outdoors
and indoors, the shielding properties of the indoor location, and the size of the individual (taken to berelated to age). The three age groups used for the assessment were considered to be representative ofparticular social groups; 20-year-old adults (representative of people aged 16 years and older in 2011),
10-year-old children (representative of school children aged 6 to 15 years in 2011) and 1-year-old
infants (representative of preschool children up to 5-years old in 2011). The group of adults was
subdivided into those working mostly outdoors and those working mostly indoors. The group of indoor
workers also included students and pensioners because their behaviour in this respect—as reported inJapanese demographic data—was similar.
C39. For these population groups, shielding properties of three types of house typical of Japan wereconsidered: (a) a wooden house with one to three storeys; (b) a wooden fireproof (plastered) house with
one to three storeys; and (c) a concrete multi-storey apartments. Location factors are time-dependent

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171

and their values decline with time because of radionuclide migration in the environment owing toweathering, cleaning and other factors. The initial values of location factors for these three types ofdwellings were 0.4, 0.2 and 0.1, respectively (see attachment C-12). In total, 12 combinations ofsocial/age groups and house types were considered. The main results are presented for two typical
population groups: (a) adults living in wooden houses and working indoors; and (b) infants living inwooden houses. The choice of these two groups was based on statistical data that showed that the
majority of the population of Fukushima Prefecture and the Group 3 prefectures reside in wooden or
wooden fireproof one-to-two-storey houses.
C40. For the assessment of dose in the first year following the accident, the dose conversion
coefficients based on the computational phantom for adults specified by the International Commission
on Radiological Protection (ICRP) [I24] and other voxel phantoms for the age groups [G7, P6] wereapplied. For the long-term exposure assessments, the growth of 1-year-old infants and 10-year-old
children was taken into account. The group of 1-year-old infants (as of 2011) had the same doseconversion coefficients applied for the first five years (up to 5-years old, preschool). For the 10-year
period from March 2016, the dose conversion coefficients for 10-year-old children were applied; andfrom March 2026, the dose conversion coefficients for adults were used. A similar approach was used
for the children aged 10 years in 2011: appropriate dose conversion coefficients were applied for the
first five years after the accident; and for March 2016 onwards, dose conversion coefficients for adults
were applied.
C41. Occupancy factors (i.e. the amounts of time spent by different population groups in different
types of location) were based on data from Japanese national surveys [N18]. The values used are given
in table C1. These occupancy factors were used in combination with the 12 combinations of social/age
groups and house types. It was assumed that typical adults spend 60% of their time in wooden one-totwo-storey houses and 30% of their time at work in multi-storey buildings. Typical preschool children
were assumed to spend all of their indoor time (80%) in wooden houses.
Table C1. The occupancy factors used to assess doses due to external exposure to members of the
public in Japan
Occupancy factor (dimensionless)Type of location

Adults10-year old

1-year old

0.9

0.85

0.8

0.3

0.1

0.15

0.2

Paved environment

0.2

0.05

0.05

0.1

Unpaved environment

0.1

0.05

0.1

0.1

Outdoor worker

Indoor worker or pensioner

Indoors

0.7

Outdoors including:C42. The MEXT ground-survey dataset was used to provide data on the deposition density ofradionuclides. From this dataset, values were available as follows: 134Cs and 137Cs in all the soil
samples; 110mAg in 343 samples; 129mTe in 799 samples and 131I in 419 samples. In many samples,129m
Te (half-life 33.6 d), 131I (half-life 8.02 d) and 110mAg (half-life 250 d) were not detected because ofradioactive decay and/or low deposition levels. In the absence of measurable levels of theseradionuclides, the deposition densities were estimated from the 137Cs concentrations in soil using
average values for the ratios of the radionuclide concentrations derived from locations where theseradionuclides were detected. Table C2 summarizes the average values of the ratios of theconcentrations of 110mAg, 129mTe, 131I and 134Cs, to those of 137Cs. For most of the locations, the ratios
were relatively consistent.

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UNSCEAR 2013 REPORT

C43. However, the measurement data showed that there was a narrow region along thecoast to the south of FDNPS (the so-called “south trace”) where the ratios for 129mTe and
131I were significantly elevated, although their concentrations were still strongly correlatedwith those of 137Cs. The Committee used these elevated ratios to assess doses for the towns ofTomioka, Naraha and Hirono and for Iwaki City.
C44. There was a statistically significant correlation between the concentrations in soil samples of
110m
Ag with respect to those of 137Cs. The correlation coefficient was however smaller than those for129m
Te and 131I. Nevertheless, the uncertainty in using the concentration ratio for 110mAg from table C2
to estimate the concentrations of this radionuclide in soil where no measurement data were available
did not substantially influence the dose estimates, because the contribution of this radionuclide toexposure in the first year following the accident was of the order of 0.1%.
Table C2. Ratio of the concentrations of radionuclides in soil to those of 137Cs(adjusted to 00:00 15 March 2011)
Area

Characteristic

Radionuclide (half-life)
110m
Ag(250 d)129m
Te(33.6 d)0.0028

1.1

All ofJapan
exceptfor the
south
trace

Ratio to 137Csconcentration

Correlation
coefficient (n)a

0.47
(343)

0.97
(689)

South
traceb

Ratio to 137Csconcentration

0.00287.9

132

Te+132I(3.2 d)131
I(8.02 d)134
Cs
(2.06 a)136
Cs
(13.2 d)

8

11.5

1.0

0.17

0.07
(2 181)

0.02
(56)

1.0

0.17

Standard
deviation (n)aCorrelation
coefficient (n)a

0.85
(110)

137

Cs+137mBa(30.2 a)
1.0

0.72
(339)
59

74

1.0

0.89
(73)

a

n is the number of soil samples.

b

The towns of Tomioka, Naraha and Hirono, and Iwaki City of Fukushima Prefecture.

C45. The deposition densities of 136Cs were inferred from the measured levels of 137Cs. From themeasurements of soil samples from various sites in Japan [E1, T1] the average isotopic ratio,
136
Cs/137Cs, was estimated to have been 0.17 ± 0.02 (n = 56) on 15 March 2011. Based on analysis of
air samples (n = 565) from CTBTO (see attachment B-1) and in Europe [K16], the average isotopic
ratio 136Cs/137Cs was estimated to be 0.21 ± 0.02 on 11 March 2011. These calculated ratios differ fromthe value of 0.31 derived from inventory calculations [N16] and used by the Committee in table B3.
For consistency, the ratios derived from the soil sample measurements were used for this dose
assessment.
C46. For the non-evacuated areas, the deposition densities of 132Te on the ground were inferred fromthe measured levels of 129mTe, using ratios for these radionuclides derived from other publishedmeasurement data. The ratio 132Te/129mTe varied substantially. It was estimated as 9.1 ± 1.6 (n = 14)
from soil samples in Japan [T1] and 5.8 ± 0.1 (n = 14) from air samples collected over Europe [K16].
For the Committee’s assessment, a rounded value of 7 was used, based on environmental
measurements, although the theoretical ratio calculated for Unit 2 of FDNPS gave higher, but diverse
values of 22 [N16] and 13 [K16]. The decay corrected ratio 132Te/137Cs was essentially constant for
about 80 days after the accident, which indicates that radiotellurium was retained in the surface soil likeradiocaesium [T2]. For the evacuated areas, the deposition densities of 132Te on the ground were
derived from the ATDM results, which used a single value of 12.4 for the 132Te/137Cs ratio (seetable B3), based on the reactor inventories.

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2.

173

External exposure from radionuclides in the air

C47. There were insufficient measurements of gamma dose rate and of radionuclides in air during thepassage of the radioactive plumes for an assessment to be made of external exposure based on
environmental measurements. Therefore, the radionuclide concentrations in air were estimated from themeasurements of deposition density and the ATDM results. External exposures due to radionuclides in
air were then calculated based on the assumption that the plume could be represented by a semi-infinite
cloud. This assumption was considered appropriate where the distribution of radionuclides in air could
be considered to be uniform over distances of hundreds of metres. Estimates of radionuclide
concentrations in air were averages for the grid cells of approximately 5-km squares.
C48. Within Fukushima Prefecture (except the evacuation areas) and other prefectures of Japan where
there were measurements of the deposition densities of radionuclides, the concentrations of 131I, 134Cs
and 137Cs in air were estimated from these using the ratios of estimates from ATDM of the timeintegrated activity concentrations in air to the deposition density for each radionuclide as a function oflocation.
C49. The duration of the radioactive plume passing overhead was short (a few hours) and thecontribution of this exposure pathway to the total dose was minor compared with that from depositedradionuclides. It was assumed that people were mostly outdoors during the passage of the plume. This
would have overestimated the actual exposure because it ignores the effect of the shielding of buildings
when people were indoors. Full details of the methods of calculation of external exposures fromradionuclides in air and related parameter values are given in attachment C-12.

C. Assessment of doses in non-evacuated areas frominhalation of radionuclides
C50. The assessment of internal exposures in the non-evacuated areas from the inhalation ofradionuclides required information on the concentrations of radionuclides in air, the age-dependent
breathing rates and the dose conversion coefficients for intake via inhalation. As outlined in theprevious section on assessing external exposure from radionuclides in the air, the radionuclide
concentrations in air were estimated from the measurements of deposition density of radionuclides on
the ground and the ATDM results using the methods described in detail in attachment C-12.
C51. The Committee used standard values of the age-dependent breathing rates and dose conversion
coefficients for absorbed doses to the thyroid and red bone marrow, and for effective dose [I15, I25].
These dose conversion coefficients were based on a default particle size of 1 µm. The inhalation rates
applied were the average rates over a day from the ICRP model of the respiratory tract. The doseconversion coefficients for inhalation were based on the inhalation rates for males [I18]. No allowance
was made for any possible reduction in activity concentrations in air indoors over those outdoors.
C52. The ICRP dose conversion coefficients are based on generic anatomical and physiological humandata and, as such, may not be entirely appropriate for the assessment of absorbed doses to the thyroid ofJapanese individuals because of the high iodine content of the Japanese diet. This factor may havemeant that both the uptake of radioiodine by the thyroid [Z4] and the thyroid mass [L5, Z6] were
smaller.

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D. Assessment of doses from ingestion of radionuclides
1. Internal exposure from the ingestion of radionuclides in food in the firstyear
C53. The assessment of exposure from the ingestion of radionuclides required information on theirconcentrations in foodstuffs and drinking water over the period of interest, the appropriate agedependent intake rates and dose conversion coefficients for intake via ingestion of the radionuclides.
Full details of the methodologies used to estimate the doses from ingestion are given in
attachment C-13.
C54. The dose conversion coefficients used were those published by ICRP [I25]. Within Japan,
extensive measurements were made of the activity concentrations of radionuclides in different
foodstuffs (terrestrial and aquatic) starting in parts of Fukushima Prefecture a few days after theaccident. These measurements were mainly intended to identify where restrictions on food supplies
were required rather than to assess the doses to different population groups. In time, the monitoring was
extended to the whole of Japan and became more systematic. The FAO/IAEA food database only
included measurement data for 131I, 134Cs and 137Cs and so only these radionuclides were considered in
the assessment of doses from ingestion. However, these assessed doses would only have increased
marginally if additional radionuclides had been explicitly considered, owing to their short half-lives orthe very small quantities released.
C55. The FAO/IAEA food database included measured concentrations of radionuclides in immature
crops or in areas where restrictions were in place but these data were not used in the assessment. The
measurement data used were for foodstuffs as marketed (see attachment C-8). Many of themeasurements were at or below the limits of detection and in these cases, it was generally assumed thatthe concentrations of each of the radionuclides considered (131I, 134Cs and 137Cs) was 10 Bq/kg in eachtype of foodstuff, the nominal limit of detection. This was considered to be more appropriate thanassuming that all of the values were zero but may have led to some overestimation of the doses fromingestion. However, in view of the short half-life of 131I (8.02 days), all values for this radionuclide
were assumed to be zero beyond four months after the accident. Furthermore, the activity
concentrations of the radionuclides in rice were assumed to be zero until six months after the accident
when rice was expected to be harvested.
C56. There were insufficient data in the first months following the accident to adopt a fine spatial
resolution for the assessment of the doses from ingestion of radionuclides. It was assumed that the
majority of people in Japan obtain their food from supermarkets where food is sourced from the wholeof the country. It was therefore considered appropriate to base the assessment on the average
concentrations of radionuclides in foodstuffs over wide areas in order to estimate the average exposuresof groups within the population. Therefore, the mean concentrations measured in groups of foodstuffs
in Fukushima Prefecture, five surrounding prefectures (Miyagi, Tochigi, Gunma, Ibaraki and Chiba),
and the rest of Japan formed the basis of the main assessment of doses. For Iwate Prefecture, the doseto people was taken to be the same as that to the rest of the Japanese population.
C57. Information on how much of particular foodstuffs were consumed per capita of the population,
based on surveys carried out in Japan, were provided by the Government of Japan for use in theassessment. The most extensive data were available for adults but there were also data for infants andchildren. Table C3 below summarizes the food intakes used in this study based on the groups offoodstuffs considered.

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175

Table C3. Data on food intake by age group used in the dose assessment
These age ranges are from the reports of the surveys provided by the Government of Japan and were adopted by theCommittee without amendment for age

Per capita food intake by age group (g/d)
Food category
Adults (≥20 years)

Children (7–14 years)

Infants (1–6 years)

Leafy vegetables

71.3

60.4

35.7

Root vegetables

75.1

77.7

52.7

Other vegetables

193.0

161.8

96.7

Soya and soya products

57.5

38.1

25.9

Rice and rice products

342.2

312.1

190.1

Wheat and wheat products

96.4

88.8

65.1

Other cereals

8.3

7.6

4.8

Fresh and processed fruits

86.0

81.9

76.8

Juices

22.4

20.0

16.3

Marine and migratory fish

37.1

25.3

14.9

Crustaceans and molluscs

42.8

29.2

17.2

Eggs

34.3

33.6

23.8

Beef/cattle

13.6

17.6

9.5

Pork (excluding wild boar)

43.1

55.9

30.1

Poultry

21.4

27.7

15.0

Other meat

1.7

2.2

1.2

Milk

83.2

259.7

174.8

Milk and dairy products

7.8

24.4

16.4

Mushrooms

16.5

13.2

8.6

Algae

10.9

8.7

5.8

2. Internal exposures from ingestion of radionuclides in food beyond thefirst year
C58. For the assessment of doses from ingestion beyond the first year after the accident, a modelling
approach was used to estimate the concentrations of radionuclides in foodstuffs as a function of time.
Information was obtained on the agricultural practices in Japan, such as the times when different crops
are planted and harvested, and crop yields, and on any Japanese-specific data on the transfer ofradionuclides to specific foodstuffs. In the absence of a Japanese-specific model, these data were thenused in a modified version of the FARMLAND model [B21] for predicting the transfer ofradionuclides through terrestrial food chains. Foods of particular importance were green vegetables,
rice and milk but a range of different food groups were considered. Following an accidental release, thetransfer of radionuclides to foodstuffs is very dependent on the time of year that the release occurs. The
levels of radionuclides would be much higher in the first year if a release were to occur when crops areclose to harvest and animals are grazing outdoors, than if it were to occur before crops are planted andanimals are being given stored feed and housed indoors. The accident at FDNPS occurred in Marchwhen only a few crops were being grown and animals were being given stored feed; this led to lower
concentrations of radionuclides in foodstuffs than would have been the case if the accident had
happened later in the year (as was the case for the Chernobyl accident in 1986).

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UNSCEAR 2013 REPORT

C59. A modelling approach was also used to estimate doses from seafood consumption in subsequent
years. As discussed in appendix B, there were significant difficulties in determining the releases ofradionuclides to the ocean and therefore the dose estimates should be considered very uncertain.
Nevertheless, estimates of the possible exposures beyond the first year were derived from thecalculated levels of 137Cs in seawater over the next 10 years based on the modelling of the marine
environment carried out by [N3].
C60. The restrictions on food supplies were implicitly taken into account in the estimation of doses
from ingestion in the first year from the database of measurements, because the measurements were forfoodstuffs as marketed (measurements of foodstuffs with activity concentrations over the set levels,
which were removed from sale, were not included). For the assessment of doses from ingestion basedon the modelled concentrations of radionuclides in foodstuffs, it was assumed that no food at levels
above those specified by the Japanese authorities was or would be consumed. From March 2011 until
April 2012, the levels were those specified by MHLW [M15], and are reproduced in table C4. In April
2012, lower levels were introduced for radiocaesium and these were taken into account in theassessment of doses from ingestion after the first year.
Table C4. Concentrations of radionuclides in foodstuffs and drinking water above which restrictions
on supplies were introduced in Japan from March 2011 until the end of March 2012, in accordancewith the Japan Food Sanitation Act
Radionuclide
Radioiodine(representative radionuclides amongmixed radionuclides: 131I)

Provisional regulation values of radioactive material in foodstuffs(Bq/kg)Drinking water300
Milk, dairy productsa
Vegetables (except root vegetables and tubers)
2 000
Fishery productsRadiocaesium

Drinking water
200
Milk, dairy products
Vegetables
Grains500

Meat, eggs, fish etc.
Uranium isotopes

Infant foods
Drinking water

20

Milk, dairy products
Vegetables
Grains100

Meat, eggs, fish etc.
Alpha-emitting isotopes of plutonium
and transuranic elements（total radioactive concentration of
238
Pu, 239Pu, 240Pu, 242Pu, 241Am, 242Cm,
243
Cm, 244Cm)

Infant foods
Drinking water

1

Milk, dairy products
Vegetables
Grains10

Meat, eggs, fish etc.
a

Guidance was provided so that materials with activity concentrations exceeding 100 Bq/kg were not used in milk supplied for

direct consumption or used in making powdered milk for babies.

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177

3. Assessment of internal exposures from ingestion of radionuclides indrinking water
C61. Measurements of radionuclides in drinking water were made by the Japanese authorities and were
provided to the Committee. The estimated exposures were based on these measurements with accountbeing taken of any restrictions that had been introduced (see table C4). Levels were only elevated for alimited period in the months following the accident.
C62. Within Fukushima Prefecture, average effective doses to people living in each district were
estimated. For the rest of Japan, average effective doses to people living in each prefecture were
estimated. Doses were calculated as weekly or monthly averages. For the districts within Fukushima
Prefecture, average weekly doses were calculated for the period from March 2011 to the end of
May 2011. After this period, monthly averages were calculated because the concentrations ofradionuclides in drinking water had fallen significantly and fewer measurements had been made. For
prefectures other than Fukushima, monthly averages were calculated for the period from March 2011 toMarch 2012. All monthly averages were based on calendar months.

E. Assessment of doses to residents of evacuatedcommunities
C63. As outlined in section I of this appendix, the Japanese authorities took extensive measures toreduce radiation exposures. There was widespread evacuation at different times following the accident
and there were also restrictions on food supplies.
C64. People within a distance of 20 km of the FDNPS site were evacuated as a precaution between
11 and 15 March 2011. Most of the residents of the towns of Futaba, Hirono, Naraha, Okuma andTomioka and Kawauchi Village, as well as those residents of the cities of Minamisoma and Tamura,
Namie Town and Katsurao Village living within the 20-km area were evacuated on 12 March 2011.
Most were therefore absent from the more affected areas when the later radionuclide releases occurred.
Exposures of these residents were estimated based on the evacuation scenarios described below.
However, the evacuation of patients in hospitals and nursing homes within the 20-km evacuation zone,
together with a small number of residents, was not completed for some days after 12 March 2011 [T4].
C65. The Government of Japan subsequently initiated the additional deliberate evacuation based on
environmental measurements, notably to the north-west of the FDNPS site. The residents of the wholeof Iitate Village as well as parts of the towns of Namie, Kawamata and Katsurao Village were
evacuated between March and June 2011. For the resident groups from these locations, doses wereassessed for the period before, during and after the evacuation. For the external and inhalation exposure
pathways, the assessment was based solely on the ATDM results; for the ingestion exposure pathway,
the assessment was based on measurements of the activity concentrations of radionuclides infoodstuffs. After people reached the evacuation destinations, some of them stayed there but many,
especially young families, moved to other areas of Japan. However, to provide an estimate of the doses
to evacuees received during the first year, it was assumed that they remained in the evacuation
destinations for the whole year.
C66. The dose assessment for the period before and during the evacuation was based on the resultsfrom a questionnaire survey issued by the local authorities to all residents within Fukushima Prefecture(two million people) to ascertain their activities and, specifically, their locations and movements.
Approximately 21% of the population completed the questionnaires. The National Institute forRadiological Science (NIRS) used the results of this survey to define 18 scenarios representative of the
movements of residents local to FDNPS, following the accident [A5]. All 18 scenarios are outlined intable C5. Information on the numbers of evacuees by settlement is provided in attachment C-12.

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Table C5. Eighteen evacuation scenarios based on the NIRS survey
Scenario

Location at
11 March 2011

Evacuation destinations

1

Tomioka Town

12 March: Kawauchi Village
Office16 March: Big Pallet
Fukushima, (Koriyama
City)

2

Okuma Town

12 March: Funahiki
Vocational Improvement
Center, (Tamura City)

3

Futaba Town

12 March: Kawamata
Elementary School at 08:00

19 March: Saitama Super
Arena

31 March: former
Kisai Prefectural
Senior High School,(Kazo City)

4

Futaba Town

12 March: Kawamata
Elementary School at 21:00

19 March: Saitama Super
Arena

31 March: former
Kisai Prefectural
Senior High School,(Kazo City)

5

Naraha Town

12 March: Iwaki City Office

31 March: Funahiki
Vocational Improvement
Center, (Tamura City)

6

Naraha Town

12 March: Iwaki City Office

16 March: Aizu-Misato
Town Office, (Aizumisato
Town)

7

Namie Town

12 March: Tsushima Centerof Activation

16 March: Adachi
Gymnasium,(Nihonmatsu City)

8

Tamura City

12 March: Denso
Higashinihon

31 March: Big Pallet
Fukushima, (Koriyama
City)

9

Minamisoma City

15 March: Date City Office

31 March: Azuma General
Gymnasium, (Fukushima
City)

10

Hirono Town

12 March: Ono Town Office,(Ono Town)

11

Kawauchi Village

13 March: Kawauchi
Elementary School

12

Katsurao Village

14 March: Azuma General
Gymnasium, (Fukushima
City)

13

Namie Town
Tsushima Centerof Activation

23 March: Adachi
Gymnasium, (Nihonmatsu
City)

14

Katsurao Village

21 March: Azuma General
Gymnasium, (Fukushima
City)

15

Iitate Village

29 May: Iino Branch Officeof Fukushima City Office,(Fukushima City)

16

Iitate Village

21 June: Iino Branch Officeof Fukushima City Office,(Fukushima City)

16 March: Big Pallet
Fukushima, (Koriyama
City)ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Scenario

Location at
11 March 201117

Minamisoma City

20 May: Minamisoma City
Office, (Minamisoma City)

18

Kawamata Town
Yamakiya Region

01 June: Kawamata Town
Office, (Kawamata Town)

179

Evacuation destinations

C67. Within the 18 evacuation scenarios, four types of human activities were considered: normal living
conditions; residents preparing for evacuation; evacuation; and sheltering. For the normal living
conditions, the assumptions on human behaviour were the same as those used in the external andinhalation exposure calculations for the non-evacuated areas. For the evacuation preparation,
evacuation, and sheltering activities, the Committee assumed occupancy factors and breathing rates thatreflected the nature of activities undertaken (distinct from those considered for normal living
conditions). The NIRS survey was used to identify the building types in each location, and temporaland spatial movements of residents local to FDNPS. The assessments for the 18 evacuation scenarios
used the deposition density and air concentration results from NOAA–GDAS ATDM. Otherwise, thesame input parameters and methods as detailed in the previous sections for the assessment for external
exposure and dose from inhalation for the non-evacuated areas were applied.
C68. At present, detailed information about the scale and effectiveness of the environmental
remediation is not available and therefore assessments of doses allowing for the effectiveness of thesemeasures were not possible. Estimates were made of the doses that would be received by the residentsof evacuated settlements if they were to return to their homes and regular lifestyle one, two or three
years after the accident, without the implementation of remediation (see table C19 below).

F. Assessment of collective doses
C69. The collective dose to the general public is an instrument primarily for optimization of protection
or comparing radiological technologies or protection measures. The aggregation of very low individual
doses over extended time periods is inappropriate. Comparisons have been made of the collective dose
integrated over a defined time period with those from other events associated with radionuclide releases
to the environment (such as global fallout following the testing of nuclear weapons in the atmosphereand the Chernobyl accident). The Committee has estimated the collective effective dose and thecollective absorbed dose to the thyroid for the population of Japan. The main contributors to thecollective effective dose to the public were the long-term exposure pathways: external exposure from134
Cs and 137Cs deposited on the ground and internal exposure from ingestion of the same radionuclides
in foods.
C70. The collective dose due to external exposure for a particular area depends on the population size,radionuclide deposition densities, dwelling type and occupation of the local population. Based onnational statistical data, it was assumed that about 30% of the Japanese population live in wooden oneto-three-storey houses, another 30% live in wooden fireproof one-to-three-storey houses, and about
40% live in concrete multi-storey apartments. Also, it was assumed that about 10% of the adult
population are outdoor workers.
C71. The collective doses from the ingestion of terrestrial foods were estimated from the total
production of foods, taking into account food wastage, in different regions of the country. In estimatingcollective doses, it was assumed that any foods with activity concentrations above the levels
recommended by the Japanese authorities were not eaten. The activity concentrations in most of thefood produced in Japan following the accident were below the set levels and the restrictions are known
to have been widely implemented. If there had been a limited consumption of some food with activity

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UNSCEAR 2013 REPORT

concentrations above the restriction levels, the impact on the assessed collective dose is likely to havebeen small.
C72. The estimated collective effective dose and collective absorbed dose to the thyroid were based on
the age and social composition of the population of Japan and the population distribution by district andprefecture as provided by the Japan 2010 Census [M20]. The collective doses were assessed for
populations residing in all localities of Fukushima Prefecture and the other prefectures of Japan. A
detailed description of the methodology is provided in attachment C-12.

III. RESULTS
C73. The methodologies described in section II were used to derive detailed estimates of the doses by
age group (20-year-old adults, 10-year-old children and 1-year-old infants) for the settlements inFukushima Prefecture that were evacuated according to the 18 evacuation scenarios (Group 1), the nonevacuated districts within Fukushima Prefecture (Group 2), the Group 3 prefectures, and the rest ofJapan (Group 4). A detailed dose assessment was conducted for all districts in Fukushima Prefectureand some districts of the Group 3 prefectures of Iwate, Miyagi, Tochigi, Gunma, Ibaraki and Chiba.
Additional estimates of dose were made for those districts that were in the evacuation zones and for
those districts that were partially evacuated (the cities of Minamisoma and Tamura and Kawamata
Town). The uncertainties associated with the measurement data and the additional modelling approach
are discussed in the next section.
C74. The datasets and ATDM did not provide sufficient information for the estimation of doses tomembers of the public in neighbouring countries and elsewhere in the world. The Committee has reliedon the estimates of these doses published in the literature, including the WHO preliminary dose
estimation [W11], or provided by Member States of the United Nations.

A. Estimates of doses in Japan in the first year
1.

Effective dose

C75. Table C6 summarizes the estimated district- or prefecture-average effective doses received in thefirst year following the accident, for 20-year-old adults, 10-year-old children and 1-year-old infants
residing in the non-evacuated districts of Fukushima Prefecture (Group 2), the Group 3 prefectures andthe remaining prefectures in Japan (Group 4). The doses are summed over the main exposure pathways
and are intended to be characteristic of the district- or prefecture-average doses received by people
living in each location. The estimates in table C6 reflect the range of average doses across the districts
within prefectures, not the ranges of doses received by individuals within the populations at theselocations. The relative contribution of each main exposure pathway to the total estimated doses varied
from location to location reflecting the levels of radionuclides in the environment and exposure
conditions. Detailed results for each district and age group are provided in attachment C-14.
C76. Figure C-VI shows the district-average effective doses in the first year following the accident for
1-year-old infants living in districts of Fukushima Prefecture and some districts of the Group 3
prefectures that were not evacuated. The spatial distribution in the estimated doses shown in this figurereflects the pattern of the releases and depositions of radionuclides in the different settlements in thearea.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

181

Figure C-VI. The district-average effective doses in the first year following the accident for 1-year-old
infants living in districts of Fukushima Prefecture and some districts of Group 3 prefectures thatwere not evacuated

C77. The highest estimated doses were to those individuals who were not evacuated in Fukushima
Prefecture, the districts that partly fall within the 20-km evacuation zone (Minamisoma City) and thosewith high levels of deposition density (the cities of Fukushima, Nihonmatsu, Date, Motomiya andKoriyama, Koori Town and Otama Village). The district-average total effective doses to adults in theseareas were in the range of 2.5 to 4.3 mSv in the first year. The contribution of external exposure from
deposited radionuclides to the total effective dose was dominant. One-year-old infants were estimatedto have received average effective doses in the first year up to twice those received by adults.
C78. For the districts of the Group 3 prefectures (Chiba, Gunma, Ibaraki, Iwate, Miyagi and Tochigi),
the district-average total effective doses to adults were in the range of 0.2 to 1.4 mSv in the first year,with the contribution from ingestion of food in the prefectures of Chiba, Gunma, Ibaraki, Miyagi andTochigi being 0.2 mSv. In Iwate Prefecture, the contribution to dose from ingestion of food was
0.1 mSv, the same as for the remainder of Japan. The prefecture-average total effective doses to adults
for the prefectures in the remainder of Japan were in the range 0.1 to 0.3 mSv in the first year, withingestion contributing 0.1 mSv, and generally being the dominant pathway.
C79. Figure C-VII shows the prefecture-average effective doses in the first year to 1-year-old infants in
the rest of Japan. Prefecture-average doses in other prefectures were lower than those in Fukushima
Prefecture and were considerably lower in the more distant prefectures, where the dose estimates wereless than the variation in background doses from natural sources of radiation. Measurement results
reported by a number of groups, including the online community group SafeCast [S1], also showeddose rates in most areas across Japan distant from Fukushima Prefecture to be at the background level.

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UNSCEAR 2013 REPORT

Figure C-VII. Estimated total effective doses to 1-year-old infants in the first year following theaccident
The main map shows the prefecture-average effective dose. Fukushima Prefecture average includes non-evacuated districts
only. The inset map shows the district-average effective doses for non-evacuated districts of Fukushima Prefecture

C80. External exposures of the foetus and breast-fed infant from gamma radiation (mainly from 134Cs
and 137Cs) would have been approximately the same as those to adults and infants, respectively. The
doses from inhalation and ingestion would have been dominated by intakes of radiocaesium andradioiodine. For radiocaesium, the effective doses to the foetus and breast-fed infant would have beenless than those to the mother [I19, I20, O1]. For radioiodine, including 131I, the breast-fed infant may
have received absorbed doses to the thyroid up to a factor of two higher than those to the thyroid of themother. Overall, the doses received by the foetus and breast-fed infant would have been lower than orwithin the range of doses estimated for the three main age groups [O1].
C81. For districts within Fukushima Prefecture (Group 2) and Group 3 prefectures, the relative
contribution of each exposure pathway varied from location to location, reflecting the levels andcomposition of radionuclides in the environment and foodstuffs. In the areas of higher deposition
density, the greatest contribution to effective dose was from external exposure to deposited material.
Inhalation of radionuclides in air was an important exposure pathway for the thyroid. The relative
contribution to effective dose in the first year from the ingestion of food varied, depending on thecontribution from other pathways. This variability in the contribution from the different pathways arose
because doses from ingestion reflected concentrations of radionuclides averaged over much larger areas
than the doses from other pathways. In areas of Japan far away from the FDNPS site, doses fromingestion predominated for most prefectures. The doses presented here are representative of the average
doses to the different populations and, as discussed later, the actual doses to individuals would havevaried about these averages depending on factors such as what foods were consumed and location
within districts. The variability is such that the estimates of the effective dose to an individual could be
up to about two to three times higher or lower in some locations than the average for the district.

Table C6. Estimated district- or prefecture-average effective doses in the first year following the accident for residents of Japan for locations that were not evacuated
The reported doses are the ranges of the district-average doses for the Group 2 and Group 3 prefectures and the prefecture-average doses for the Group 4 prefectures. These estimates of dose are intended to be
characteristic of the average dose received by people living at different locations and do not reflect the range of doses received by individuals within the population at these locations

Effective dose by pathway (mSv)
Residential area

AdultsExternal + Inhalation

10-year old

Ingestion

a

Total

External + inhalation

1–year old
Total

External + inhalation

Ingestiona

Total

1.2

1.2–5.9

0.1–5.6

1.9

2.0–7.5

IngestionaGroup 2b—Fukushima Prefecture
Districts notevacuatedc

0.0–3.3

0.9

1.0–4.3

0.0–4.7

Chiba Prefecture

0.1–0.8

0.2

0.3–1.1

0.1–1.0

0.3

0.4–1.3

0.1–1.1

0.5

0.6–1.7

Gunma Prefecture

0.1–0.6

0.2

0.3–0.8

0.1–0.8

0.3

0.4–1.1

0.1–0.9

0.5

0.6–1.5

Ibaraki Prefecture

0.1–0.6

0.2

0.3–0.8

0.1–0.9

0.3

0.4–1.2

0.1–1.0

0.5

0.6–1.5

Miyagi Prefecture

0.1–0.3

0.2

0.3–0.5

0.1–0.9

0.3

0.4–1.2

0.1–1.0

0.5

0.6–1.6

Tochigi Prefecture

0.1–1.2

0.2

0.3–1.4

0.1–1.7

0.3

0.4–2.0

0.2–2.0

0.5

0.7–2.5

Iwate Prefecture

0.1–0.3

0.1

0.2–0.5

0.1–0.5

0.1

0.2–0.6

0.1–0.6

0.2

0.3–0.8

0.1

0.1–0.4

0.0–0.3

0.2

0.2–0.5

Group 4e—rest of Japan
40 remaining
prefecturesa0.0–0.2

0.1

0.1–0.3

0.0–0.2

The ingestion dose for Iwate Prefecture is the same as for the prefectures in the rest of Japan.

bGroup 2: Members of the public living in the non-evacuated districts of Fukushima Prefecture.

c

Excluding specific areas that were evacuated within these districts.

dGroup 3: Members of the public living in the prefectures of Miyagi, Gunma, Tochigi, Ibaraki, Chiba and Iwate. The prefectures of Chiba, Gunma, Ibaraki, Miyagi and Tochigi were grouped together to calculate thedose from ingestion in these prefectures. For Iwate Prefecture, the dose from ingestion was assumed to be the same as that for the rest of Japan.
eGroup 4: Members of the public living in the remaining prefectures of Japan.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Group 3d prefectures

183

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UNSCEAR 2013 REPORT

2.

Contribution of external exposure to the total effective dose

C82. The gamma-radiation dose rates in air from the deposited radionuclides were estimated as afunction of time and location from the measurements of the deposition density of radionuclides on the
ground. Figure C-VIII shows the contributions of the main radionuclides to the dose rate. While themore important radionuclides contributing to the external exposure were 131I, 134Cs and 137Cs in the firstweeks following the release, there were also significant contributions from the short-lived
radionuclides, in particular, 132Te and 132I. The dose rate due to deposited material fell by a factor of 10
in the first month and, after two months, the dose rate was predominantly due to 134Cs and 137Cs.
Figure C-VIII. Percentage contribution of different radionuclides to the dose rate in air at 1 m above
the ground in the first months after the accident

C83. The deposition of radionuclides on the ground at locations within the south trace (the towns ofTomioka, Naraha and Hirono and Iwaki City of Fukushima Prefecture) was significantly enhanced in132
Te, 131I and 132I compared with the rest of Japan. As a consequence, for the assessment for the nonevacuated areas, the external exposure per unit deposition density of 137Cs in the first year was larger bya factor of about two for Iwaki City than in the rest of Japan, as shown in figure C-IX.
C84. The estimated district- or prefecture-average effective doses to the various age and populationgroups in the first year for all the districts of Fukushima Prefecture, the Group 3 prefectures and theremaining prefectures in Japan (Group 4) are summarized in table C6. The contribution of external
exposure was larger in the districts with the higher deposition densities of radionuclides on the ground.
In the non-evacuated districts of Fukushima Prefecture, the district-average effective doses to infants inthe first year from external exposure were not more than 5 mSv (Fukushima City) and for adults, notmore than 3 mSv.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

185

Figure C-IX. Accumulated effective doses per unit deposition density from external exposure of
typical adults living on the south trace and in the rest of JapanThe doses are normalized to the deposition density on the ground of 1 MBq/m2 of 137Cs. A typical adult is defined as an adultliving in a wooden house and working indoors in a concrete multi-storey building

C85. The estimated effective doses to the various age and population groups due to external exposure
from deposited radionuclides varied depending on the dwelling type and people’s occupation,
especially, on the time spent outdoors, and on body size (which is correlated with age). Table C7
presents the ratios of the average effective dose to each of the various age/population groups in the firstyear to that of a typical adult (defined as an adult living in a wooden house and working indoors in a
concrete multi-storey building). The effective doses to the most exposed group (preschool children
living in wooden houses) and to the least exposed group (indoor workers living in apartment blocks)
deviate from that to the typical adult by no more than a factor of two.
Table C7. Ratios of the effective dose to each of various age/population groups of the Japanese
population to that to the typical adult from external exposure in the first year
A typical adult is defined as an adult living in a wooden house and working indoors in a concrete multi-storey building

Ratio of effective doses
Dwelling type

Adults10-year old

1-year old

1.3

1.4

1.7

1.0

0.7

0.9

1.1

0.8

0.5

0.6

0.8

Outdoor worker

Indoor worker

Wooden one-to-three-storey house

1.4

Wooden fireproof one-to-three-storey house
Concrete multi-storey apartment

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UNSCEAR 2013 REPORT

3.

