United Nations Scientific Committee on the Effects of Atomic Radiation

ATTACHMENT A-22

ESTIMATION OF THYROID DOSES TO
EVACUEES FROM INHALATION OF
RADIOIODINE AND COMPARISON WITH
THOSE DERIVED FROM MEASUREMENTS OFPEOPLE AND ESTIMATED BY OHBA ET AL.
UNSCEAR 2020/2021 Report, Annex B, Levels and effects of radiation exposuredue to the accident at the Fukushima Daiichi Nuclear Power Station: implicationsof information published since the UNSCEAR 2013 Report
Content
This attachment contains an assessment of thyroid doses to evacuees from the inhalation ofradioiodine. The doses have been estimated using the methodology described in attachment A-10
for each of the evacuation scenarios specified in attachment A-11. The estimated doses havebeen compared with those derived from measurements of radioiodine in people (seeattachment A-2) and those estimated independently by Ohba et al. [Ohba et al., 2020]. These
comparisons were made for the purposes of validating the methodology used by the Committee
for assessing doses from inhalation and how it was implemented. Additional analyses were made toprovide further insights into uncertainties associated with the Committee’s estimates of distributionsof doses to evacuees and to identify the origins of differences with those of Ohba et al.
Notes
The designations employed and the presentation of material in this publication do not imply theexpression of any opinion whatsoever on the part of the Secretariat of the United Nations
concerning the legal status of any country, territory, city or area, or of its authorities, orconcerning the delimitation of its frontiers or boundaries.
Information on Uniform Resource Locators (URLs) and links to Internet sites contained in thepresent publication are provided for the convenience of the reader and are correct at the time ofissue. The United Nations takes no responsibility for the continued accuracy of that informationor for the content of any external website.
© United Nations, April 2022. All rights reserved, worldwide.
This publication has not been formally edited.

ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. … 3

CONTENTS
I. INTRODUCTION .................................................................................................................. 5
II. EVACUATION SCENARIOS .............................................................................................. 5
III. COMPARISONS WITH [OHBA ET AL., 2020] .................................................................. 7
IV. FURTHER, MORE DETAILED ANALYSIS....................................................................... 9
REFERENCES ........................................................................................................................... 15

ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. … 5

I.

INTRODUCTION

1.
This attachment contains an assessment of thyroid doses to evacuees from the inhalationof radioiodine and its precursors where appropriate (e.g., isotopes of tellurium). The doses havebeen estimated using the methodology described in attachment A-10 for each of the evacuation
scenarios specified in attachment A-11. The estimated doses have been compared with thosederived from measurements of radioiodine in people (see attachment A-2) and those estimatedindependently by Ohba et al. [Ohba et al., 2020]. These comparisons were made for the purposesof validating the methodology used by the Committee for assessing doses from inhalation andhow it was implemented. Additional analyses were made to provide further insights into
uncertainties associated with the Committee’s estimates of distributions of doses to evacuees andto identify the origins of differences with those of Ohba et al.

II.

EVACUATION SCENARIOS

2.
Doses were estimated for 40 groups of evacuees who were evacuated at different times
and moved to different locations (see table A-22.1 and for more details see attachment A-11).
Doses were estimated separately for the period before and during the evacuation (up to 25 March
2011) and were based on atmospheric transport, dispersion and deposition modelling (ATDM)
of radionuclide concentrations in air and deposition densities in the days following the accident
provided by Terada et al. [Terada et al., 2020] (see attachment A-9).
3.
In 2011 prefectural authorities issued a questionnaire to all residents within Fukushima
Prefecture (two million people) to ascertain their activities and, specifically, their locations andmovements during and after the accident. Approximately 21% of the population completed thequestionnaire. The National Institute for Radiological Science (NIRS) used the results of thissurvey to define 18 scenarios representative of the movements of residents within a few tens ofkilometres of the Fukushima Daiichi Nuclear Power Station (FDNPS), following the accident[Akahane, 2013]. In the UNSCEAR 2013 Report [UNSCEAR, 2014], these 18 evacuation
scenarios were used to estimate doses to evacuees.
4.
Ohba et al. [Ohba et al., 2020] refined these evacuation scenarios by conducting ahierarchical clustering analysis of 100 to 300 randomly sampled behavioural questionnaires ofchildren from each of the seven municipalities in the evacuation area. This resulted in 37 new
representative evacuation scenarios; these have been used for the updated assessment of doses
to evacuees from evacuated localities, as outlined in table A-22.1 (No. 1 to No. 37) and in
attachment A-11. These 37 new evacuation scenarios did not include evacuees from Hirono
Town and Katsurao Village; the Committee, therefore, included three of the original
18 evacuation scenarios to represent evacuees from these two locations (resulting in
40 evacuation scenarios in total, see table A-22.1 (No. 38 to No. 40).
5.
The methodology for assessing doses to evacuees from the plume of airborne
radionuclides for these scenarios is described in attachment A-10, and the scenarios themselvesin attachment A-11. The resulting doses (from all pathways and radionuclides and to each of thethree age groups considered) can be found in attachment A-18. The focus of the remainder ofthis attachment is doses to the thyroid of evacuees from inhalation of radioiodine (and its
precursors where relevant), in particular by 1-year-old infants, and on comparisons with theestimates presented by [Ohba et al., 2020].

