Presentation at the Reviewer Meeting of Research Grant by Ministry of Environment

Assessment of the Initial Radiation
Exposure to Residents in Iitate village
up to Evacuation after the Fukushima-1
NPP Accident
Imanaka T.
Research Reactor InstituteKyoto University
December 4, 2013
At NSRA, Shinbashi, Tokyo
1

Our study before this Year:
Soil sampling and gamma-ray analysis
March 29, 2011
105
132

Te

Cs 129mTe

I

132

I

134

129

Cs

Te

104

Counts per channel

137

131

136

Cs

1000
140

La

100

1010500

1000

1500
Channel

2000

2500

Our study before this year:
Reconstruction of radiation exposure rate based onradionuclide deposition

100Measured above the flowerbed

MP readig near Town Hall

Total calculation

I-131

Te-132

I-132

Cs-134

Cs-137

Cs-136-1

Exposure rate or dose rate, Gy h or Sv h-1

Comparison between measurement and calculation: Soil sample was taken at
MADEINA house at 100 m from the monitoring post.

1010.1
0510

15

20

25303540

Time after deposition, days

Only nuclides of Te132/I132, I131, Cs134, Cs137 contributed radiation
exposure. Beck’s conversion factor (BNL-378, 1980) are used to calculate
exposure rate from deposition density.

3

Our study before this year:Radionuclide composition in soil samples in Iitate village
Radioactivity ratio in 5 soil samples taken on March 29, 2011.

Deposition ratios of I131 and Te132 to Cs137.
Corrected at 18:00 of March 15, 2011.
Cs137
kBq/m2

I131/Cs137
ratio

Te132/Cs137
ratio

Usuishi

956

9.6

6.9

Sasu

774

10.9

8.9

Yamazumi

588

10.1

10.0

Town Hall672

8.2

7.9

Magata2188

7.0

8.0

9.2 ± 1.5

8.3 ± 1.2

AverageSample location. The size of red circle
indicates Cs137 deposition

The same composition can be assumed even though
the amounts of Cs137 are different.

4Our study before this year:
Cs137 deposition map based on NNSA aerial survey data

Helicopter survey byNNSA

Trajectories of air survey above Iitatevillage.
Green(plane): 15th April and 3rd MayBlack(helicopter): 1st April

Study before this year:
Estimation of initial Cs137 deposition for all housepositions in Iitate village

Cs137 counter map based on NNSA data

Study before this year:
Cs137 deposition distribution at 20 settlements inIitate village.
600Maximum 2.36 MBq/m2
Minimum 0.12 MBq/m2
Average 0.89 MBq/m2
Median 0.84 MBq/m2

Number of houses

500
400
300
200
100<10<20<30<40<50<60<70<80<90<100<110<120<130<140<150<160<170<180<190<200<210<220<230<240

0Cs137 deposition, ×10kBq/m2

Histogram of Cs137 deposition in Iitate village. 1768 houses.

1816
14

Okura 34 houses
Ave. 0.37M

120

Itamizawa 194 houses
Ave. 0.71M

100

12

戸数201510880
6061040452

200<10<20<30<40<50<60<70<80<90<100<110<120<130<140<150<160<170<180<190<200<210<220<230<2400<10<20<30<40<50<60<70<80<90<100<110<120<130<140<150<160<170<180<190<200<210<220<230<240

戸数25140×万Bq/m2

×万Bq/m2

0<10<20<30<40<50<60<70<80<90<100<110<120<130<140<150<160<170<180<190<200<210<220<230<2403020Nagadoro 68 houses
Average 1.9M

戸数35×万Bq/m2

Study before this year:
Cumulative exposure at 1 m above ground after deposition
Per 1 MBq/m2 of initial Cs137 depositionCumulative exposure at 1m aboveground, mGy

40

Te-132

I-132

Cs-134

Cs-137

I-131

30

20

100
1

16

31

46

61

76

91

106

Elapsed time after deposition, days
Cumulative radiation exposure at 1 m above ground after the radioactivity deposition on
May 15th per Cs137 deposition of 1 MBq/m2.

Assuming the deposition at 18:00 of March 15 at a time andstaying outside until 12:00 of June 30 (107 days after), thecumulative exposure is obtained to be 32.6 mGy.

8

Consequently,
individual external exposure can be
estimated with “reasonable grounds”only when we can get information about
personal behavior after the accident.