Contribution of internal exposure from ingestion to total dose

C86. Doses to a range of organs and for various age groups from ingestion were calculated from themonthly intakes of radionuclides in foods in the first year following the releases, using the database ofactivity concentrations in food. The estimates of effective dose and absorbed dose to the thyroid fromingestion in the first year are given in table C8.
C87. The doses from intakes of radionuclides via ingestion in the first month following the accident
contributed the major part of the total doses received from ingestion during the first year. For example,
intakes in the first month contributed over 80% of the effective dose to adults and over 90% of theeffective dose to infants from the ingestion pathway. The doses from intakes via ingestion after the firstmonth showed some fluctuation from month to month. The doses in months 2 to 4 and then in months
5 to 12 were essentially constant given the uncertainties in the dose assessment. This was partly as aresult of the use of a constant value for the activity concentrations of radionuclides in foodstuffs whenthe measurements were below the limits of detection.
C88. In using the database of radionuclides in foods, the Committee assumed that the results wererepresentative of the activity concentrations in food as consumed in the different prefectures. However,
the measurements were taken to indicate where restrictions were required and so were likely to bebiased towards the higher end of the range of actual activity concentrations in foods. If it had been
assumed that only 25% of the food consumed was from the local prefecture and the remaining 75%
from the rest of Japan then the estimated doses would have been lower. For example, for Fukushima
Prefecture, the estimated effective dose to a 1-year-old infant in the first year would have been 0.6 mSv
rather than 1.9 mSv and the absorbed dose to the thyroid would have been 10 mGy rather than 33 mGy.
More detailed results of the assessment are provided in the attachment C-15.
Table C8. Estimated doses to adults, children and infants, living in different locations, from theingestion of radionuclides in food in the first year
Effective dose (mSv)

Absorbed dose to thyroid (mGy)

Location
Adults10-year old

1-year old

Adults10-year old

1-year oldGroup 2—Fukushima
Prefecture

0.94

1.2

1.9

7.8

15

33

Group 3 prefectures

0.21

0.31

0.53

2.1

4.3

9.4

Group 4—rest of Japan

0.11

0.13

0.18

0.53

1.2

2.6

4.

Estimates of doses from drinking water

C89. Table C9 summarizes the estimates of the district- or prefecture-average effective doses andabsorbed doses to the thyroid from the ingestion of radionuclides in drinking water between March2011 and March 2012. The maximum average doses were estimated for Iitate Village, with the intakes
occurring before the deliberate evacuation. The detailed results of the assessment of doses fromdrinking water are provided in attachment C-15.

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187

Table C9. Estimated district- or prefecture-average effective doses and absorbed doses to thethyroid from drinking water in Fukushima Prefecture and other locations in Japan
Effective dose (mSv)

Absorbed dose to thyroid (mGy)

Location
Adults10-year old

1-year old

Adults10-year old

1-year oldGroup 2—Fukushima
Prefecturea

0.02

0.02

0.06

0.38

0.44

1.1

Group 2—Iitate Village

0.16

0.19

0.48

3.2

3.7

9.6

0.001–0.03

0.001–0.03

0.002–0.06

0.02–0.55

0.02–0.64

0.05–1.2

0–0.0100–0.011

0–0.027

0–0.18

0–0.21

0–0.54

Group 3 prefecturesbcGroup 4—rest of Japana

Population-weighted average determined from doses for non-evacuated districts of Fukushima Prefecture.

b

Range of doses for prefectures of Iwate, Gunma, Tochigi, Miyagi, Ibaraki and Chiba.

c

For the majority of prefectures in Japan radionuclides were not detected in drinking water above detection limits. Only theprefectures of Akita, Kanagawa, Niigata, Saitama, Shizuoka, Tokyo, Yamagata and Yamanashi detected radionuclides above
detection limits. Tokyo reported the highest results for prefectures in the rest of Japan.

C90. Two papers have reported estimates of average doses from drinking water to Japanese citizens.
Murakami and Oki [M26] estimated absorbed doses to the thyroid from a number of pathways
including ingestion of drinking water for citizens of Tokyo for the first year following the accident.
Amano et al. [A9] estimated committed effective doses due to ingestion of tap water in the two months
directly following the accident for Chiba residents. The estimated doses to adults and infants in both
papers show very good agreement, within 10% of those estimated here. Differences of factors of about
two for the doses to children could be attributed to the use of dose conversion coefficients for different
age groups.

5. Estimates of absorbed doses to the thyroid, red bone marrow and female
breast from exposure in the first year
C91. It is particularly important to consider the absorbed doses to the thyroid of infants from intakes ofradioiodine because of the radiosensitivity of their thyroids. The first-year absorbed doses to the thyroidof various age groups for all the districts of Fukushima Prefecture, most districts of the Group 3
prefectures and for the rest of Japan (Group 4) are presented in detail in attachment C-16 andsummarized in table C10. Most of the absorbed dose to the thyroid was received by the public over the
first month after the accident.
C92. Figure C-X shows the estimated absorbed doses to the thyroid of 1-year-old infants in the firstyear by district for the different locations in Fukushima Prefecture and districts of some neighbouring
prefectures. Again, districts where the communities were evacuated are not included in these estimates,
but are discussed in the following section. The highest district-average doses to the thyroid were toindividuals in the cities of Iwaki and Fukushima. The highest district-average absorbed dose to thethyroid was estimated to have been 52 mGy for a 1-year-old infant living in Iwaki City, withapproximately one third of this due to inhalation and two thirds to ingestion. The contribution of
inhalation to the absorbed dose to the thyroid was higher in districts with the higher deposition densityof radionuclides on soil. Within each district, there was also a marked spatial variability in theconcentration of 131I in air and the estimates of the absorbed dose to the thyroid of an individual frominhalation could be up to about two to three times higher or lower in some locations within districts

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than the average dose for the district. The estimated absorbed doses to the thyroid for adults and10-year-old children in the first year were about 30% and 50%, respectively, of those for 1-year-old
infants.
Figure C-X. The district- average absorbed doses to the thyroid in the first year following theaccident for 1-year-old infants living in districts of Fukushima Prefecture and some districts ofGroup 3 prefectures that were not evacuatedC93. For Group 3 prefectures (Chiba, Gunma, Ibaraki, Iwate, Miyagi and Tochigi), the district-averageabsorbed doses to the thyroid of infants were estimated to be in the range of 3 to 15 mGy, with thedominating exposure pathway being ingestion; the contribution of the inhalation pathway ranged from a
few to about thirty per cent. In the remaining 40 prefectures of Japan, the prefecture-average absorbed
doses to the thyroid of infants were estimated to have been about 3 mGy, with between 75% and 100%of the dose from the ingestion of food.
C94. For the non-evacuated districts within Fukushima Prefecture, the district-average absorbed doses
to the red bone marrow and the female breast of adults, children and infants in the first year were
estimated to be in the range of 0.6 to 3.6 mGy, 0.4 to 4.6 mGy and 0.3 to 5.3 mGy, respectively. For
Group 3 prefectures (Chiba, Gunma, Ibaraki, Iwate, Miyagi and Tochigi), the district-average absorbed
doses to the red bone marrow and the female breast of adults, children and infants in the first year were
estimated to be in the range of 0.1 to 1.2 mGy, 0.1 to 1.6 mGy and 0.1 to 1.9 mGy, respectively. In theremaining 40 prefectures of Japan, the prefecture-average absorbed doses to the red bone marrow andthe female breast in the first year were estimated to have been less than 0.3 mGy for adults, children
and infants. The absorbed doses to the red bone marrow of various age groups in the first year
following the accident for all the districts of Fukushima Prefecture, most of districts of the Group 3
prefectures and for the rest of Japan (Group 4) are presented in detail in attachment C–17.

Table C10. Estimated district- or prefecture-average absorbed doses to the thyroid in the first year following the accident for residents of Japan for locations that were notevacuated
Absorbed dose to thyroida (mGy)
Residential area

AdultsExternal + inhalation

10-year old

Ingestionb

Total

External + inhalation

Ingestionb

1-year old
Total

External + inhalation

Ingestionb

Total

15

15–31

0.2–19

33

33–52

c

Group 2 —Fukushima Prefecture
Districts notevacuatedd

0.1–9.6

7.8

7.8–17

0–16

Chiba Prefecture

0.2–2.1

2.1

2.3–4.2

0.2–3.3

4.3

4.6–7.7

0.3–4.0

9.4

9.7–13

Gunma Prefecture

0.2–1.4

2.1

2.3–3.5

0.3–2.2

4.3

4.6–6.5

0.3–2.6

9.4

9.7–12

Ibaraki Prefecture

0.2–1.5

2.1

2.3–3.6

0.3–2.4

4.3

4.6–6.7

0.3–2.9

9.4

9.7–12

Miyagi Prefecture

0.1–1.5

2.1

2.2–3.6

0.2–2.4

4.3

4.6–6.8

0.2–3.0

9.4

9.6–12

Tochigi Prefecture

0.2–3.0

2.1

2.3–5.1

0.3–4.8

4.3

4.6–9.1

0.4–5.8

9.4

9.7–15

0.1–0.9

0.5

0.6–1.4

0.2–1.4

1.2

1.3–2.5

0.2–1.7

2.6

2.7–4.2

1.2

1.2–1.8

0–0.8

2.6

2.6–3.3

Iwate PrefecturebGroup 4f—rest of Japan
40 remaining
prefectures

0–0.4

0.5

0.5–0.9

0–0.6

a

The reported doses are the ranges of the district-average doses for the Group 2 and Group 3 prefectures and the prefecture-average doses for the Group 4 prefectures. These estimates of dose are intended to be
characteristic of the average doses received by people living at different locations and do not reflect the range of doses received by individuals within the population at these locations.

b

The dose from ingestion for Iwate Prefecture is the same as for the prefectures in the rest of Japan.

cGroup 2: Members of the public living in the non-evacuated districts of Fukushima Prefecture.

dExcluding specific areas that were evacuated within these districts.

eGroup 3: Members of the public living in the prefectures of Miyagi, Gunma, Tochigi, Ibaraki, Chiba and Iwate. Chiba, Gunma, Ibaraki, Miyagi, and Tochigi were grouped together to calculate the dose from ingestion inthese prefectures. For Iwate Prefecture, the dose from ingestion was the same as that for the rest of Japan.

fGroup 4: Members of the public living in the remaining prefectures of Japan.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Group 3e prefectures

189

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UNSCEAR 2013 REPORT

6.

Estimates of doses to residents of evacuated communities

C95. The evacuations undertaken to protect the public from the releases from FDNPS reduced theradiation exposures that would otherwise have been received. Doses were estimated for the 18 groupsof people in the NIRS scenarios who were evacuated at different times and moved to different locations(see table C5). The doses were assessed for the period before and during the evacuation. The lastevacuation occurred on 21 June 2011. These dose estimates were based on the ATDM results forradionuclide concentration in air and deposition density in the days following the accident.
C96. The estimated settlement-average effective doses to adults in these groups from external
irradiation from deposited radionuclides and from the plumes and internal irradiation following
inhalation of radionuclides in air and ingestion of foods are summarized in table C11. The estimates ofsettlement-average total effective dose over the periods of these evacuations were less than 3 mSv for
those evacuated by 15 March 2011, and less than 10 mSv for those evacuated at later times. These
values are consistent with those obtained in a previous assessment of external doses to evacuees by
NIRS that used a similar methodology but a different dispersion model and source term [A4].
C97. The estimated effective doses in the first year to those who were residents of the evacuateddistricts are the sum of the doses received before and during evacuation and during the remainder of theyear at the location to which they were evacuated. These doses are also summarized in table C11. The
settlement-average effective doses to adults who were evacuated in March 2011 were estimated to beless than 6 mSv in the first year and to those evacuated in April to June 2011 less than 10 mSv in thefirst year. Ten-year-old children and 1-year-old infants were estimated to have received average
effective doses in the first year up to twice those for adults. Detailed results of the estimates of effective
doses to the evacuees are provided in attachment C-18. Doses to the foetus and breast-fed infants were
not explicitly estimated but would have been approximately the same as those to adults and 1-year-old
infants, respectively.
C98. The estimates of settlement-average absorbed doses to the thyroid of a 1-year-old infant are
shown in table C12. The settlement-average absorbed doses to the thyroid of 1-year-old infants before
and during the evacuations were estimated to be up to about 50 mGy for those evacuated by 15 March2011 and up to about 70 mGy for those evacuated at later times. These doses were principally frominhalation during the passage of the airborne radioactive material through the affected areas in the earlydays of the accident and from ingestion over the subsequent period. The absorbed doses to the thyroidfor the first year for the 1-year-old infants who were evacuated ranged from 15 up to about 80 mGy.
Detailed results of the estimates of absorbed dose to the thyroid of the evacuees are provided inattachment C-18. The protective effect of iodine blocking possibly implemented by some residents was
not taken into account in the assessment.
C99. For the precautionary evacuated settlements (scenarios 1−12), the settlement-average absorbed
doses to the red bone marrow in the first year were estimated to be in the range of 0.6 to 7 mGy and forthe deliberately evacuated settlements (scenarios 13−18), in the range of 4 to 10 mGy, for all age
groups. The first-year absorbed doses to the red bone marrow of various age groups for all theevacuated settlements of Fukushima Prefecture are presented in detail in attachment C–18. For
evacuated girls and women, the settlement-average absorbed doses to the breast were estimated to be up
to about 10 mGy for all age groups.

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191

Table C11. Estimated settlement-average effective doses to adults evacuated from localities ofFukushima Prefecture
The doses calculated are settlement-average effective doses for each evacuation scenario, before and during evacuation, andfor the first year following the accident. The dose estimates are intended to be characteristic of the average effective doses
received by people evacuated from each settlement. Scenarios 1 to 12 correspond to the precautionary evacuatedsettlements; scenarios 13 to 18 correspond to the deliberately evacuated settlements

Effective dose to adult (mSv)

NIRS
scenariono.

Destination

Tomioka Town

1

Okuma Town

Locality

Evacuationa

Destinationb

Total firstyearc

Projectedd

Avertede

Koriyama City

0.2

3.1

3.3

51

48

2

Tamura City

0.0

1.5

1.5

47

45

Futaba Town

3

Saitama

0.9

0.2

1.1

38

37

Futaba Town

4

Saitama

0.9

0.2

1.1

38

37

Naraha Town

5

Tamura City

2.2

1.5

3.7

7

3

Naraha Town

6

Aizimisato
Town

1.3

1.2

2.5

7

4

Namie Town

7

Nihonmatsu
City

1.3

3.7

5.0

25

20

Tamura City

8

Koriyama City

0.4

3.1

3.5

1.5

-

Minamisoma
City

9

Fukushima City

1.4

4.3

5.7

4

-

Hirono Town

10

Ono Town

0.0

1.3

1.3

4

3

Kawauchi Village

11

Koriyama City

0.2

3.1

3.3

2

-

Katsurao Village

12

Fukushima City

0.0

4.3

4.3

6

2

Tsushima
Activation
Center, Namie
Town

13

Nihonmatsu
City

4.3

2.7

7.0

25

18

Katsurao Village

14

Fukushima City

2.7

3.3

6.0

6

-

Iitate Village

15

Fukushima City

5.7

2.1

7.8

11

3

Iitate Village

16

Fukushima City

6.2

1.8

8.0

11

3

Minamisoma
City

17

Minamisoma
City

3.8

1.0

4.8

4

-

Yamakiya
Region,Kawamata Town

18

Kawamata
Town

8.5

0.8

9.3

2

-

a

Estimate of the dose that people received before and during evacuation.

b

Estimate of the dose that people received for the rest of the first year following evacuation.

c

Estimate of the dose in the first year that people received before and during evacuation and at destination for remainder of year.

d

Estimate of the dose that people would have received in the first year if they had not been evacuated.

e

Estimate of the dose that people avoided by being evacuated.

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Table C12. Estimated settlement-average absorbed doses to the thyroid of 1-year-old infants
evacuated from localities of Fukushima Prefecture
The doses calculated are settlement-average absorbed doses to the thyroid for each evacuation scenario, before and during
evacuation, and for the first year following the accident. The dose estimates are intended to be characteristic of the averageabsorbed doses to the thyroid received by people evacuated from each settlement. Scenarios 1 to 12 correspond to theprecautionary evacuated settlements; scenarios 13 to 18 correspond to the deliberately evacuated settlements

Absorbed dose to thyroid of 1-year-old infant (mGy)

NIRS
scenariono.

Destination

Tomioka Town

1

Okuma Town

Locality

Evacuationa

Destinationb

Total firstyearc

Projectedd

Avertede

Koriyama City

5.2

42

47

795

750

2

Tamura City

0.0

36

36

507

470

Futaba Town

3

Saitama

12

3

15

288

270

Futaba Town

4

Saitama

16

3

19

288

270

Naraha Town

5

Tamura City

46

36

82

138

60

Naraha Town

6

Aizimisato
Town

35

34

69

138

70

Namie Town

7

Nihonmatsu
City

37

44

81

145

60

Tamura City

8

Koriyama City

1.9

42

44

36

-

Minamisoma
City

9

Fukushima City

6.4

47

53

39

-

Hirono Town

10

Ono Town

0.0

34

34

76

40

Kawauchi Village

11

Koriyama City

5.0

42

47

40

-

Katsurao Village

12

Fukushima City

0.0

49

49

61

12

Tsushima
Activation
Center, Namie
Town

13

Nihonmatsu
City

59

24

83

145

60

Katsurao Village

14

Fukushima City

46

27

73

61

-

Iitate Village

15

Fukushima City

52

3.8

56

80

24

Iitate Village

16

Fukushima City

53

2.7

56

80

24

Minamisoma
City

17

Minamisoma
City

45

2.3

47

39

-

Yamakiya
Region,Kawamata Town

18

Kawamata
Town

63

1.9

65

45

-

a

Estimate of the dose that people received before and during evacuation.

b

Estimate of the dose that people received for the remainder of the first year following evacuation.

c

Estimate of the dose in the first year that people received before and during evacuation and at destination for rest of year.

d

Estimate of the dose that people would have received in the first year if they had not been evacuated.

e

Estimate of the dose that people avoided by being evacuated.

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193

C100. The evacuation of settlements within the 20-km zone was estimated to have averted effective
doses to adults of up to about 50 mSv and absorbed doses to the thyroid of 1-year-old infants of up to
about 750 mGy. In some areas, the doses received by the evacuees were similar to those that would
have been received had they stayed in place. The estimated doses are averages for the various age
groups and communities, and while some individual doses may have been higher, it was not possible toquantify the range of doses from the data available at the time. For the small number of hospital andnursing-home patients, residents and other individuals in the 20-km zone for whom the 18 evacuation
scenarios were not applicable, higher doses could not be ruled out. The doses that were averted, when
added to the estimates of dose received before and during the evacuation, can be used as estimates ofthe doses to people who might have stayed in the evacuation zone, and as an upper bound for any
individual who might have gained access to the zone.

B. Estimation of doses in Japan from exposure over futureyears
C101. Estimates have also been made of district- and prefecture-average doses accumulated over the
first 10 years after the accident and up to age 80 years. The doses from external exposure were assessedwith similar methods as for the first year, but taking account of the reduction in dose rate due toradioactive decay and the removal of radionuclides by physico-chemical processes over the period of
the exposure. The detailed methodology is presented in attachment C-12. Table C13 shows thedependence of doses from external exposure on the exposure duration and location for various age
groups of the Japanese population. Because of a lack of detailed information on the implementation andeffectiveness of remediation at specific locations, no account was taken of the possible reduction in
exposure as a consequence of remediation.
Table C13. Dependence of the effective dose from external exposure normalized by deposition
density of 137Cs on the exposure duration
Effective dose from external exposure per unit deposition densitya(mSv per 0.1 MBq/m2 as of June 2011)
Exposure duration

Age/population group (as of 2011)
Adults10-year old
Outdoor worker

1-year old

Indoor worker

Entire Japan except south traceb
1 year

1.8

1.6

1.8

2.1

10 years

3.9

3.8

4.2

4.9

Up to age 80 years

5.6

5.6

6.0

6.7

South traceba

1 year

4.0

3.7

4.1

4.9

10 years

6.2

5.9

6.5

7.6

Up to age 80 years

7.9

7.7

8.3

9.4

Because of a lack of detailed information on the implementation and effectiveness of remediation at specific locations, noaccount was taken of the possible reduction in exposure as a consequence of remediation.
b

Towns of Tomioka, Naraha and Hirono and Iwaki City of Fukushima Prefecture.

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C102. The doses from the ingestion of radionuclides were estimated using the FARMLAND model,[B21] taking account of radioactive decay. The estimated effective doses and absorbed doses to thethyroid for adults, 10-year-old children and 1-year-old infants, integrated over 10 years after theaccident and up to age 80 years are available in attachment C–19. The total doses from external andinternal exposures are summarized in table C14.
Table C14. Estimated district- or prefecture-average effective doses to adults, 10-year-old children
and 1-year-old infants (as of 2011) over the first year and first ten years and to age 80 years
District- or prefecture-average effective dosea (mSv)
Age groupGroup 3cprefectures

Group 2—

Group 4d—rest of Japan

Fukushima Prefectureb
1-year exposure
Adults

1.0–4.3

0.2–1.4

0.1–0.3

10-year old

1.2–5.9

0.2–2.0

0.1–0.4

1-year old

2.0–7.5

0.3–2.5

0.2–0.5

10-year exposure
Adults

1.1–8.3

0.2–2.8

0.1–0.5

10-year old

1.3–12

0.3–4.0

0.1–0.6

1-year old

2.1–14

0.3–6.4

0.2–0.9

Exposure to age 80 yearsa

Adults

1.1–11

0.2–4.0

0.1–0.6

10-year old

1.4–16

0.3–5.5

0.1–0.8

1-year old

2.1–18

0.4–6.4

0.2–0.9

The reported doses are the ranges of the district-average doses for the Group 2 and Group 3 prefectures and the prefecture-

average doses for the Group 4 prefectures. These estimates of dose are intended to be characteristic of the average doses
received by people living at different locations and do not reflect the range of doses received by individuals within the population
at these locations.
bGroup 2: Members of the public living in the non-evacuated districts of Fukushima Prefecture.

cGroup 3: Members of the public living in the prefectures of Miyagi, Gunma, Tochigi, Ibaraki, Chiba and Iwate. The prefecturesof Chiba, Gunma, Ibaraki, Miyagi and Tochigi were grouped together to calculate the dose from ingestion in these prefectures.
For Iwate Prefecture, the dose from ingestion was the same as that for the rest of Japan.
dGroup 4: Members of the public living in the remaining prefectures of Japan.

C103. Figure C-XI shows the estimated district-average effective dose as a function of age group forthe different integration times for people living in Fukushima City. Infants aged 1 year at the time of
the accident had the highest estimated doses, followed by 10-year-old children and then those adults
who spent more time outdoors (see also tables C7 and C13). Adults who spent more time indoors had
the lowest estimated doses. However, the differences in the effective doses estimated for the same
exposure periods were not large, being less than a factor of two.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

195

Figure C-XI. Estimated district-average effective doses to typical adults, children and infants(as of 2011) living in Fukushima City

C104. The estimated average effective doses incurred over the 10-year-exposure period and theeffective doses up to age 80 years are larger by factors of up to two and three, respectively, than thosereceived in the first year. The greatest increases in dose were in the areas with the highest deposition
densities.
C105. Most of the absorbed dose to the thyroid of the residents of Japan was received during the firstyear from inhalation of 131I and ingestion of food containing this radionuclide. Continued exposure
from the longer-lived radioisotopes of caesium is estimated to result in an absorbed dose to the thyroid
up to age 80 years less than 50% higher than that received in the first year.

C. Radiation exposure outside of Japan
1.

Countries neighbouring Japan

C106. When WHO undertook its preliminary dose estimation in 2011 [W11], very few measurement
data were available for countries outside of Japan. In the absence of measured data, WHO applied amodelling approach to estimate doses received by people in these countries. The countries and regions
considered were the far-eastern part of the Russian Federation, Indonesia, the Philippines, the Republicof Korea and South-East Asia. The effective doses and the equivalent doses to the thyroid for theseplaces were all less than 0.01 mSv in the first year following the accident and the key exposure
pathways were ingestion of radionuclides in food and external irradiation by deposited radionuclides. In
all cases, most of the estimated dose was from the ingestion pathway.

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UNSCEAR 2013 REPORT

C107. Following the FDNPS accident, Keum et al. also estimated the radiation doses to people in the
Republic of Korea [K10]. These were based on measured levels of activity concentration anddeposition density of radionuclides. Estimates of effective doses and equivalent doses to the thyroid infive age groups (infants, 5-year olds, 10-year olds, 15-year olds and adults) were made. The doses
estimated for the Republic of Korea and in the WHO report are summarized in table C15.

2.

Rest of the world

C108. The assessment of doses for countries outside of Japan was based on a review of estimatespublished in the literature, including the results of the WHO preliminary dose estimation [W11],
supported by the extensive measurements, and dose assessments carried out by Member States of theUnited Nations. These dose estimates are summarized in table C15. Based on an analysis of this bodyof information, the Committee concluded that the total effective doses to individuals living outside ofJapan were less than 0.01 mSv in the first year following the accident.

Table C15. Estimated doses in the first year following the accident reported for regions outside of Japan
Estimated effective dose (mSv)
Geographic location

Comments
Adults10-year old

1-year old
Neighbouring countries

The Republic of Korea, Indonesia, thePhilippines, far-eastern part of theRussian Federation and South-East
Asia [W11]

The Republic of Korea [K10]<0.01

1.4 × 10

<0.01

−4

WHO applied a modelling approach to doses received by people outside of Japan. The key exposure pathways
were ingestion of radionuclides in food and external irradiation by deposited radionuclides. In all cases, mostof the estimated dose was from the ingestion pathway. An estimate of equivalent doses to the thyroid was
also made and these were also less than 0.01 mSv

<0.01

−4

1.9 × 10−5

5.7 × 10

Rest of the world

Rest of the world [W11]

<0.01

<0.01

<0.01

WHO applied a modelling approach to doses received by people outside of Japan. The key exposure pathways
were ingestion of radionuclides in food and external irradiation by deposited radionuclides. In all cases, mostof the estimated dose was from the ingestion pathway. Estimates of equivalent dose to the thyroid weremade and these were also less than 0.01 mSv
Estimated the equivalent doses to the thyroid of children aged 1 to 2 years from inhalation of radioiodine.
These ranged from 5 × 10−7 to 7 × 10−5 mSv. The maximum values were registered 24 days after the accident

Belarus [K6]
Cuba [A8]2 × 10−3

Estimated the effective doses from the inhalation of 131I and 137Cs using measured concentrations in aerosols

France [I32]

2 × 10−4

Estimated the maximum potential exposures (effective doses in adults and equivalent doses to the thyroid of
1-year-old infants) by inhalation and ingestion of 131I. Based on measurements from mid-March 2011 to
May 2011. The reported equivalent dose to the thyroid of 1-year olds in France was 4.5 × 10−2 mSv

Germany [B9]3 × 10−5

Greece [K21]1.1 × 10−6

Italy [I30]

3.5 × 10−2

5 × 10−5

Estimated the effective doses for the first year after the accident from inhalation and external exposure for 131I,
134
Cs and 137Cs from measurements of air samples and deposition density from late March to end of April 2011
in the south-west of Germany
Estimated the effective doses from the inhalation of 131I using measured concentrations in aerosols; no doses
from ingestion were calculated

1.9 × 10−6

1.8 × 10−1

Estimated the effective doses from external exposure, inhalation and ingestion of 131I, 134Cs, 137Cs in milk andwater. Ingestion of radionuclides in water was the major contributor of dose. Very conservative assumptions
were applied as the highest concentration values measured for each radionuclide in rainwater were used to
calculate the dose from ingested water

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Estimated the effective doses and equivalent doses to the thyroid for five age groups (infants, 5-year olds,
10-year olds, 15-year olds and adults) for the first year and up to age 70 years. Equivalent doses to the thyroid
ranged from 5.0 × 10−4 for infants to 1.2 × 10−3 mSv for adults in the first year. Estimates were made using
measured levels of airborne activity concentration and deposition density

197

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Estimated effective dose (mSv)
Comments
Adults10-year old

1-year old

Netherlands [K17]<1 × 10−5

Estimated the total effective doses from inhalation pathway using the measured airborne concentration of 131I

Portugal [C1]4.6 × 10−5

Estimated the total effective doses from inhalation and ingestion pathways for 132Te, 131I, 134Cs and 137Cs frommeasured concentrations in aerosol samples and deposition densities from late March to mid-April 2011

Romania [C8]8.5 × 10−5

Estimated the total monthly effective doses from ingestion of 131I in sheep milk and meat in Romania for the
first year after the accident

Serbia [B11]7.2 × 10−3

Estimated the effective doses from 131I concentrations in food, milk, air and rainwater. Doses were frominhalation and ingestion of food during one month. Ingestion of radionuclides in milk was the major pathway

UNSCEAR 2013 REPORT

Geographic location

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199

D. Estimates of collective doses
C109. The collective effective doses and the collective absorbed doses to the thyroid from the major
exposure pathways (external exposure, inhalation and ingestion) were estimated for the first year,
10 years and to age 80 years following the accident for Fukushima Prefecture, neighbouring prefectures
and the rest of Japan, and are summarized in table C16.
Table C16. Collective effective doses and absorbed doses to the thyroid for the population of Japan(128 million in 2010)
Exposure duration
Exposure pathway
First year

10 years

Up to age 80 years

Collective effective dose (thousand man-sieverts)
Inhalation

1.2

1.2

1.2

External

10

25

36

Ingestion

6.5

10

11

Total

18

36

48

Collective absorbed doses to thyroid (thousand man-grays)
Inhalation

22

22

22

External

10

25

36

Ingestion

50

53

54

Total

82

100

110

C110. The main contributor to the collective effective dose in the first year was external exposure
from deposited radionuclides; the ingestion of radionuclides in food was the next most important
contributor. The collective effective dose will increase over the first 10 years owing to the continued
external exposure and the ingestion of residual radionuclides in foods. After the first 10 years, theincrease in the collective effective dose will continue predominantly due to external exposure.
C111. Most of the collective absorbed dose to the thyroid in the first year was caused by ingestion
and inhalation of 131I in the spring of 2011, with a smaller contribution from external exposure over thewhole year. The collective absorbed dose to the thyroid will slowly increase over the first 10 years
owing to the continued external exposure and the ingestion of radionuclides in foods. After the first
10 years, the slow increase will continue because of external exposure.
C112. These collective doses to the population of Japan due to the FDNPS accident can be comparedto those to the populations of European countries exposed to radiation following the Chernobyl accident
in the former Soviet Union in 1986. The collective effective dose and collective absorbed dose to thethyroid from the Chernobyl accident determined for the 20-year period (1986–2005) by the Committee
from the results of both environmental and human measurements were about 360,000 36 man Sv and2,300,000 man Gy, respectively. The lifetime doses would be about 400,000 man Sv and36

About 260,000 man Sv without the contribution of the dose to the thyroid (see annex D [U12]).

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UNSCEAR 2013 REPORT

2,400,000 man Gy, respectively. The estimated collective effective dose to the population of Japan due
to a lifetime exposure following the FDNPS accident is approximately 10–15% of the corresponding
value for European populations exposed to radiation following the Chernobyl accident. The estimatedcollective absorbed dose to the thyroid for the Japanese population is approximately 5% of that for
European populations due to the Chernobyl accident.

IV. UNCERTAINTIES
C113. The doses presented are settlement-, district- or prefecture-averages for representative
members of the public. The estimated doses were based on the best available models and input data at
the time of the study. However, there are uncertainties associated with the results of any assessment of
this type because of incomplete knowledge or information, and the assumptions that were made. The
main sources of uncertainty are discussed here.

A. Assessment of dose from external irradiation andinhalation
C114. The estimated doses for external exposure in the non-evacuated areas were largely based on
measured levels of deposition density of radionuclides on the ground. The uncertainties associated withindividual measurements of 134Cs and 137Cs are relatively small but those for 131I are larger because of
the significant amount of radioactive decay that occurred before the measurements were made.
C115. There are also uncertainties in how well the measurements represented the spatial distributionof the radionuclides for each district or prefecture when estimating district- or prefecture-average doses.
For Fukushima Prefecture, there are extensive measurements with adequate spatial information.
Comparisons were made between the measurements of deposition density from the MEXT groundsurveys, the USDOE airborne radiometric survey and the NOAA–GDAS ATDM results for total
ground deposition. These data were analysed over the grid cells of approximately 1-km squares, withall data corrected for radioactive decay to 1 April 2011. The resultant spreadsheets and maps areprovided in attachments C-20 and C-21. The analysis shows good agreement between the measured
deposition densities of 137Cs on the ground from the MEXT and USDOE surveys. The marked spatial
variability is consistent with the spatial variability seen in other datasets. Based on a comparison of themeasured values, uncertainties associated with spatial variability in deposition density contribute an
uncertainty of about a factor of two to the uncertainties in the estimated district-average doses. For theGroup 4 prefectures, comparatively fewer measurements were made and the uncertainties in prefectureaverage doses are likely to be larger.
C116. For external irradiation from deposited radionuclides, a further source of uncertainty is fromthe reduction in exposures from being indoors and the shielding effects of the building materials. The
doses presented in previous sections are for the wooden houses which are the most common type ofhouses in Fukushima Prefecture. For people who live in wooden fireproof houses or concrete multistorey apartments, the doses were estimated to be about factors of two and four lower, respectively,
than those presented in the tables above. However, these factors were based mostly on European dataobtained following the Chernobyl accident and not on measurements conducted in Japan. A further

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201

factor directly influencing the estimation of dose from external exposure is the indoor occupancy forthe various age and social groups of the Japanese population.
C117. The estimates of exposure of the communities evacuated in March were based on the source
term and NOAA–GDAS ATDM results directly. The agreement between the NOAA–GDAS ATDM
results and the measured data for the deposition density of 137Cs is good for many areas but for somelocations, the ATDM results under- or overestimated the levels by up to a factor of ten. On average, thedistrict-average deposition densities of 137Cs obtained from NOAA–GDAS ATDM are about a factor of
two higher than the values from the MEXT surveys. For 131I, the district-average values obtained fromNOAA–GDAS ATDM range from overestimates by up to a factor of two, to underestimates by up to afactor of 10, with an average of about one.
C118. A source of uncertainty in the estimation of doses to evacuees from inhalation derives fromincomplete knowledge about the release rates of radionuclides over time and the weather conditions
during the releases. The ATDM results have large uncertainties when used to estimate doses at specificlocations. These uncertainties are discussed in section III.E in appendix B where the NOAA–GDAS
ATDM results are compared with the ATDM results obtained by the French Institute for Radiation and
Nuclear Safety (IRSN) [S3]. The ratios of the IRSN ATDM estimates for air concentrations of 131I to
those of the NOAA–GDAS ATDM results varied from about 0.5 and 12. These ratios reflect theuncertainty in the settlement-average doses from inhalation for these populations for specific locations
and times. For deposition density, the ratio of the IRSN ATDM estimates to those of the NOAA–GDAS
ATDM results varied between about 0.2 and 8. Again, these ratios reflect the uncertainty in thesettlement-average doses from external exposure. The uncertainties in the total doses in the first year
across all exposure pathways for the evacuated settlements are smaller than these ranges because of thecontributions to the total doses from the other pathways and at other locations.
C119. Similar uncertainties with the NOAA–GDAS ATDM results are relevant to the assessment ofdoses from external exposure and inhalation of radionuclides from the passing plume outside of theevacuated areas. For this assessment, the impact of these uncertainties were partially reduced by theapplication of a scaling method based on the measured deposition densities of radionuclides on the
ground and the ratio of air concentration to deposition density derived from NOAA–GDAS ATDM. As
detailed in section III of appendix B, the ratio of the bulk deposition velocities for 131I estimated by
IRSN ATDM to those estimated by NOAA–GDAS ATDM ranged from a factor of about 4 higher to afactor of about 30% lower, depending on the location. These factors imply concentrations in air (andconsequently doses from inhalation for the non-evacuated population) ranging from a factor of about
30% higher to a factor of about 4 lower, depending on the location. In addition, the doses from external
exposure and inhalation from the passing plume usually contributed less than half of the total dose andthe uncertainties introduced by the uncertainties in the NOAA–GDAS ATDM results are less important
than for the evacuated population.
C120. The weather conditions during the passage of the plumes following the accident and the natureof the deposition (such as dry or wet deposition, amount of precipitation) significantly influenced theradionuclide distribution in the urban and forest environments. Lack of detailed information on thesefactors can cause significant uncertainty in the estimation of the dose from external exposure. Future
work to provide a more detailed reconstruction of the dispersion and deposition conditions in March2011 may allow for better estimates of early doses from external exposure and inhalation, particularlyin the evacuated areas.
C121. An additional factor that affects the estimation of absorbed dose to the thyroid from inhalationis the ratio of particulate to gaseous forms of 131I in the air. Measurement data were limited andavailable mostly at substantial distances from the release site. For Fukushima Prefecture, where

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UNSCEAR 2013 REPORT

absorbed doses to the thyroid could be more significant, there were no measurement data for the
relative amounts of particulate and gaseous forms of 131I in air; this ratio was therefore estimated fromthe modelling of the reactor releases and the ATDM results. The estimated value for this ratio has an
uncertainty of up to a factor of two.