6 ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. …

Table A-22.1. Evacuation scenarios considered in the dose assessment (inhalation doses
received or committed between 11–25 March)
Scenario01(FT1)02(FT2)03(FT3)04(FT4)05(FT5)06(TM1)07(TM2)08(TM3)09(TM4)10(NR1)11(NR2)12(NR3)13(NR4)14(NR5)15(OK1)16(OK2)17(OK3)18(OK4)19(OK5)20(NM1)21(NM2)22(NM3)23(NM4)24(NM5)25(IT1)26(IT2)27(IT3)28(IT4)29(OD1)30(OD2)31(OD3)32(OD4)33(OD5)34(HK1)35(HK2)36(HK3)37(HK4)38 (10e)39 (12e)40 (14e)

Location at 11 March 2011

Start > Route > Destination

Evacuation starttimea,bFutaba Town
Futaba > Kawamata > OOPc
AM2 on 12 MarchFutaba Town
Futaba > Iwaki > OOP
PM1 on 12 MarchFutaba Town
Futaba > Odaka > Fukushima > OOP
AM2 on 12 MarchFutaba Town
Futaba > Haramachi> Koriyama
PM2 on 12 MarchFutaba Town
Futaba > Namie > Kawamata > OOP
PM1 on 12 March
Tomioka Town and Kawauchi Village Kawauchi > OOP
PM2 on 15 March
Tomioka Town
Tomioka > Ono > OOP
PM1 on 12 March
Tomioka Town
Tomioka > Kawauchi > Koriyama > OOP
AM2 on 12 March
Tomioka Town
Tomioka > Iwaki
PM1 on 12 March
Naraha Town
Naraha > Iwaki > OOP
AM2 on 12 March
Naraha Town
Naraha > Iwaki > OOP
AM2 on 12 March
Naraha Town
Naraha > Iwaki
AM2 on 12 March
Naraha Town
Naraha > Hirono > Aizu District > OOP
AM2 on 12 March
Naraha Town
Naraha > Iwaki > OOP > Iwaki
AM2 on 12 March
Okuma Town
Okuma > Tamura > Aizu district
PM1 on 12 March
Okuma Town
Okuma > Tamura
AM2 on 12 March
Okuma Town and Futaba Townd
Futaba > Kawamata > Iwaki > OOP
AM2 on 12 March
Okuma Town and Tamura Cityd
Tamura(no further evacuation)
Okuma Town
Odaka > Haramachi > Sukagawa > OOP
AM1 on 12 March
Namie Town
Namie > Haramachi > OOP
AM2 on 12 March
Namie Town
Namie > Soma
PM1 on 12 March
Namie Town
Namie > Tsushima > Koriyama
AM2 on 12 March
Namie and Tsushimad
Tsushima > Nihonmatsu
AM2 on 16 March
Namie Town
Namie > Kawamata > OOP
AM2 on 13 March
Iitate Village
Iitate > Koriyama
AM2 on 16 March
Iitate Village
Iitate > Kawamata > Fukushima > Aizu district
AM2 on 15 March
Iitate Village
Iitate > OOP
AM2 on 19 March
Iitate Village
Iitate22 June
Odaka ward of Minamisoma City
Odaka > Haramachi > Iwaki > OOP
PM2 on 12 March
Odaka ward of Minamisoma City
Odaka > Kawamata > Aizu District > OOP
PM1 on 12 MarchHaramachi ward of MinamisomaHaramachi > Date > Haramachi > OOP
AM2 on 12 March
City
Odaka ward of Minamisoma City
Odaka > Haramachi > Fukushima > OOP
PM2 on 12 March
Odaka ward of Minamisoma City
Odaka > Haramachi > Soma > OOP
PM1 on 12 MarchHaramachi ward of MinamisomaHaramachi > Fukushima > OOP
PM1 on 17 MarchCity
Iitate Village
Iitate > Koriyama > OOP
AM1 on 12 March
Kashima ward of Minamisoma City
Kashima > Haramachi > Iitate > OOP
AM2 on 12 MarchHaramachi ward of MinamisomaHaramachi > Soma
PM1 on 18 MarchCity
Hirono Town
Hirono Town > Ono Town Office
12 March
Katsurao Village
Katsurao Village > Azuma Gymnasium
14 March
Katsurao Village Office
Katsurao Village > Azuma General
21 March
Gymnasiuma AM1, AM2, PM1, PM2 refer to early morning, late morning, early afternoon and late afternoon, respectively.
b The focus of Ohba et al. [Ohba et al., 2020] was on evacuation before 26 March 2011. The timings of later evacuations (inparticular, of the municipalities of Iitate Village and parts of Tamura City in May and June 2011) are as set out in the
UNSCEAR 2013 Report.
c OOP denotes out of prefecture and indicates that the destination was a prefecture other than Fukushima Prefecture.
d In these scenarios, people were evacuated from the first named location to the second named location on the day of theearthquake (11 March 2011).
e Number in brackets corresponds to the number of the evacuation scenario in the UNSCEAR 2013 Report [UNSCEAR, 2014].

ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. … 7

III. COMPARISONS WITH OHBA ET AL. [OHBA ET AL., 2020]
6.
Ohba et al. [Ohba et al., 2020] used estimates of air concentrations of radioiodine fromthe ATDM results of Terada et al. [Terada et al., 2020] in their assessment of doses to evacuees,
and made similar assumptions about the dose coefficients for intakes of radioiodine and of the
reduction in doses due to sheltering inside buildings as have been used in the Committee’s
assessment. Table A-22.2 provides a summary of the main similarities and differences between
the modelling approaches used by the Committee and Ohba et al. [Ohba et al., 2020].
Table A-22.2. Main differences in the modelling approaches used by the Committee and Ohba et
al. [Ohba et al., 2020] for estimating inhalation doses to evacuees
The Committee’s assessment

Ohba et al. (2020)

Effect on the estimated thyroid doses
from inhalation

Spatial resolution
Concentrations of radionuclides in air were
derived from the full 1 × 1 km grid of the
ATDM local model [Terada et al., 2020],
i.e., from about 35 000 grid cells

Concentrations of radionuclides
in air were derived from nearestof 152 landmarks, for which
ATDM results [Terada et al.,2020] were provided

Could have some influence in areas withstrong gradient of air concentration

Time resolution
Basic data:
Concentrations of radionuclides in air
were derived from the full 1-hour time
grid of the ATDM local model [Terada etal., 2020]
Evacuation routes:
If evacuation was assumed for a 6-hoursegment, the evacuation route wasmodelled as a straight line connecting thestart point and the end point, and a linear
movement along this route was assumed
during the 6 hours (i.e., it was assumed thatthe evacuation started at the beginning of
the 6-hour-segment, the destination wasreached at the end of that period and that
exposure during evacuation only occurred
while the plume was estimated to havebeen present along the evacuation route)

Basic data:
Concentrations of radionuclides in
air were derived from averaging
over 6-hour-segments based on
the full 1-hour time grid of the
ATDM local model [Terada et al.,2020]
Evacuation routes:
Not clear from the publication
how exactly modelling was
performed during the evacuation
itself. It is possible that the airconcentration at the starting pointof evacuation was applied for thefull 6-hour-segment, during which
evacuation was assumed

The differences in how the exposure wasestimated during the evacuation could
have a significant effect, in particularwhere the plume arrived during the 6-hoursegment assumed for when the evacuation
occurred: in these cases the Committee’s
dose estimates would be lower than thoseof [Ohba et al., 2020] due to the latteraveraging over the full 6 hours. This is thecase for e.g., scenarios FT1, OK2, OD2,
NM1, HK4 (as indicated by (b) in the lastcolumn of table A-22.5)