9Task of this year:
Iitate village initial dose assessment projectInterview by the project member with Iitate village
residents about behaviors of their family from theearthquake on March 11 up to July 31, 2011.
 Based on the interview information, individual doseis estimated to obtain the average exposure of Iitate
village as well as each settlement.
 Target number of interview is 500 (30 % of the wholevillage).
10

Project members for interview in 2013
Office address: Skae-machi 10-5, Fukushima city
Akashi S.

Reportage Institute

Sakuma J.

Rikkyo University

Ieda O.

Hokkaido University

Sawai M.

NPO CNIC

Ishida K.

Femin newspaper

Shiroshita H.

Kwansai University

Ichikawa K.

Office Brain Co. Ltd.

Sugai M.

Kokugakuin University

Itonaga K.

Nippon University

Sagawa Y.

Project staff

Uragami K.

Nippon University

Sawano N.

Kanazawa Seiryo University

Endo S.

Hiroshima University

Nasu K.

Fukushima-to-Iwaijima project

Ohtaki M.

Hiroshima University

Niwada S.

Reportage InstituteOzawa S.

NPO EAS

Hatakeyama H.

Freelance writer

Kamisawa C.

NPO CNIC

Hayasi G.

Tohoku University

Kawano N.

Hiroshima University

Furitsu K.

Hyogo College of Medicine

Kitoh S.

University of Tokyo

Watanabe M.

NPO CNIC

11

Project office was opened near JR
Fukushima station in July.
Approaching methods to Iitate residents.
 Letters were sent to 1680 Iitate families

asking to accept interview.
 Our member visited temporary housings totake interviews.
 Telephone call to Iitate residents asking

appointment for interview.
12

Example of interview sheet

Daily behavior was recorded about where they
were after the earthquake up to July 31th.
13

Total number of interview until October,31.
498 families; information on 1812 people
Percentage of interviewed families
Settlement

Number ofhouses

Number ofinterview％

Kusano221

6429.0%

Fukaya102

2019.6%

Itamizawa

1002626.0%Sekisawa

772735.1%

Komiya128

5139.8%

Yagisawa-Ashiwhara

40

1230.0%Okura

341235.3%Sasu

63

2133.3%

Miyauchi

72

2636.1%

Iitoimachi

1172723.1%

Maeda-Yawagi

90

2831.1%

Okubo-Sotouchi

681420.6%

Kami_iitoi

1243024.2%Hiso

882225.0%

Nagadoro

682841.2%

Warabidaira49

1632.7%

Sekine-Matsuzaka

43

1944.2%

Usuishi

881517.0%Maeda

532649.1%

Nimaibashi-Sugaya

60

1423.3%

Total

1,685

498

29.6%

20 settlements in Iitate

About 30 % of families in Iitate were interviewed. Big bias is notseen in values of interview fraction for 20 settlements.

14

Age structure of our interview and thewhole Iitate village>90 yr2%
80<90 yr
9%<10 yr9%10<20 yr
7%
20<30 yr
8%

70<80 yr
16%

30<40 yr
9%50<70 yr
15%
50<60 yr
17%

40<50 yr8%

Age structutre of interviewed 1812
people80< yr,11.0%<10 yr,
8.1%
10<20 yr,
9.1%

70<80 yr,
13.9%

20<30 yr,
8.2%
30<40 yr,
9.1%

60<70 yr,
13.4%
50<60 yr,
17.3%

40<50 yr,
9.9%

Age structure of whole Iitate village(March 1st, 2011: 6,132 people)

Age structure of our interview data is very
similar to the whole population in Iitate.

15

Assumptions used in the process converting
cumulative in-field exposure (air KERMA) to
external dose (effective dose)A transmission factor of 0.4 is applied to all houses inIitate.

People are supposed to stay outside and inside houses
for 8 hr and 16 hr, respectively.

Conversion factor of Gy to Sv is assumed to be 0.8 forages less than 10, while 0.7 is for ages more than 10 yrold.

Radiation exposure while they were outside or
evacuated from Iitate village was neglected for the time
being.
16

External dose distribution of 1812
persons we got behavior information200

All persons: 1812
Ave. 7.0 mSv

10050

<10yr

Number ofpeople
155

Average externaldose, mSv
3.8

1020 yr

128

5.1

2030 yr139

6.33040 yr

1715.54050 yr

151

7.65060 yr

315

8.16070 yr

262

8.57080 yr

292

7.5>80 yr

194

7.3

Age group

0~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~24

Number of persons

150

Average external dose by age group

Cumulative external dose up to July 31, 2011. mSv

The maximum value of 23.5 mSv was obtained by a male of 60’s
in Nagadoro settlement.