B. Assessment of dose from ingestion
C122. Using the FAO/IAEA food database of concentrations of radionuclides in foodstuffs, theCommittee estimated doses from ingestion as a function of time in the first year following the releases
for a range of organs and age groups. The full results are given in attachment C-15 and were all basedon the food marketed at the location of interest, thereby allowing for the proportion of each food typethat was imported into Japan. Some uncertainties in these dose estimates can be expected, reflecting theuncertainties in the measurement data and the types of foods that were available at different times. The
doses in the first year were based on measurements made on food that was not randomly sampled,
because priority was given to the identification of foods with the highest radionuclide concentrations. It
is therefore, likely that the mean concentrations used in the Committee’s assessment are overestimatesof the true means, particularly in the first months after the accident when relatively few measurements
were made.
C123. As discussed in section III.A of this appendix, if it is assumed that only 25% of food was fromthe local prefecture then the estimated doses would have been about a factor of three lower than thosepresented in this study. For doses beyond the first year, the uncertainties in the modelled values ofradionuclide concentrations in foods would be reflected in uncertainties in the estimated doses. It wasdifficult to quantify the uncertainties in these modelled values as there was insufficient information on
the transfer of radionuclides to food as a function of time for foods produced in Japan.
C124. The use of a constant activity concentration of 10 Bq/kg for foods when the measurements
results were below the limits of detection also contributed to the uncertainty in the doses from intakes
in the first year. This value was used for 131I, 134Cs and 137Cs for the first four months following theaccident, but only for 134Cs and 137Cs after four months. This is the reason for an apparent marked
reduction in estimated doses from intakes in the fifth and subsequent months, particularly for the
thyroid. The results also reflect the impact of the restrictions on food supplies, because products fromthe areas more affected by the accident were excluded from the market. Further information on thepossible impact of this assumption is given in the compilation of information on doses from ingestion
provided in attachment C-15. Sato et al. [S2] have shown the cautious nature of this assumption,
particularly after the first few months. A duplicate-diet study conducted with a large number ofvolunteers in Fukushima Prefecture showed that many people were likely to have had lower doses fromradiocaesium than those estimated by the Committee. However, the study could not consider the firstfew months after the accident when levels in food were higher and it did not consider intakes of 131I,
which contribute most to the doses in the first year. They also noted that the study group was not a
random sample and that participants had a high degree of concern about their exposures, so they may
not have been representative of the population as a whole.
C125. There were significant differences in the levels of radionuclides in different foodstuffs
depending on where they were grown, reflecting differences in the deposition densities of radionuclides
on the ground as well as local factors, such as the time of planting of the crop and the soil type. A key
factor is where people obtain their food. In Japan, the majority of people use supermarkets to obtain
their food and that food could have come from anywhere in the country, with a fraction being imported.

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203

However, some people may grow their own vegetables and also provide these to neighbours, andfarmers may consume their own produce. If individuals living in the areas of higher deposition density
had eaten locally produced food even though restrictions had been introduced following the accident,
then they could have received exposures significantly higher than those presented here. The impact of
this can only be quantified using the modelled results, based on deposition data. Further information isprovided in the compilation of doses from ingestion given in attachment C-15. This shows that the
impact of the restrictions was to reduce doses by up to two orders of magnitude in Fukushima
Prefecture, depending on age group and location.
C126. The Committee’s estimates of doses beyond the first year from ingestion were obtained using
the modelling approach based on deposition data. It was assumed that 25% of food was from theprefecture where the individual lived and 75% from elsewhere in Japan, with allowance made for foods
being imported into Japan. In order to assess the uncertainties associated with these assumptions,estimates were made for Fukushima Prefecture assuming that 100% of the local food consumed wasfrom the prefecture, both with and without allowing for imported food. The effect of this is seen intable C17.
Table C17. Influence on effective doses to adults in Fukushima Prefecture of assuming that 100% of
local food consumed was from the prefecture
Effective dose (mSv) with food restrictions;values without restrictions shown in parentheses
Time (years)
25% local, standard result

100% local, but allowing
for imports

100% local, no allowance
for imports

10.06 (2.0)

0.20 (7.9)

0.27

10

0.14 (2.1)

0.50 (8.3)

1.4

up to age 80

0.17 (2.1)

0.62 (8.4)

1.5

C127. The effect of assuming that 100% of local food consumed were from the prefecture isparticularly marked when restrictions on food supplies were taken into account. Because the vast
majority of people in Japan eat food from supermarkets, the above dose estimates do not apply to many
individuals. It is very unlikely that anyone would have eaten only locally produced food and so thedoses presented above should be viewed as the upper bound of possible doses from ingestion.
Conversely, it should be recognized that following the accident, many people avoided produce from
Fukushima Prefecture or even from Japan, and the settlement-average doses from ingestion would havebeen lower than those given above.
C128. It took some days for the food restrictions to be introduced in Japan and it is possible thatsome people ate food with activity concentrations of radionuclides above the restriction levels during
this time. For most communities, this was unlikely to have resulted in a significant exposure relative tothe exposure received over a full year. However, in the case of Iitate Village, there was a period of anumber of weeks when the residents were living in the area and potentially eating local produce anddrinking the locally sourced water. The estimates of dose from ingestion for Iitate Village are includedin the evacuation scenarios using the standard parameters for ingestion, but an adult living in Iitate
Village and eating only locally produced vegetables could have received an additional effective dose ofabout 10 mSv in the first week following the accident. This assumption is unlikely given the time ofyear and the limited availability of green vegetables growing in the open, but cannot be excluded as apossibility.

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C129. Standard models have been used to determine the radiation doses following intakes ofradionuclides into the body. These are based on a standard-sized person with particular metabolic
characteristics. It has not been possible to generally consider the effect of the variability between people
on the doses from intakes or the uncertainty in the models and data used. However, one aspect that has
been briefly considered is that the Japanese diet is relatively high in stable iodine and this could have
led to less transfer of radioiodine to the thyroid than in the standard model. There are indications thatthe transfer of iodine from blood to the thyroid is 20% [Y8] rather than the value of 30% used in thestandard ICRP model [I25]. This could lead to slightly lower doses from intakes of 131I, but the effectoverall would be small (less than a 30% reduction in dose), compared with the other uncertainties
associated with the dose assessment.
C130. The doses in the first year from ingestion of radionuclides in seafood were based on themeasurement data contained in the database. Information on the contribution of ingestion of seafood tothe total dose from ingestion was only available for individual radionuclides and for each month
separately; these show that their contribution to the total dose was not greater than 10% overall. This
reflects the restrictions put in place on the consumption of seafood from Fukushima Prefecture.
C131. Table C18 shows the estimates of future radiation doses from the ingestion of seafood. Theseestimates were based on the calculated levels of 137Cs in seawater over the next 10 years frommodelling the marine environment, based on work carried out by [N3]. The modelling of the changes inconcentrations of radionuclides in seawater with time beyond 10 years is based on results frommeasurements of fallout from the testing of nuclear weapons in the atmosphere. These estimatedeffective doses are all very low and are less than those from the ingestion of terrestrial foods, even two
years after the accident. This is because of the significant dilution of radiocaesium in the water andtherefore the very low concentrations in seafood away from the FDNPS site. It is assumed thatmonitoring and restrictions on seafood will continue so that any products above the levels specified by
the Japanese authorities will not be consumed.
Table C18. Estimated effective doses to different age groups from the consumption of radionuclides
in seafood at various times after the accident
Annual effective dose to different age groups (mSv in a year)

Time after the accident(years)Adults10-year old

1-year old

2

3.9 × 10−5

2.1 × 10−5

1.4 × 10−55

8.2 × 10−6

4.3 × 10−6

3.1 × 10−6

10

3.2 × 10−6

1.7 × 10−6

1.2 × 10−620

2.3 × 10−6

1.2 × 10−6

8.6 × 10−750

8.1 × 10−7

4.3 × 10−7

3.1 × 10−7

C132. There are two published papers that used a probabilistic approach for estimating doses fromingestion [K19, Y2]. The paper by Yamaguchi estimated a range of doses from ingestion that areconsistent with those given here and which do not show a significant variation. The range of doses
estimated by Koizumi et al. were lower than those given here but were based on a very limited set ofmeasurements.

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205

C. Future remediation and protective measures
C133. Since mid-2011, extensive remediation work has been underway or is being planned in theregions of Japan with the higher deposition densities, to reduce the dose rate and concentrations ofradionuclides in areas where people live or grow food [S6]. This work includes the use of technologies
for decontamination of inhabited areas, and of countermeasures in agriculture (such as
phytoremediation) and in forestry. The experimental studies and tests in Fukushima Prefecture wereplanned to be completed by the first half of 2012. At that time, a large-scale environmental remediation
programme was planned to be launched in the affected areas of Fukushima Prefecture. In some affectedareas beyond the restricted area, local authorities initiated decontamination activities, mostly focused on
public areas and especially on children’s facilities (kindergartens, schools, hospitals and so on). Similar
work, although in the temperate European environment, was intensively conducted in the Chernobylaffected areas two decades ago, and the conclusions and recommendations from this work weresummarized by the Chernobyl Forum [I1] and UNSCEAR [U12].
C134. It was not possible to include consideration of remediation in the dose assessment at this stage,
because the effectiveness of the different measures to be applied in Japan was not known. Estimates ofthe effective doses from external irradiation that would be received by those who were evacuated ifthey were to return to their homes and regular lifestyles without any environmental remediation having
been implemented are however shown in table C19. These estimates provide an upper bound to thedoses that might be received in the future.
Table C19. Effective doses from external exposure of adults who were evacuated from localities ofFukushima Prefecture, if they were to return to their homes
Effective dose from external exposure (mSv in period indicated)a
Municipalitya

11 March 2012–
11 March 2013

11 March 2013–
11 March 2014

11 March 2014–
11 March 2015

Futaba Town

11

6.7

4.5

Hirono Town

0.42

0.25

0.17

Iitate Village

4.1

2.5

1.7

Katsurao Village

2.0

1.2

0.83

Kawamata Town

0.50

0.30

0.20

Kawauchi Village

0.37

0.22

0.15

Minamisoma City

0.61

0.37

0.25

Namie Machi

9.8

6.0

4.0

Naraha Town

0.66

0.40

0.27

Okuma Town

12

7.3

4.9

Tamura City

0.19

0.12

0.08

Tomioka Town

5.3

3.2

2.2

External exposure from deposited radionuclides.

C135. Although remediation may result in reduction in the activity concentrations of radionuclides incrops and animal products, if it is assumed that the restriction criteria for foodstuffs given above would
continue to apply, the estimated doses from ingestion would not be affected. In future, more detailed

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UNSCEAR 2013 REPORT

studies could be carried out to investigate the impact of remediation on ingestion doses but this isbeyond the scope of this assessment.
C136. The annual external doses to adults are already substantially below the Japanese criteria forevacuation (20 mSv). Decontamination of settlements with techniques that from past experience reducethe doses by about 1.5 would further reduce external doses for all the population groups [I1, U3]. The
results in table C19 indicate that, after March 2014, the settlement-average effective doses to adults
from external exposure were estimated to be less than 1 mSv in a year in seven of the evacuatedlocalities.

V. COMPARISON WITH OTHER ASSESSMENTS

A. Direct measurements of radionuclides in people
C137. Measurements of radionuclides in people provide a direct source of information on their
exposure. Two main sets of data were available to the Committee, the first from in vivo measurementsof 131I in the thyroid, particularly of children, and the second from in vivo whole-body monitoring for134
Cs and 137Cs. Such measurements can only indicate the levels of these radionuclides that are inindividuals at the time that they were monitored. Assumptions have to be made to estimate total
radiation exposures (such as when the intakes took place and how much was by inhalation oringestion).
C138. Only a limited number of in vivo measurements of 131I activity in the thyroid were reported forthe weeks following the accident. Thyroid monitoring was carried out by local authorities on 1,080
children aged between 1 and 15 years in Iwaki City, Kawamata Town and Iitate Village over the period
from 26 to 30 March 2011 using hand-held dose-rate instruments [K13]. The absorbed doses to thethyroid from internal exposure were calculated assuming exposure was continuous over the period from12 to 24 March 2011. The results of the Committee’s analysis of the measurement data for infants andchildren were consistent with the assessment by the Japanese authorities. In its analysis, the Committee
assumed a single exposure on 15 March 2011. The Committee's estimates of settlement-averageabsorbed doses to the thyroid from internal exposure were two to five times higher than thecorresponding values derived from the direct monitoring of these children.
C139. Tokonami et al. [T20] reported the results of measurements made on the thyroid from 12 to 16
April 2011 on 62 evacuees from Tsushima District of Namie Town and the coastal area of Minamisoma
City. They detected 131I in 46 people and, for the adults in this group, estimated that the absorbed doses
to the thyroid were in the range of 2 to 35 mGy. While three quarters of their estimates of absorbed
dose to the thyroid were below 10 mGy, a quarter of the estimates were in the range 15 to 35 mGy. The
estimates in this higher range are consistent with the estimates of absorbed doses to the thyroid for
adults made by the Committee, but the lower range is lower by a factor of up to four. There is likely
some overestimation introduced by the overall chain of models (i.e. in the assumed magnitude andpattern of the releases, the assumed protective measures, and the dosimetric and other factors) adopted
by the Committee to estimate absorbed doses to the thyroid for the evacuees.

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207

C140. As part of the Health Examination for Citizens in Fukushima Prefecture programme, wholebody counting of more than 106,000 residents of Fukushima Prefecture and neighbouring prefectures
was conducted by the end of January 2013 [H5, M24].
C141. The paper of Momose et al. [M24] details a series of whole-body measurements on about
10,000 evacuees made from July 2011 to January 2012. The presence of 134Cs and 137Cs could be
detected in the body in only 20% of the evacuees (minimum detectable activity was about 300 Bq). The
Committee estimated the average effective dose from the intake of 134Cs and 137Cs since March 2011
from these measurements to be about 0.05 mSv to adults and about 0.03 mSv to adolescents. For almost
all of the evacuees, the effective dose was estimated to have been below 1 mSv; an effective dose tojust one person in about 5,000 adults and adolescents was estimated to have been about 1 mSv.
C142. According to Hayano et al. [H5], 33,000 residents of Fukushima Prefecture and neighbouring
prefectures were examined by whole-body monitoring at Hirata Central Hospital located south-west of
FDNPS in Fukushima Prefecture between October 2011 and February 2012. Only 12% of thosemonitored had an activity of 134Cs and 137Cs in the body above the minimum detectable level of about
300 Bq. Between March and November 2012, this proportion fell to 1%. This confirms that most of theradionuclide intake occurred soon after the accident. Based on the whole-body measurements
conducted on adults between October 2011 and February 2012, the Committee estimated the average
effective doses from the intake of 134Cs and 137Cs since March 2011 to be in the range of about 0.02 to
0.07 mSv, respectively.
C143. Both estimates, based on the large number of measurements [H5, M24], are substantiallylower than the doses estimated in this study from the inhalation and ingestion of 134Cs and 137Cs.
Although the aim of this study was to provide as realistic as possible an assessment of the doses to theJapanese population, these results would indicate that some of the assumptions made were still
cautious, an inevitable consequence of the incompleteness of the information available to theCommittee.

B. WHO study
C144. The preliminary exposure assessment by WHO [W11] and the related health risk assessment[W12] used data available up to September 2011. Although the assessments were intended to berealistic, given the limited information available at the time, some of the assumptions made by WHO
were likely to lead to overestimation of doses.
C145. In table C20, the WHO results for the effective dose to adults and the absorbed doses to thethyroid of 1-year-old infants are compared with the results obtained in this study. This assessment used
more comprehensive data than were available for the WHO study and it was therefore possible to makemore realistic assumptions in parts of the assessment. In general, the estimates from this study of theeffective doses in the first year in districts of Fukushima Prefecture are within the dose ranges in the
WHO preliminary dose estimation. There is also good agreement in the estimates of the absorbed doses
to the thyroid. Table C20 shows that in some cases, the estimated doses for specific locations werelower in this assessment than in the WHO study. This reflects the additional information available, inparticular, for the evacuated areas, where more detailed information on the patterns of movement of theevacuees was available than for the WHO preliminary dose estimation [W11]. However, there are also
locations where the estimated doses in this study were higher than those in the WHO study.

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UNSCEAR 2013 REPORT

Table C20. Comparison of estimates of the effective dose to adults and of the absorbed dose to thethyroid of 1-year-old infants
WHO assessment [W12]Committee’s assessment

LocationFirst year

Lifetime

First year

Up to age 80 years

EFFECTIVE DOSE TO ADULTS (mSv)
Namie Town

22

24

5.0a

d

Naraha Town

4

8

3.7a

d

Iitate Village

12

14

8.0b

d

Katsurao Village

5

6

6.0b

d

Minamisoma City

5

8

5.7

d

Iwaki City

1

2

2.2

4.2

Rest of Fukushima Prefecture

1−5

2−10

1.0−4.3

1.2−12Neighbouring prefectures~1~1

0.2−1.4

0.2−4.1

ABSORBED DOSE TO THYROID OF 1-YEAR-OLD (mGy)
Namie Town

122

123

81c

d

Naraha Town

39

42

82c

d

Iitate Village

73

74

56c

d

Katsurao Village

48

48

73

d

Minamisoma City

43

46

53c

d

Iwaki City

31

32

52

d

Rest of Fukushima Prefecture31−39(or 30−40)

32−42

33−52

d

Neighbouring prefectures

≤9

≤10

3−15

d

a

Within restricted zone.

bWithin deliberate evacuation zone.

c

Assessed NIRS evacuation scenario.

d

Not assessed by Committee.

VI. CONCLUSIONS
C146. For the great majority of people in Japan, the additional radiation doses received in the firstyear following the radioactive releases from the accident at FDNPS were less than the background
doses received each year from natural sources of radiation (about 2.1 mSv [N23]). This is particularly
the case for people living in prefectures remote from Fukushima Prefecture where doses of 0.2 mSv orless were estimated to have been received.
C147. For those residents who were evacuated in the first days after 11 March 2011, the estimatedsettlement-average total effective doses to adults in the first year were on average less than 6 mSv. For
those who were evacuated at later times, the estimated settlement-average total effective doses to adults

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

209

in the first year were on average less than 10 mSv. These doses include those received before andduring evacuation and for the remainder of the year at the evacuation destination. The estimatedsettlement-average absorbed doses to the thyroid of one-year-old infants in the first year ranged fromabout 15 up to about 80 mGy. This is significantly higher than absorbed doses to the thyroid fromnatural background radiation; the average annual absorbed dose to the thyroid from naturally occurringsources of radiation is typically of the order of 1 mGy. For a small number of hospital and nursinghome patients, residents and other individuals who may have remained in the 20-km zone for longer
periods, higher exposures may have occurred.
C148. For those people who were not evacuated, the highest district-average doses were received bythose living in Fukushima City, where the district-average total effective doses in the first year were
4.3 mSv for adults and 7.5 mSv for 1-year-old infants. If no remediation were undertaken, people who
were infants at the time of the accident could receive effective doses up to about 20 mSv, in addition to
those received from natural sources of radiation, over their lifetimes. People living in a number ofsettlements within the districts of Koori Town, Otama Village, and the cities of Date, Iwaki, Koriyama,
Nihonmatsu and Minamisoma were estimated to have received average effective doses in the first year
in the range of 2 to 4 mSv for adults and 5 to 7 mSv for infants. For the remaining districts within
Fukushima Prefecture the district-average effective doses were in the range of 1 to 2 mSv for adults and
2 to 5 mSv for infants. To provide context, 80-year cumulative effective doses from backgroundexposure to natural sources of radiation in Japan are on average about 170 mSv (i.e. 2.1 mSv annuallyfor 80 years). The variability of the deposition density of radionuclides in the environment andvariations in human behaviour and food habits are such that the estimates of the effective dose to anindividual could be up to about two to three times higher or lower in some locations than the average
effective dose for the district.
C149. The highest estimated absorbed doses to the thyroid of individuals in non-evacuated districtsin the first year were in the cities of Iwaki and Fukushima, with the district-average absorbed dose to
the thyroid of 1-year-old infants in the first year being about 50 mGy. The estimated doses to 10-yearold children and adults were lower than those of 1-year-old infants by factors of about two and about
three to four, respectively. For the Group 3 prefectures (Chiba, Gunma, Ibaraki, Iwate, Miyagi andTochigi), the district-average absorbed doses to the thyroid of infants in the first year were assessed to
be in the range of about 3 to 15 mGy. In the remainder of the 40 prefectures of Japan, the prefectureaverage absorbed doses to the thyroid of infants in the first year were assessed to be about 3 mGy.
C150. There were only a limited number of direct in vivo measurements of 131I in the thyroid
reported for the weeks immediately following the accident. The estimates of absorbed dose to thethyroid from these measurements were up to two to five times lower than the settlement-averageabsorbed doses to the thyroid estimated in this study. There is likely some overestimation introduced by
the overall chain of models (i.e. in the assumed magnitude and pattern of the releases, the assumed
protective measures, and the dosimetric and other factors) adopted by the Committee to estimate
absorbed doses to the thyroid for the evacuees. The estimates of dose from internal exposure by
gamma-emitting radionuclides derived from whole-body monitoring are substantially lower than thedoses estimated in this study and therefore reflect some caution in the assumptions used in assessing thedoses from internal exposure in this study.
C151. The estimated doses to evacuees have the largest associated uncertainties for all of theestimates made by the Committee during this study, and in view of the absence of measurements ofconcentrations of radionuclides in air at the time of exposure, are likely to remain so. Doses had to be
estimated from the ATDM results, and assumptions about the temporal pattern of the releases, the timevarying location of people during the evacuation and any protective measures that were applied, all ofwhich have associated uncertainties. Further information will, in time, become available on the pattern

210

UNSCEAR 2013 REPORTand magnitude of the releases and this may lead to some reduction in the overall uncertainty in theestimation of doses to evacuees.
C152. For the locations with the highest estimated doses, the most important exposure pathway was
external exposure from deposited material, although there may also have been a significant contribution
from inhalation and ingestion of radionuclides. For the locations with lowest estimated doses, ingestionof radionuclides in food gave the most significant contribution.
C153. The estimated doses depend on the radionuclide concentrations in the environment and on theage/social group of the population. Infants aged 1 year at the time of the accident had the highest
estimated doses, followed by 10-year-old children and then by those adults who spent more time
outdoors. Adults who spent more time indoors had the lowest estimated doses. However, thedifferences in the estimated effective doses among the considered groups were not large, being less thana factor of two.
C154. Generally, the total effective doses that will be incurred over the 10-year period following theaccident were estimated to be a factor of up to two larger than those received in the first year. Lifetime
doses were estimated to be up to a factor of three greater than the doses received in the first year, withthe greatest increases in dose being in the areas with the highest levels of deposition density ofradionuclides. Most of the absorbed doses to the thyroid were received by the residents of Japan during
the first year by the pathways of inhalation of 131I in air and ingestion of food containing 131I. The doses
to the thyroid over a lifetime were estimated to be less than 50% higher than those received in the firstyear. Children born over the next decades will not receive any dose to the thyroid from 131I since it will
have totally decayed, but will receive some exposure from 134Cs and 137Cs.
C155. The doses presented here are considered to be typical of the average exposures for each groupof people. Doses would be significantly lower for some people, particularly those living in concrete
multi-storey apartments and who had avoided locally produced fresh food after the accident. Doses
would be higher for those who spent a significant proportion of each day outdoors and who ate locally
produced food.
C156. The actions taken to protect the public significantly reduced the radiation exposures that could
have been received. This was particularly the case for settlements within the 20-km evacuation zone
and the deliberate evacuation zones, where the protective measures reduced the potential exposures in
the first year by up to a factor of 10. The Committee estimated that effective doses thus averted ranged
up to 50 mSv for adults; the absorbed doses to the thyroid of 1-year-old infants averted by evacuation
ranged up to about 750 mGy.
C157. Collective doses to the Japanese population were also estimated for comparative purposes. The
estimated lifetime collective effective dose to the population of Japan following the FDNPS accident isapproximately a factor of eight lower than the corresponding value for European populations exposed
to radiation following the Chernobyl accident, while the collective absorbed dose to the thyroid is afactor of about 20 lower.
C158. Based on an analysis of doses reported for countries neighbouring Japan and for the rest of theworld, the Committee concluded that the total effective doses to individuals in populations living
outside of Japan were less than 0.01 mSv in the first year following the accident.
C159. While the Committee has aimed to make realistic estimate of dose to public based on theavailable information, it is likely that some overestimation has been introduced generally by the overall
chain of models used by the Committee and the lack of information on individual protective measures.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

211

APPENDIX D. ASSESSMENT OF DOSES TO WORKERSI.

INTRODUCTION................................................................................................................................. 211

II. DOSE STATISTICS.............................................................................................................................. 213
III. MONITORING AND DOSIMETRY.................................................................................................. 224
A. Monitoring of internally incorporated radionuclides ................................................. 224
B. Evaluation of information provided on monitoring of internallyincorporated radionuclides .................................................................................................. 226
C. Monitoring of external exposure........................................................................................ 227
D. Evaluation of information provided on monitoring external exposure............... 228
IV. DETAILED RESULTS OF THE COMMITTEE’S DOSE ASSESSMENT ..................................... 229
A. Selection of workers for independent assessments of dose .................................... 229
B. Methodology for assessing internal exposure .............................................................. 229
C. Results for workers with the highest internal exposure............................................. 230
D. Results for the 55 randomly selected workers with lower internal
exposure ...................................................................................................................................... 234
E. Summary of the conclusions of the Committee’s dose assessment...................... 243

I. INTRODUCTION
D1. Up until 31 October 2012, a total of 24,832 occupationally exposed workers (“radiation
workers 37”) had been involved in mitigation and other activities at the Fukushima Daiichi Nuclear
Power Station (FDNPS). In addition, a few hundred emergency workers were deployed on the FDNPS
site: these included fire-fighters, police and Self-Defence Force workers. An assessment of risks tohealth for these workers would need to be based on assessments of absorbed dose to relevant organs foreach worker; however the quantity “effective dose” is usually reported in a radiation protection context.
In general, assessments of effective dose resulting from occupational exposures to external sources ofradiation (“external exposure”) are based on readings from alarm pocket dosimeters worn by theworker; whereas for occupational exposures to internal sources of radiation resulting from intakes ofradionuclides (“internal exposure”), committed effective doses or committed doses to specific organs
37

In Japan, occupationally exposed workers are called “radiation workers”, a term which applies to personnel engaged inradiation-related work in a controlled area. These workers are engaged in the installation, operation, utilization or maintenance of
nuclear reactors, or are engaged in the transport, storage, disposal or removal of nuclear fuel material or nuclear fuelcontaminated material.

212

UNSCEAR 2013 REPORT

are assessed using biokinetic and dosimetric models to interpret the results of bioassay monitoring. The
term “bioassay” refers to measurements of the activities of radionuclides in the body (in vivo
measurements) or measurements of activities in excreta samples (in vitro measurements).
D2. During the normal operation of the reactors, a few thousand occupationally exposed workers
were employed at the site. This number increased dramatically following the accident, with almost
twenty five thousand occupationally exposed workers having been involved in recovery and related
operations by October 2012. The majority of these (about twenty one thousand) were employed bycontractors of the Tokyo Electric Power Company (TEPCO) or subcontractors, rather than by TEPCO
itself.
D3. As a result of the tsunami, initial capabilities for monitoring radiological conditions, both on-siteand off-site, were severely hampered. Few on-site monitoring systems remained. Most electronic
personal dosimeters, computer systems for activating and recording doses measured by these devices,
installed contamination monitors, and many portable survey instruments were lost in the flooding.
D4. One of the aims of the Committee’s assessment of doses to workers was to judge the extent towhich the individual doses reported in Japan (section II of this appendix) provided a true and reliablemeasure of the doses actually incurred, and therefore the extent to which the reported doses could be
used to support a reliable assessment of potential effects on health. Here, the term “reliable” wasapplied to a measure or assessment to indicate that it could be considered with confidence to be ofsound and consistent quality.
D5. Given the typical time and effort required to perform a single dose assessment, it would not havebeen possible for the Committee to review or reassess the individual assessments of dose for such alarge number of workers. Therefore, a two-stage approach was adopted. First, the methodologies usedin Japan for assessing doses were reviewed (section III of this appendix). Second, independent dose
assessments were made for defined groups of workers, and comparisons made with the doses reported
in Japan for these workers (section IV).
D6. Doses received by workers with the highest exposures were of particular interest for theassessment of potential effects on health, and so assessments were performed for twelve of the thirteen
workers 38 with the highest reported doses from internal exposure (whose committed effective doses,
E(50), were more than 100 mSv), with the aim of judging the reliability of the doses reported for these
individual workers. These thirteen workers were all TEPCO workers, the measurements of internallyincorporated radionuclides were all performed at the same (or similar) facilities, and the methods forassessing doses due to internal exposure were also similar. Internal exposure made the dominant
contribution to the effective dose for the twelve workers, and seven workers with the highest reported
committed doses from internal exposure also had the highest reported effective doses.
D7. In contrast, the much larger number of workers who received lower doses had different types of
employment status (such as TEPCO employee, contractor or subcontractor employee, or emergency
services worker), and both the type of facilities used for measurements of radionuclide activities andthe method used to assess doses could have depended on the level of the assessed dose. The Committee
evaluated the reliability of the dose assessments for these groups of workers by performing independent
dose assessments for samples of workers randomly selected from the various groups, as described in
section IV of this appendix.
38

At the suggestion of the Committee, the Japanese organizations initiated a reassessment of the doses received by the workers
which was completed only by July 2013. This reassessment showed there to be thirteen (rather than the original twelve) workers(all TEPCO workers) with committed effective doses higher than 100 mSv. However, this information came too late for theCommittee to carry out an independent detailed assessment of the dose from internal exposure that this thirteenth worker
received.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

213

II. DOSE STATISTICS
D8. Tables presenting the numbers of occupationally exposed workers in specified effective dosebands (and showing contributions from external and internal exposure) for each month since theaccident up to October 2011 have been published by TEPCO [T8]; these were subsequently updated by
the Committee with results from a reassessment conducted by Japanese organizations in July 2013—
the updated data are given in tables D1, D2 and D3. These tables show that the highest effective doses
resulted mainly from intakes of radioactive material, and that monthly doses in excess of 100 mSv only
occurred in March 2011. Since November 2011, TEPCO has presented data in terms of the number ofworkers with cumulative effective doses over defined periods in various dose bands; the data publishedin November 2012 (and subsequently updated by Japanese organizations) are produced in table D4.
These show that the number of workers with cumulative effective doses exceeding 100 mSv increasedby 65% between the end of March 2011 and the end of October 2012.
D9. The data presented in this section only take into account the number of workers involved in the
mitigation operations conducted between 11 March 2011 and 31 October 2012. Given the turnover ofstaff on site, the number of workers involved in such operations was increasing and consequently the
distribution of workers across the different dose bands was constantly evolving. For updated
information, one source of publicly available information was the website of TEPCO 39 which
published a monthly update of information on the numbers of workers and their doses.
D10. Although tables D1–D4 40 provide useful statistics on the numbers of workers in specified dosebands, they do not provide information on internal and external exposure for individual workers. For
instance, it was not possible to determine from these tables whether the single worker who wasrecorded with a committed dose from internal exposure in the 150–200 mSv range (table D2) was oneof the thirteen workers with a total effective dose in the same range, or one of the six workers with a
total effective dose in the “over 250 mSv” range (table D3). However, the Japanese authorities
separately provided data to the Committee in spreadsheet form on the individual monthly andcumulative doses from internal and external exposures reported for 21,776 TEPCO and contractors’
workers up to April 2012. Tables D5, D6 and D7 show reported cumulative effective doses up to April
2012 for the 20 workers with the highest effective doses, highest committed effective doses frominternal exposure and highest effective doses from external exposure, respectively, extracted from thisspreadsheet. The highest reported effective dose was 679 mSv, for the TEPCO worker who also had thehighest reported committed effective dose due to internal exposure (590 mSv). The highest reported
effective dose from external exposure was 199 mSv, for a contractors’ worker who had a reported total
effective dose (from internal and external exposure) of 238 mSv.
D11. Tables such as tables D5–D7 40 can only show individual data for a limited number of workers.
However, a contour plot was used to summarize the individual dosimetric data for all 21,776 TEPCO
and contractors’ workers for whom individual doses were reported up until April 2012 (figures D-Ia,b).
These contour plots show the number of workers reported with effective doses from internal andexternal exposure within specified intervals. For instance, it can be seen that two workers had acommitted effective dose in the interval 80–90 mSv from internal exposure and an effective dose in theinterval 0-10 mSv from external exposure. Figure D-Ia shows the effective doses from internal andexternal exposure for each of the thirteen individual workers who had doses from internal exposure
greater than 100 mSv, and also shows that most workers had significantly lower doses. There was little
correlation between individual recorded values of dose from internal and external exposure. For thegreat majority of workers, the major contribution to their recorded dose was from external exposure,with a smaller contribution from internal exposure, as demonstrated by the elevated numbers of39

http://www.tepco.co.jp/
Tables D1, D2, D3, D4, D5, D6 and D7 were updated by the Committee with the results from the reassessment performed by
the Japanese organizations in July 2013.
40

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UNSCEAR 2013 REPORT

workers close to the y- (external exposure) axis (figure D-Ib). The arithmetic mean of the reported
doses from external exposure was 10 mSv, while the arithmetic mean of the reported doses frominternal exposure was 1.7 mSv. Comparison with versions of figures D-Ia and D-Ib generated before
the reassessment of doses by the Japanese authorities showed that there were some changes in the
distribution of individual doses from internal and external exposure, but that these changes wererelatively minor.
D12. A comparison between the distributions of the cumulative effective doses for TEPCO and forcontractors’ workers (see figure D-II) shows that they shared common features: they were asymmetricwith a rightward skewness. Although log-normal distributions are often observed within exposed
populations, it appears that the dose distributions here were generally not described well by such a
distribution. The reasons for this were unclear (there may have been different distributions for various
subgroups or for different phases of the accident, but this was not analysed). The distributions did show
some differences, with a wider range of values for TEPCO workers than for contractors’ workers. The
difference of the means, 25 mSv (standard deviation: 38 mSv) for TEPCO and 10 mSv (standard
deviation: 13 mSv) for contractors, respectively, was statistically significant between the two groups(t-test and Fisher test both gave p-values less than 0.001). Regarding the dose from internal exposure,
82% of contractors and 68% of TEPCO workers had zero dose recorded from internal exposures. The
difference between these two groups is statistically significant (chi-squared test, p less than 0.001).