Reduction factor
A dose reduction factor of 0.5 was applied
only for those 6-hour-segments, in whichpeople remained at the same location
throughout (to take account of staying
indoors and the filtering effect ofbuildings). But for those 6-hour-segments,
in which people were evacuated and for the
6-hour-segment
immediately
beforeevacuation no shielding (i.e., a reduction
factor of 1.0) was applied (as theCommittee assumed that people would
wait outdoors before evacuation and also
assumed that the shielding effect duringtransportation would be negligible)

A generic dose reduction factorof 0.5, relative to that outdoors,
was applied to take account oftime spent indoors before, and/or
in vehicles during evacuation

The differences in the application of
reduction factors during and before
evacuation can lead to a difference of up to
50% in estimated doses, if a significant
contribution to the total dose occurred during
and before evacuation. Scenarios where asignificant dose contribution (i.e., >50%)
occurred before and/or during evacuation
result in doses higher than those estimated by[Ohba et al., 2020] (due to the assumption of
no dose reduction during evacuation) include
e.g., FT2, IT1, OD1 and OD4 (as indicatedby (a) in the last column of table A-22.5)

8 ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. …

The Committee’s assessment

Effect on the estimated thyroid doses
from inhalation

Ohba et al. (2020)
Dose coefficientsJapan-specific dose coefficients forinhalation of radioiodine were adopted(see attachment A-2); these range from
0.45–0.57 of the ICRP values for 131I for
1-year-old infants (the range varying withthe chemical form of iodine, the isotope
and the age group)

Dose coefficients from ICRP
publication 71 [ICRP, 1995,
Publication 71] were reduced by ageneric factor of 0.62 to takeaccount of a Japan-specific diet

The differences in dose coefficients are small
and would not greatly affect comparisons
between the respective dose estimates

Contribution of short-lived radionuclides
For each of the 35 000 cells of the ATDM
grid the contribution of short-lived
radionuclides was assessed for each 1-hourtime step (based on the ATDM results for
132Te and an assumed ratio of 133I/131I in airof 1.1 at 12:00 on 12 March). The
contribution of short-lived radionuclides tothe dose to the thyroid were in the range of
2 to 50% of those from 131I, varying withplume arrival time/s

The contributions of short-lived
radionuclides to the dose to thethyroid were 59% of those from
131I for exposure to plumes on the
12–13 March 2011 and 8% for
those on 15–16 March 2011

The contributions of short-lived radionuclides
are broadly comparable: but some small
differences in estimated doses may haveoccurred at locations where [Ohba et al.,2020] assumed a higher contribution of
59% (i.e., for Futaba, Namie and Odaka
scenarios) relative to that assumed by theCommittee

7.
A comparison of the Committee’s dose estimates with those of Ohba et al. [Ohba et al.,2020] therefore provides a good quality check on the Committee’s estimates. However, somecaution is warranted in making such comparisons. In deriving their distributions of doses, Ohba
et al. have taken account of the individual variability of behaviour, based on the sampled
questionnaire results, as well as uncertainties in dose coefficients and dose reduction factors, but
not in the air concentration estimates derived using ATDM. The Committee, on the other hand,
has not taken account of individual variability of behaviour (as it did not have access to thequestionnaire results), but has taken account of uncertainties in air concentrations derived using
ATDM, as well as in other factors, including dose coefficients and dose reduction factors (seeattachment A-12 for further details). Parameters of the dose distributions (medians, percentiles)
presented by Ohba et al. are therefore not strictly comparable with equivalent parameters of thedose distributions derived by the Committee, although comparisons of average doses are valid.
Nevertheless, because many of the detailed results of Ohba et al. are presented in terms of
medians, median dose estimates are also compared in section IV below, although the limitationsof the comparisons should be noted.
8.
Table A-22.3 provides a comparison between the average thyroid doses to evacuees frominhalation of 131I 1 estimated by the Committee and those estimated by Ohba et al. [Ohba et al.,2020]. Because Ohba et al. only presents average (as opposed to median) doses for each
evacuated locality, and not for each scenario, the doses are the averages over all scenarios
relevant to each locality. For all localities, the results are consistent, with the Committee’s
estimates within the uncertainty intervals of the Ohba et al. results. The largest difference is for
Odaka ward, where the average doses differ by a factor of 1.6. This difference is mainly causedby differences for scenario OD4, which dominates the average dose for Odaka ward (as it
represents 71.5% of all evacuees from Odaka ward). In scenario OD4, a significant contribution(i.e., >50%) to the total inhalation dose occurred before and/or during evacuation (see table
A-22.4 below). Ohba et al. assumed a reduction factor of 0.5 relative to the inhalation dose
“outdoors” to take account of being indoors before, and/or in a vehicle during, evacuation; in theCommittee’s estimates, no reduction was assumed.
1

The average doses from inhalation of radioiodine (and precursors) as a whole estimated by the Committee andOhba et al. showed similar agreement.

ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. … 9

9.
The good agreement (within the uncertainties) between the Committee’s estimates ofmean doses to the thyroid from inhalation of radioiodine and those of Ohba et al. is not surprising,
given that both used largely comparable methodologies and input data. However, this good
agreement provides a quality check on the methodology used by the Committee to estimate doses
from inhalation or radionuclides and how it has been implemented.
10.
The doses estimated by the Committee from inhalation of 131I by evacuees have also
been compared with doses derived from measurements of the thyroids of evacuees (seeattachment A-2). The broad agreement, within their respective uncertainties, between the two
estimates provides further validation of the methodology used by the Committee and how it
has been implemented.
Table A-22.3. Comparison of the Committee’s estimates of mean absorbed doses (via inhalationof 131I) to the thyroid of 1-year-old evacuees from localities within Fukushima Prefecture withthose of Ohba et al. [Ohba et al., 2020]
Mean absorbed dose to the thyroid from inhalation of 131I (mGy)Haramachi/
Odaka ward
Kashima(Minamisoma
wards
City)
(MinamisomaCity)

Municipality

FutabaTown

TomiokaTown

Naraha
Town

Okuma
Town

Namie
Town

Committee’s
estimates

2.7

1.3

2.0

2.9

3.9

16.1

4.2

4.1

Ohba et al.

3.6(0.9, 7.5)

1.1
(0.3, 2.3)

2.1
(0.5, 4.4)

2.1
(0.5, 4.3)

4.0
(1.0, 8.4)

9.8
(2.4, 21)4.7
(1.2, 9.9)

4.0
(1.0, 8.5)

IitateVillageIV. FURTHER, MORE DETAILED ANALYSIS
11.
To provide some further insight into uncertainties associated with the Committee’s
estimates of doses to evacuees and differences with those of Ohba et al., additional analyses andcomparisons have been made for each evacuation scenario, while recognizing that the respective
medians and other percentiles being used for the comparison are of very different distributions(see paragraph 7).
12.
The Committee’s estimated absorbed doses (averages and medians of the distribution ofdoses) to the thyroid of a 1-year-old infant from inhalation of radioiodine in air in the period
11 to 25 March 2011 are summarized in table A-22.4.
13.
The percentages of the inhalation dose committed before and/or during evacuation are
also presented in table A-22.4; the remaining percentage was received at the evacuation
destination up to 25 March 2011. For nine of the evacuation scenarios this percentage is morethan 50%, but needs to be qualified as follows:− Firstly, the estimated doses may be strongly influenced by the assumptions on protective
measures implemented before and/or during the evacuation as well as at the finaldestination (i.e., sheltering, shielding while travelling inside vehicles, etc.);− Secondly, the estimated doses may be strongly influenced by the assumptions about theexact timing of the evacuations, in particular when they began.

10ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. …

Table A-22.4. Estimated average and median absorbed doses from the inhalation of radioiodine
to the thyroids of 1-year-old evacuees from localities within Fukushima Prefecture
The doses tabulated are average and median values for each evacuation scenario and comprise doses
received or committed before and during evacuation and at the final destination up to 25 March 2011

Scenario

Start > Route > Destination

Absorbed dose in the thyroid(mGy)
Average

MedianPercentage of dose
received before andduring evacuation (%)

01(FT1)

Futaba > Kawamata > OOP

1.1

0.4

3

02(FT2)

Futaba > Iwaki > OOP

12.1

3.8

83

03(FT3)Futaba > Odaka > Fukushima > OOP

7.6

2.1

13

04(FT4)

Futaba > Haramachi> Koriyama

9.8

3.7

63

05(FT5)

Futaba > Namie > Kawamata > OOP

0.5

0.2

63

06(TM1)

Kawauchi > OOP

0.0

0.0

0

07(TM2)

Tomioka > Ono > OOP

1.6

0.7

2

08(TM3)

Tomioka > Kawauchi > Koriyama > OOP

1.2

0.5

21

09(TM4)

Tomioka > Iwaki

7.6

3.2

0

10(NR1)

Naraha > Iwaki > OOP

0.9

0.3

5

11(NR2)

Naraha > Iwaki > OOP

3.3

1.3

0

12(NR3)

Naraha > Iwaki

7.7

3.2

0

13(NR4)

Naraha > Hirono > Aizu District > OOP

0.3

0.1

2

14(NR5)

Naraha > Iwaki > OOP > Iwaki

4.5

1.9

3

15(OK1)

Okuma > Tamura > Aizu District

3.1

1.0

58

16(OK2)

Okuma > Tamura

3.6

1.2

53

17(OK3)Futaba > Kawamata > Iwaki > OOP

2.7

1.1

9

18(OK4)

Tamura

0.8

0.3

0

19(OK5)

Odaka > Haramachi > Sukagawa > OOP

4.3

1.7

33

20(NM1)

Namie > Haramachi > OOP

3.3

1.4

0

21(NM2)

Namie > Soma

10.9

4.4

1

22(NM3)

Namie > Tsushima > Koriyama

1.0

0.4

83

23(NM4)

Tsushima > Nihonmatsu

6.9

2.7

43

24(NM5)

Namie > Kawamata > OOP

10.2

3.0

1

25(IT1)

Iitate > Koriyama

7.9

3.2

93

26(IT2)

Iitate > Kawamata > Fukushima > Aizu District

0.3

0.1

25

27(IT3)

Iitate > OOP

3.2

1.3

0

28(IT4)

Iitate

4.0

1.6

0

29(OD1)

Odaka > Haramachi > Iwaki > OOP

25.7

10.1

81

30(OD2)

Odaka > Kawamata > Aizu District > OOP

0.1

0.0

37

31(OD3)Haramachi > Date > Haramachi > OOP

0.2

0.1

4

32(OD4)

Odaka > Haramachi > Fukushima > OOP

18.9

7.4

97

33(OD5)

Odaka > Haramachi > Soma > OOP

10.7

4.3

16

34(HK1)

Haramachi > Fukushima > OOP

3.3

1.3

1

35(HK2)

Iitate > Koriyama > OOP

0.5

0.2

0

ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. … 11

ScenarioaStart > Route > Destination

Absorbed dose in the thyroid(mGy)
Average

MedianPercentage of dose
received before andduring evacuation (%)

36(HK3)

Kashima > Haramachi > Iitate > OOP

7.6

3.1

0

37(HK4)

Haramachi > Soma

13.7

5.6

27

38(10)aHirono Town > Ono Town Office

1.2

0.5

-

39(12)a

Katsurao Village > Azuma Gymnasium

0.2

0.1

-

40(14)a

Katsurao Village > Azuma General
Gymnasium

7.3

2.8

-

Number in bracket corresponds to number of evacuation scenario in UNSCEAR 2013 Report [UNSCEAR, 2014].

14.
For some evacuation scenarios the estimated doses are very strongly influenced by theexact timing of evacuation assumed in the model. The influence of this parameter was evaluatedby comparing the following doses:(a) Doses estimated for the evacuation patterns described by [Ohba et al., 2020] for eachscenario (i.e., assuming that the evacuation started exactly at the beginning of the 6-hourperiod during which evacuation was estimated to have occurred – this was the assumption
adopted by the Committee in its assessment of doses presented in this attachment andelsewhere in its update of the UNSCEAR 2013 Report); and(b) Doses estimated with an evacuation pattern shifted by +6 hours (i.e., assuming that theevacuation started exactly at the end of the 6-hour period during which evacuation was
estimated to have occurred).
15.
Doses for these two assumptions are shown in table A-22.5 and the extent to which theydiffer varies greatly between the evacuation scenarios. For 5 of the scenarios, the doses increasedby more than a factor of 2 if the evacuation occurred at the end rather than the beginning of theperiod when evacuation was estimated to have occurred (i.e., 6 hours later); e.g., for scenario
FT4 the estimated median dose increased from 3.7 mGy to about 14 mGy assuming theevacuation to have occurred at the end rather than the beginning of the period. Uncertainty in theexact time at which evacuation actually began may, therefore, result in large uncertainties in theestimated doses for some scenarios.
16.
The estimated doses are medians or averages (for 1-year-old infants) for groups ofevacuees who followed similar evacuation routes. There will have been considerable variation
about these values for individuals depending on various factors (e.g., their behaviour before
evacuation, when they began to evacuate, mode and duration of evacuation, etc.). Taking accountof this variability and uncertainties in ATDM, individual doses have been estimated to range
from about 10 times higher to 11 times lower than the median dose (at the 5th and95th percentiles) when averaged over all 40 evacuation scenarios. For the small number ofhospital and nursing-home patients and other individuals in the 20-km zone for whom the
40 evacuation scenarios were not representative, higher doses may have been received.
17.
Selected parameters of the distributions of thyroid doses to evacuees from inhalation ofradioiodine estimated by the Committee are presented in table A-22.5 and a comparison is madewith the median doses estimated by Ohba et al. [Ohba et al., 2020]. As has been noted, therespective medians represent medians of different (and in many respects not directly comparable)
distributions. The doses estimated by the Committee are broadly consistent with those of Ohba
et al. when account is taken of their respective uncertainties and the different meaning of medianvalues. A trend can be observed that the median doses estimated by the Committee aresystematically lower than the median values estimated by Ohba et al.; this can be explained by

12ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. …

the fact that the uncertainty distributions estimated by the Committee are wider than the dose
distributions of Ohba et al. For 3 of the 37 scenarios (FT5, TM1 and OD2) the median doses
estimated by Ohba et al. fall outside the uncertainty interval (5th–95th percentile) of theCommittee’s estimates; the origins of these differences are addressed below.
Table A-22.5. Comparison of the Committee’s estimates of median absorbed doses (viainhalation) to the thyroid of 1-year-old evacuees from localities within Fukushima Prefecturewith those of Ohba et al. [Ohba et al., 2020]
Dose from inhalation of radioiodine (mGy)
Committee’s estimates
Scenario

Ohba et al.

MedianStart > Route > Destination

Comments

5th
95th
Evacuation Evacuation
percentile percentile at start ofat end of
6-h-segment 6-h-segment

Median01(FT1)

Futaba > Kawamata > OOP

0.0

3.9

0.4

0.7

0.4

b

02(FT2)

Futaba > Iwaki > OOP

0.4

43.9

3.8

12.3

4.2

a, b

03(FT3)Futaba > Odaka > Fukushima >
OOP

0.1

30.2

2.1

3.8

7.9

b

04(FT4)

Futaba > Haramachi> Koriyama

0.4

36.5

3.7

14.3

8.8

a, b

05(FT5)

Futaba > Namie > Kawamata >
OOP

0.0

2.0

0.2

2.2

9.7

a, b

06(TM1)

Kawauchi > OOP

0.0

0.0

0.0

0.2

0.1

b

07(TM2)

Tomioka > Ono > OOP

0.1

6.0

0.7

0.7

1.6

08(TM3)

Tomioka > Kawauchi >Koriyama > OOP

0.0

4.4

0.5

0.5

0.5

09(TM4)

Tomioka > Iwaki

0.3

28.3

3.2

3.2

9.4

10(NR1)

Naraha > Iwaki > OOP

0.0

3.5

0.3

0.3

0.6

11(NR2)

Naraha > Iwaki > OOP

0.1

12.5

1.3

1.3

2.8

12(NR3)

Naraha > Iwaki

0.3

28.0

3.2

3.2

6.4

13(NR4)

Naraha > Hirono > Aizu
District > OOP

0.0

1.0

0.1

0.1

<0.1

14(NR5)

Naraha > Iwaki > OOP > Iwaki

0.2

16.3

1.9

1.3

4.3

c

15(OK1)

Okuma > Tamura > Aizu
District

0.1

12.1

1.0

1.0

2.2

a

16(OK2)

Okuma > Tamura

0.1

13.9

1.2

1.5

1.5

a, b

17(OK3)Futaba > Kawamata > Iwaki >
OOP

0.1

10.2

1.1

1.5

2.9

b

18(OK4)

Tamura

0.0

2.9

0.3

0.3

0.7

19(OK5)

Odaka > Haramachi >Sukagawa > OOP

0.2

15.8

1.7

3.0

8.2

b

20(NM1)

Namie > Haramachi > OOP

0.1

12.5

1.4

1.6

2.9

b

21(NM2)

Namie > Soma

0.5

40.6

4.4

6.2

21

b

22(NM3)

Namie > Tsushima > Koriyama

0.0

3.6

0.4

0.4

0.3

a

23(NM4)

Tsushima > Nihonmatsu

0.3

26.0

2.7

2.7

5.9

24(NM5)

Namie > Kawamata > OOP

0.1

41.6

3.0

3.0

11

25(IT1)

Iitate > Koriyama

0.3

29.5

3.2

3.2

5.2

a

ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. … 13

Dose from inhalation of radioiodine (mGy)
Committee’s estimates
Scenario

Ohba et al.