Table D1. Numbers of occupationally exposed FDNPS workers with effective doses from external exposure in each dose band, by month (March to October 2011)[T8, T11, T16]
The precision used by TEPCO is also used here to reproduce literally the reported values. If the values for “average dose” were to be reported elsewhere, it would be appropriate to round them to 2 significant
figures in order not to imply spurious accuracy

Monthly effective dose (mSv)
March

April

June

July

AugustSeptember

October

10 – <20

20 – <50

50 – <100

100 – <150

150 – <200

200 – <250

>250

Total

Maximum

Average

TEPCO

673

598

292

105

20

6

0

0

1 694

182.33

19.41

Contractor

1 697

331

182

58

8

3

0

0

2 279

199.42

9.07

Total

2 370

929

474

163

28

9

0

0

3 973

199.42

13.48

TEPCO

559

35

8

0

0

0

0

0

602

46.29

3.95

Contractor

2 734

186

42

0

0

0

0

0

2 962

47.75

3.11

Total

3 293

221

50

0

0

0

0

0

3 564

47.75

3.25

TEPCO

289

8

2

0

0

0

0

0

299

25.05

2.51

Contractor

2 680

119

21

0

0

0

0

0

2 820

41.59

2.67

Total

2 969

127

23

0

0

0

0

0

3 119

41.59

2.65

TEPCO

179

4

0

0

0

0

0

0

183

12.44

1.13

Contractor

1 811

104

17

0

0

0

0

0

1 932

43.00

2.55

Total

1 990

108

17

0

0

0

0

0

2 115

43.00

2.42

TEPCO

189

0

0

0

0

0

0

0

189

4.69

0.78

Contractor

1 804

65

8

0

0

0

0

0

1 877

34.42

2.27

Total

1 993

65

8

0

0

0

0

0

2 066

34.42

2.13

TEPCO

93

0

0

0

0

0

0

0

93

2.63

0.42

Contractor

1 005

30

1

0

0

0

0

0

1 036

20.40

1.87

Total

1 098

30

1

0

0

0

0

0

1 129

20.40

1.75

TEPCO

52

0

0

0

0

0

0

0

52

1.99

0.47

Contractor

897

25

8

0

0

0

0

0

930

31.21

2.07

Total

949

25

8

0

0

0

0

0

982

31.21

1.99

TEPCO

49

1

0

0

0

0

0

0

50

10.21

0.64

Contractor

772

5

2

0

0

0

0

0

779

23.10

1.25

Total

821

6

2

0

0

0

0

0

829

23.10

1.22

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

May

<10

215

Table D2. Numbers of occupationally exposed FDNPS workers with committed effective doses from internal exposure in each dose band, by month (March to October 2011) [T8, T11, T16]

216

The precision used by TEPCO is also used here to reproduce literally the reported values. If the values for “average dose” were to be reported elsewhere, it would be appropriate to round them to 2 significant

UNSCEAR 2013 REPORT

figures in order not to imply spurious accuracy

Monthly committed effective dose (mSv)<10

10 – <20

20 – <50

50 – <100

100 – <150

150 – <200

200 – <250

>250

Total

Maximum

Average

March

TEPCO

1 038

398

186

37

6

1

1

5

1 672

590.0011.97

Contractor

1 837

249

99

21

0

0

0

0

2 206

98.53

5.12

Total

2 875

647

285

58

6

1

1

5

3 878

590.00

8.07

TEPCO

579

1

0

0

0

0

0

0

580

18.81

0.11

Contractor

2 618

9

1

0

0

0

0

0

2 628

38.40

0.31

Total

3 197

10

1

0

0

0

0

0

3 208

38.40

0.27

TEPCO

278

0

0

0

0

0

0

0

278

7.89

0.04

Contractor

1 978

5

2

0

0

0

0

0

1 985

32.80

0.15

Total

2 256

5

2

0

0

0

0

0

2 263

32.80

0.13

TEPCO

154

0

0

0

0

0

0

0

154

6.94

0.06

Contractor

1 383

0

0

0

0

0

0

0

1 383

7.10

0.01

Total

1 537

0

0

0

0

0

0

0

1 537

7.10

0.02

TEPCO

165

0

0

0

0

0

0

0

165

0.00

0.00

Contractor

1 399

0

0

0

0

0

0

0

1 399

0.50

0.00

Total

1 564

0

0

0

0

0

0

0

1 564

0.50

0.00

TEPCO

85

0

0

0

0

0

0

0

85

0.00

0.00

Contractor

802

0

0

0

0

0

0

0

802

2.61

0.00

Total

887

0

0

0

0

0

0

0

887

2.61

0.00

TEPCO

44

0

0

0

0

0

0

0

44

0.00

0.00

Contractor

689

0

0

0

0

0

0

0

689

1.13

0.00

Total

733

0

0

0

0

0

0

0

733

1.13

0.00

TEPCO

44

0

0

0

0

0

0

0

44

0.00

0.00

Contractor

615

0

0

0

0

0

0

0

615

1.82

0.00

Total

659

0

0

0

0

0

0

0

659

1.82

0.00

April

May

June

July

AugustSeptember

OctoberTable D3. Numbers of occupationally exposed FDNPS workers with effective doses (from both internal and external exposure) in each dose band, by month (March to
October 2011) [T8, T11, T16]
The precision used by TEPCO is also used here to reproduce literally the reported values. If the values for “average dose” were to be reported elsewhere, it would be appropriate to round them to 2 significant
figures in order not to imply spurious accuracy

Monthly effective dose (mSv)
March

April

June

July

AugustSeptember

October

10 – <20

20 – <50

50 – <100

100 – <150

150 – <200

200 – <250

>250

Total

Maximum

Average

TEPCO

346

530

539

195

63

15

0

6

1 694

670.36

31.23

Contractor

1 337

461

361

99

17

2

2

0

2 279

238.42

14.03

Total

1 683

991

900

294

80

17

2

6

3 973

670.36

21.36

TEPCO

555

38

9

0

0

0

0

0

602

49.11

4.05

Contractor

2 709

203

50

0

0

0

0

0

2 962

49.61

3.38

Total

3 264

241

59

0

0

0

0

0

3 564

49.61

3.49

TEPCO

289

8

2

0

0

0

0

0

299

25.05

2.54

Contractor

2 659

137

24

0

0

0

0

0

2 820

41.61

2.77

Total

2 948

145

26

0

0

0

0

0

3 119

41.61

2.75

TEPCO

179

4

0

0

0

0

0

0

183

12.44

1.18

Contractor

1 811

103

18

0

0

0

0

0

1 932

43.00

2.55

Total

1 990

107

18

0

0

0

0

0

2 115

43.00

2.44

TEPCO

189

0

0

0

0

0

0

0

189

4.69

0.78

Contractor

1 804

65

8

0

0

0

0

0

1 877

34.44

2.27

Total

1 993

65

8

0

0

0

0

0

2 066

34.44

2.13

TEPCO

93

0

0

0

0

0

0

0

93

2.63

0.42

Contractor

1 004

31

1

0

0

0

0

0

1 036

20.40

1.87

Total

1 097

31

1

0

0

0

0

0

1 129

20.40

1.75

TEPCO

52

0

0

0

0

0

0

0

52

1.99

0.47

Contractor

897

25

8

0

0

0

0

0

930

31.21

2.07

Total

949

25

8

0

0

0

0

0

982

31.21

1.99

TEPCO

49

1

0

0

0

0

0

0

50

10.21

0.64

Contractor

772

5

2

0

0

0

0

0

779

23.10

1.26

Total

821

6

2

0

0

0

0

0

829

23.10

1.22

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

May

<10

217

218

UNSCEAR 2013 REPORT

Table D4. Numbers of occupationally exposed FDNPS workers with cumulative effective doses forthe period from March 2011 to 31 October 2012 in each dose band
Cumulative dose (mSv)

TEPCO

Contractor

Total

Over 250

60

6200–<250

1

2

3

150–<200

24

2

26

100–<150

118

20

138

50–<100

508

529

1 037

20–<50

610

3 216

3 826

10–<20

498

3 136

3 634

10 or less

1 883

14 27916 162

Total

3 648

21 18424 832

Maximum

678.80238.42678.80

Average

24.56

10.31

12.41

Table D5. External and internal exposures for the 20 workers with the highest cumulative effective
doses for the period March 2011 to April 2012
The precision expressed in the data provided is used here to reproduce literally the reported values, and also to allow crossreferencing of individual entries among the tables. If these values were to be reported elsewhere, it would be appropriate toround them to 2 significant figures in order not to imply spurious accuracy

Employer

Cumulative effective dose (mSv)
External exposure

Internal exposure

Total

TEPCO

88.80

590.00678.80TEPCO

105.54540.00645.54

TEPCO

43.96

433.05477.01

TEPCO

32.95

327.90360.85TEPCO

110.27241.81352.08

TEPCO

51.31

259.66

310.97

TEPCO

73.18

166.06239.24Contractors

199.4239.00

238.42Contractors

191.9035.00

226.90TEPCO

184.9213.13

198.05

TEPCO

188.14

9.19

197.33

TEPCO

106.7590.21

196.96

TEPCO

67.06

119.96187.02

TEPCO

48.81

137.27186.08TEPCO

153.3329.87

183.20ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

Employer

219

Cumulative effective dose (mSv)
External exposure

Internal exposure

Total

TEPCO

165.51

17.41

182.92

TEPCO

122.3960.01

182.40

TEPCO

83.42

97.01

180.44TEPCO

162.0114.07

176.08Contractors

93.00

83.00

176.00

Table D6. External and internal exposures for the 20 workers with the highest cumulative committed
effective doses from internal exposure for the period March 2011 to April 2012
The precision expressed in the data provided is used here to reproduce literally the reported values, and also to allow crossreferencing of individual entries among the tables. If these values were to be reported elsewhere, it would be appropriate toround them to 2 significant figures in order not to imply spurious accuracy

Employer

Cumulative effective dose (mSv)
External exposure

Internal exposure

Total

TEPCO

88.80

590.00678.80TEPCO

105.54540.00645.54

TEPCO

43.96

433.05477.01

TEPCO

32.95

327.90360.85

TEPCO

51.31

259.66

310.97

TEPCO

110.27241.81352.08

TEPCO

73.18

166.06239.24

TEPCO

48.81

137.27186.08

TEPCO

67.06

119.96187.02

TEPCO

34.24

119.59153.83

TEPCO

23.64

117.33140.97

TEPCO

38.87

109.91148.78

TEPCO

42.03

101.27143.30Contractors

8.28

98.53

106.81

TEPCO

83.43

97.01

180.44Contractors

11.35

96.84

108.19

TEPCO

52.88

95.85

148.73

TEPCO

46.10

92.96

139.06

Contractors

11.35

90.88

102.23

TEPCO

106.7590.21

196.96

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UNSCEAR 2013 REPORT

Table D7. External and internal exposures for the 20 workers with the highest cumulative effective
doses from external exposure for the period March 2011 to April 2012
The precision expressed in the data provided is used here to reproduce literally the reported values, and also to allow crossreferencing of individual entries among the tables. If these values were to be reported elsewhere, it would be appropriate toround them to 2 significant figures in order not to imply spurious accuracy

Employer

Cumulative effective dose (mSv)
External exposure

Internal exposure

Total

Contractors

199.4239.00

238.42Contractors

191.9035.00

226.90TEPCO

188.14

9.19

197.33

TEPCO

184.9213.13

198.05Contractors

175.620.00

175.62

TEPCO

165.51

17.41

182.92

TEPCO

162.0114.07

176.08TEPCO

159.888.79

168.67

TEPCO

153.3329.87

183.20TEPCO

152.85

9.67

162.52

TEPCO

144.1325.40

169.53

TEPCO

140.9715.50

156.47TEPCO

132.203.13

135.33

TEPCO

130.7220.37

151.09TEPCO

129.688.49

138.17

TEPCO

129.6023.21

152.81

TEPCO

129.3615.67

145.03

TEPCO

128.0724.68

152.75

TEPCO

127.92

3.85

131.77

TEPCO

126.2541.74

167.99

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

221

Figure D-Ia. Contour plot showing the numbers of workers with a specified combination of dosefrom internal exposure and dose from external exposure
Cumulative doses for the period March 2011–April 2012. The width of the interval for effective doses from both internal andexternal exposure is 10 mSv. The figures can be thought of as 3-dimensional plots, where the x- and y-coordinates represent
effective dose from internal and external exposure, respectively, while the number of workers with doses within a particularinternal or external exposure interval is plotted on the z-coordinate, and represented by the colour(Diagram courtesy of A.L. Shutt, Centre for Radiation, Chemical and Environmental Hazards, Public Health England)

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UNSCEAR 2013 REPORT

Figure D-Ib. Contour plot, expanded to show the numbers of workers in the 0–100 mSv dose range
Cumulative doses for the period March 2011–April 2012. The width of the interval for effective doses from both internal andexternal exposure is 10 mSv. The figures can be thought of as 3-dimensional plots, where the x- and y-coordinates represent
effective dose from internal and external exposure, respectively, while the number of workers with doses within a particularinternal or external exposure interval is plotted on the z-coordinate, and represented by the colour(Diagram courtesy of A.L. Shutt, Centre for Radiation, Chemical and Environmental Hazards, Public Health England)ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

223

Figures D-II. Distributions of effective doses from external and internal exposure combined, andfrom external and internal exposure separately, to FDNPS occupationally exposed workers in eachcumulative dose band from March 2011 to April 2012
The red curve is the probability density of a log-normal distribution with the designated values of average (μ) and standard
deviation (σ), fitted among the workers with measurable exposure for the period. The value n is the number of workers who
were not measurably exposed during the period and who are represented by the small bar close to the origin

224

UNSCEAR 2013 REPORTIII. MONITORING AND DOSIMETRY

A. Monitoring of internally incorporated radionuclides
D13. TEPCO, the Japan Atomic Energy Agency (JAEA) and the National Institute of Radiological
Sciences (NIRS) in Japan provided the Committee with detailed information on instruments,
measurement systems, calibration phantoms and methodologies used for in vivo monitoring, together
with monitoring data for selected workers. The following is a summary of the information received onmonitoring systems and methods.
D14. At the request of TEPCO, JAEA started individual in vivo monitoring of workers who were
responding to the emergency on 22 March 2011. The location chosen for conducting the monitoring
was the town of Onahama, about 55 km south of the FDNPS site. Measurements were made with asimple mobile whole-body counter (WBC), the Canberra FASTSCAN™ system, which employs twothallium-activated sodium iodide (NaI(Tl)) detectors in a “shadow-shield” arrangement made of 10 cm
thick steel. However, accurate quantification of radionuclide activities was difficult because of:

The complexity of the gamma-ray spectrum. (NaI(Tl) detectors have relatively low energy
resolution compared with semiconductor detectors and so cannot resolve complex spectra);

Contamination on the ground and thus elevated background radiation levels affected themeasurements at Onahama;The differences in the distribution of caesium and iodine radionuclides in the body(measurements were made of whole body activity but no measurements were madespecifically of thyroid activity);The large number of workers to be measured, which exceeded the available capacity.

D15. Later, JAEA provided additional monitoring capabilities at the Nuclear Fuel Cycle Engineering
Laboratories (JAEA-NFCEL). In addition to a FASTSCAN™ WBC, the JAEA facilities included: (a) achair-type WBC that employed two semiconductor (high purity germanium (HPGe)) detectors in ashielded chamber made of 20 cm thick steel, with which both whole body and thyroid measurements
could be made; and (b) an NaI(Tl) spectrometer used mainly for thyroid measurements. These facilities
were used for workers whose committed effective dose from internal exposure as assessed from theresults of monitoring at Onahama exceeded 20 mSv, and also for all female employees. Monitoring at
JAEA was carried out for a total of 560 workers during the period 20 April 2011 to 5 August 2011.
JAEA provided the monitoring results to TEPCO, but did not provide dose assessments. Further
information is given in a report of the NIRS [N11].
D16. Where the assessed dose from internal exposure was in excess of 100 mSv, the worker wasadditionally monitored by NIRS. Measurements were performed using six HPGe detectors installed in ashielded chamber made of iron (200 mm), lead (3 mm), copper (0.1 mm) and acrylic (2 mm) [S13].
NIRS staff performed a dose assessment for each worker monitored, although TEPCO reassessed thedose for some of these workers.
D17. TEPCO made the final dose assessments reported for its workers using the results of the JAEA
and NIRS measurements, where available. The Committee understood that those contractors with theability to make the dose assessments reported these to TEPCO for their own workers, using results from

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

225

the JAEA measurements, from a number of other monitoring locations, and information from a detailed
interview. Contractors without the ability to make dose assessments used the doses assessed by TEPCO
based on the results of the JAEA measurement, without considering other data or information.
D18. For most workers, the only radionuclides detected were 131I, 137Cs and 134Cs, and reported doses
due to internal exposure only took account of intakes of these radionuclides. For some of the workers
with higher doses, 136Cs and 129mTe were also detected, but the contribution to the assessed dose frominternal exposure due to intakes of these radionuclides was small. The delay in starting reliable in vivo
monitoring meant that the shorter-lived radioisotopes which were likely to be present, including 132Te,
132 133
I, I and 136Cs, would not have been detectable.
D19. In vitro monitoring was performed by NIRS on urine samples for seven among twelve of thethirteen workers with the highest internal exposure, although the results were not used for formal dose
reporting. Each worker provided a single “spot” sample, mostly during June 2011, followed by two
24-hour samples during June or July 2011. Results were obtained for 131I, 134Cs and 137Cs. No bioassay
measurements were performed for tritium, 89Sr, 90Sr or transuranic radionuclides.
D20. The Committee was provided with information on personal status, employment status, details of
individual monitoring performed and exposure conditions for each worker selected for independent
assessment of dose from internal exposure, as follows:

Age, sex and employment status (TEPCO employee, contractor employee, or emergency
services worker);Work period(s) during which intakes could have taken place;Work activities during these periods;Date and time of any urine samples taken;Date, time and place of measurement;Type of measurement (whole body, thyroid or urine);

The radionuclides for which measurements were performed;



The activities measured for the radionuclides detected (in general, the radionuclides detected
were 131I, 134Cs and 137Cs; other radionuclides were detected in a small number of cases);

Date(s) of intake assumed in the reported Japanese assessment;

Results of the dose assessments that were performed, in particular the assessed effective dose;

Details of any corrections made for short-lived radionuclides that may not have beenmeasurable at the time of measurement;

Brief descriptions of the dose assessment methodology used, including assumptions madeabout the physico-chemical form (including activity median aerodynamic diameter and lungclearance type).

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UNSCEAR 2013 REPORT

B. Evaluation of information provided on monitoring ofinternally incorporated radionuclides
D21. The Committee evaluated information provided on the instruments, measurement systems,
calibration phantoms and methodologies used for in vivo monitoring, with the following findings:(a) Information provided on the in vivo measurement systems used at Onahama, JAEA and NIRS
was deemed adequate for the Committee’s purposes, and the measurement systems were judged tohave been adequate for the purpose of assessing in vivo radionuclide levels, intakes and committed
effective doses from internal exposure for workers during a radiation emergency;(b) Sufficient information was provided on the calibration phantoms used for in vivo
measurements at JAEA; the calibration phantoms were judged to be appropriate for the types of invivo measurements needed and performed;(c) Comprehensive calibration data and quality control data were provided relating to the in vivo
measurements made by JAEA at its own laboratories, and by JAEA and TEPCO at Onahama; it
was judged that adequate calibration methods and quality control procedures for in vivo
measurements were in place.
D22. An important factor to be considered in both the Japanese and the Committee’s independent dose
assessments was the delay in performing reliable in vivo measurements of radioiodine in the thyroid.
For most of the twelve workers with the highest committed effective doses from internal exposure (i.e.
more than 100 mSv) for whom the Committee performed an independent assessment (out of thirteen
workers), monitoring of 131I in the thyroid did not start until mid- or late-May, although, for threeworkers, it started in mid-April. For most of the randomly-selected workers with lower committed
effective doses from internal exposure, initial monitoring was not performed until mid-May to lateJune 2011, although a few workers were monitored during April 2011. For many of the selected
workers, the first possible date of intake was in the period 12–22 March. Given that the radioactive
half-life of 131I is 8 days, this delay in starting thyroid monitoring was significant. As a result of thedelay, 131I was not measurable in the thyroid of many workers, and Japanese assessors had to make anestimate using one of two methods: (a) the “environmental ratio” method used environmental
measurements to determine a time-dependent 131I:137Cs ratio, which was then used to estimate 131I
intake on a certain date from an intake of 137Cs on that date determined from whole-body measurement
data; and (b) the MDA (Minimum Detectable Activity) method assumed that the activity of 131I present
in the thyroid at the time of the measurement was equal to the detection limit of the 131I measurement
made. Japanese assessors chose the lower of the two intake estimates to derive subsequently acommitted dose from internal exposure (see section IV.D below).
D23. Assessments of internal exposure for TEPCO workers were performed either by TEPCO or (in afew cases of high exposure) by NIRS, using the software packages MONDAL [N12] and IMBA [B12],
respectively. Both were quality-assured software packages, and were judged by the Committee to beappropriate for the types of dose assessments needed and performed.
D24. The results of the Committee’s independent assessments of doses from internal exposure are
discussed in section IV of this appendix.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

227

C. Monitoring of external exposure
D25. TEPCO provided detailed information to the Committee on the types of personal dosimeter used,
the technical standards and calibration methods used, and the system used for allocating personal
dosimeters to individuals during March 2011, for both TEPCO and contractors’ employees. The
Committee requested similar information for emergency services workers, but the information provided
by the municipal authorities was rather sparse. The following is a summary of the information received
from TEPCO.
D26. Two types of automated electronic personal dosimeter were used; the response characteristics are
summarized in tables D8 and D9.
Table D8. Personal dosimeter response: gamma(X) ray
Characteristics

Gamma(X) ray

1.

Energy range

50 keV to 6 MeV

2.

Detector

Silicon semiconductor

3.

Dose equivalent range

0.001 mSv to 999.999 mSv

4.

Indication range

0.01 mSv to 99.99 mSv (by 0.01 mSv)
100.0 mSv to 999.9 mSv (by 0.1 mSv)
automatic changeover

5.

Accuracy of indication±10% (0.1 mSv to 999.9 mSv, 137Cs)

6.

Energy response

EP2 type±20% (60 keV to 6 MeV, 137Cs)±30% (50 keV to 6 MeV, 137Cs)

7.

Angular response

AP1 type±20% (up to ±60 degree, vertical and horizontal, 137Cs)±50% (up to ±60 degree, vertical and horizontal, 241Am)

8.

Linearity for wide range of dose rate

R1 type±20% (0.1 mSv/h to 1 Sv/h: 1 mSv/h basis)

Table D9. Personal dosimeter response: beta particle
Characteristics

Beta particle

1.

Energy range

300 keV to 2.3 MeV

2.

Detector

Silicon semiconductor

3.

Dose equivalent range

0.001 mSv to 999.999 mSv

4.

Indication range

0.01 mSv to 99.99 mSv (by 0.01 mSv)
100.0 mSv to 999.9 mSv (by 0.1 mSv)
automatic changeover

5.

Accuracy of indication±10% (0.1 mSv to 999.9 mSv, 90Sr–90Y)

6.

Energy response

EB1 type±30% (500 keV to 2.3 MeV, 90Sr–90Y)

7.

Angular response

AB2 type±50% (up to ±60 degree, vertical and horizontal, 90Sr–90Y)

8.

Linearity for wide range of dose rate

R1 type±20% (0.1 mSv/h to 1 Sv/h: 1 mSv/h basis)

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UNSCEAR 2013 REPORT

D27. Dosimeters were calibrated according to Japanese Industrial Standards JIS-Z-4312 [J4], for which
the reference international standards were IEC 61525 [I27] and IEC 61526 [I28]; and JIS-Z-4511 [J5],for which the reference international standards were ISO 4037-1 [I34] and ISO 4037-3 [I35].
D28. When the power station was flooded, the Automatic Personal Dosimeter System became
inoperable and about 5,000 personal dosimeters were rendered unusable, so that between 12 March2011 and 1 April 2011, only 320 personal dosimeters were available for use. After 1 April, personal
dosimeters were again provided to every worker. During the period when there were not enoughpersonal dosimeters, those that were available were allocated to representatives of each working group[T11]. TEPCO stated that, for both its workers and contractors’ workers, representative measurements
were conducted when the following conditions were fulfilled:The effective dose for a job was not greater than 10 mSv;



The workplace environmental dose rate was known;The gradient of ambient dose equivalent rates at the respective site was not large;All members of an operational group were always together at a work site.

D. Evaluation of information provided on monitoring external
exposure
D29. The Committee’s evaluation of the information provided found that the instrumentation, technicalstandards and calibration methods used appeared to meet generally accepted requirements formonitoring. The major factor potentially affecting the reliability of the monitoring performed was theuse of shared personal dosimeters between 12 March and 1 April 2011. According to TEPCO [I6], themanagement system for individual dosimetry became inoperable immediately following the tsunami
and associated damage, and it was not possible to gather access control information for “Radiation
Controlled Areas” or personal dose data. Owing to the loss of personnel monitoring capabilities,
emergency responders had to share dosimeters (with only one worker in a team wearing a dosimeter for
many missions), and workers had to log their individual doses manually [I6]. Given the short supply of
dosimeters during March 2011, and the absence of information on the extent to which the conditions
described in paragraph D28 above were met for individual workers, some reservations remained about
the reliability of the external dosimetry performed before 1 April 2011.
D30. An issue not considered by the Committee, but which should be mentioned, related to concerns
raised in news reports published in July 2012 about the reliability of doses from external exposure (e.g.
[A1]). These reports stated that some subcontractor workers had been told to cover their dosimeterswith lead casings in order to falsify readings (i.e. to underplay exposures). According to a later press
release from TEPCO [T14], the doses for five workers from external exposure were reassessed, andsubsequently TEPCO took actions aimed at avoiding such problems in the future.

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

229

IV. DETAILED RESULTS OF THE COMMITTEE’S DOSEASSESSMENT

A. Selection of workers for independent assessments of dose
D31. As explained in section I of this appendix, independent assessments of internal exposure were
performed for twelve of the thirteen workers (all TEPCO employees) with the highest reported internal
exposure (i.e. with committed effective doses, E(50), greater than 100 mSv), and for a sample ofworkers with lower internal exposure who were randomly selected from various predefined groups.
This random selection was intended to provide a reasonably representative sample from the 21,776
TEPCO and contractors’ workers for whom individual doses were reported up to April 2012. In total,
42 workers were randomly selected, of whom 21 were TEPCO workers and 21 were contractors’
workers. In addition, 13 emergency services workers (understood to be all from the police force) wereselected. For the TEPCO and contractors’ workers, equal numbers were randomly selected from each of
the 0–5 mSv, 5-20 mSv and 20–100 mSv bands of committed dose from internal exposure as reported
in Japan. It should be noted that no selection criterion was set for external exposure, and no information
was provided on the doses from external exposure reported for the selected workers.
D32. A similar comparative approach could not be used to assess the reliability of reported dosimetricresults for external exposure because they were obtained from personal dosimeter readings that could
not be independently verified on an individual basis. Therefore, the assessment of the reliability of
external exposure data was limited to reviewing and evaluating the information provided by TEPCO on
personal dosimeters, technical standards, calibration methods and the system used for allocating
personal dosimeters to individuals during March 2011 (see section III above of this appendix).

B. Methodology for assessing internal exposure
D33. The Committee identified seven assessors to make independent assessments, with each assessor
using his/her own established procedures and expert judgement on issues such as choice of monitoringdata and parameter values for biokinetic models. No single methodology is described here in detail;rather this section describes the general approach adopted.
D34. Retrospective assessments of internal exposure from the results of such monitoring data generally
followed the steps below:(a) The intake of a specified radionuclide was estimated from monitoring data using retention or
excretion functions calculated on the basis of biokinetic models specified by the International
Commission on Radiological Protection (ICRP) [I10, I11, I14, I15, I16, I17];(b) Time-dependent retention of the radionuclide in source organs was then determined usingorgan retention functions calculated using the same biokinetic models;(c) The projected number of radioactive disintegrations over a 50-year time period in each source
organ was then determined;

230

UNSCEAR 2013 REPORT(d) Values of “absorbed fractions” provided by an ICRP Task Group were then used to determine
committed absorbed doses to target organs;(e) Committed equivalent doses to organs were then determined using radiation weighting factors(wR) specified by ICRP [I12];(f) Committed effective dose were then determined using tissue weighting factors (wT) specified
by ICRP [I12].
D35. In practice, dosimetry services use various methods ranging in complexity from computer
programs that implement the biokinetic models and calculate doses from internal exposure from firstprinciples, to simple spreadsheets that make use of tabulated bioassay data and dose conversion
coefficients provided by ICRP. Methods and software used by dosimetry services have generally been
subject to formal quality assurance and/or accreditation procedures.
D36. For quality assurance purposes, every assessor who performed an assessment for workers with thehighest internal exposures performed an assessment for worker A. Comparisons of these fiveindependent assessments indicated good agreement. For each of the other 11 workers, at least two
assessments were made, again with good agreement, with the possible exception of the results forworker K.

C. Results for workers with the highest internal exposure
D37. The Committee’s independent dose assessments were made using the types of monitoring dataand of information on exposure conditions described in section III of this appendix. For twelve of thethirteen workers with the highest internal exposures, the results of the Committee’s independent dose
assessments, the results of assessments by NIRS and TEPCO, and the results formally reported, arecompared in tables D10, D11 and D12. These assessments were all based on in vivo measurements ofradionuclide activities in the whole body and 131I activity in the thyroid. The three tables show thecommitted effective dose from intakes of all the radionuclides for which monitoring results werereported, the contribution that intakes of 131I made to that committed effective dose, and the absorbed
dose to the thyroid from intakes of 131I.
D38. The delay in starting in vivo monitoring with high energy resolution detectors meant that shorterlived radionuclides other than 131I (half-life = 8 d), specifically 132Te, 132I, 133I and 136Cs, would havebeen undetectable in the body at the time of measurement. Because of the short half-lives of theseradionuclides, additional contributions to dose would have arisen mainly from intakes occurring during
the days immediately following the shutdown of the reactors. The Committee assessed the implicationsin attachment D-1. A rigorous assessment was not possible because of incomplete knowledge of thework histories of individual workers during this period, incomplete knowledge of the time-varying
levels of radionuclides in places where they worked and rested, and because of the lack of information
on specific protective measures taken by individual workers. Nevertheless, the Committee made anumber of plausible but simplifying assumptions about the time period(s) when intakes could havetaken place, and the radionuclide composition of airborne activity to which the workers might havebeen exposed during these periods.
D39. The radionuclide composition of an intake would have been time-dependent, and was assumed tobe similar to the time-dependent radionuclide composition of the releases on the FDNPS site, which
varied considerably from day to day. The time period(s) of intake for an individual worker would have

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

231

depended on three main factors: (a) the periods when the worker was exposed to radionuclides on thesite (predominantly in the form of airborne activity); (b) the times and administered amounts of any
stable iodine provided to individual workers for the purposes of “thyroid blocking”; and (c) the periods
when items of personal protective equipment such as respirators or face masks were being usedeffectively by each worker.
Table D10. Assessed committed effective doses, E(50) (in millisieverts), for workers with the highest
internal exposures from all measured radionuclides
Independent assessor
Working period

1

2

3

4

5

NIRS

TEPCO

Japanese
final
reported
value

Worker

Start

End

IMBA

AIDE

MONDAL
IMBA
CALIN

IMBA

IMBA

IMBA

MONDALIMBA (A-B)
MONDAL (C-L)

A

2011-03-11

2011-04-16

616

580

596

643

495

590

ND

590

B

2011-03-11

2011-04-17

517

496

ND

ND

ND

540

ND

540

C

2011-03-11

2011-05-20

384

ND

ND

ND

383

380

433

433

D

2011-03-11

2011-05-17

322

ND

330

ND

ND

290

328

328

E

2011-03-11

2011-06-01

304

ND

ND

387

ND

270

260

260

F

2011-03-11

2011-04-10

ND

222

216

ND

ND

230

242

242

G

2011-03-11

2011-05-19

172

ND

ND

186

ND

160

166

166

H

2011-03-11

2011-05-22

ND

95

149

ND

ND

ND

137

137

I

2011-03-11

2011-05-27

ND

130

155

ND

ND

ND

120

120

J

2011-03-11

2011-06-01

125

ND

ND

117

ND

ND

120

120

K

2011-03-18

2011-05-12

ND

87

ND

ND

173

ND

117

117

L

2011-03-18

2011-05-10

ND

ND

ND

124

134

ND

101

101

ND: Not determined.
Owing to surface contamination and background radiation levels, TEPCO did not take into account measurements made at
Onahama in their dose assessments.
With the exception of assessor 2, the assessors did take into account the Onahama measurements, but the effect on assessed doses
was not large.
For workers C, D, E, F and G, measurements were made at NIRS, but the dose assessment was performed by TEPCO.
NIRS assumed a chronic exposure (11–12 March 2011); TEPCO assumed an acute exposure (12 March 2011); this explains why
NIRS estimates were sometimes lower than TEPCO estimates.
IMBA – Integrated Modules for Bioassay Analysis [B12].
AIDE – Activity and Internal Dose Estimates [B8].
CALIN – Calcul d’Incorporation [A11].
MONDAL – Support System for Internal Dosimetry [N12].

D40. Work history information for 10 out of 12 of the workers with the higher reported internal
exposures (i.e. committed effective doses greater than 100 mSv) indicated that there was reasonably
good evidence that intakes commenced on 12 March 2011. However, the available evidence for thisgroup of workers did not allow a clear conclusion to be drawn about whether intakes effectively ceased
at some time during 12 March, or whether they continued for a few days. For all of the workers in this232

UNSCEAR 2013 REPORT

group for whom intakes probably commenced on 12 March, it was likely that significant intakes hadceased by 15 March. Indicatively, the additional contribution to effective dose due to internal exposure
from the intakes of these short-lived radionuclides by those workers on site in the first few days of theaccident may have been in the order of 20% relative to the contribution from 131I; this contribution is
likely to have varied considerably between individuals. However, the uncertainty on the time period of
intake means that it was only possible to estimate ranges for the potential additional contributions toeffective dose from intakes of short-lived radionuclides, rather than single values. Assuming that
intakes took place only on 12 March provided an upper bound on the potential additional contribution
to dose, while assuming that intakes could have taken place continuously between 12 and 15 Marchprovided a lower bound. Thus, for this group of workers, the additional contribution to effective dosefrom internal exposure due to intakes of short-lived radionuclides could have been in the range 16−45%
relative to the contribution due to 131I intakes, depending on the time pattern of intake. The equivalent
range for the additional contribution to absorbed dose to the thyroid was 6–28%.
Table D11. Assessed committed effective doses, E(50) (in millisieverts), for workers with the highest
internal exposures (contribution from 131I intake only)
Independent assessor
Working period

1

2

3

4

5

NIRS

TEPCO

Japanese
final reported
value

Worker

Start

End

IMBA

AIDE

MONDAL
IMBA
CALIN

IMBA

IMBA

IMBA

MONDALIMBA (A-B)
MONDAL (C-L)

A

2011-03-11

2011-04-16

610

573

588

635

488

580

ND

580

B

2011-03-11

2011-04-17

515

479

ND

ND

ND

540

ND

540

C

2011-03-11

2011-05-20

383

ND

ND

ND

383

380

433

433

D

2011-03-11

2011-05-17

322

ND

330

ND

ND

290

327

327

E

2011-03-11

2011-06-01

303

ND

ND

386

ND

270

259

259

F

2011-03-11

2011-04-10

ND

221

215

ND

ND

230

240

240

G

2011-03-11

2011-05-19

172

ND

ND

186

ND

160

166

166

H

2011-03-11

2011-05-22

ND

94

148

ND

ND

ND

136

136

I

2011-03-11

2011-05-27

ND

130

155

ND

ND

ND

120

120

J

2011-03-11

2011-06-01

124

ND

ND

117

ND

ND

119

119

K

2011-03-18

2011-05-12

ND

86

ND

ND

172

ND

116

116

L

2011-03-18

2011-05-10

ND

ND

ND

123

133

ND

100

100

ND: Not determined.
Owing to surface contamination and background radiation levels, TEPCO did not take into account measurements made at
Onahama in their dose assessments.
With the exception of assessor 2, the assessors did take into account the Onahama measurements, but the effect on assessed doses
was not large.
For workers C, D, E, F and G, measurements were made at NIRS, but the dose assessment was performed by TEPCO.
NIRS assumed a chronic exposure (11–12 March 2011); TEPCO assumed an acute exposure (12 March 2011); this explains why
NIRS estimates were sometimes lower than TEPCO estimates.
IMBA – Integrated Modules for Bioassay Analysis [B12].
AIDE – Activity and Internal Dose Estimates [B8].
CALIN – Calcul d’Incorporation [A11].
MONDAL – Support System for Internal Dosimetry [N12].

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

233

Table D12. Assessed committed absorbed dose to the thyroid (in grays) for workers with the highest
internal exposures (from 131I intake only)
Independent assessor
Working period
Worker

Start

End

1

2

3

4

5

IMBA

AIDE

MONDAL

IMBA

IMBA

NIRS

TEPCO

IMBA

MONDAL

IMBA

Japanese
final reported
value
IMBA (A-B)
MONDAL (C-L)

CALIN

A

2011-03-11

2011-04-16

12.1

11.3

11.8

12.6

9.7

11.6

ND

11.6

B

2011-03-11

2011-04-17

10.3

9.5

ND

ND

ND

10.8

ND

10.8

C

2011-03-11

2011-05-20

7.6

ND

ND

ND

7.6

7.6

8.7

8.7

D

2011-03-11

2011-05-17

6.4

ND

6.8

ND

ND

5.8

6.5

6.5

E

2011-03-11

2011-06-01

6.0

ND

ND

7.7

ND

5.4

5.2

5.2

F

2011-03-11

2011-04-10

ND

4.4

4.3

ND

ND

4.6

4.8

4.8

G

2011-03-11

2011-05-19

3.4

ND

ND

3.7

ND

3.2

3.3

3.3

H

2011-03-11

2011-05-22

ND

1.9

3.0

ND

ND

ND

2.7

2.7

I

2011-03-11

2011-05-27

ND

2.6

3.1

ND

ND

ND

2.4

2.4

J

2011-03-11

2011-06-01

2.5

ND

ND

2.3

ND

ND

2.4

2.4

K

2011-03-18

2011-05-12

ND

1.7

ND

ND

3.4

ND

2.3

2.3

L

2011-03-18

2011-05-10

ND

ND

ND

2.4

2.6

2.0

2.0

ND: Not determined.
Owing to surface contamination and background radiation levels, TEPCO did not take into account measurements made at
Onahama in their dose assessments.
With the exception of assessor 2, the assessors did take into account the Onahama measurements, but the effect on assessed doses
was not large.
For workers C, D, E, F and G, measurements were made at NIRS, but the dose assessment was performed by TEPCO.
NIRS assumed a chronic exposure (11–12 March 2011); TEPCO assumed an acute exposure (12 March 2011); this explains why
NIRS estimates were sometimes lower than TEPCO estimates.
IMBA – Integrated Modules for Bioassay Analysis [B12].
AIDE – Activity and Internal Dose Estimates [B8].
CALIN – Calcul d’Incorporation [A11].
MONDAL – Support System for Internal Dosimetry [N12].

D41. Based on information provided on work periods and dates of administration of stable iodine forthe worker with the highest dose (worker A), the assumption that there was a single intake ofradioiodine on 12 March was considered to provide the best estimate of absorbed dose to the thyroid ofworker A of approximately 12 Gy. An investigation to determine the effect of the assumed period of
intake on the assessed absorbed dose to the thyroid found that making alternative but reasonableassumptions about periods of intake for worker A could result in a reduction in the assessed absorbed
dose to the thyroid by up to perhaps 30%.
D42. As noted in section III of this appendix, in vitro monitoring (including for beta–gamma emitters)of urine samples was performed for seven of the twelve workers. An investigation of the consistency
between intakes assessed from in vitro data and from in vivo data was carried out for six of these234

UNSCEAR 2013 REPORT

workers. For two workers, the intake assessed from the in vitro data was about a factor of 2 less thanthat assessed from in vivo data, while for two other workers, the in vitro assessments were factors of
2 and 4 greater. For the remaining two workers, the in vitro measurements were all below the detection
limit. Probable reasons for the differences include the delay in initiating urine sampling and the use of
spot sampling for the first of the three urine samples collected for each worker. Spot samples are known
to provide a less reliable measure of daily excretion than samples collected and amalgamated over
24 hours.
D43. The following conclusions were drawn about the internal exposure assessments for twelve of thethirteen workers with the highest internal exposures:(a) There was good agreement between the Committee’s independent assessments of committed
effective dose from internal exposure and the assessments reported in Japan.
(b) For all twelve workers, the independently assessed committed effective dose arose almost
completely from the estimate of absorbed dose to the thyroid due to 131I intake.
(c) The largest absorbed dose to the thyroid was assessed for worker A; the independent
assessments of absorbed dose to the thyroid for this worker ranged from 9.7 to 12.6 Gy, with anarithmetic mean (rounded to two significant figures) of 12 Gy.
(d) The delay in starting monitoring of 131I in the thyroid increased the uncertainty in the dose
assessments over what would normally be achievable, because of uncertainties in the retentionfunction for iodine in the thyroid for individual workers. Given the lack of repeated measurements
soon after intake, it was not possible to quantify this increase in uncertainty.
(e) The delay in starting in vivo monitoring meant that the shorter-lived isotopes of tellurium,
iodine and caesium, in particular 132Te and 133I, were not detected. Indicatively, the additional
contribution to effective dose due to internal exposure from the intakes of these short-lived
radionuclides by those workers on site in the first few days of the accident may have been in theorder of 20% relative to the contribution from 131I; this contribution is likely to have varied
considerably between individuals.
(f) The absence of adequate urine monitoring data meant that it was not possible to confirm thereliability of doses assessed from thyroid activity measurements using results obtained
independently with a different monitoring method.

D. Results for the 55 randomly selected workers with lower
internal exposure
D44. The method used to randomly select the workers for assessment is described at the beginning of
this section. A single independent dose assessment was performed for each of these cases. Assessments
were made using the types of monitoring data and the types of information on exposure conditions
described in section III of this appendix. While the information provided for TEPCO workers was
reasonably comprehensive, that for contractors’ workers was less so. In particular, for 7 cases out of 21,
the only data provided that clearly related to the formally reported dose assessment were the assessedvalues of committed effective dose, E(50). For the remaining 14 cases, data were additionally providedon (a) the work period (only in some cases); (b) the place of measurement (only in some cases); andANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

235(c) the assumed date of intake (only in some cases). Monitoring data were provided for all 21 cases, but
it was unclear which monitoring data (from Onahama, JAEA or a number of other locations) were used
for the formally reported dose assessment. New information was provided too late (in July 2013) to betaken into consideration by the Committee.
D45. Comparisons between the independent dose assessment and the formally reported doses areshown in table D13. The formally reported doses were those reported by the employer of each worker,
that is, TEPCO or its contractors (or subcontractors).
D46. These assessments were all based on in vivo measurements of radionuclide activities in the body.
The table shows the committed effective dose from intakes of all the radionuclides for whichmonitoring results were reported, and the contribution to committed effective dose from 131I intakes.
Assessments of absorbed doses to the thyroid from 131I intakes were also made by the Committee’s
assessors, but are not reported here. Approximate values (within 2% of the assessed values) could bedetermined by dividing the 131I contribution to E(50) given in table D13 by the value of the thyroid
tissue weighting factor (wT) used in the definition of effective dose, 0.05 [I12].
D47. For most workers, initial monitoring was not performed until the period mid-May to end ofJune 2011. A few of the selected workers were monitored during April, but none during March 2011.
For many of the workers, the first possible date of intake was between 12 and 22 March 2011. As aresult of this delay, 131I was not measurable in the thyroid of many workers. For these workers,
Japanese assessors had to make an estimate, using either an “environmental ratio” method or an“MDA” method (described in section III of this appendix).
D48. Because initial monitoring was not performed until the period mid-May to end of June 2011, 131I
was not detected in the thyroid by any of the measurement methods performed, for a significant fractionof the 42 TEPCO and contractors’ workers selected (tables D13 and D14). For three TEPCO workers
and two contractors’ workers with committed effective doses in the 0–5 mSv dose band (worker IDs:
101, 105, 107, 122 and 126), inspection of the monitoring results for other radionuclides indicated thatany 131I present could have been at levels low enough to be undetectable even if monitoring had been
carried out promptly. However, for the other 17 cases (that is, about 40%), the absence of an 131I
measurement result above the detection limit is attributed to the delay in initiating monitoring.

236

Note: “-“: no value recorded, or “not applicable”; “Method”: the method used to assess 131I intake when 131I was not detected in the thyroid. The results of the final and reported Japanese assessments are presented
with the precision with which they were reported

Working period
Worker
ID

Start

End

Committee’s assessment

Japanese final reported assessment

Committed effective dose, E(50) (mSv)

Committed effective dose, E(50) (mSv)131

I measurement
above detection
limit?
(Yes/No)

From 131I

MethodRatio

Total E(50)Method
Ratio

MDA

Total
E(50)

From 131IMDATEPCO WORKERS
Cases selected in the E(50) committed effective dose band: 0–5 mSv
101

2011-04-07

2011-04-07

N

0.0

-

-

0.0

0.0

-

-

0

102

2011-03-11

2011-06-01

N

1.7

Y

N

1.7

2.2

Y

N

2.2

103

2011-03-11

2011-04-21

Y

3.1

N

N

3.2

2.9

N

N

3.0

104

2011-04-19

2011-04-23

Y

0.3

N

N

0.3

0.3

N

N

0.3

105

2011-04-27

2011-04-27

N

0.0

-

-

0.0

0.0

-

-

0.0

106

2011-03-15

2011-03-18

N

-

Y

N

-

4.8

Y

N

4.8

107

2011-05-13

2011-05-17

N

0.0

-

-

0.0

0.0

-

-

0.0

Cases selected in the E(50) committed effective dose band: 5–20 mSv
108

2011-03-21

2011-05-13

Y

15

N

N

15

13.5

N

N

13.6

109

2011-03-11

2011-05-06

Y

11

N

N

11

9.1

N

N

9.2

110

2011-03-22

2011-05-25

Y

13

N

N

13

14.1

N

N

14.1

111

2011-04-06

2011-05-29

Y

22

N

N

22

18.8

N

N

18.8

112

2011-03-11

2011-05-18

N

7.8

Y

N

7.8

7.8

Y

N

7.9

113

2011-03-12

2011-05-11

N

-

Y

N

-

6.6

Y

N

6.6

114

2011-03-18

2011-04-21

Y

15

N

N

16

13.3

N

N

14.7

Alternative
assessmenta

UNSCEAR 2013 REPORT

Table D13. Assessed committed effective doses, E(50), for 42 randomly selected TEPCO and contractors’ workers, and 13 emergency services workers

Working period
WorkerID

Start

Committee’s assessment

Japanese final reported assessment

Committed effective dose, E(50) (mSv)

Committed effective dose, E(50) (mSv)131

I measurement
above detection
limit?

End

From 131I(Yes/No)

MethodRatio

Total E(50)MDA

From 131I

Method
Ratio

MDA

Total
E(50)

Alternative
assessmenta

Cases selected in the E(50) committed effective dose band: 20–100 mSv
2011-03-11

2011-04-23

Y

28

N

N

28

30.5

N

N

30.6

116

2011-03-12

2011-04-16

Y

21

N

N

22

21.3

N

N

22.2

117

2011-03-18

2011-05-10

Y

23

N

N

25

18.0

N

Y

20.0

118

2011-03-11

2011-05-17

N

30

N

Y

31

30.1

N

Y

31.9

119

2011-03-11

2011-05-23

N

186

Y

N

187

25.3

N

Y

27.1

120

2011-03-13

2011-03-30

Y

50

N

N

50

32.0

N

N

32.7

121

2011-03-11

2011-05-21

Y

66

N

N

66

66.9

N

N

67.0

CONTRACTORS’ WORKERSb

Cases selected in the E(50) committed effective dose band: 0–5 mSv
122

2011-06-12

2011-06-23

N

0.0

-

N

0.0

-

Y

N

0.00

0.00

123

c

No values reported by contractor

N

0.1

Y

N

0.1

-

Y

N

0.06

0.06

124

No values reported by contractor

N

0

N

N

<0.1

N

N

0.00

0.02

125

2011-04-06

2011-05-20

N

1.2

Y

N

1.3

-

Y

N

1.30

1.31

126

2011-06-16

2011-06-26

N

0.0

-

-

0.0

-

Y

N

0.00

0.00

127

No values reported by contractor

N

-

-

-

-

Y

N

0.00

0.42

128

2011-03-16

N

0.0

N

N

0.1

-

Y

N

0.40

0.43

2011-06-10

Cases selected in the E(50) committed effective dose band: 5–20 mSv
2011-03-24

2011-04-27

N

10

Y

N

10

-

Y

N

2.90

9.92

130

2011-03-30

2011-06-14

N

6.9

Y

N

7.1

-

Y

N

1.70

3.12

131

No values reported by contractor

Y

6.9

N

N

7.1

-

N

N

0.00

7.16

132

2011-03-29

2011-04-21

N

16

Y

N

17

-

Y

N

1.30

2.52

133

2011-03-17

2011-03-20

N

6.8

Y

N

6.8

-

Y

N

6.83

6.83

134

2011-03-18

2011-04-09

N

-

-

-

-

-

N

Y

7.20

7.20

135

2011-03-23

2011-05-21

Y

7.5

N

N

7.6

-

N

N

6.60

6.65

237

129

ANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

115

StartEnd

I measurement
above detection
limit?

Japanese final reported assessment

Committed effective dose, E(50) (mSv)

Committed effective dose, E(50) (mSv)

From 131I(Yes/No)

MethodRatio

MDA

Total E(50)

From 131I

Method
Ratio

MDA

Total
E(50)

Alternative
assessmenta

Cases selected in the E(50) committed effective dose band: 20–100 mSv
136

2011-03-17

2011-03-19

Y

83

N

N

83

-

N

N

0.00

0.76

137

2011-03-12

2011-03-23

Y

29

N

N

30

-

N

N

37.10

38.48

138

No values reported by contractor

Y

85

N

N

85

-

N

N

13.80

14.21

139

No values reported by contractor

Y

117

N

N

117

-

N

N

60.10

66.28

140

No values reported by contractor

N

109

Y

N

110

-

N

Y

27.2

27.27

141

2011-03-16

2011-03-31

Y

22

N

N

23

-

N

N

18.20

20.45

142

2011-03-11

2011-05-30

Y

35

N

N

35

-

N

N

35.6

35.65

EMERGENCY SERVICES WORKERS143

2011-03-17

-

N

0.012

N

N

0.026

0.012

N

N

0.042

144

2011-03-17-

N

0.0075

N

N

0.022

0.008

N

N

0.037

145

2011-03-17-

N

0.0026

N

N

-

0.004

N

N

0.018

146

2011-03-17

-

N

0.004

N

N

0.0094

0.004

N

N

0.016

147

2011-03-17

-

N

0.004

N

N

0.014

0.005

N

N

0.022

148

2011-03-17

-

N

-

-

-

-

0.006

N

N

0.021

149

2011-03-17

-

N

0.004

N

N

0.030

0.004

N

N

0.029

150

2011-03-17

-

N

0.003

N

N

0.008

0.004

N

N

0.014

151

2011-03-17

-

N

0.003

N

N

0.018

0.004

N

N

0.034

152

2011-03-17

-

N

0.004

N

N

-

0.006

N

N

0.016

153

2011-03-17

-

N

0.004

N

N

0.0087

0.004

N

N

0.014

154

2011-03-17

-

N

0.005

N

N

-

0.006

N

N

-

155

2011-03-17

-

N

-

-

-

-

0.006

N

N

-

a

In July 2013, TEPCO conducted a reassessment of doses for contractors’ employees, reported here as alternative assessment.

b

Independent assessment doesn’t take into account new information that Japanese organizations provided too late to the Committee. Japanese final reported assessment and alternative assessment take into account theresults of reassessment that the Japanese organizations performed in July 2013. Differences between independent and Japanese assessments are presented in table D15.
c

The Committee performed its own assessment for this worker. Information on the working period was provided more recently.

UNSCEAR 2013 REPORT

WorkerID

Committee’s assessment

131

238

Working period

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Table D14. Numbers of selected TEPCO and contractors’ workers for whom 131I was not detected in
the thyroid
Employer

TEPCO

Total

Contractor

Reported committed dose, E(50) (mSv)

0–5

5–20

20–100

0–5

5–20

20–100

Number ofworkers

selected

7

7

7

7

7

7

42

of those, 131I not detected

5

2

2

7

5

1

22

D49. For 12 of the 17 cases, the independent assessor chose to use the environmental ratio method,while the MDA method was used for one case (table D13). For the remaining four cases (worker IDs:
124, 127, 128 and 134), the assessor judged that the quality of the information provided did not justify
the use of either method. Where sufficient information to make a comparison was available, the choiceof alternative estimation method for the final reported value could be seen to be broadly similar for the
independent assessments and for the Japanese final reported assessments (table D13). The exceptions
were for workers with IDs 117 and 119, where the MDA method was used to give the Japanese final
reported assessment.
D50. Two of the independent assessors performed checks on the reliability of the environmental ratio
method. For eight cases where 131I activity measurements above the detection limit were available andhad been used to make an assessment of the contribution to E(50) from 131I intakes, the environmental
ratio method was used to make a second estimate. (The cases selected were workers with IDs: 104, 108,
109, 115, 116, 136, 137 and 139.) Values for E(50) estimated by the environmental ratio method andexpressed as a fraction of the E(50) assessed from the measurements of 131I activity, were: 0.03, 0.05,
0.27, 0.45, 0.84, 2.7, 4.6 and 5.1 (geometric mean = 0.56). This distribution of values indicated thelarge variability in doses estimated using the environmental ratio method, and therefore the large
uncertainty associated with the method, although the small sample size meant that the uncertainty could
not be reliably quantified. The Committee judged that precise information on the timing of intakes
would be needed in order to confirm the reliability of the E(50) estimates using the environmental ratio
method.
D51. The independent assessors gave no specific consideration to the reliability of the MDA method,
because it depended on the detection limits computed for the measurement system and measurement
conditions (for example, the length of the counting period) used for each individual measurement.
Because the methodologies used for in vivo monitoring were judged to be adequate (section III of thisappendix), the calculations of detection limits were expected to be reliable; the method was therefore
considered to be valid for assessing the upper limit for the activity in the thyroid at the time of themeasurement. However, the method could not be taken to provide a reliable estimate of the true activity
in the thyroid. Taking these considerations into account, together with the large uncertainty associatedwith the environmental ratio method, the Committee considered the Japanese assessors’ practice ofadopting the lower of the two estimates to be the best available course of action.
D52. The effect of this choice on the magnitude of under- or overestimates of the 131I intake wasconsidered. Where the method using the environmental ratio gave an anomalously high estimatedintake (owing to the large uncertainty in the method) that should have yielded a measurement ofactivity in the thyroid above the detection limit, the estimate using the MDA method would have beenreported instead. On the other hand, anomalously low intakes estimated using the environmental ratio
method would have been reported in preference to those estimated using the MDA method.
Furthermore, anomalously high intakes estimated using the environmental ratio method were less likely
to have been replaced by the estimate using the MDA method where the true 131I intake was relatively

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low, because the estimate could still have fallen below the estimate using the MDA method. Over thewhole population of workers for whom the alternative estimation methods had to be used, themagnitude of the overestimates of 131I would have been less than the magnitude of the underestimates,
but the extent of this asymmetry could not be evaluated from the information that was available at thetime.
Table D15. Comparison of committed effective doses, E(50), for 21 randomly selected contractors’
workers assessed by the Committee with those from the Japanese final reported assessment, initialalternative assessment and alternative reassessment

WorkerID

Committed effective dose E(50)(mSv)
Committee’s
assessment

Japanese final
reported assessment

Initial alternative
assessment (TEPCO)

Alternative
reassessment (TEPCO)

122

0.0

0.00

0.00

0.00

123

0.1

0.06

0.06

0.06

124

<0.1

0.00

0.02

0.02

125

1.3

1.30

1.31

1.31

126

0.0

0.00

0.00

0.00

127

−

0.00

0.42

0.42

128

0.1

0.40

0.14

0.43

129

10

2.90

13.46

9.92

130

7.1

1.70

9.19

3.12

131

7.1

0.00

7.16

7.16

132

17

1.30

16.77

2.52

133

6.8

6.83

6.83

6.83

134

−

7.20

7.20

7.20

135

7.6

6.60

6.65

6.65

136

83

0.00

88.05

0.76

137

30

37.10

30.33

38.48

138

85

13.80

47.70

14.21

139

117

60.10

87.77

66.28

140

110

27.2

27.27

27.27

141

23

18.20

24.78

20.45

142

35

35.6

35.65

35.65

D53. Where available, the results of alternative dose assessments for contractors’ workers performed
by TEPCO are presented in table D13, as well as alternative reassessments performed by TEPCO in
July 2013. (It should be noted that these alternative estimates were not routinely reported, but were
provided to the Committee for the selected contractors’ workers.) Where the results of the contractor
assessment and of the initial TEPCO assessment were significantly different, reasons were given in theinformation provided to the Committee. The reasons listed were: “Discrepancy in record level”,“Discrepancy in measurement data”, “Discrepancy in assumed intake date” or “Discrepancy in essential
figure”. The meaning of the latter comment is unclear. By the end of 2013, the Committee had notANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

241

elucidated the reasons for these differences. The results of the reassessment that TEPCO performed
were provided too late for the Committee to reassess independently the 21 contractors’ workers using
the new information. Table D15 compares the Committee’s assessments with the Japanese final
reported assessment, TEPCO’s initial alternative assessment, and TEPCO’s alternative reassessment.
This table compares the Japanese final reported assessment and TEPCO’s alternative reassessment forworkers with IDs: 129, 130, 131, 132, 139 and 141.
D54. The following general conclusions were drawn about the internal exposure assessments for the
42 TEPCO and contractors’ workers:For all of the workers with assessed committed effective doses from internal exposure above
0.1 mSv, the dose to the thyroid resulting from 131I intake made the dominant contribution to
the committed effective dose, E(50).

For workers with assessed internal exposure to 131I, on average 98% of the committed effective
dose was due to the absorbed dose to the thyroid resulting from 131I intake (according to theCommittee’s independent assessment).



A high degree of uncertainty was associated with committed doses estimated for 131I using theenvironmental ratio method in those cases where 131I was not measured in the thyroid. The
E(50) could have been underestimated by a factor of up to about 30, or overestimated by afactor of up to about 5.

For four out of the 21 TEPCO cases, the TEPCO final reported assessment used theenvironmental ratio method; information on which contractors’ assessments used this method
was not available. For three out of the 21 TEPCO cases, the TEPCO final reported assessment
used the MDA method; again, this information was not available for contractors’ assessments.
It was difficult to make an accurate estimate of the percentage of the 21,776 TEPCO andcontractors’ workers with reported doses for whom dose estimates were made using either theenvironmental ratio or the MDA methods; it might have been in the region of 40%.

D55. The following conclusions were drawn about the internal exposure assessments for the
21 TEPCO workers:

There was good agreement between the Committee’s independent assessments of E(50) andthe TEPCO assessments for those cases where measurements of 131I activity in the body above
the detection limit were available.

Good agreement was also found for those cases where the independent assessment and the
TEPCO assessment both used the environmental ratio method, as well as for the case where
both used the MDA method. This agreement confirmed that both methods had been appliedcorrectly. However, it could not be taken to confirm the reliability of the dose values assessedusing the environmental ratio method because of the large uncertainties.



The independent assessments of E(50), expressed as a fraction of the TEPCO-assessed E(50),
lay in the range 0.76–1.24 (13 values, standard deviation = 0.12), with two outliers at 1.54 and
6.91. The arithmetic mean value including the outliers was 1.46, and without the outliers
was 1.03. There was no obvious trend in this value with dose. (Note that the 6.91 value was fora case—worker ID: 119—where the Committee’s independent assessment used theenvironmental ratio method. A re-examination indicated that use of the MDA method would
have been justified, which would have resulted in a lower value close to the TEPCO value.)242

UNSCEAR 2013 REPORT

D56. The following conclusions were drawn about the internal exposure assessments for the
21 contractors’ workers:

There were a number of significant differences between the Committee’s independent
assessments of E(50) and the contractors’ assessments, as shown in table D13. There were also
some significant differences between TEPCO assessments and the contractors’ assessments,
also shown in table D13 and table D15. In most, but not all, cases the independent assessment
was in reasonable agreement with the TEPCO assessment.

The most extreme discrepancy was for worker with ID 136. The values of E(50) assessed by
the Committee and by TEPCO were 83 mSv, 88 mSv (TEPCO’s initial alternative
assessment), and 0.8 mSv (TEPCO’s alternative reassessment), respectively, but the contractor
reported 0 mSv. The Committee was not able to reanalyse the information used for TEPCO’salternative reassessment because it came too late. For worker with ID 138, E(50) assessments
by the Committee and by TEPCO were 85 mSv, 48 mSv (TEPCO’s initial alternative
assessment) and 14 mSv (TEPCO’s alternative reassessment), respectively, but the contractor
reported 14 mSv. Similar differences at lower dose levels were found for workers with IDs:
129, 130, 131 and 132.

In two cases, TEPCO and the contractor were in reasonable agreement, but the Committee’s
assessment was significantly higher (workers with IDs: 139 and 140), even when TEPCO’s
reassessment was taken into consideration. This may have arisen from the use in the
independent assessment of whole-body monitoring data from Onahama. After the assessments
were completed, information was provided to the Committee that Onahama data were known
to give overestimates (because of levels of environmental contamination and elevated radiation
background). These data were discarded in Japanese assessments for those cases where otherin vivo data (from JAEA or NIRS in particular) were available.

D57. The following conclusions were drawn about the dose assessments for the 13 emergency services
workers:

Independent assessments of E(50) were low (10–30 µSv).

The contribution to E(50) from dose to the thyroid resulting from 131I intake was 33% (averagevalue).



Measurements of activity in the whole body were of total radiocaesium only (134Cs and 137Cs
combined), and a 1:1 isotopic ratio for the measured amount was assumed in both theCommittee’s and Japanese assessments.



The Committee’s assessments and the values reported in Japan were in reasonable agreement
for the contribution made to E(50) by the absorbed dose to the thyroid from 131I intake.



Doses from caesium intakes reported in Japan were overestimated by a factor of 2. Given that
total doses were low, this was not a significant issue.

D58. The potential additional contribution to committed doses from intakes of short-lived radionuclides
was discussed earlier for workers with the highest internal exposures. For that group of workers, intakes
probably took place within the period 12–15 March 2011, although there was uncertainty about theexact periods of intake. For other groups of workers with lower reported doses (for whom individual
work history information was not available), the period of intake may have extended to later dates andso the possible range on the additional contributions to dose extended to lower values. For these groups

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of workers, the additional contribution to effective dose from intakes of short-lived radionuclides could
have been in the range 6−45% relative to the contribution from 131I, depending on the time pattern ofintake. The corresponding range for the additional contribution to absorbed dose to the thyroid was
2−28%. These estimates of the additional contributions to committed dose assumed that intakescommenced on 12 March. The additional contributions to committed dose from short-lived
radionuclides would have been negligible for all workers who commenced work at FDNPS after about
19 March. For those members of the FDNPS workforce who were working during the period 12–19
March, the indicative additional contribution to effective dose from intakes of short-lived radionuclides
may be in the order of 20% relative to the contribution from 131I, although this value was likely to be
subject to large variations between individuals, mainly because of variations in the time period of
intake.

E. Summary of the conclusions of the Committee’s dose
assessment
D59. With respect to the information collected for 24,832 workers, 13 workers received a cumulative
dose from internal exposure above 100 mSv and 173 workers received a total effective dose above
100 mSv. The highest reported effective dose was 679 mSv, for the TEPCO worker who also had thehighest reported committed dose from internal exposure (590 mSv). The highest reported effective dosefrom external exposure was 199 mSv, for a contractor’s worker who had a reported total effective doseof 238 mSv. The Committee’s evaluations showed that the committed effective dose E(50) arose almost
completely from the committed absorbed dose to the thyroid resulting from 131I intake. It was notpossible to make a definitive judgement about potential exposures to neutrons and to nuclides otherthan 131I, 134Cs and 137Cs, because those exposures were not evaluated sufficiently to make a reliable
assessment.

1.

Assessments of dose from internal exposure

D60. The Committee’s independent assessments of committed effective dose agreed reasonably withthe assessments reported by TEPCO for those workers for whom 131I in the thyroid was measured,
including for twelve of the thirteen workers with the highest internal exposures.
D61. For a significant fraction of the TEPCO and contractors’ workers assessed (22 out of 42), 131I was
not detected in the body by any of the measurements performed because of the delay in initiating
monitoring. For several of the cases, the “environmental ratio” method was used to estimate the 131I
intake. An evaluation of the method showed that it produced highly variable results; owing to theuncertainty in the assumed ratio of 131I to 137Cs intake, E(50) could, in extreme, have been
underestimated by a factor of up to about 30, or overestimated by a factor of up to about 5. The
Committee judged that estimates derived using this method had very large uncertainties and that precise
information on the timing of the intakes would be needed to confirm their reliability.
D62. For several other cases, the “MDA” method was used to estimate the 131I intake. The method was
judged to provide a reliable estimate of the upper limit on 131I intake, but could not be taken to provide
a reliable estimate of the true intake.

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UNSCEAR 2013 REPORT

D63. The reliability of assessments reported by TEPCO for those of its workers where 131I was
measured in the body could be confirmed. The twelve workers (independently assessed by theCommittee) of the thirteen workers with the highest internal exposures from 131I are all in this category.
The largest absorbed dose to the thyroid from 131I was assessed as 12 Gy; the estimates from theindependent assessments ranged from 9.7 to 12.6 Gy, depending on assumptions made in thesimulation, including the timing of the main intakes of 131I.
D64. The reliability of assessments reported for those workers for whom 131I was not detected in the
body cannot be confirmed. Neither of the methods available to estimate 131I intake in thesecircumstances provided a reliable estimate of the true intake, and the resulting dose estimates were
subject to a high degree of uncertainty. Although workers in this category could have comprised about
40% of the 21,776 TEPCO and contractors’ workers for whom individual internal and external
exposures were reported, they were, in general, more likely to have received lower doses.
D65. The delay in starting in vivo monitoring meant that shorter-lived radionuclides, specifically 132Te,
132 133
I, I and 136Cs, would have been undetectable in the body at the time of measurement. For thosemembers of the FDNPS workforce who were working during the period 12–19 March, the indicative
additional contribution to effective dose from intakes of short-lived radionuclides may have been of theorder of 20% relative to the contribution from 131I intake, although this value was likely to be subject tolarge variations between individuals (see attachment D-1 for details). For workers who commenced
work after 19 March, the contribution of short-lived radionuclides would not have been significant.
D66. An assessment of health risk would need to make use of estimates of absorbed doses to organs.
The Committee made indicative estimates of absorbed doses to selected critical organs, specificallythyroid, red bone marrow and colon using three scenarios (see attachment D-1). However, informationon the timing of intakes was not yet available at the end of 2013 for the great majority of the 21,776
TEPCO and contractors’ workers for whom individual internal and external exposures had beenreported.
D67. Evidence from this investigation indicated that many of the dose estimates reported by contractors
for their workers may have been significant underestimates. Based on the comparative assessments
carried out, the Committee was therefore unable to confirm the reliability of assessments reported bycontractors for their workers 41.

2.

Assessments of doses from external exposure

D68. The evaluation of the information provided on dosimetric methods for external exposure indicatedthat the instrumentation, technical standards and calibration methods used appeared to meet generallyaccepted requirements for monitoring. The major factor potentially affecting the reliability of themonitoring performed was the use of shared personal dosimeters during March 2011. Further work
would be needed to quantify the resulting uncertainties in reported doses from external exposure.
41
After the Committee drew this initial conclusion, doses for contractors’ workers were reassessed in Japan [M17], and theCommittee understands that at least some of the discrepancies have been resolved.

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245

APPENDIX E. HEALTH IMPLICATIONS FOR THE PUBLIC ANDWORKERSI.

INTRODUCTION................................................................................................................................. 245
A. Objectives and structure ....................................................................................................... 245
B. Recapitulation of knowledge on health effects and risks fromexposure to ionizing radiation ............................................................................................ 246

II. HEALTH IMPLICATIONS OF RADIATION EXPOSURE OF THE PUBLIC RESULTING FROM
THE FDNPS ACCIDENT ........................................................................................................................... 248
A. Observed health effects......................................................................................................... 248
B. Risk assessment conducted by WHO ................................................................................ 249
C. The Committee’s commentary on health implications for the public.................. 251
D. Long-term medical monitoring .......................................................................................... 256
III. HEALTH IMPLICATIONS OF RADIATION EXPOSURE OF WORKERS RESULTING FROM
THE FDNPS ACCIDENT ........................................................................................................................... 258
A. Observed health effects......................................................................................................... 258
B. Risk assessment conducted by WHO ................................................................................ 260
C. The Committee’s commentary on health implications for workers ...................... 261
D. Long-term medical monitoring .......................................................................................... 264

I. INTRODUCTION

A. Objectives and structure
E1. The objectives of this appendix are to provide a commentary on the immediate and long term
health implications of exposures to ionizing radiation resulting from the accident at the Fukushima
Daiichi Nuclear Power Station (FDNPS), and to consider the on-going health monitoring programmes.
E2. The phrase “health implications” is used here to express the Committee’s interpretation of
information on the consequences for health based on its assessment of radiation exposure from the
FDNPS accident, specifically (a) to provide information on health effects that have been observed in
exposed populations within the time frame considered by the Committee (generally about two years

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UNSCEAR 2013 REPORT

after the accident but in some cases longer); (b) to provide insight into the magnitude of risks of future
health effects from the assessed radiation exposure of these populations; and (c) to provide information
as to whether it was likely that risks would become manifest and discernible in the future diseasestatistics covering these populations. In addition to the interpretation of information on health
implications of the radiation exposure, some contextual commentary is made on broader health
implications, such as the impact on mental health, that are related to the accident and the response to it,
as well as to the natural disaster itself.
E3. Section I.B briefly recapitulates current knowledge on the health effects and risks from exposure
to ionizing radiation. Consideration is then given separately to the health implications for the public(section II) and for those exposed occupationally or in responding to the FDNPS accident (section III).
The commentary on health implications for the public relied upon the Committee’s assessment of
exposures of different population groups in Japan, as outlined in appendix C. The commentary on
health implications for workers was based on the exposures reported to—and to the extent possible
independently assessed by—the Committee, and outlined in appendix D. The health risk assessment
conducted by the World Health Organization (WHO) based on its preliminary dose assessment wasalso reviewed. Health effects, irrespective of their cause, that were observed within about the first two
years following the accident, and risks of future health effects are discussed. The Committee drew upon
the experience from the Chernobyl accident and its implications for the health of the general public andof workers. The radiation exposure resulting from the FDNPS accident is also put into perspective byusing some other sources of exposure as a frame of reference, to help provide some context forunderstanding the overall radiation exposure of the population of Japan.

B. Recapitulation of knowledge on health effects and risks
from exposure to ionizing radiation
E4. Exposure of tissues or organs to ionizing radiation can induce the death of cells that can beextensive enough to impair the function of the exposed tissue or organ. Effects of this type, which arecalled “deterministic effects”, are clinically observable in an individual if the absorbed dose to a tissue
exceeds a threshold level specific to that tissue. Such effects include the acute radiation syndrome(ARS), skin burns, loss of hair, hypothyroidism and developmental damage to an unborn child. Abovethe relevant threshold level, the severity of such a deterministic effect increases with the absorbed dose.
The International Commission on Radiological Protection (ICRP) has introduced the term, “tissue
reaction”, which encompasses deterministic effects, circulatory disease and cataracts [I26].
E5. Exposure to radiation can also induce non-lethal changes to cell constituents, including DNA
lesions. Different consequences can occur following such an event: the cell is successfully repaired (i.e.
it returns to normal); or the cell remains unrepaired or is misrepaired (i.e. it remains abnormal). The
human body’s immune system is very effective in detecting and destroying abnormal cells. However,any abnormal cells that escape the immune defence over time may proliferate and contribute tocarcinogenesis or hereditary effects. Such effects are called “stochastic” effects and are characterized
by an increased incidence with increased dose to an exposed population but are indistinguishable fromsimilar effects that occur in the absence of exposure. The Committee has conducted extensive reviewson these effects, most recently in [U7, U8, U9], and has also considered some key issues in this areathat require further scientific attention [U10, U15]. Findings from these past reviews related to the most
relevant health consequences of radiation from the FDNPS accident are recapitulated below, updated as
appropriate with more recent information.