MedianStart > Route > Destination

Comments

5th
95th
Evacuation Evacuation
percentile percentile at start ofat end of
6-h-segment 6-h-segment

Median26(IT2)

Iitate > Kawamata > Fukushima> Aizu District

0.0

1.0

0.1

0.1

0.2

27(IT3)

Iitate > OOP

0.1

12.0

1.3

1.3

5.3

28(IT4)

Iitate

0.2

14.8

1.6

1.6

6.1

29(OD1)

Odaka > Haramachi > Iwaki >
OOP

1.0

96.6

10.1

10.0

15

30(OD2)

Odaka > Kawamata > Aizu
District > OOP

0.0

0.5

0.0

0.3

8.2

31(OD3)Haramachi > Date > Haramachi
> OOP

0.0

0.6

0.1

0.1

<0.1

32(OD4)

Odaka > Haramachi >Fukushima > OOP

0.7

71.6

7.4

7.5

10

a

33(OD5)

Odaka > Haramachi > Soma >
OOP

0.4

39.7

4.3

6.6

20

b

34(HK1)

Haramachi > Fukushima > OOP

0.1

12.2

1.3

1.4

3

35(HK2)

Iitate > Koriyama > OOP

0.0

1.8

0.2

0.2

0.4

36(HK3)

Kashima > Haramachi > Iitate >
OOP

0.3

28.1

3.1

3.1

9.6

37(HK4)

Haramachi > Soma

0.6

50.9

5.6

6.2

22

b

b

Comments:a – More than 50% of inhalation dose estimated to have occurred before and/or during evacuation.
b – Increase of inhalation dose if evacuation occurred at the end rather than the beginning of the period when evacuation was estimated to haveoccurred (i.e., 6 hours later).
c – Decrease of inhalation dose if evacuation occurred at the end rather than the beginning of the period when evacuation was estimated to haveoccurred (i.e., 6 hours later).

18.
Differences in the doses estimated by the Committee and those of [Ohba et al., 2020]
have resulted from differences in the modelling approaches adopted (see table A-22.2 for moredetail):− For the evacuation scenarios FT2, FT4, FT5, OK1, OK2, NM3, IT1, OD1 and OD4 asignificant contribution (i.e., >50%) to the total inhalation dose occurred before and/or
during evacuation (see table A-22.4). Ohba et al. [Ohba et al., 2020] assumed a reduction
factor of 0.5 relative to the inhalation dose “outdoors” to take account of being indoors
before, and/or in a vehicle during, evacuation; in the Committee’s estimates, no reduction
was assumed (i.e., evacuees assumed to be outdoors before evacuation and any reduction
in doses during transportation assumed to be negligible). These different modellingassumptions would result in the doses estimated [Ohba et al., 2020] being lower thanthose estimated by the Committee by up to 50%;
− For the evacuation scenarios FT5 and OD2 the plume was estimated to have arrived atsome time during the 6-hour period when evacuation was assumed to have occurred. Insuch cases the Committee’s modelling approach resulted in lower doses than thoseestimated by [Ohba et al., 2020]. Ohba et al. assigned the average dose during the full
6-hour-segment to the evacuees, whereas the Committee assigned only the dose received
from the estimated arrival of the plume till the evacuees reached their destination at the14ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. …

end of the 6-hour period (i.e., evacuation was assumed in all cases to start at the beginningof a 6-hour-segment (i.e., before plume arrival in these cases));− For the evacuation scenarios FT1, FT2, FT3, FT4, FT5, TM1, OK5, OD2, OD5 and NM2
the estimated doses were strongly influenced by the exact timing of the evacuation
assumed in the model (see table A-22.5). Changing the assumed time of evacuation fromthe start to the end of the 6-hour period of evacuation would have resulted in significant
increases in the Committee’s estimates of median doses, e.g., from 3.8 to 12.3 mGy for
FT2, from 3.7 to 14.3 mGy for FT2, and from 4.3 to 6.6 mGy for OD5.

ANNEX B, ATTACHMENT A-22: ESTIMATION OF DOSES TO EVACUEES AND COMPARISON WITH DOSES ESTIMATED BY OHBA ET AL. … 15

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Ohba, T., T. Ishikawa, H. Nagai et al. Reconstruction of residents' thyroid equivalent doses frominternal radionuclides after the Fukushima Daiichi nuclear power station accident. Sci
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