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247

E6. Solid cancer. The Committee previously estimated the increased risk of solid cancer for thegeneral populations of China, Japan, Puerto Rico, the United States and the United Kingdom following
exposure to low-LET radiation 42 [U9]. The estimated lifetime risk depended on the absorbed dose, themodel assumed for describing the risk of cancer following radiation exposure, the baseline cancer rate(i.e. the prevailing cancer rate in the absence of radiation exposure) in the respective country/area, andmortality rates for specific causes of death.
E7. The lifetime baseline risk of solid cancer in the general population of Japan is about 35% on
average (males about 41%; females about 29%) [W12]. Following a hypothetical exposure of a groupfrom the same population corresponding to an acute uniform whole-body dose of 1 Sv (equivalent to anabsorbed dose of 1 Gy of low-LET radiation to all organs and tissues of the body), the Committee
previously estimated the additional lifetime risk of solid cancer due to that exposure to beapproximately 13% on average (annex A, table 70 in the Committee’s 2006 Report [U9]). Following
doses of 0.1 Sv and 0.01 Sv, the additional lifetime risk due to the exposure was estimated to be smaller
by factors of about 10 and 100, respectively.
E8. The Committee has evaluated the uncertainty associated with its estimates of risk due to radiation
exposure [U14]. For a hypothetical group of male radiation workers in the United Kingdom, theCommittee estimated the average additional lifetime risk of solid cancer due to a whole-body dose of
100 mSv to be about 1%, and the 95% subjective confidence interval on this value to be from a factorof 2.5 lower to a factor of 2 higher. These estimates are similar to those made by the United States
Committee on the Biological Effects of Ionizing Radiation [N22] and imply that for a population
incurring an acute exposure of 100 mSv, the lifetime risk of cancer would increase from about 41% toabout 42%. For 10 mSv, the theoretical increase would be from about 41% to 41.1%.
E9. Leukaemia. In Japan, the lifetime baseline risk of leukaemia in the general population is about
0.5% on average [W12]. The Committee has previously assessed the risk of mortality from leukaemia
due to radiation exposure for the general population of Japan [U9]. Depending on the model applied,
the additional lifetime risk after an acute low-LET exposure with an absorbed dose of 1 Gy to the redbone marrow was estimated to be in the range from 0.05% to 0.47% for the general population, and in
the range from 0.11% to 0.84% for children exposed between 0 and 9 years of age.
E10. Exposure during childhood. The increase in cancer risk due to radiation exposure duringchildhood is generally greater than that for exposures at older ages (annex A of [U9]). However, theradiosensitivity of children is not the same for all organs and tissues. In annex B to this report to theGeneral Assembly, the Committee describes evidence for children being more likely than adults todevelop, for example, breast cancer, thyroid cancer and leukaemia (other than chronic lymphocytic
leukaemia, CLL) after radiation exposure [U16]. It also discusses those tumour types for whichchildren have the same or less sensitivity than adults. The increased likelihood for development ofcertain cancers after exposure during childhood need special recognition in the context of the FDNPS
accident.
E11. Thyroid cancer. The risk of thyroid cancer following radiation exposure is strongly modified by
the age at exposure with young children under age 6 years being at highest risk and risk decreasing
with increasing age at exposure [U9]. The Committee estimated lifetime additional absolute risk ofthyroid cancer due to irradiation for a hypothetical group of Ukrainians who received an absorbed doseto the thyroid of 0.2 Gy low-LET radiation at age ten years [U14]. For males, the exposure wasestimated to add 0.07% (95% confidence interval, CI: 0.01%, 0.21%) to the baseline risk of thyroid
cancer of 0.14%. Corresponding values for females were 0.59% (95% CI: 0.11%, 2.1%) and 0.62%.
42

As radiation interacts with matter, it loses its energy through interactions with atoms. The Linear Energy Transfer (LET) is ameasure of the average amount of energy lost over a defined distance. The same absorbed dose of low-LET radiation (such as
beta particles and gamma rays) creates less biological damage than of high-LET radiation (such as alpha particles). The radiation
exposure from the FDNPS accident was essentially all from low-LET radiation.

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UNSCEAR 2013 REPORT

E12. In utero exposure. The large and comprehensive Oxford Survey of Childhood Cancers (OSCC)
that studied children who had been exposed in utero because of obstetric use of X-rays found a
statistically significant increased risk among children of leukaemia and all solid cancers of about 40%
relative to the baseline (i.e. a relative risk of 1.4) [W2]. Although no individual dose estimates wereavailable, doses to the foetus were likely to have been of the order of 10 mGy. Similar results havebeen obtained in a number of other, smaller studies of the effects of obstetric radiography [U7].
However, the causal nature of such low doses following in utero exposure has been debated. Analysesof the survivors of the atomic bombings in Japan who were exposed in utero have only shown astatistically significant increase in incidence of adult-onset cancers at doses higher than about 50 mGy
or so [P16]. While the magnitude of the risk of cancer from in utero exposures to diagnostic X-rays
remains a matter for discussion [N5], it is possible to estimate upper bounds for any risk.
E13. Hereditary effects. Radiation exposure has never been demonstrated to cause hereditary effects inhumans, despite extensive studies of the children of survivors of the atomic bombings in Japan, and of
the children of cancer survivors treated with radiotherapy throughout the world. However, experimental
studies on plants and animals have demonstrated that radiation can induce hereditary effects, andhumans are unlikely to be an exception in that regard. Based on animal experiments, the Committee
estimated 3,000 to 4,700 cases of hereditary effects per gray of low-LET radiation per one million
progeny of the first generation after the exposed generation [U8]. This is equivalent to an absolute riskof hereditary effects per unit dose of 0.3% to 0.5% per gray. Thus, for a given whole-body exposure,the estimated risk that an individual’s offspring will have a hereditary disease is on average less than
one tenth of the individual’s own risk of cancer.
E14. Non-cancer somatic effects. In its 2006 review, the Committee considered the scientific data to be
insufficient to derive a causal relationship between radiation exposures and non-cancer somatic
diseases for absorbed doses of less than about 1–2 Gy [U9]. In 2012, the ICRP estimated that a dose of
0.5 Gy represented a threshold for developing circulatory diseases as a result of irradiation more than
10 years after exposure [I26]. However, at such a dose it cannot be excluded that the risk of circulatory
disease per unit dose is lower [S5] or even non-existent, although the subject remains a matter of muchdebate [L8].

II. HEALTH IMPLICATIONS OF RADIATION EXPOSURE OF THE
PUBLIC RESULTING FROM THE FDNPS ACCIDENT

A. Observed health effects
E15. Effects of radiation exposure. In the short term, no deterministic health effects due to radiation
exposure after the FDNPS accident were observed among members of the public and none are expectedin the long term because the doses were far below the threshold values for such effects [N1, U9, U12].
E16. Effects from other causes. The most important and manifest health effects of the nuclear accident
in the short term would appear to be on mental and social well-being [B20]. This aspect was
exacerbated by the enormous impact of the earthquake and tsunami, the uprooting of thousands ofpeople as a consequence of the evacuation and their displacement to unfamiliar surroundings, and thefear and stigma related to radiation exposure. It is outside of the Committee’s mandate to assess theoccurrence and severity of such effects. However, they are part of the broad definition of health as usedby WHO and such effects may also continue in the long term. Furthermore, the evacuation following

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the accident caused immediate aggravation of the condition of already vulnerable groups; for example,
it was reported that more than 50 hospitalized patients died either during or soon after the evacuation,
probably because of hypothermia, dehydration or deterioration of underlying medical problems [T4],and that upwards of 100 elderly people may have died in subsequent months because of a variety ofconditions linked to the evacuation [Y6]. Understanding the full health impact of the accident forms animportant context for the Committee’s commentary on health implications directly related to radiation
exposure.

B. Risk assessment conducted by WHO
E17. The WHO published in 2013 a health risk assessment of the FDNPS accident to estimate thepotential public health impact so that future health needs could be anticipated and public health actions
taken [W12]. It estimated risks based on preliminary estimates of radiation doses using data gathered
up until September 2011 [W11]. In contrast, the Committee used more comprehensive and recent datafor its scientific assessment of doses, and made more realistic assumptions where data were sparse,
particularly for the evacuated areas. Nevertheless, the Committee’s dose estimates and the doses
estimated by WHO were generally consistent; the ranges of estimates presented by WHO (seeappendix C) encompassed the results of the Committee’s dose assessment, although the WHO
estimates were higher for a number of the evacuated settlements.
E18. The WHO did not expect any deterministic effects in any of the various groups it considered[W12]. It did not expect prenatal exposure to increase “... the incidence of spontaneous abortion,
miscarriages, perinatal mortality, congenital effects or cognitive impairment.” WHO considered the“...
hereditary risk in the offspring of an exposed person ... [to] be much lower ... than the additional
cancer risk of that exposed person.” These statements are consistent with the views of the Committee
for exposures typical of those estimated to have been incurred by the public as a result of the FDNPS
accident.
E19. The WHO made the following main assumptions in its estimation of cancer risks [W12] (theCommittee’s remarks on those assumptions follow each one below):(a) A linear non-threshold (LNT) dose–response model for solid cancer and a linear-quadratic
non-threshold dose–response model for leukaemia. While the Committee noted that these models
had been used for radiation protection purposes [I21], it also noted that the current state ofknowledge on the risk of cancer from doses of the order of 100 mSv or less was quite limited,
although some but not all data were compatible with the risks of cancer from such doses not being
seriously underestimated by the LNT model. The Committee has previously decided not to use
models to project absolute numbers of health effects among populations exposed at such levels,
because of large and unavoidable uncertainties in the predictions (annex D to [U12]).
(b) A dose-and-dose-rate effectiveness factor (DDREF) of one. This is not incompatible with theCommittee’s estimates of cancer risks after doses of 0.01, 0.1 and 1.0 Sv delivered acutely [U9,U11], with recent results for solid cancer in the Life Span Study (LSS) of Japanese survivors
exposed as a result of the atomic bombings at Hiroshima and Nagasaki [O8], or with a metaanalysis of low-dose-rate, moderate-dose exposures [J2]. In contrast, experimental evidence
indicates values of DDREF greater than one for high-dose exposures at low dose rate [I21, U5].
(c) An onset of increased cancer risk from irradiation after minimum latency periods of 2 years
for leukaemia, 3 years for thyroid cancer, and 5 years for breast cancer and all solid cancers
combined. WHO assumed values for minimum latency period that are shorter than those fromprevious reviews of the literature by the Committee [U9] and represent a cautious assumption.
Because radiation risks are not expected to be fully expressed already at the presumed minimum

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latency period, the WHO assumption, in general, leads to a slight overestimation of the cancer risk
for the first decade after exposure. For longer time periods the impact is negligible.
(d) Risk models derived from the LSS cohort of survivors of the atomic bombings in Japan. The
WHO justified its choice of risk model by the general consistency of LSS risk estimates (which arethemselves based on a Japanese population) with those found in populations exposed to protracted
exposures, and with populations exposed during childhood or adolescence to radioiodine released
after the Chernobyl accident, although there is inevitably some uncertainty about the level ofconsistency.
(e) Weights assigned to additive and multiplicative models in the transfer of LSS risk functions to
the populations in Fukushima Prefecture. For leukaemia and all solid cancers, WHO gave equal
weight to these two models of transfer, because the true interaction of radiation exposure withother causes of cancer is not generally known. For breast cancer, the WHO used an additive model
because a pooled study had shown a smaller variability of excess absolute risk estimates thanexcess relative risk estimates [P14]. The choices made for all solid cancers and breast cancer werebroadly consistent with assumptions made by ICRP, BEIR VII and USEPA, although there is lessconsensus for leukaemia [E2, I21, N22]. However, these organizations have proposed amultiplicative risk transfer model for thyroid cancer. WHO justified their choice of assigning equal
weight for additive and multiplicative models by comparing the LSS results with data from studies
after the Chernobyl accident. In past reviews, the Committee had applied additive andmultiplicative models separately in order to assess the implications of the mode of transfer [U9].
The choice of model, although relevant because the population of Fukushima Prefecture has somedifferent characteristics from the population exposed to radiation from the atomic bombings, wasless important because the transfer was from one exposed Japanese population to another, rather
than to another population of different ethnicity.
E20. According to WHO’s preliminary dose estimation, average lifetime doses due to the accident tothe colon, breast and bone marrow of people in the areas with the highest deposition densities ofradionuclides (namely Namie Town in Futaba District and Iitate Village in Soma District) were
estimated to be up to about 20 mSv [W12]. WHO estimated absorbed doses to the thyroids of adults
and young children (delivered mainly within the first year) to be about 50 mGy and 100 mGy,
respectively. They estimated that populations in other areas with high deposition densities received
doses lower by a factor of at least two.
E21. WHO [W12] estimated, for the areas with the highest deposition densities of radionuclides, themean lifetime risk of all solid cancer due to radiation exposure during infancy to be about 0.6% and1.2% for males and females, respectively (table E1). This would be in addition to a baseline risk
expected in the absence of radiation exposure from the accident of 41% and 29% of males and females,
respectively. This estimated increase in risk due to radiation exposure was small compared with thetemporal and regional variability of cancer incidence [C3]. For females, about 20% of the increase incancer risk was estimated to be due to the risk of breast cancer. For exposure during infancy, nearly
40% of the estimated increase in risk of cancer for females was due to the risk of thyroid cancer; thiswas because the absorbed dose to the thyroid was significantly higher than that to other organs, and theexcess relative risk of thyroid cancer per unit dose for this population group was high. However,
because of the very low baseline lifetime incidence of thyroid cancer, WHO expected the additional
absolute lifetime thyroid cancer risk due to radiation exposure to be small. The WHO estimates of risk
per unit dose were compatible with estimates of the Committee in its earlier reports (see section I.B ofthis appendix).

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Table E1. WHO’s estimates of lifetime baseline risk, LBR, and lifetime attributable risk, LAR for areas
within Fukushima Prefecture with effective doses of 12–25 mSv in the first year [W12]The calculations were based on absorbed doses to the colon, bone marrow and breast of 20 mGy for the whole population,
and absorbed doses to the thyroid of about 100, 75 and 50 mGy for an age at exposure of 1, 10 and 20, respectively
The values calculated by WHO were quoted to two significant figures and have been reproduced here. The use of such
precision should not imply that the numbers are accurately known. For example, consideration of the uncertainty associatedwith the LAR estimates would suggest that the actual values likely lie within bounds that are perhaps 2–3 times higher orlower. The LBR are also associated with uncertainty and variability between different years

Age atexposure (y)
1

10

20

Risk quantity

All solid
cancera

Leukaemia

Breast cancer

Male

LAR
LBR

0.6%
41%

0.03%
0.60%

−

0.10%
0.21%

Female

LAR
LBR

1.2%
29%

0.02%
0.43%

0.26%
5.5%

0.43%
0.77%

Male

LAR
LBR

0.5%
41%

0.02%
0.58%

−

0.04%
0.21%

Female

LAR
LBR

0.8%
29%

0.01%
0.41%

0.17%
5.5%

0.19%
0.77%

Male

LAR
LBR

0.3%
41%

0.01%
0.57%

−

0.01%
0.21%

Female

LAR
LBR

0.5%
29%

0.01%
0.40%

0.11%
5.6%

0.07%
0.76%

Sex

ThyroidcanceraIncludes the risk of thyroid cancer taking into account the relatively high absorbed dose to the thyroid, while the WHO report
calculated the risk of all solid cancer assuming that the absorbed dose to all organs was equal to the dose to the colon.

E22. The WHO remarked that the “ultrasound screening for thyroid disease is likely to lead to anincrease in the [reported] incidence of thyroid diseases due to earlier detection of non-symptomaticcases (screening effect)” (see section D below). In its calculations, WHO did not consider explicitly theeffect that the ultrasound screening programme in Fukushima Prefecture would have on detection rates
and therefore on the observed/reported prevalence and incidence rates of thyroid disease. Nevertheless,the survey was expected to lead to an increase in the detection of cases of thyroid cancer, both ofbaseline ones and those that may be related to radiation exposure, which are currently
indistinguishable.

C. The Committee’s commentary on health implications forthe public
E23. The Committee based its commentary on (a) its own dose estimates for subsets of the Japanese
population as reported in appendix C and relevant attachments; (b) its estimates of disease risks fromexposures to ionizing radiation including new estimates of the risk of thyroid cancer as summarized in
section I.B; and (c) results of the WHO report [W12] as reviewed in section II.B (but modified byconsidering the risk of solid cancer including the full risk of thyroid cancer, whereas the WHO
estimates for the risk of solid cancer were based on doses to the colon not taking into account that
doses to the thyroid were in general higher). The Committee’s commentary considers quantitative andqualitative estimates of potential disease outcomes among the exposed populations that may or may not
be observable in future disease statistics. For the purpose of this study, the Committee has used thephrase “no discernible increase” where, although a disease risk in the longer term can be theoreticallyinferred on the basis of existing risk models, an increased incidence of effects is unlikely in practice to252

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be observed in future disease statistics using currently available methods, because of the combinationof the limited size of population exposed and low exposures, i.e. consequences that are small relative tothe baseline risk and their uncertainties. To gain insight as to whether increased incidence might bediscernible, the Committee considered some indicative numbers of individuals within doses bands,
based on the population and dose information in appendix C and associated attachments.

1.

Population of Japan and of Fukushima Prefecture

E24. For the general public of Japan, inhabiting areas where exposures from the FDNPS accident in
the first year were of the order of or below annual background exposure to natural sources of radiation(and lifetime exposures are expected to be much below those incurred from background radiation), theCommittee estimated that risks over their lifetimes were so low that no discernible increase in the
future incidence of health effects due to radiation exposure would be expected among the population or
their descendants. Disease risks for people who were evacuated and for people in districts ofFukushima Prefecture that were not evacuated (who received, in the first year, doses from the accident
that exceeded the annual background exposure to natural sources) are discussed in detail below.
E25. The radiation exposure of the population resulting from the FDNPS accident had two main
components: (a) doses due to external exposure and to internal exposure from incorporated
radiocaesium, both of which are relatively homogeneous in the body. For such homogeneous wholebody exposures of adults with effective doses spanning up to about 100 mSv, the value of effective
dose could be used to estimate absorbed doses to particular organs and qualitatively evaluate theexposure to explore whether a more sophisticated risk analysis was necessary; and (b) absorbed doses
to the thyroid due to incorporation of radioiodine, which is discussed separately below.
E26. The quantity effective dose is itself not suited for quantitative risk estimations, having beendeveloped for radiation protection and for demonstrating compliance with regulatory limits. It does
allow partial body exposures as well as exposures due to intakes of radionuclides to be combined into
an aggregate quantity that is useful in radiation protection, but not quantitative risk assessment. It
includes judgements on values for tissue weighting and radiation weighting factors, and averages over
all ages and both sexes. It thus does not represent risk to an individual or groups of similar individuals
with the same characteristics, and is not useful for quantitative risk estimation. Therefore, theCommittee based its estimates of risk from exposure during childhood on estimates of absorbed doses
to specific organs.
E27. All cancer. The Committee estimated settlement averages of effective doses to adult evacuees tobe less than 10 mSv in the first year after the accident (table C11). In the most affected districts of theareas that were not evacuated, average lifetime effective doses to adults were up to just over 10 mSv
above natural background (table C14). Individual doses could be lower or higher by a factor of about
2 to 3. The Committee estimated that perhaps 15,000 people in the highest dose bands might havereceived average lifetime effective doses of about 25 mSv.
E28. Definite evidence for an increase in the incidence of some cancers from acute (weighted colon)
doses of 100 mSv or more has been reported for population groups such as the survivors of the atomic
bombings in Hiroshima and Nagasaki (see section I.B in this appendix and [U9]). While there is little
or no direct evidence for an increase in the incidence of cancer as a whole in adult populations fromhomogeneous whole-body exposures with effective doses of 100 mSv or less, risks can be inferred atsuch levels (e.g. using a linear dose–response model). However the values of inferred risks are so smallthat in general no discernible radiation-related increase of overall cancer incidence would be expectedamong exposed members of the general public. However, separate consideration of certain
malignancies has been made for particular groups (see below).

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E29. Thyroid cancer. During the first year, incorporated radioiodine from the accident led to higher
absorbed doses to the thyroid than to other organs and tissues. For adults in areas that were notevacuated, the district-average absorbed doses to the thyroid were less than 20 mGy in the first year
after the accident (table C10). Available evidence indicates that the thyroid is not particularly sensitive
to such doses during adulthood.
E30. In contrast, for 1-year-old infants who were evacuated after the accident, the Committee
estimated settlement-average absorbed doses to the thyroid to be up to about 80 mGy (table C12). In
the areas that were not evacuated, district-average doses to the thyroid were up to about 50 mGy(table C10). For example, the Committee estimated that about 35,000 children in the age range of 0−5
years lived in districts where the average absorbed dose to the thyroid was between 45 and 55 mGy.
E31. The Committee previously evaluated the risk of thyroid cancer from an absorbed dose to thethyroid of 200 mGy at age of ten years [U14]: the lifetime risk of thyroid cancer was estimated to beapproximately doubled by the exposure. However, even for a hypothetical exposure of 10,000 children
with such a dose to the thyroid, the uncertainty of the risk estimate is large, ranging from a relative riskof about 1.15 to about 4.0. The WHO estimates of the risk of thyroid cancer due to radiation exposure[W12] were consistent with those of the Committee, if the risk dependence on dose to the thyroid wereassumed to be linear from several hundred milligrays down to the levels of dose received after theaccident.
E32. From an estimate of absorbed dose of 50 mGy to the thyroid of infants, and assuming that the riskof thyroid cancer could be extrapolated down to these dose ranges using a linear dose–response
function, a relative lifetime risk of thyroid cancer due to the exposure over the baseline risk could be
inferred to be about 1.3. Such an increase in principle ought to be discernible if the effect of increased
detection rate due to sensitive screening and other factors could be isolated, although most of theincreased incidence would be expected to appear several decades after the exposure. Furthermore,
direct measurements of radioiodine content in the thyroid have suggested that actual doses to thethyroid for some individuals might be lower than the average doses estimated by the Committee using
environmental measurements and modelling, although there are some questions about how
representative the thyroid measurements generally were. A detailed re-evaluation of the absorbed doses
to the thyroid taking into account all available information relevant to thyroid exposure including the
thyroid measurements, their quality assurance and information on individual protective measures ishighly desirable.
E33. The Committee estimated that the doses to the thyroid varied considerably among individuals,
indicatively from about 2 to 3 times higher or lower than the average for a district. It considered thatfewer than a thousand children might have received absorbed doses to the thyroid that exceeded
100 mGy and ranged up to about 150 mGy. The risk of thyroid cancer for this group could be expected
to be increased. However, it would be difficult, if not impossible, to identify precisely those individuals
with the highest exposure, and risks at these low doses have not been convincingly demonstrated;moreover, as noted above, the lower dose values suggested by direct thyroid measurements on some
populations should be reviewed, as well as their associated uncertainties. Information on dose
distribution and uncertainties was not sufficient for the Committee to draw firm conclusions as towhether any potential increased incidence of thyroid cancer would be discernible among those exposed
to higher thyroid doses during infancy and childhood.
E34. Leukaemia. The Committee estimated settlement-average absorbed doses to the red bone marrowof 1-year-old evacuees before and during their evacuation to be up to 10 mGy (appendix C, section
III.A.6). In the areas not evacuated, district-average doses in the first year were estimated to be up to
about 5 mGy (appendix C, section III.A.5). For example, about 18,000 children in the age range of
0−5 years were estimated to live in districts where the average absorbed doses to the red bone marrow
were 4 to 6 mGy. The Committee has previously assessed the risk of mortality from leukaemia due toradiation exposure for the general population of Japan [U9]. Depending on the model applied, the254

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lifetime risk from an absorbed dose of 1 Gy to the red bone marrow in children aged 0 to 9 years at
exposure was estimated to be in the range from 0.11% to 0.84%. The risk estimates were mainly basedon the LSS. In the past, (e.g. at the time when childhood leukaemia could be observed in the LSS),
mortality rates of the disease were very high. Therefore, the risk function for mortality from childhood
leukaemia is now often used to represent the risk function for incidence of childhood leukaemia as
well. For the accident at FDNPS, the WHO estimates of the risks of leukaemia due to radiation
exposure [W12] were consistent with those of the Committee.
E35. Most of the radiation-induced leukaemia risk after exposure during infancy would be expressed
during childhood. WHO estimated the risk of leukaemia for the first 15 years after exposure during
infancy. An absorbed dose of 26 mGy to the red bone marrow was estimated to increase the risk from abaseline of 0.03% to 0.05% [W12]. This is slightly lower but broadly consistent with some recent
studies of childhood leukaemia after radiation exposure [W5]. The Committee’s estimates of exposure
were lower than those of WHO. Considering the exposures and risks, and the size of the exposedgroup, any increase in childhood leukaemia is not expected to be discernible.
E36. Breast cancer. The Committee estimated settlement-average absorbed doses to the breast of girls
before and during their evacuation to be up to 10 mGy. In areas that were not evacuated, districtaverages of lifetime doses to the breast were up to 20 mGy. The Committee previously calculated alifetime risk of breast cancer of about 0.3% for the general female population of Japan from anabsorbed dose to the breast of 100 mGy [U9]. The difference in risk due to exposure as a childcompared to as an adult depends on the assessment model used [U16]. However, in some studies therisk of breast cancer from exposure as a child was estimated to be higher by a factor of three to fivethan the risk from exposure as an adult [U16]. Compared to a baseline risk for breast cancer of about
5.5% [W12], the Committee does not expect that any increase in future incidence of breast cancer due
to radiation exposure would be discernible.
E37. Childhood cancer after exposure in utero. Absorbed doses in utero may increase the relative riskof childhood cancer including leukaemia [U7] (see section I.B above). The Committee estimatedsettlement-average doses to the uterus of pregnant women who were evacuated to districts with highdeposition densities to be up to 9 mGy. It could not exclude the possibility that a small number ofpregnant women may have received absorbed doses to the uterus of up to about 20 mGy. However,
because of the small numbers of pregnant women and foetuses exposed at such levels, it is not expectedthat any increase in the incidence of childhood leukaemia or other childhood cancers would bediscernible. Further, low-dose prenatal exposure at these levels would not be expected to increase theincidence of spontaneous abortion, miscarriages, perinatal mortality, congenital effects or cognitive
impairment.

2. Experience from the Chernobyl accident and comparison with othersources of exposure(a) Experience from the Chernobyl accident relevant to the public health
implications of the accident at FDNPS
E38. The doses received by the public due to the March 2011 FDNPS accident are in general much lessthan those received by the population residing near Chernobyl due to the April 1986 accident. There
were no deterministic effects reported among the general population after the Chernobyl accident, andaccordingly none are expected after the Fukushima accident, where the doses were considerably lower.
The highest doses from the Chernobyl accident were to the thyroid as a result of the intake of 131I into
the body [U12]. The largest doses resulted from the failure to restrict the consumption of foodstuffs
containing high concentrations of 131I, in particular of milk; millions of children were exposed throughANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

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ingestion with tens of thousands of them receiving doses to the thyroid exceeding 1,000 mGy [U12].
After the FDNPS accident, transfer to foodstuffs was more limited because the accident occurredearlier in the growing season. Moreover, restrictions on the sale of foodstuffs with radionuclide
concentrations exceeding regulatory levels were implemented relatively promptly (the first instructions
on restrictions were introduced on 17 March); this greatly reduced and constrained exposures fromingestion [N1].
E39. An increase in the incidence of thyroid cancer associated with the Chernobyl accident was first
identified about four years after the accident [K4]. By 2005, approximately 6,000 people, under age
18 years at the time of the accident, had been diagnosed with thyroid cancer [I2, U9, U12, W3]. It has
been estimated that about 30% in Ukraine and about 60% in Belarus of the incidence of diagnosed
thyroid cancer could be attributed to the radiation exposure [J1]. In comparison, doses to the thyroid forthe general public following the FDNPS accident were lower.
E40. No convincing increase in the incidence of childhood leukaemia or of solid cancer (except cancerof the thyroid) was reported as a result of exposures received from the Chernobyl accident, which is not
unexpected given the levels of exposure that occurred [B13, U12]. No significant increases in theincidence of birth anomalies or foetal deaths were identified that could be attributed to radiation
exposure resulting from the accident [W9].
E41. Reports about survivors of the atomic bombings of Hiroshima and Nagasaki indicated a
psychological aftermath that included stigma, economic and social discrimination, anxiety, depression,and post-traumatic stresses that were long term [H8, K14, L6]; these were independent of any resulting
physical sicknesses [Y1] and were associated with perceptions of disease risks [K14, O4]. The
psychological impact of the accidents at Three Mile Island and Chernobyl followed a similar pattern asthat of the atomic bombings [B19, B20, H4]. Two studies, conducted 6–7 years after the Chernobyl
accident [H3, V2], found that the exposed population had significantly poorer mental health thancontrols. In Gomel Oblast, mothers with young children were found to be a particularly high risk
group. Both studies found that the perception of harmful levels of exposure to radiation, as opposed tothe actual levels of exposure, was the key risk factor. Similarly, an increase in the incidence of
psychological effects has already been observed among the general population after the FDNPS
accident [Y4, Y5]. Such long-term psychological effects can be expected to occur in the population of
Fukushima Prefecture.
E42. In summary, the radiation exposures resulting from the FDNPS accident are substantially lower
than those after the Chernobyl accident. This suggests that any increase in the incidence of healtheffects among the general public resulting from radiation exposure from the FDNPS accident will
likely not be discernible.

(b) Comparison with other sources of exposure
E43. Background exposure to natural sources of radiation results in a global average effective dose ofabout 2.4 mSv annually, with wide variation about this value depending on geographical location(indicatively in a range of about 1–13 mSv) [U11]. The average annual effective dose in Japan is about
2.1 mSv [N23]. The effective dose over a lifetime from naturally-occurring sources of radiation in
Japan (about 170 mSv) is significantly higher than that estimated as a result of the accident for an
average person living in Fukushima Prefecture (see appendix C). In contrast, the annual absorbed doseto the thyroid from natural sources of radiation is about 1 mGy, and thus the lifetime dose to the thyroid
is about 80 mGy.

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D. Long-term medical monitoring
E44. The Fukushima Health Management Survey [A4, Y4, Y5] was launched to “evaluate radiation
doses of citizens and [record] their health conditions, with the intention of utilizing the results forprevention, early detection and treatment of possible illness”. It includes a basic survey to estimate
doses from external exposure to radiation of all 2.05 million residents of Fukushima Prefecture at thetime of the accident, and the following detailed surveys for selected population groups: a thyroid
ultrasound examination of children, a health check, a mental health and lifestyle survey, and apregnancies and birth survey. The investigation is planned to continue for 30 years [Y5].
E45. The basic survey started in June 2011. A questionnaire was distributed to collect information on
the activities and locations of residents during the period 11 March to 11 July 2011. The response rate
to the questionnaire was low, less than 30% [Y5]. Individual doses from external exposure were
estimated based on a respondent’s location, using a system for assessing external doses developed byNIRS in Japan [N10]. Doses from internal exposure were measured using whole-body counting. Manymeasurements were performed a considerable time after the accident, making it difficult to estimate
doses from internal exposure for those radionuclides with short physical or biological half-lives.
E46. Improvements in the sensitivity of diagnostic techniques for thyroid cancer, such as the advent of
ultrasound and fine-needle aspiration, have enabled the detection of subclinical disease. To ensure theearly identification and treatment of any thyroid cancer in the child population, and their lifelong
follow-up, ultrasound examinations of the thyroid were being performed on all individuals inFukushima Prefecture who were aged 18 years or younger on 11 March 2011. Assessment of thecurrent thyroid status of some 360,000 eligible subjects was expected to be completed within 3 years(by March 2014). Thereafter, individuals would undergo thyroid examinations every 2 years until age
20 and every 5 years thereafter [Y5]. As of 31 July 2013, in total 41,296 children living in
13 municipalities were selected for ultrasound examinations of the thyroid before April 2012, and135,586 children in another 13 municipalities were selected for the period April 2012 to March 2013(table E2) [F3]. The remaining 34 municipalities of Fukushima Prefecture were selected for
ultrasonographic examinations in the period April 2013 to March 2014. The participation rate wasabout 82%. Nodules were detected in about 1% of the surveyed persons. The rate of cysts increased
from 36% among persons from the municipalities examined in 2011/2012 to 45% among persons fromthe municipalities examined in 2012/2013. It should be noted that these examinations were made withmodern, sensitive ultrasound equipment which could detect very small cysts and nodules. Similarequipment was used from November 2012 to January 2013 in an ultrasound survey of 4,365 children
and adolescents (aged between 3 and 18 years) in the prefectures of Aomori, Nagasaki and Yamanashi[T5]. These prefectures were far from FDNPS and were not significantly affected by the accident.
Thyroid nodules were detected in 1.6% of the children and cysts in about 57%, rates that were evenhigher than those found in Fukushima Prefecture. The Committee considered that the detectedprevalence in the more distant prefectures represented the normal baseline risks under intensive
screening conditions and were not related to radiation exposure.
E47. Children and adolescents with cysts with a diameter larger than 20 mm or with nodules larger
than 5 mm were selected for secondary examination. About 0.5% of the children surveyed in themunicipalities of Fukushima Prefecture before April 2012 met these criteria (table E2) [F3]. Again, thisrate was somewhat higher for children of the municipalities examined in the period April 2012 toMarch 2013. In the unaffected prefectures of Aomori, Yamanashi and Nagasaki, the rate was slightly
higher at 1.0%, which might be due to regional variability [T5].

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Table E2. Numbers of persons participating in thyroid examinations, or having a specified diagnosis
Districts of Fukushima Prefecture were selected targeted for the first ultrasonography examinations in three time periods.
Results for the first two groups given here are as of 31 July 2013 [F3]. Districts of Fukushima Prefecture with very low
deposition densities were to be targeted for 2013/2014. Data for three prefectures with insignificant deposition densities
were as of May 2013 [T5]

Municipalities in Fukushima
Prefecture
targeted before April 2012aMunicipalities in Fukushima
Prefecture targeted April 2012
to March 2013b

Prefectures of
Aomori, Nagasaki
and Yamanashi

41 296

135 586

4 365

With nodules

438 (1.0%)

1 623 (1.2%)

72 (1.6%)

With cysts

14 728 (36%)

60 382 (45%)

2 483 (57%)

Required secondary
examination

214 (0.5%)953 (0.7%)

44 (1%)

Examination /diagnosis
UltrasonographyaDate, Futaba, Hirono, Iitate, Katsurao, Kawamata, Kawauchi, Minamisoma, Namie, Naraha, Okuma, Tamura, and Tomioka.

b

Fukushima, Hisanohama of Iwaki, Izumizaki, Kori, Koriyama, Kunimi, Miharu, Motomiya, Nihomatsu, Nishigo, Otama,

Shirakawa, and Tenei.

E48. In the municipalities of Fukushima Prefecture with examinations before April 2012, 76%(165 persons) of those selected for secondary examination had been examined by 31 July 2013(table E3). This enabled a preliminary estimation to be made of the frequency of malignancies in thispopulation group. Cytological analysis of thyroid tissue taken from biopsies by fine-needle aspiration
classified fourteen of the nodules to be malignant. Surgery had been performed for ten of these patients.
In nine cases papillary carcinoma had been confirmed. One nodule turned out to be benign; theremaining thirteen cases of suspected or confirmed malignancy corresponded to a prevalence of
13/41,296, or about 0.03%. The increased prevalence of thyroid cancer may reflect the identification ofpreviously undetected disease with these improved diagnostic techniques and increased screening rates,
rather than a true increase in the prevalence of thyroid cancer [J8]. The prevalence of clinically occult
small papillary thyroid cancers (i.e. asymptomatic tumours that would remain latent, but detectable)
could be as high as 35% in many parts of the world, according to findings from autopsies of young
people from the general population [R4]. A fraction of these would be detected by any ultrasoundscreening programme. Following treatment, the 10-year survival from those types of cancer that areradiation-induced is high (about 90%) [H14].
Table E3. Persons in areas of Fukushima Prefecture participating in thyroid examinations, or having
a specified diagnosis, as of 31 July 2013 [F3]Persons in municipalities
examined before April 2012a

Persons in municipalities
examined from April 2012 toMarch 2013b

41 296

135 586

Required secondary examination

214 (0.5%)953 (0.7%)

Completed secondary examination

165

431

Malignancy according to biopsy cytology

1430

Surgery

10

9Confirmation of papillary carcinoma

99Examination
Primary ultrasonographyabDate, Futaba, Hirono, Iitate, Katsurao, Kawamata, Kawauchi, Minamisoma, Namie, Naraha, Okuma, Tamura, Tomioka.

Fukushima, Hisanohama of Iwaki, Izumizaki, Kori, Koriyama, Kunimi, Miharu, Motomiya, Nihomatsu, Nishigo, Otama,
Shirakawa, Tenei.

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E49. This is consistent with results from a study of a cohort of Ukrainians (the “UkrAm cohort”) who
had been exposed during childhood or adolescence to 131I from the Chernobyl accident, where an
ultrasound screening programme detected higher prevalence and incidence rates of thyroid cancer thanpreviously reported [T23]. During the first screening of the cohort between 1998 and 2000, forty-fivecases of thyroid cancer were observed among 13,127 individuals. Part of the apparent increase could be
attributed to the increased detection rate due to the programme of ultrasound screening of the cohort. It
was estimated that about eleven of these cases would have been detected even if there had been noradiation exposure from the accident. The component of the incidence observed after the screening but
not associated with radiation exposure was estimated to be considerably higher than the normal cancer
rate for the whole of Ukraine [B16, F2]. The results corresponded to a prevalence of thyroid cancer
cases not related to the accidental radiation exposure of about 0.09%, a value considerably larger thanthat observed in Fukushima Prefecture. (The difference between screenings of the UkrAm cohort andof people in Fukushima Prefecture could be explained, in part, by differences in the average age at firstscreening. The UkrAm cohort was first screened at an average age of about 21 years, which was older
than the average age for the Fukushima screenings. Because the incidence rate of thyroid cancer
increases strongly with increasing age during adolescence and early adulthood, the prevalence in the
UkrAm cohort was higher than among those screened after the FDNPS accident.)
E50. A comprehensive health check (involving measurements of height, weight, body mass index,
blood pressure, blood cell counts, blood chemistry, and urine testing) was being performed for people
who lived in the precautionary evacuation areas (radius 20 km from FDNPS) and in Yamakiya Districtin Kawamata Town, Namie Town, and Iitate Village. A survey on mental health and lifestyle wasasking parents to evaluate their children using the Strength and Difficulties Questionnaire [M7]. A selfadministered questionnaire was provided to those 16 years or older [K9, W6]. Clinical psychologists
and other mental health specialists offered telephone counselling and psychiatric referral based on
answers to the questionnaires. The size of the selected population for the health check and the mental
health and lifestyle survey was 210,189 people [Y5].
E51. The pregnancy and birth survey aimed to collect data on all pregnancies and births among all
women in Fukushima Prefecture who were pregnant on 11 March 2011. Survey questionnaires
included antenatal health, delivery records and mental health. Telephone and e-mail hotlines had been
set up and midwives or public health nurses were providing consultation services and medical referral
if necessary. The total number of women targeted was 15,954 [Y5].

III. HEALTH IMPLICATIONS OF RADIATION EXPOSURE OF
WORKERS RESULTING FROM THE FDNPS ACCIDENT

A. Observed health effects
E52. As of November 2012, seven deaths had been reported since 11 March 2011 among FDNPS
workers (i.e. workers of TEPCO and contractors) [T11]:(a) Two workers, aged 21 and 24, died on 11 March 2011, directly as a result of the earthquake
and tsunami. They were performing inspections in the turbine building of Unit 4 of FDNPS when
the tsunami inundated the site and flooded the building [I29].
(b) Three contractors died from acute myocardial infarctions while at work on 14 May 2011,
9 January 2012, and 22 August 2012, respectively. All three workers had received effective doses

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from external exposure of 0.7, 6.7 and 25 mSv, respectively. Whole-body counting of two of theworkers carried out a few weeks prior to their deaths showed that they had received minimal doses
from internal exposure. No effect attributable to radiation exposure on the mortality frommyocardial infarction has been observed among the survivors of the atomic bombings ofHiroshima and Nagasaki, who received much higher doses [S9].
(c) On 16 August 2011, a contractor died from acute leukaemia. He received an effective dosefrom external exposure following the accident that was recorded as 0.5 mSv; whole-body counting
carried out on 7 August 2011 showed minimal dose from internal exposure. Given the very low
level of exposure and the minimal latency period of 2 years for leukaemia, this death could not be
attributed to radiation exposure resulting from the accident.
(d) On 6 October 2011, a contractor died from septic shock owing to a retroperitoneal abscess. He
received an effective dose of 5 mSv from external exposure following the accident. Whole-bodycounting carried out on 9 September 2011 showed that he had received minimal dose from internal
exposure. The retroperitoneal abscess could not be attributed to radiation exposure resulting fromthe accident.
Acute radiation syndrome was neither reported nor expected because whole-body doses were below thethreshold levels for such effects.
E53. On 24 March 2011, the feet of three contractors were reportedly exposed to radioactive water in aturbine building. The absorbed doses to the skin from the radioactive water were subsequently
estimated to be about 450 mGy for two of the contractors and for the third essentially no dose to theskin from the radioactive water was estimated. However, in addition, during the same day the workers’skin was also exposed to gamma radiation in the air. Conservative estimates of the dose from this routeof exposure were added to the dose to the skin from the radioactive water to give total absorbed doses
to the skin of the feet, specifically about 650 mGy for two of the contractors and about 170 mGy for thethird [T10]. After four days of hospitalization they were released with a prognosis of no likelihood ofsignificant long-term harm [I6]. Assuming the dose estimates were correct, the Committee agreed withthis prognosis. Further, no radiation-induced health effects were ever observed from this exposure; theestimated doses were far lower than the threshold values for skin damage [I13].
E54. On 29 October 2011, an accident occurred in which two workers were struck by the release ofretaining wires on a crane. One worker had both of his legs broken and the other sustained injuries tohis shoulders and other areas of his body. The worker with broken legs had surgery at Fukushima
Medical University Hospital and was transferred to an Intensive Care Unit. The other worker wastransported to Sogo Iwaki Kyoritsu Hospital after first receiving treatment at the medical unit at
J-Village, which was a facility used as a base for FDNPS workers following the accident [I4].
E55. Approximately 17,500 stable iodine tablets (50 mg as potassium iodide) were distributed to about
2,000 workers involved in the emergency response [K11]. No immediate side effects, such as
anaphylaxis with iodine hypersensitivity, were observed. Approximately 230 workers received healthcheck-ups (from 13 March 2011 to 3 October 2011) because either they took stable iodine continuallyfor more than 14 days, or received more than 20 tablets. Health check-ups were performed by J-Village
Medical Centre or the Health Management Group of TEPCO Head Office. Blood tests were performed.
Three workers had transient changes in the thyroid hormones TSH and FT4. Four workers had TSHlevels greater than 5.0 µIU/mL and normal FT4 levels. This was not acknowledged as an increased rateof hypothyroidism attributable to distribution of stable iodine for thyroid blocking, because between
1% and 3.5% of males in the population normally has potential hypothyroidism.

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B. Risk assessment conducted by WHO
E56. WHO conducted a health risk assessment [W12] that considered FDNPS workers employed by
TEPCO and contractors exposed during the emergency phase. A preliminary dose estimation had been
performed based on data provided by the Japanese government and TEPCO by mid-September 2011.
The WHO assessment addressed 23,172 workers assigned to one or other of the following four
exposure scenarios:

Scenario 1: workers with very low doses to all tissues (absorbed doses to bone marrow, colonand thyroid: 5 mGy);



Scenario 2: workers who received moderate doses to the thyroid and low doses to other tissues(dose to bone marrow and colon: 24 mGy; dose to thyroid: 140 mGy);



Scenario 3: workers who received moderate doses to tissues (dose to bone marrow and colon:
200 mGy; dose to thyroid: 200 mGy);



Scenario 4: twelve workers who received high doses to the thyroid and low to moderate doses
to other tissues (dose to bone marrow and colon: 100 mGy; dose to thyroid: 11,800 mGy).

About 99% of the workforce involved with the emergency and subsequent mitigation were covered by
Scenarios 1 and 2; the remaining 1% of workers assigned to Scenarios 3 and 4 comprised those at theupper bounds of internal and external exposure. These scenarios had been developed as part of the
WHO study before individual dosimetric and bioassay data were available. They are, however, broadly
consistent with the individual dosimetric data that were made available to the Committee (see section V
and appendix D).
E57. More recent data have indicated that the doses from internal exposure for the majority of workers
included in Scenario 1 were predominantly due to 131I rather than 134/137Cs alone as assumed by WHO;
this would have resulted in higher estimates of doses to the thyroid but lower estimates of effective
doses. Data made available to the Committee also showed that there were 173 workers who hadreceived effective doses greater than 100 mSv, rather than the 87 identified by WHO in specifying
Scenarios 3 and 4.
E58. Lifetime attributable risk (LAR) of cancer occurring as a result of radiation exposure wascalculated using the same method as was used for the general population (see section II.B of thisappendix). According to the WHO report, about 50% of the workers were in the age range from 30 to49 years at 31 January 2012. Estimated risks for workers exposed at age 40 are summarized intable E4; the LAR for exposure at age 20 was estimated to be higher by about 70%, and that at age 60
to be lower by about 50%.
E59. The WHO also assessed risks of effects other than cancer for the emergency and mitigation
workers [W12]. They did not expect any deterministic effects, apart from possible thyroid disorders
among the twelve workers of Scenario 4. They identified that there might be an increase in the risk oflong-term circulatory disease among the workers of Scenario 3. They stated that any risk of hereditaryeffects among the offspring of workers involved in the emergency and subsequent mitigation would bemuch lower than the additional cancer risk for these workers.

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Table E4. WHO estimates for FDNPS workers of lifetime attributable risks of leukaemia, thyroid
cancer and all solid cancer, and percentage increase over lifetime baseline risk [W12]Results are given for age 40 years at exposure and rounded

Exposure
scenario
3

4

Assumed dose(mGy or mSv)a

Lifetime risk (%)
attributable toradiation exposure

Percentage increase overthe lifetime baseline risk

Leukaemia

200

0.12

23

Thyroid cancer

200

0.02

8

All solid cancer

200

2.0

5

Leukaemia

100

0.06

11

11 800

0.9

480

1.9

5

Cancer type

Thyroid cancercAll solid cancer
a

100

b

Dose to bone marrow for leukaemia, dose to thyroid for thyroid cancer, and dose to colon for all solid cancer combined.

b

Dose to all organs except to the thyroid, which was assumed to be 11,800 mGy.

c

Includes the risk of thyroid cancer taking into account the relatively high absorbed dose to the thyroid, while the WHO report

calculated the risk of all solid cancer assuming that the absorbed dose to all organs except the thyroid was equal to the dose to
the colon.

C. The Committee’s commentary on health implications forworkers
E60. The Committee based its commentary on the same assumptions as for members of the public,
modified as appropriate to match the worker population, and on the doses to workers reported inappendix D. Similar to its commentary on health implications for the public, qualitative estimates weremade of disease outcomes, where the Committee has used the phrase “no discernible increase” where,
although a disease risk in the longer term can be theoretically inferred on the basis of existing risk
models, an increased incidence of effects is unlikely in practice to be observed in future diseasestatistics using currently available methods, because of the combination of the limited size of
population exposed and low exposures, i.e. consequences that are small relative to the baseline risk andtheir uncertainties.

1.

FDNPS workers

E61. The effective doses received by most of the FDNPS workers (99.3%) as a result of the accident
were estimated to be less than 100 mSv with an average of about 10 mSv. The risk of these workers
developing radiation-induced cancer is low (cf. the WHO estimates [W12]). There are distinct groups
of more highly exposed workers; an assessment of the health implications for these groups is madebelow.
E62. Cancer among workers receiving the highest effective doses. A group of 160 workers received aneffective dose equal to or in excess of 100 mSv, predominantly from external irradiation. The average
effective dose in this group was about 130 mSv. If the group of 13 workers with high doses to thethyroid were included, the average effective dose would increase to about 140 mSv among a group of
173 workers (see below). Based on current understanding of risks, about two to three additional casesof cancer could on average occur in this group in addition to about seventy baseline cancers expected tooccur in the absence of exposure (see table E1), although the uncertainties in such estimates are

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substantial. Such an increase occurring during the lifetime of the exposed individuals would not,however, be discernible because fluctuations of cancer incidence in groups of this size are considerablylarger. The statistical power of detecting such an increase would be about 10%; for conducting ameaningful epidemiological study, a statistical power of 80% would usually be required.
E63. About one baseline leukaemia case would be expected to occur among a group of 173 male adultJapanese workers during their lifetime (noting the uncertainties associated with such estimates). A
whole-body exposure of an adult male with an effective dose of about 140 mSv has been assessed tolead to a relative risk of about 1.2 for exposure at age of 20 years, and lower for exposure at older ages
[W12]. Because of the small numbers involved, it is not expected that any potential increase inleukaemia incidence would be discernible.
E64. Thyroid disease and disorder. Approximately 2,000 workers (as of June 2013) received thyroid
doses exceeding 100 mGy [M16], with an average dose of the order of 400 mGy. The question ofwhether the risk of thyroid cancer is elevated following exposure during adulthood in the interval
100 mGy to 1,000 mGy is under debate [M1, R5]. WHO estimated the risk at different ages at
exposure: for a thyroid dose of 400 mGy at an age of 40 years, they estimated the relative increase of
lifetime thyroid cancer risk to be 16% [W12]. Ultrasound surveys of these workers will increase thedetection rate of baseline and potential radiation-induced thyroid cancer cases; the number expected to
be detected will exceed considerably the number expected on the basis of reported incidence of thyroid
cancer among population groups that do not undergo such surveys. Although there are very large
uncertainties in estimating the risk of radiation-induced thyroid cancer, any increase in the incidence
due to radiation exposure is not expected to be discernible.
E65. Thirteen TEPCO workers were estimated to have received committed absorbed doses to thethyroid in the range of 2 to 12 Gy, with an average of about 5 Gy. The two TEPCO operators in thecontrol rooms for Units 3 and 4 who received the highest total effective doses (679 and 646 mSv,
respectively), the highest cumulative effective doses from internal exposure (590 and 540 mSv,
respectively), and who had not taken potassium iodine for thyroid blocking prior to their exposures,
had no early deterministic health effects as a result of their exposures [I29]. The probability ofoccurrence of excess thyroid cancer cases during the lifetimes of the thirteen workers is small, because
thyroid cancer is a rare disease even after high exposures (see the WHO estimate as outlined intable E4).
E66. Hypothyroidism (i.e. transient elevation of TSH) is a late deterministic effect observed after
external radiotherapy of the neck and following nuclear medicine procedures using radioactive isotopesof iodine that deliver several grays [H2, H15, L2, M9, M10, O6, P5]. It has also been observed
following heavy fallout from nuclear weapons testing in 1954 [C10]. Excess incidence of thyroid
nodules have also been reported following external irradiation resulting from medical procedures orhigh levels of radioactive fallout [C10, N4, R7] and following protracted exposure to radioactive iodine[H1, L1, L2, Z1]. Given the magnitude of inherent uncertainties in the dose estimates, the Committee
could not preclude the possibility of hypothyroidism among the more exposed workers. A particularissue is the suggestion that ionizing radiation induces Hashimoto thyroiditis (autoimmune thyroiditis).
In its 2008 Report, the Committee stated that there had been few studies of significant size that had
addressed the relationship between this disease and exposure to radiation, and that the largest study
could not demonstrate any conclusive evidence of a relationship [U12].
E67. Other diseases and health effects. There is little likelihood of an excess incidence of circulatory
diseases at the dose levels incurred by the group of workers with the highest effective doses [I26, S5,
U9]. Beta particles may have contributed substantially to the dose to the eye lens of the workers. No
direct information on beta-radiation fields at FDNPS was available to the Committee. For workers
involved in response and recovery after the Chernobyl accident, the contribution of beta particles to thedose of the eye lens ranged between 0% and 350% of the dose from gamma irradiation (see annex D[U12]). Recently, ICRP published a statement on tissue reactions and considered a threshold level ofANNEX A: LEVELS AND EFFECTS OF RADIATION EXPOSURE DUE TO THE NUCLEAR ACCIDENT ...

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absorbed dose to the lens of the eye of 500 mGy for tissue reaction effects [I26]. If the relative
contribution of beta particles to the dose to the eye lens of workers at FDNPS were not higher thanafter the Chernobyl accident where posterior subcapsular cataracts have been detected, then no
discernible excess incidence of cataracts due to the FDNPS accident would be expected. However,uncertainties remain about the doses to the eye lens and the dose–response relationship for cataracts.
E68. After technological disasters, the prevalence of post-traumatic stress disorder (PTSD),
characterized by symptoms such as flashbacks, nightmares, hyper-vigilance and avoidance ofreminders of the event, ranges from 15% to 75% [N9], depending on the gravity, severity and level of
threat from the disaster, the population affected and the timing of the study.
E69. Initial observations have identified severe psychological effects following the earthquake,tsunami and FDNPS accident among emergency workers [M8, S7, S8, W1]. An initial voluntary selfreported questionnaire on the psychological status of workers at TEPCO’s Fukushima Daiichi andDaini nuclear power stations was conducted 2 to 3 months after the disaster [S7]. Psychological distressand PTSD were observed among radiation workers. They reported intrusive flashbacks, avoidance ofthe plant, hyper-vigilance toward aftershocks, fear of irradiation and dissociative episodes. These
health implications should not be attributed to radiation exposure itself, because they have been evokedby many other causes. Some workers suffered public harassment and were severely discriminatedagainst as a result of TEPCO’s negative image. In addition, many of them lived within the 20-km
radius of the FDNPS while their families had been evacuated; they had experienced first-hand deaths
from the tsunami, were placed in temporary housing with poor living conditions, and had been working
long hours. Occupational health physicians and nurses provided mental health checks and consultations
for the workers; however, there is a lack of trained psychiatrists for primary prevention of stress [S7,W1].

2. Experience from the Chernobyl accident relevant to the health
implications of the FDNPS accident for workers
E70. In terms of health implications for workers, the Chernobyl accident differed from the FDNPS
accident in many ways. The average effective dose received by the 530,000 Chernobyl recovery
workers between 1986 and 1990, mainly from external exposure, was estimated to have been about
120 mSv. Some recovery workers received very high doses; for example, for 51 Russian Federationand 168 Ukraine recovery operation workers each receiving an effective dose in excess of 1 Sv, theiraverage dose was as high as 9.4 Sv and 6.9 Sv, respectively [U12].
E71. In comparison, there were only 3,973 workers on-site at FDNPS during the first month after theaccident and they received an effective dose during this period of about 21 mSv on average (seetable D3). The highest effective doses (250−679 mSv) occurred among 6 TEPCO workers in the firstmonth. During the first 19 months, 99.3% of 24,832 TEPCO and contractor workers were recorded ashaving an effective dose lower than 100 mSv and on average about 10 mSv; the remaining 173 workers
received doses in excess of 100 mSv with an average of about 140 mSv. For all these workers, recorded
doses over this period ranged from less than 10 mSv to 679 mSv. Although the periods of exposure
differ significantly, these levels are far below those experienced by the Chernobyl recovery workers.
Only doses to the thyroid of the six TEPCO workers with the highest effective doses reached levels
received by the most exposed Chernobyl recovery workers.
E72. After the Chernobyl accident, acute radiation sickness (ARS) was diagnosed for 134 of the first
responders and firefighters, 28 of whom died of ARS within a few months [U12]. In contrast, the
FDNPS accident did not result in any cases of ARS.
E73. A radiation-related increase in the incidence of all solid cancers has been reported for the Russian
Chernobyl recovery workers [I37], although not in another, albeit much smaller, study of recovery

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workers from Estonia [R2]. Owing to the much smaller number of workers exposed and their lower
exposures, it is not expected that there will be an observable radiation-related general increase in theincidence of solid cancer among the FDNPS workers [P15, U11, U12].
E74. Elevated rates of thyroid cancer among the Chernobyl recovery workers compared with thegeneral population have been reported; but no clear association with radiation dose has been found[I36, K8, M1, U12]. Similar results might be expected for the FDNPS workers, as a result of intensive
thyroid screening, although substantially fewer workers were involved and they received lower doses.
E75. Studies of the Chernobyl recovery workers suggest an increase in the incidence of leukaemia. The
limitations of these studies include uncertainties in dose reconstruction, potential biases andconfounding factors [I38, K7, R6, U12]. A recent article reported statistically significant effects [Z2],however exposure estimates were based on proxy interviews, which implies a high uncertainty andpotential for bias. The workers at FDNPS who incurred the highest external exposure received doses tothe bone marrow of at most 200 mSv. Owing to the small number of workers involved, no discernible
effect of the radiation exposure on leukaemia incidence is expected.
E76. Few studies assessed circulatory disease among the Chernobyl workers. More evidence is needed
to conclude whether or not radiation exposure at doses below 500 mGy increases the risk of circulatory
disease. Radiation doses of FDNPS workers were too low to expect an observable excess incidence ofradiation-induced circulatory disease in the future. However, there may be secondary effects due topsychological stress that confound any relationship with radiation exposure.
E77.
There have been two lines of research on the psychological impact of the Chernobyl accident
on recovery workers: (a) potential radiation-related cognitive impairment; and (b) the psychiatriceffects of exposure-related stress [B18].
(a) Four studies conducted in Kiev provide suggestive evidence of measurable cognitive or neuropsychiatric effects of radiation exposure among highly exposed recovery workers [G1, L11, L12,
P11]. Although consistent and suggestive, methodological limitations of the studies prevent
general conclusions being drawn [B17, B19, W7].
(b) Significant long-term psychiatric effects are well documented among recovery workers
following the Chernobyl accident [L10, R1, R3, V1]. Initial observations have identified
psychological effects among FDNPS radiation workers following the earthquake, tsunami andnuclear accident [M8, S7, S8, W1].

D. Long-term medical monitoring
E78. On 3 August 2011, the Japanese Ministry of Health, Labour and Welfare (MHLW) announced the“grand design of a long-term health management of all the emergency operations workers at TEPCO’s
No. 1 Fukushima Nuclear Power Plant” [M14]. The database would be constructed to contain radiationdose records that are systematically collected, and information about long-term health conditions ofemergency operations workers. Health management would be provided by employers while workers
were employed, and contact points located throughout Japan would be determined to provide
appropriate long-term health management, consultation and regular health examinations of workers
after leaving their workplace. Periodic health examinations would be given to workers to monitor for
potential late radiation-related health effects. Special health examinations would be given to workers
with the highest exposures, including annual eye check-ups (for lens opacity), and monitoring of the
thyroid, stomach, large intestine and lung for cancer.

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E79. Ultrasonography was planned to be performed for all emergency workers with absorbed doses tothe thyroid exceeding 100 mGy. The eligible group consisted of about 2,000 workers. Modern
ultrasonography is able to detect very small tumours; however the probability of occurrence of thyroid
cancer due to radiation exposure in adulthood is small and would be unlikely to manifest as adiscernible increase in statistics on cancer incidence [D2, F6].
E80. Three studies of cancer mortality among Japanese workers exposed occupationally in the nuclear
industry have been previously conducted [A7, H11, I39]. The average cumulative effective dose ranged
from about 12 to 15 mSv in these studies; this is similar to the dose received by most FDNPS workers
as a result of the accident (average about 12 mSv from the accident until October 2012, see table D4).
In one of the three analyses [I39], 4,161 workers had received doses over 100 mSv, with a mean doseof 154 mSv. This compares to only 173 FDNPS workers with doses greater than 100 mSv and an
average dose of about 140 mSv. Because no change in the mortality rates due to cancer was detectedamong Japanese nuclear industry workers with follow-up from 1986 to 2002, it is unlikely that a studyof the FDNPS workers would discern a difference in the mortality rate from that of the general
population, or that a significant relationship between radiation dose and cancer mortality be any
different from that found among other Japanese nuclear industry workers. Studies would lack sufficient
statistical power to assess the risk of cancer due to irradiation; the doses would be too low and the
population size too small [B13, W4]. Likewise, excess screening and diagnostic suspicion may bias
studies of FDNPS workers, in particular detecting a greater incidence of small tumours, unrelated toradiation exposure, than would otherwise have been detected.
E81. Despite these scientific limitations, it is important that FDNPS workers be included in theexisting Japanese nuclear worker cohort, and that long-term cohort studies of these workers be
conducted. Finally, studies of the mental and physical health of workers exposed after the Chernobyl
accident were conducted separately instead of integrating cohort studies of cancer and other disease
outcomes with mental health research. If mental health measures were embedded in the Japanese
nuclear worker cohort, the combined approach would track mental health effects and provide a unique
opportunity to advance understanding of risk factors, such as perceptions about the health impact ofradiation exposure and synergistic psychological effects of stress with radiation exposure [B19, B20].
Indeed, future studies of the FDNPS workers could improve understanding of the association of PTSD
and depression with circulatory risk and recovery [K26] and other medical conditions [V5].

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APPENDIX F. ASSESSMENT OF DOSES AND EFFECTS FOR
NON-HUMAN BIOTAI.

INTRODUCTION................................................................................................................................. 267

II. METHODOLOGY TO ESTIMATE DOSES TO NON-HUMAN BIOTA .................................... 269
A. Terrestrial environment ......................................................................................................... 270
B. Aquatic environments............................................................................................................ 273
III. ESTIMATED DOSE RATES AND INFERRED EFFECTS .............................................................. 274
A. Terrestrial environment ......................................................................................................... 274
B. Aquatic environment.............................................................................................................. 279
IV. UNCERTAINTIES ................................................................................................................................ 282
V. CONCLUSIONS................................................................................................................................... 283

I. INTRODUCTION
F1. This appendix underpins the Committee’s findings regarding the exposure of non-human biota toionizing radiation resulting from the accident, and any associated effects. Similar to humans, anyorganism in the natural environment can be exposed both (a) internally to incorporated radionuclides
taken up from the environment, and (b) externally to radiation from sources in its habitat. The
Committee had assessed exposures of non-human biota and associated effects in general in its scientificannexes to the 1996 [U6] and 2008 [U12] Reports. The consequences of radiation exposure for nonhuman biota can include increases in morbidity and mortality, decreases in fertility and fecundity, andincreases in mutation rate. These types of effects, if observed at the level of the individual organism,may have consequences for a population of species. The Committee concluded that chronic dose rates
of less than 100 µGy/h to the most highly exposed individuals would be unlikely to have significant
effects on most terrestrial communities, and that maximum dose rates of 400 µGy/h to any individual inaquatic populations of organisms would be unlikely to have any detrimental effects at the populationlevel [U12]. Benchmarks developed for other contrasting purposes have also been published. For
example, the ERICA 43 and PROTECT 44 projects [A10, G2] suggested a generic dose rate of 10 µGy/h
for use in screening out situations of environmental exposure that were of negligible concern. The
International Commission on Radiological Protection (ICRP) has also published “derived considerationreference levels” (DCRLs), which can be used to identify where there is likely to be some chance of
43

ERICA = “Environmental Risks from Ionising Contaminants: Assessment and Management” an EC EURATOM Framework 6
funded project.
44
PROTECT = “Protection of the Environment from Ionising Radiation in a Regulatory Context” EC EURATOM Framework 6
funded project.

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deleterious effects of exposure to ionizing radiation on individual reference animals and plants [I22].
The values of DCRLs published are broadly consistent with the benchmarks presented above (see[U12]).
F2. As a consequence of the accident at the Fukushima Daiichi Nuclear Power Station (FDNPS),
terrestrial, freshwater and marine ecosystems were exposed to ionizing radiation. The exposure of nonhuman biota varied greatly in space and time reflecting large heterogeneities in radionuclide
concentrations in the environment and in the time-dependent processes influencing radionuclidetransfer through the environment and into organisms. Moreover, in any case, radiosensitivity of nonhuman biota varies widely between species and according to a complex dynamic of interactions
between absorbed doses (or dose rates) and responses to radiation expressed at different levels of
biological and ecological organization.
F3. Published assessments. Garnier-Laplace et al. [G3] calculated dose rates to selected organisms forthe first three-week period after the accident. Their estimates of the absorbed dose rate to forest biota(including contributions from internal and external exposure) ranged from 2 mGy/d (in birds) to
6 mGy/d (in small mammals), accounting for a series of measured radionuclides. They considered thatcytogenetic damage would certainly be measurable but that potential alterations to reproduction for
conifers and vertebrates might be difficult to discern against the high natural variability. They
estimated that, as a consequence of the peak release to the marine coastal zone, maximum dose rates toselected marine organisms ranged from 210 to 4,600 mGy/d. The authors considered that “At such highdose rates, marked reproductive effects, and even mortality for the most radiosensitive taxa are
predicted for all marine wildlife groups whose life history characteristics confine them to the near-field,
contaminant release area”. These exposure estimates were orders of magnitude higher than those
calculated by Kryshev and Sazykina [K25], who considered a more limited set of radionuclides,
restricted their analyses to internal exposure, and used substantially lower values for concentrations ofradionuclides in seawater as input data. Kryshev and Sazykina considered that no detrimental effects topopulations of marine organisms would arise from their calculated dose rates.
F4. Reported observations. As of December 2012, a few papers had been published reporting fieldobservations on wildlife in terrestrial ecosystems within 100 km of FDNPS. Møller et al. [M22]reported an apparent negative correlation between the levels of ambient dose equivalent rate and theabundance of common birds in the Fukushima area. The abundance of several invertebrates and birds
were determined by Møller et al. [M23] at over one thousand sites in the vicinity of the Chernobyl
nuclear power plant and FDNPS. While all taxa showed significant declines in abundance withincreasing level of ambient dose equivalent in the Chernobyl case, only three out of seven taxa showedsuch an effect for the Fukushima case.
F5. Hiyama et al. [H6] studied morphological and genetic characteristics of the pale grass blue
butterfly Zizeeria maha. They collected first-voltine adults in the Fukushima area in May 2011. Someof these individuals showed relatively mild abnormalities. The F1 offspring from the first-voltine
females showed more severe abnormalities, which were inherited by the F2 generation. Furthermore,
adult butterflies collected in September 2011 showed more severe abnormalities than those collected inMay. The authors concluded that artificial radionuclides from FDNPS caused physiological and genetic
damage to this species and that the cumulative effects of exposures could have resulted in deteriorationof the population.
F6. With regard to the above field studies, the Committee noted that uncertainties with regard to
dosimetry and possible confounding factors (including the impact of the tsunami itself) made it difficult
to substantiate firm conclusions. Furthermore, the main body of scientific data did not support theappearance of such effects at the dose rates recorded [A10, G2, I22, U12]. Most notably, in the study of
Hiyama et al. [H6], manifestation of similar effects under laboratory conditions required radiation
exposures that were considerably higher than those observed in the field.

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F7. The Committee assessed the impact of radiation exposure resulting from the FDNPS nuclear
accident on non-human biota inhabiting terrestrial, freshwater and marine ecosystems. The assessment
was based largely upon measured data provided to the Committee, other relevant reports and publishedscientific papers. The radiation exposures were considered in terms of (a) the intermediate phase after
the accident (approximately the first two months) and (b) the late phase (months to years). The
Committee considered some areas of Fukushima Prefecture and neighbouring prefectures in detail
within approximately 100 km of FDNPS with the highest deposition density of radionuclides.

II. METHODOLOGY TO ESTIMATE DOSES TO NON-HUMAN
BIOTA
F8. Apart from direct observation, the presence or absence of radiation effects on non-human biota
can be inferred through comparing exposure levels with relevant benchmarks. Prerequisites are robust
estimates of absorbed dose and dose rates to biota in both time and space; the estimates are made by
applying suitable assessment models. The primary source of data for the Committee’s assessment was
the information provided by the Government of Japan, which is discussed in appendix A along withconsiderations of its quality for the purpose of the assessment. Other datasets were also used [G11].
The datasets covered terrestrial, freshwater and marine environments, and characterized the levels ofterrestrial deposition density of radionuclides and radionuclide concentrations in soils, aquatic
sediments, and terrestrial and aquatic biota. The methodology used is described in detail in attachment
F-1; a summary is provided below.
F9. The dose assessment methodology used by the Committee was based on the ERICA Integrated
Approach [L3], making use of the ERICA assessment tool [B22], a software tool with supporting
databases developed to calculate absorbed doses to non-human biota and to assist with analysing
effects. The methodology consisted of the following steps: (a) select key species and radionuclides foranalysis; (b) conduct the assessment preferably using actual radionuclide concentrations in biota,
measured over time and space from the first day of the accident; additionally or alternatively (c) use
equilibrium models (applying concentration ratios) to derive radionuclide concentrations in biota fromthose in media (such as soil and water) or (d) use dynamic models to calculate dynamic concentrations
in biota based on measured concentrations in media; and (e) perform dose calculations using doseconversion coefficients (DCCs) from the ERICA Tool and make projections of dose rate as a functionof time, from which integrated doses can be calculated. From this, the possibility of radiation effects on
non-human biota could be assessed. This approach was considered to be the most appropriate, robust
and practicable way of estimating the absorbed doses and dose rates to non-human biota, drawing on
empirical data as far as possible, while relying on generic transfer parameters when such data were
unavailable.
F10. In view of the great variety of plants and animals that can be exposed at any given site, it has beenargued [P2] that an assessment can be reduced to manageable proportions by adopting reference
exposure and dose models. The Committee has adopted this approach [U12], which is also in line withrecommendations of the ICRP [I22]. The reference organisms selected in the UNSCEAR 2008 Reportformed the basis for the exposure estimates made in the Committee’s assessment (table F1). The
radionuclides considered were selected primarily on the basis of data availability, their relative
importance radiologically, and experience from other situations where radioactive material was
released into the environment (e.g. past accidents).

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Table F1. Reference organisms selected by the Committee [U12] for assessing exposures
Earthworm/soil invertebrate

Rat/burrowing mammal

Bee/above ground invertebrate

Wild grass/grasses, herbs & crops

Pine tree/tree

Deer/herbivorous mammal

Duck/bird

Frog/amphibian

Brown seaweed/macroalgae

Trout/pelagic fish

Flatfish/benthic fish

Crab/crustacean

F11. For terrestrial biota the equilibrium-based whole-body concentration ratio (CR) is defined as theconcentration of a radionuclide in the whole organism at equilibrium divided by the concentration of
the same radionuclide in soil. For aquatic organisms, the denominator is the concentration of theradionuclide in water. The Committee used the database on transfer factors in the ERICA Tool (based
upon [B4, H12]), supplemented by more updated information provided by ICRP [I23], to derive
radionuclide concentrations in non-human biota. While the intended application of this approach wasfor assessing the impact of routine releases of radionuclides to the environment, the approach was usedby the Committee for a dynamic situation. Consequently, there may be substantial inaccuracies in theestimates of exposure.
F12. In contrast to equilibrium models, dynamic models typically characterize the environment interms of compartments that represent distinct features, for example, soil layers and body organs. Rate
constants are often used to express the exchange between compartments. When simulations are
performed using a mathematical representation of the system, the net result is a description of theevolution of radionuclide concentration with time. Because of their somewhat different attributes, thedynamic models used for terrestrial and aquatic ecosystems are described separately below.
F13. Once radionuclide concentrations in environmental media and biota had been calculated,absorbed dose rates were derived by applying DCCs from the ERICA Tool. Occupancy factors fororganisms were selected to represent exposure to simplified, yet realistic, source geometries. Absorbed
dose rates were weighted by modifying factors to reflect the relative biological effectiveness ofdifferent radiation types in line with those applied in the UNSCEAR 2008 Report, and then theweighted absorbed dose rates from external and internal exposure were summed. The dosimetriccalculations underpinning the derivation of DCCs are explained in detail elsewhere [U1, U2].
Radionuclide decay chains were truncated at the first radionuclide with a half-life of more than
10 days. The DCCs of shorter-lived radioactive progeny in the decay chain were then amalgamatedwith the DCC of their longer-lived parent. DCCs for internal exposure were derived assuming ahomogeneous distribution of the radionuclide in the organism; the error introduced by this assumption
is, in view of the assessment goals, considered to be of minor significance [G10].

A. Terrestrial environment
1.

Using direct measurements and equilibrium models

F14. Data on radionuclide deposition densities were available for the period June–July 2011 andmeasurements of radionuclide concentrations in animals and birds were available primarily from
September 2011 to March 2012. In order to estimate the corresponding deposition densities at thelocations where direct measurements of radionuclide concentrations in animals were available and overtheir home range, it was necessary to interpolate between points where deposition densities had beenmeasured. Empirical Bayesian Kriging (EBK) was used to construct maps of interpolated radionuclide
deposition density and absorbed dose rate for the Fukushima area [G12, K22, P8]. Kriging methods
also provide an estimate of uncertainty in the calculated values; in contrast, deterministic interpolation

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methods, like inverse distance weighting (which produce an interpolated raster based on surrounding
data only) do not. The advantage of using EBK was that it required only minimal tuning of the semivariogram model. The resulting raster for deposition density of 137Cs is presented in figure F-I, together
with the sampling locations of the animals measured.
F15. The Committee used available measurements of concentrations of 131I, 134Cs and 137Cs inmammals and birds to derive absorbed dose rates due to internal exposure directly. Additional
information such as mass and length of the animal was used in selecting an appropriate model
geometry to derive DCCs for internal exposure. Life history data sheets, containing basic ecologicalinformation such as the home range for selected organisms, were collated (attachment F-2) to assist
calculation of absorbed dose from external exposure. There were distinct geographical clusters ofsamples for wild boar, whereas the data were more spread and without apparent clustering for othermammals and birds. For the spatial clustering of the wild boar data, an algorithm [K2] was applied tofocus analysis on wild-boar groups with an average home range of 3 km. Owing to the limitation ofavailable empirical data, this cluster approach was not applicable to other biota. To determine the rangeof exposure for other mammals and birds, data from Koriyama City were used as input to the dose-rate
calculations (attachment F-2) because they covered all species of interest and reflected a wide range ofdeposition density. In order to extend data on deposition density for 137Cs to all other radionuclides,
scaling was applied using radionuclide ratios.
F16. Maps of interpolated absorbed dose rates to selected organisms were created, starting from
deposition density data and using CRs to calculate values of radionuclide-specific absorbed dose rates.
For comparison, both planar and volumetric source geometries were assumed to estimate absorbed
doses from external exposure to large mammals; this comparison showed that using a volumetricsource geometry provided slightly higher estimates of absorbed dose rate for radioisotopes of caesium.
Locations of maximum deposition density, such as Okuma Town, were considered in detail to derive
upper estimates of the absorbed dose rates and to gain insight on the various contributors to theabsorbed dose rate. The input data used are provided in attachment F-2.
F17. Preliminary work on the data for Koriyama City showed that using default values of CRs had atendency to overestimate the radionuclide concentrations in the organisms considered. Because
caesium isotopes were the main contributors to absorbed dose rates once short-lived radionuclides had
decayed, the available information was used to derive values of CRs that were more region-specific for
caesium and for the animal groups under consideration. These values were then used in the subsequentdose-rate mapping. A further equilibrium-based analysis accounted for radioactive decay between thetime of sampling and the initial deposition event.

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Figure F-I. Deposition density of 137Cs with sampling locations of mammals and birds overlaid
The municipal areas of Okuma Town (furthest East) and Koriyama (mid-figure) are delineated. There were 12 measurement
points that exceeded 5 MBq/m2 but these extreme data values are not illustrated with the Kriging interpolation method

2.

Using dynamic models

F18. The FASTer model is a multi-compartmental model that can be used to simulate radionuclidetransfer through a simple terrestrial food chain. The model was used to derive radionuclide
concentrations in flora (vegetation including herbaceous plants, shrubs and trees) from deposition
densities, using an expression that accounts for interception by foliage, growth dilution, weathering
losses of radionuclides from vegetation, and the direct deposition onto soil and subsequent uptake fromsoil to plant. The model is described in more detail elsewhere [A13, B6, F1]. However it wasparameterized using values specific to the environmental conditions at the time of the accident andsubsequent months (see attachment F-1).
F19. As detailed in appendix B, a major wet deposition of radionuclides occurred on 15 March in thenorthern part of Fukushima Prefecture. This date was thus selected as a suitable time for which toassign the initial values for parameters, such as the biomass and the interception fraction, needed forthe model simulations.

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B. Aquatic environments
1.

Using measurements of biological samples

F20. Freshwater environment. Results of measurements of 131I, 134Cs and 137Cs in freshwater biota(predominantly radiocaesium concentrations in fish) from the prefectures of Fukushima, Iwate, Miyagi,
and Ibaraki were provided to the Committee. None of the sampling stations were from the area of
maximum deposition density (above 1,000 kBq/m2); therefore, levels in fish for this area werereconstructed using correlations between deposition densities and radionuclide concentrations in fish
for Japanese lakes. These data and interpolated values constituted the input datasets for estimating
exposure (attachment F-3).
F21. The highest concentrations of radiocaesium in freshwater fish had been measured in a local area
situated to the north and north-west of the FDNPS site (37.6–37.7N; 140.5–140.9E), characterized bydeposition density of 137Cs in the range 100–200 kBq/m2. The typical concentration of radiocaesium infish in this area was about 2–3 kBq/kg fresh weight; the maximum concentration measured had been ina single fish sampled in March 2012 and was 18.7 kBq/kg fresh weight. The very limited data onradionuclide concentrations in sediment from water bodies in this area indicated levels of 4.4 kBq/kg(dry weight) of 134Cs, and 5.5 kBq/kg (dry weight) of 137Cs.
F22. Marine environment. Results of measurements of marine organisms were provided to theCommittee. The data for 137Cs in marine fish, collated for the period from May 2011 until June 2012,were too scattered to confirm any definite trends, and there appeared to be no obvious substantial
decrease in concentrations over one year of monitoring [B24]. On closer inspection there was asuggestion of an increase up to a maximum value around mid-May 2011, possibly followed by a slightdecrease in levels. In contrast, changes in 137Cs concentrations in seawater with time for the offshore
coastal zone (out to 15–20 km from the FDNPS site) were quite dramatic, falling from levels exceeding
100 kBq/m3 to around 1 kBq/m3 by the end of 2011. Some of the highest levels of radiocaesium
concentration, of the order of several hundred thousand becquerels per kilogram (fresh weight), werereported in benthic fish collected from within the port area adjacent to FDNPS in early 2013 [T18].
These later reports were outside of the period considered by the Committee’s assessment, but thevalues reported imply substantially higher estimates of absorbed dose rates to fish for the late phase at
locations close to FDNPS. This is an issue for follow-up by future scientific studies.
F23. Concentrations of 137Cs in the marine organisms varied, ranging from a few becquerels per
kilogram to more than one kilobecquerel per kilogram. Concentrations of 131I tended to fall more
rapidly than those of 134Cs or of 137Cs because of physical decay, environmental dispersion andturnover in biota. Values of radionuclide concentrations in seawater expressed in becquerels per litre
were on average two orders of magnitude below values of concentrations in sediment expressed inbecquerels per kilogram.
F24. The Committee established a spreadsheet-based method to organize the marine data and performthe dose calculations using a bespoke scripting language code. This involved several steps: (a)categorization of marine organisms—the 202 different species of marine biota were accommodated
within nine categories of reference organisms used in the ERICA approach plus six newly-defined
categories of organism; (b) calculation of absorbed dose rates from internal exposure for 131I, 134Cs and137
Cs using values of DCCs derived from the ERICA assessment tool; (c) assignment, for each given
radionuclide measurement sample in biota, of concomitant radionuclide concentrations in the habitat(water and sediment); and (d) calculation of absorbed dose rates and doses due to external exposure
from the assigned radionuclide concentrations in sediment and water.

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2.

Using dynamic models

F25. The rate of radionuclide turnover by marine organisms can be determined experimentally andused to derive values for biological loss rates to be applied in dynamic models (see, for example, [O5,
S14, V3, W13, W14]). The Committee used an improved version of a recent model, D-DAT [V4], tosimulate biological transfer. This was a compartment model based upon the working simplification thatmarine organisms absorb radionuclides mainly from the surrounding seawater with a single phasefunction describing the biological loss rate for the radionuclides considered (131I, 134Cs and 137Cs).
F26. In addition, computations were made using the “ECOMOD” modelling approach, which
describes the dynamic processes of radionuclide migration in aquatic biota as radioactive tracers of
analogous stable elements involved in the growth and metabolism of the organisms [K23, K24, S4].
The “ECOMOD” modelling approach had been developed to simulate non-equilibrium, non-linear
processes in aquatic ecosystems. In view of the novel application of dynamic models to assessing theeffects of the FDNPS releases on biota, the use of two independent modelling approaches wasconsidered beneficial because this imbued more confidence in the results.

III. ESTIMATED DOSE RATES AND INFERRED EFFECTS

A. Terrestrial environment
1. Assessment for the late phase using measurements and equilibriumbased methods
F27. The Committee estimated weighted absorbed dose rates for the reference date of June 2011 based
upon empirical data to various representative birds and mammals sampled at several terrestrial
locations within a 100-km radius around FDNPS. Weighted absorbed dose rates were in the range of
0.8 to 1.1 µGy/h for all wild boar clusters and resulted primarily from 137Cs and 134Cs. However, theseestimates were specifically for this one species of mammal and they poorly characterized variability indose rates because the wild boar clusters pertained to areas of similar environmental concentrations.
Thus, the Committee also determined weighted absorbed dose rates from internal and external exposure
to four biota groups in Koriyama City (see table F2). The arithmetic mean of the estimated dose rates
showed low variability among the biota groups; a value for the 95th percentile slightly exceeding
2 µGy/h was derived for wild boar. The contribution from 134Cs dominated the dose rate to all biotagroups with a substantial, but smaller, contribution from 137Cs.
F28. The estimated dose rates are approximately an order of magnitude greater than those due to thepresence of naturally occurring radionuclides in the environment as assessed by Beresford et al. [B5],although the Committee’s earlier quantifications of these dose rates (in the order of a few micrograys
per hour) [U6], would render this putative difference insubstantial. The estimated dose rates werecompared with a benchmark for chronic effects (the lower bound of the ICRP’s DCRL, whose purpose
was to guide protection efforts rather than as an indicator of environmental damage) (see table F2). The
calculated 95th percentile of the dose-rate distribution was divided by the aforementioned benchmark
and this ratio (also known as a “risk index”) suggested that effects were unlikely for these particularanimals.

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Table F2. Estimates of weighted absorbed dose rate in June 2011 to various species of wild
terrestrial vertebrate within a 100-km radius of FDNPS
Species

Ratio to the dose-rate benchmarka

1.1b (cluster 3)
2.2 (Koriyama City)

0.28

Sika deer

1.3 (Koriyama City)

0.33

Asian black bear

1.2 (Koriyama City)

0.30

Birdc

1.5 (Koriyama City)

0.38

Wild boara95th percentile of the dose-rate distribution(μGy/h) (location)

0.55

The dose-rate benchmark used was the lower bound of the ICRP DCRL band, namely 4 µGy/h for cervidae and anatidae, taken

to be representative for mammals and birds, respectively.
b

Maximum value.

cIncluded grey duck, mallard and Japanese pheasant. The benchmark for reference duck was used.

F29. Dose rates to all biota groups were calculated based upon an equilibrium assessment using themean deposition densities reported for Okuma Town (table F3). The maximum weighted absorbed dose
rate to biota estimated for this area, for mid-June 2011, was for deer/herbivorous mammals andamounted to 71 µGy/h (or 1.7 mGy/d). This estimate was derived using default values for transfer anddosimetric parameters. Somewhat lower values were estimated for vegetation: 26 µGy/h and 17 µGy/h
for grass and trees, respectively. Refining the estimates for Okuma Town, by applying region-specificCRs for animals, gave weighted absorbed dose rates to large mammals in the range 13–26 µGy/h.
Radioisotopes of caesium contributed more than 90% of the dose rate and, except for the case of wildboar, the dose from external exposure predominated.
F30. These estimated weighted absorbed dose rates exceeded the ERICA screening benchmark of
10 µGy/h (for protecting ecosystem functioning and structure) by some margin and exceeded therelevant lower bound of the ICRP’s DCRL band in some cases (table F3). However, comparing the
calculated dose rates with a benchmark for manifest effects of 100 µGy/h (pertaining to viability ofbiota populations) [U12] suggested that any significant effects on terrestrial animal populations wereunlikely. Because the estimated dose rates lay between the upper (UNSCEAR) and lower (ICRP and
ERICA) benchmarks, more subtle effects at the individual level, such as cytogenetic damage or effects
on reproductive endpoints, could not be ruled out for the areas of highest deposition density.
Table F3. Estimates of weighted absorbed dose rate in June 2011 to reference organisms in an areawith relatively high deposition density (Okuma Town)
Dose-rate estimate(μGy/h)Dose-rate benchmarka(μGy/h)Ratio of estimate tobenchmarka

Bee

18

400

0.04

Deer

71

4

17.8

Duck

21

4

5.3

Earthworm

46

400

0.11

Frog

18

40

0.45

Pine tree

17

4

4.3

Rat

46

4

11.5

Wild grass

26

40

0.65

Reference organisma

The dose-rate benchmark used was the lower bound of the relevant ICRP DCRL band.

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2.

Assessment for the intermediate phase

F31. Because of the faster radioactive decay of short-lived radionuclides, the reconstructed estimatesof weighted absorbed dose rates for Okuma Town for the time of the assumed main deposition event(15 March) were substantially higher than those reported for June. The highest reconstructed dose rates
were estimated for soil-dwelling organisms with values of 290 µGy/h and 330 µGy/h forearthworm/soil invertebrates and rat/burrowing mammals, respectively. Values for deer/herbivorous
mammals were estimated to be about 240 µGy/h, with 131I and internal irradiation dominating
contributions. In contrast, the external irradiation predominated for all other organisms considered.
Reconstructed dose rates to vegetation were estimated as 110 and 130 µGy/h for pine tree and wild
grass, respectively.
F32. Maps of interpolated estimates of weighted absorbed dose rates to a large mammal are provided
in figure F-II; one map is based upon reported deposition densities of radionuclides (reference date of
14 June) and one is decay-corrected (to 15 March). The value of CR used was region-specific based on
all available data for mammals.
F33. These estimates did not account for some of the very short-lived radionuclides that were present
in fallout early on. Initial analyses suggested that the primary radionuclides contributing to dose rate at
this time were 132Te and 132I. Estimations of the concentrations of these short-lived radionuclides in soil
for an area receiving maximum deposition were reconstructed from 137Cs concentration measurements,using ratios derived from [I33]. These direct empirical data for the specific location, as opposed tothose derived from modelling the source term and dispersion of radioactive material presented inappendix B, were considered more appropriate as input for the purposes here. The analysis showed thatthese short-lived radionuclides contributed significantly to the early dose rates to organisms. The
estimates of these early dose rates to soil-dwelling organisms (reference organisms from table F1:
rat/burrowing mammal and earthworm/soil invertebrate) were higher by approximately a factor of three
than estimates for mid-March without 132Te and 132I, mainly because of external exposure, and may
have approached 1 mGy/h (1,000 µGy/h). However, such dose rates would have been of short duration,
falling to levels of a few hundred micrograys per hour within a few days.

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Figure F-II. Interpolated estimates of weighted absorbed dose rates to a large mammal

F34. The estimated variation of dose rate with time is illustrated in figure F-III. Dose rates due to 131I,
Cs and 137Cs were calculated for Okuma Town using arithmetic means of the deposition density data
and the dynamic model. The deposition densities for 131I were corrected for radioactive decay back to
15 March 2011. The highest weighted absorbed dose rates were estimated at approximately 5.6 mGy/hto grass at the time of deposition. More than 85% of this initial dose rate was due to 131I. Weighted
absorbed dose rates to trees were initially substantially lower, although dose rates declined less rapidly.
The main contribution to dose was associated with the presence of 131I on vegetation. Maximum
weighted absorbed dose rates to deer/herbivorous mammals were estimated at 370 µGy/h and to haveoccurred within the first week following the main deposition event. A large fraction of this initial dose
rate (some 64%) was associated with internal exposure due to 131I. Although dose rates would havefallen quite rapidly, they were estimated not to fall below 100 µGy/h until about 275 days after thetsunami.
134

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Figure F-III. Estimated weighted absorbed dose rates as a function of time to (a) grass or shrubby
vegetation, (b) trees and (c) deer
The main initial deposition event for this purpose was assumed to have occurred on 15 March 2011

F35. For the calculated dose rates in the intermediate phase, changes in biomarkers of various types,
potentially indicating transient loss of functions important for maintaining population stability, could
not be ruled out, especially in mammals [G5]. Nonetheless, under the cautious assumption of a
maximum continuing weighted absorbed dose rate of about 1 mGy/h, (based on estimates using anequilibrium approach and including contributions from short-lived 132Te and 132I as described above),
about 375 and 40 days of exposure would have been needed to reach a level where acute effects might
have been expected on populations of soil invertebrates and small mammals, respectively. This
assessment was based upon observations of biota exposed to radionuclides after the Chernobyl accident[U12]. Furthermore, the length of exposure needed to reach the ERICA threshold value for acuteeffects on ecosystems (1.8 Gy) [U12] would have been approximately 75 days. These comparisonsindicated that acute effects within the first two weeks after the accident would have been unlikely
because, even if weighted absorbed dose rates to biota of 1 mGy/h had occurred, these would havebeen of very short duration (theoretically lasting from a few hours to a few days). This assessment
appeared to be supported by no field observations of severe/immediate effects being reported for theintermediate phase of the accident. However, this lack of evidence per se cannot be used to confirm thecontention that no acute effects on non-human biota occurred, because no corroborated information
was available for this period.
F36. For vegetation, the weighted absorbed dose accumulated during the 30-day period after theaccident was estimated to be approximately 0.5 Gy, representing about one tenth of the maximum
doses at which no effects were observed in populations of herbaceous plants exposed after the
Chernobyl accident [U12]. For a herbivorous mammal, the weighted absorbed dose accumulated during
the 30-day period after the FDNPS accident was estimated to be about 0.2 Gy, representing about halfof the maximum doses at which no effects were observed in populations of small mammals around theChernobyl nuclear power plant after the 1986 accident [U12].

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B. Aquatic environment
1. Assessment for the late phase using measurements of biologicalsamples
F37. Weighted absorbed dose rates to freshwater fish from lakes and rivers with 137Cs deposition
densities in the range 100,000 to 200,000 Bq/m2 were estimated to be within the range 0.4–3 µGy/h.
Dose rates to fish with the highest measured radionuclide concentrations in the body were within therange 3.7–6.2 µGy/h (depending on the proportion of time the fish were assumed to stay near the lakebottom sediments). Although these dose rates were more than an order of magnitude above backgroundlevels due to natural sources of exposure (see [H13]), they did not reach the threshold levels for chronic
exposures above which acute effects in freshwater biota are expected.
F38. Estimates of weighted absorbed dose rates to biota for selected clusters of measurements for the
Fukushima coastal area are presented in figure F-IV. The dose rates are highly variable in time andspace, directly reflecting the variations in actual radionuclide concentrations in biota.
Figure F-IV. Estimated weighted absorbed dose rates to macroalgae, benthic fish and crustaceans

F39. Dose rates were estimated (summing internal and external exposure due to 131I, 134Cs and 137Cs)from the compiled arithmetic means of radionuclide concentrations for each category (for all coastal
stations where biological samples were available: 10 May 2011 to 12 August 2012). The highest
estimated values were approximately 0.17–0.25 µGy/h to ascidians, macroalgae, sea urchins andholothurians and 0.10–0.17 µGy/h to benthic fish, crustaceans and molluscs. The dominant
contribution to the dose rates to biota was from external exposure due to 134Cs and 137Cs because by theintermediate phase, much of any 131I would have substantially decayed. The maximum estimated dose
rate to biota was 4.4 µGy/h for benthic fish pertaining to a measurement in fat greenling(Hexagrammos otakii) sampled in August 2012.

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F40. These dose rate estimates could be compared with benchmarks for chronic effects (table F4).
Comparison with the lower bound of the ICRP DCRL or the UNSCEAR benchmark of 400 µGy/h (asappropriate) implied that radiation-induced effects would be negligible in the late phase. The dose rates
to biota calculated were commensurate with background dose rates to biota in the marine environment[H13] and also substantially below the ERICA screening benchmark of 10 µGy/h (the highest ratio of
estimated dose rate to the ERICA benchmark was 0.4 for benthic fish).
F41. As of August 2012, fish were still being found with radionuclide concentrations above theJapanese regulation value of 100 Bq/kg (fresh weight) for sale and human consumption [B24].
Although such a level may be of relevance to radiological protection of the public, the corresponding
dose rates to non-human biota are insignificant, falling far below any relevant benchmarks for radiation
effects. The Committee did not assess the long-term impact of continued release of various
radionuclides to the marine environment from contaminated groundwater, which was still ongoing at
the end of 2013. This issue requires consideration in future studies.
Table F4. Comparison between weighted absorbed dose-rate estimates obtained from radionuclides measured
in selected marine species at various times and locations and relevant benchmarks for effects
Reference organism
assigned to speciesaMaximum dose rate (μGy/h)(date, location)

Dose-rate benchmark(μGy/h)a

Ratio to thebenchmark

Macroalgae

0.41(16 Aug 2011; 36.9359N, 140.9149E)

40(ICRP Reference [I22] brownseaweed)b

0.01

Benthic mollusc

0.42(13 Jan 2012; 37.2030N; 141.0862E)

400
[U12]

0.001

Crustacean

0.63(07 Oct 2011; 37.8863N, 141.0266E)

400(ICRP Reference [I22] crab)

0.0016Benthic fish

4.4
(02 Aug 2012; 37.5847N, 141.0422E)

40(ICRP Reference [I22] flatfish)

0.11

Sea urchin

0.42(13 Jan 2012; 37.2030N, 141.0862E)

400
[U12]

0.0011

Holothurian

0.65(07 Oct 2011; 37.8863N, 141.0266E)

400
[U12]

0.0016

Ascidian

0.64(07 Oct 2011; 37.8863N, 141.0266E)

400
[U12]

0.0016The benchmarks used were those of the ICRP DCRLs; however the ICRP [I22] provide DCRL values for brown seaweed, crab

and flatfish only. Where DCRL values were not available for a given category of biota, the generic UNSCEAR benchmark [U12]
was used.
b

The Committee understood that the ICRP intended a DCRL value a factor of 10 lower than published in [I22].

2. Assessment for the intermediate phase using dynamic models
F42. The highest weighted absorbed dose rates to biota in the marine environment were derived fromestimated concentrations in seawater (for before 10 May 2011, when biological samples were notavailable) using the D-DAT dynamic model [V4], for a location 30 m north of the discharge channel
for Units 5 and 6 at FDNPS. For fish, the maximum dose rate was estimated to have occurred within
the first month (approximately 140 µGy/h), and the accumulated dose over one year was estimated to
be around 0.32 Gy. These doses fall substantially below levels where effects on mortality and survival,
growth or reproduction would be expected. For macroalgae at the same location, the dose rate wasdominated by the contribution from 131I. The maximum values were estimated to have occurred after
23 days, in early April 2011, and exceeded 20 mGy/h, but were estimated to have fallen rapidly below

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10 mGy/h by 32 days, largely reflecting a highly elevated uptake of short-lived radioiodine followed by
rapid decay. The weighted absorbed dose to macroalgae accumulated over a one-year period wasestimated to be approximately 7 Gy. There were few or no data on effects with which to compare, butdose rates in the range of 10–100 mGy/d were considered to cause potential effects on reproduction andgrowth rate [I22]. The estimated absorbed dose rates were therefore at a level where substantial impacts
on seaweed could have occurred, although this conclusion is tempered by the scarcity of any available
observations of actual effects.
F43. The estimated absorbed dose rates from internal exposure were generally two to three orders ofmagnitude higher than those from external exposure once biota had undergone significant uptake.
F44. To gain insight into the evolution of dose rates to selected biota with time, results from theECOMOD and CR models (the latter assuming instantaneous equilibration between modelcompartments) are presented, by way of example, in figure F-V. The more realistic dynamic modelling
approach, ECOMOD, estimated peak dose rates to fish that were an order of magnitude below thosederived using the simple CR model. In the longer term, after 50 days, the relationship was reversedwith dose rates estimated by the dynamic model substantially above those estimated by the equilibrium
model. In general, dose rates to pelagic fish, molluscs and macroalgae were estimated to fall rapidly
from their peaks within the first few weeks of the accident. The highest estimate of absorbed dose rate
to biota was for macroalgae.
F45. The estimated dose rates to fish using dynamic modelling differed substantially from thosepresented by Garnier-Laplace et al. [G3]. This partly reflected the fact that Garnier-Laplace et al.
assumed equilibrium between concentrations in organisms and in seawater [G3] whereas theCommittee’s assessment did not. Furthermore, the lack of equilibrium between radionuclide activities
in the water–sediment system in this early phase rendered the modelling of sediment concentrations in
the Committee’s assessment, using distribution coefficients, unfeasible. This contrasted with thecalculations for the late phase where such an approach was adopted. Because the sedimentation ofsuspended particles, transporting adsorbed radionuclides to the seabed, would have been a slow process
associated with further dispersion of radionuclides across large areas, the Committee assumed thatradionuclide levels in seabed sediments were such that they would not contribute substantially toabsorbed dose rates. This was consistent with the results reported in appendix B of this report (for all
areas except the port of FDNPS).

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Figure F-V. Weighted absorbed dose rates to biota in the South Channel estimated using the
ECOMOD and CR models

IV. UNCERTAINTIES
F46. Overall uncertainties associated with the types of models applied in this assessment, particularly
those involving a biological transfer component, are normally large. This is typified by the observationthat estimations using different models often differ from one another by more than an order ofmagnitude [L7]. By way of example, in order to estimate a distribution of weighted absorbed dose rate
values to a large mammal arising from exposure to isotopes of caesium, a simulation model was run
probabilistically using information on the variability in deposition density for Okuma Town and default
probability distribution functions for CR values. The resulting 95th percentile of this distribution wasapproximately two orders of magnitude greater than the 5th percentile. In view of other unsubstantiatedassumptions, such as those associated with the diet of the mammals, the uncertainties associated withdynamic modelling might have been even greater than this. In contrast, where dose rates were
estimated using directly measured concentrations of radionuclides in biota, uncertainties were much
lower.
F47. Absorbed doses to the thyroid of mammals from their inhalation of 131I would have been acomponent of exposure in the intermediate phase of the accident. The methodology applied by theCommittee did not account for this adequately: this particular pathway and the doses to specific organs(only activity concentrations in the whole organism were derived) were not modelled explicitly. Thisomission represents an additional uncertainty to the risks inferred for the first weeks and months
following the accident.
F48. Empirical Bayesian Kriging (EBK) was selected as the method to estimate the deposition densityand dose-rate rasters for the Fukushima area. EBK provides both a prediction and standard error. In
addition, a cross validation was performed by randomly selecting 5% of the deposition density data andrunning the EBK on the remaining 95%. The differences between the predicted values and themeasured values indicated the quality of the model fit. This process was repeated one hundred times to
produce a robust quantitative estimate of the uncertainty associated with the modelling approach.

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F49. The results from two dynamic models for marine biota, D-DAT and ECOMOD, using the samedatasets corresponded closely. Furthermore, there was a degree of correspondence between modelledradionuclide concentrations in biota using D-DAT and measurements made by Greenpeace for theperiod 3–10 May 2011 [G11], although the degree of agreement was not so strong because ofincomplete overlap between sampling and modelling stations. When compared with modelled data(except for the FDNPS drainage channels and most adjacent locations), the dose rates estimated fromradionuclide concentration measurements were generally within an order of magnitude. For the
FASTer model, parameters were reviewed and checked by external experts, and the model outputs
were checked by independent groups of analysts. Values of dose rates derived using the ERICA Tool
were checked by independent analysts who also ran simulations. This provided added confidence in theapproaches used.

V. CONCLUSIONS
F50. Weighted absorbed dose rates to non-human biota inhabiting terrestrial ecosystems may havesignificantly exceeded the benchmark of 100 µGy/h (the dose rate below which significant effects are
considered unlikely for most terrestrial communities) for limited periods in the intermediate phase(approximately the first two months) after the accident. However, population effects of major
significance were unlikely, and would be expected to have been only transient, owing to the shortduration of exposures at such dose rates. Changes in biomarkers for certain biota, in particularmammals, could not be excluded; however, their significance for population integrity is not wellestablished. Accumulated doses over the intermediate phase were estimated to have fallen short oflevels found to cause observable effects in non-human biota, as reported in reviews such as thoseconcerning exposures in the aftermath of the Chernobyl accident. Estimated doses to marine biota
during the intermediate phase did not indicate the potential for effects on populations of theseorganisms. This was the case even for the near field (tens of metres from the discharge channels),
where a dynamic modelling approach was applied to simulate the absorption and excretion ofradionuclides by biota. Accumulated absorbed doses over the intermediate phase were considered too
low for observable acute effects. A potential exception was for macroalgae that were close to thedischarge point.
F51. For the late phase (months to years) after the accident, a risk of effects to individuals of certain
species, especially mammals, may exist in areas of highest deposition density. Difficulties exist in
extrapolating potential effects on individuals to the significance at the population level, but effects onterrestrial biota at the population level were considered unlikely to be observable. The issue can beclarified only through continued monitoring and further study. This should also address the indicationsof harmful radiation effects in terrestrial biota reported by Møller et al. [M22, M23] and Hiyama et al.
[H6]. The fact that no direct measurement data (for terrestrial and freshwater ecosystems) wereavailable to the Committee for the areas of highest deposition density (which were evacuated) restricted
the assessment for these areas to the use of transfer models; this meant that large uncertainties wereunavoidable. Although predicted exposures for both freshwater and marine biota during the late phasewere well below thresholds above which effects could be deemed likely, there is a need for further
work to characterize radionuclide levels and potential exposures for these environments.
F52. The Committee concluded that the possibility of direct effects of radiation exposure on nonhuman biota was geographically constrained and that, in areas outside of that considered by thisassessment, the potential for such effects on biota may be deemed insignificant.
F53. The Committee’s assessment of the effects of radiation exposure due to the FDNPS accident on
non-human biota is subject to uncertainty. In particular, it was difficult to account accurately for thecontributions of short-lived radionuclides in the initial period after the accident. Although estimates

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were made for the biota in the terrestrial ecosystem, these were considered highly uncertain.
Furthermore, there are limitations associated with the modelling of doses from external exposure forthe marine environment, because it was not possible to include exposures from sediment in some of themodel simulations. This and other factors were of potential concern in view of the releases still ongoingat the end of 2013.

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GLOSSARY
Absorbed dose

Fundamental dosimetric quantity defined as the energy imparted byionizing radiation in unit mass of matter; measured in grays (Gy); 1 gray isequal to 1 joule per kilogram (J/kg).

Activity

The rate at which spontaneous transformations occur in a given amount ofradioactive material. (Strictly, the expectation value of the number ofnuclear transformations occurring in a given quantity of material per unittime). It is measured in becquerels (Bq); 1 becquerel equals one
transformation per second.

Acute exposure

Exposure received within a short time period (see also protracted exposure).

Becquerel (Bq)

The SI unit of activity, equal to one transformation per second. As the unit isso small, multiples are frequently used such as megabecquerels (MBq)
which is 106 or a million becquerels. (1 GBq is 109 Bq; 1 TBq is 1012 Bq; and1 PBq is 1015 Bq).

Biokinetic model

A mathematical model for the behaviour of radionuclides in the body whichtakes account of the movement, retention and excretion of a radionuclide
as a function of time.

Cold shutdown

Defined in the context of this report by TEPCO and the Nuclear Emergency
Response Headquarters as the state where the coolant water temperaturesof Units 1–3 were less than 100ºC, the pressure inside the reactor vessels
was the same as the outside air pressure, and where any further releases
would not result in dose rates greater than 1 mSv per year at the siteboundary.

Collective dose

The total radiation dose incurred by a population (that is the sum of all theindividual doses); measured in man–sievert (man Sv) or man–gray (man Gy).

Committed dose

The integral, over a defined period of time, of the dose rate in a particular
tissue or organ that will be received following the intake of radioactive
material into the body.

Core cooling

The process by which heat is transferred from the reactor core (the central
part of a nuclear reactor containing the fuel elements and any moderator)
to the steam generators or directly to the turbines.

Decay heat

The heat generated by the transformation of radionuclides, particularly inthe context of radionuclides in the core of a reactor.

Decontamination

The complete or partial removal of contamination by a deliberate physical,
chemical or biological process.

Deterministic effectA health effect of radiation exposure for which a threshold level of dose
generally exists, above which the severity of the effect is greater for a higher
dose.

Dose

A measure of the energy deposited by radiation in a target. Dose can beused as a shorthand for absorbed dose and effective dose when the context
is clear.

Dose coefficient/dose per unit intake

The committed effective dose or committed absorbed or equivalent dose ina tissue or organ resulting from an intake, by a specified means (usuallyingestion or inhalation), of unit activity of a specified radionuclide in a
specified chemical form.

Dose rate

Dose delivered or received per unit time. Measurements are usually made interms of the dosimetric quantity, ambient dose equivalent rate, H*(10), in
units of μSv/h.

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Dose and dose rate effectivenessfactor

The factor by which the risk of occurrence of a health effect in a specified
time period (usually over a lifetime) per unit dose for exposures at highdoses and high dose rates exceeds that for exposures at low doses and low
dose rates.

Dosimeter

A device for measuring an individual’s exposure to ionizing radiation.

Effective dose

Fundamental dosimetric quantity for the purposes of radiologicalprotection defined as the tissue-weighted sum of the equivalent doses in all
specified tissues and organs of the body; measured in sieverts (Sv).

Equivalent dose

Fundamental dosimetric quantity for the purposes of radiologicalprotection defined as the product of the absorbed dose in the tissue ororgan and the appropriate radiation weighting factor for the type ofradiation giving rise to the dose; measured in sieverts (Sv).

Evacuation

The rapid, temporary removal of people from an area to avoid or reduce
short-term radiation exposure in an emergency.

Exposure

The act or condition of being subject to irradiation. External exposure is
exposure to radiation from a source outside of the body. Internal exposureis exposure to radiation from a source within the body.

Geiger counter

A Geiger counter (or Geiger–Müller counter) detects ionizing radiation by
the ionization produced in a low-pressure gas in a Geiger–Müller tube.

Gray (Gy)

Unit of absorbed dose, equal to 1 joule per kilogram (J/kg).

In vitro measurement

A procedure used to determine the nature, activity, location or retention ofradionuclides in the body by analysis of material excreted or otherwise
removed from the body.

In vivo measurement

A procedure used to determine the nature, activity, location or retention ofradionuclides in the body by direct measurement.

Lifetime risk

Probability that a disease occurs from a given point of time (e.g. at
exposure) until the end of life. The lifetime baseline risk refers to theprobably of a disease occurring over a lifetime without exposure additional
to the background from natural and other sources of radiation. Lifetime risk
due to exposure is the additional probability of a disease occurring over a
lifetime due to additional radiation exposure.

Linear Energy Transfer (LET)As radiation interacts with matter, it loses its energy through interactions
with atoms. LET measures the average amount of energy lost over a defined
distance. The same absorbed dose of low-LET radiation (such as beta
particles and gamma rays) creates less biological damage than of high-LET
radiation (such as alpha particles).

Occupationally exposed worker

Any person who is employed, whether full time, part time or temporarily, by
an employer, and who has recognized rights and duties in relation to
occupational radiological protection. The Japanese regulations use anothersimilar term, radiation worker.

Protracted exposure

Exposure persisting in time (see also acute exposure).

Radionuclide

A radioactive isotope of an element. Different isotopes of an element havethe same number of protons but different numbers of neutrons and hence
different atomic masses. If there are too many or too few neutrons, thenuclei of the isotope tend to be unstable and transform into the nuclei ofanother element and in the process emit radiation.

Relative risk

Ratio of the risk for two groups, estimated from the relative rates of disease
between, for example, an exposed group and an unexposed group.

Relocation

The non-urgent removal or extended exclusion of people from acontaminated area to avoid protracted exposure. This corresponds to the
Deliberate Evacuation Area policy enacted in Japan.

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Remediation

Any measures that may be carried out to reduce the radiation exposure
from existing contamination of land areas through actions applied to thecontamination itself (the source) or to the exposure pathways to humans.

Scram

A safety feature that triggers immediate shutting down of a nuclear reactor,
usually by rapid insertion of control rods, either automatically or manuallyby the reactor operator. Also known as a “reactor trip”.

Shielding

The absorbing property of material between a radiation source and a
receptor which results in reduced exposure.

Sievert (Sv)

Unit of equivalent dose and of effective dose, equal to 1 joule per kilogram(J/kg).

Source term

Mathematical expression used to denote information about the actual or
potential release of radiation or radioactive material from a given source.
Here this term includes the release rate, radionuclide composition, physicochemical form and their changes over time of the radionuclides released.

Stochastic effectA radiation-related health effect, the probability of occurrence of which isgreater for a higher radiation dose and the severity of which (if it occurs) is
independent of dose.

Thyroid blocking

The administration of a compound of stable iodine (usually potassium
iodide) to prevent or reduce the uptake of radioactive isotopes of iodine by
the thyroid in the event of an accident in which these isotopes are released.

Whole-body monitoring

The measurement from outside the human body (generally extending atleast from the neck below the chin to the mid to upper parts of the thigh) of
the quantity of specific radionuclides within the body by measuring
radiation emitted by such radionuclides.

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unscear.org
This publication contains:
VOLUME I
Report of the United Nations Scientific Committee on the Effects of Atomic Radiation
to the General Assembly
Scientific Annex with appendices
Annex A: Levels and effects of radiation exposure due to the nuclear accident
after the 2011 great east-Japan earthquake and tsunami
Appendix A.
Appendix B.
Appendix C.
Appendix D.
Appendix E.
Appendix F.

Data compilation
Radionuclide releases, dispersion and deposition
Assessment of doses to the public
Assessment of doses to workers
Health implications for the public and workers
Assessment of doses and effects for non-human biota

Supplementary materials (available from www.unscear.org)

E VA L U AT I N G R A D I AT I O N S C I E N C E F O R I N F O R M E D D E C I S I O N - M A K I N G
In 1955 the United Nations General Assembly established the Scientific Committee on the Effectsof Atomic Radiation (UNSCEAR) in response to concerns about the effects of ionizing radiation
on human health and the environment. At that time fallout from atmospheric nuclear weapons
tests was reaching people through air, water and food. UNSCEAR was to collect and evaluate
information on the levels and effects of ionizing radiation. Its first reports laid the scientific grounds
on which the Partial Test Ban Treaty prohibiting atmospheric nuclear weapons testing was
negotiated in 1963.
Over the decades, UNSCEAR has evolved to become the world authority on the global levels
and effects of exposure to ionizing radiation. UNSCEAR’s independent and objective evaluationof the science are to provide for—but not address—informed policymaking and decision-making

V.14-06336 (V.13-85418)

related to radiation risks and protection.

ISBN 978-92-1-142291-7