17

Dose distribution by age groups: less than 40 yr old
50

30<10 yr old: 155 persons
Ave. 3.8 mSv

10 - 20 yr old: 128 persons
Ave. 5.1 mSv

Number of persons

30

20

10020

10~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~24~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~24

0

Cumulative external dose up to July 31, 2011. mSv

Cumulative external dose up to July 31, 2011. mSv

30

30

30 - 40 yr old: 171 persons
Ave. 5.5 mSv
Number of persons

20

1020

1000~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~24

Number of persons

20 - 30 yr olld: 139 persons
Ave. 6.3 mSv

Cumulative external dose up to July 31, 2011. mSv~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~24

Number of persons

40

Cumulative external dose up to July 31, 2011. mSv

18

Dose distribution by age groups: over 40 yr old
305050 - 60 yr old: 315 persons
Ave. 8.1 mSv
40

20

Number of persons

1020

100~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~24~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~240

Cumulative external dose up to July 31, 2011. mSv

Cumulative external dose up to July 31, 2011. mSv

50

60

60 - 70 yr old: 262 persons
Ave. 8.5 mSv

50

Number of persons

40

30

20

10> 70 yr old: 486 persons
Ave. 7.5 mSv

4030

20

100~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~24

Number of persons

30

Cumulative external dose up to July 31, 2011. mSv

0~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~24

人umber of persons

40 - 50 yr old: 151 persons
Ave. 7.6 mSv

Cumulative external dose up to July 31, 2011. mSv

19Average dose by settlements
Settlement

Persons

Average Cs-137
contamination,
kBq/m2Averageexternal dose,mSv

Kusano203682

5.8

Fukaya71789

6.3

Itamizawa

96737

8.0

Sekisawa

77867

7.8

KomiyaYagisawaAshihara
Okura

182934

8.4

45546

5.8

50343

3.5

Sasu

76

491

4.6

Muyauchi

101

661

5.7

Iitoimachi

83730

5.8

Maeda-Yawagi

103

802

7.1

Okubo-Sotouchi

65736

6.0

Kami_iitoi

117

755

6.2

Hiso

72

1,087

11.0

Nagadoro

104

1,789

12.5

Warabidaira
SekineMatska
Usuishi

53

1,321

9.3

83

763

6.3

58746

8.1

Maeda
NimaibashiS ga a
Total persons

1206855.548396

3.51812814

7.0

20 settlements in Iitate

20Comparison of our results with that of Fukushima
Health Management Survey by Fukushima prefecture
700

3102 persons
Ave. 3.6 mSv

600

200

All persons: 1812
Ave. 7.0 mSv

500

Number of persons

Persons

150

400
300
200

100

50

100

12

3

4

5

6

78

9 10 11 12 13 14 15 >15

Cumulative external dose, mSv

Fukushima Health Management Survey:
Iitate village, cumulative dose up to July11, 2011.

~1~2~3~4~5~6~7~8~9~10~11~12~13~14~15~16~17~18~19~20~21~22~23~2400

Cumulative external dose up to July 31, 2011. mSv

Our results for 1812 persons
Up to July 31, 2011.

- Our average dose is about two times larger than Fukushima HealthManagement Survey.
- Considering the basic data used for dose estimation are different
each other, two times of dose difference is not serious.

21

People who evacuated just after the accident once returned home, and thenevacuated again after Iitate village was designated as the deliberately
evacuation zone on April 22, 2011.
% of people remaining in Iitate village

100All age: 1812 persons<10 yr old: 152 persons

80

60

40

200

Mar-11Mar-11

Apr-11

May-11

May-11

Jun-11

Jul-11

Jul-11

Fraction of residents who remain in Iitate village
22Collective external dose for 1812 persons
15Person‐Sv

All age: 1812 persons
105011‐Mar

31‐Mar

20‐Apr

10‐May30‐May19‐Jun9‐Jul29‐Jul

Accumulation of collective external dose, person‐Sv- Collective external dose for 1812 persons investigated amounted to be 12.6
person-Sv, which can be converted 42.7 person-Sv for the whole Iitate villageof 6132 persons.
- Assuming cancer-death risk coefficient of 0.055 Sv-1 by ICRP, 2.3 cases ofcancer deaths are expected in Iitate village due to external dose during theearly stage after the Fukushima-1 accident, while it increases up to 17 cases
23
when risk coefficient of 0.4 Sv-1 by J. Gofman is applied.

Uncertain factors - 1
NNSA deposition estimates vs. soil measurement data
1.E+07NNSA vs meaurement by MEXT

Soil measurement, Bq/m2

NNSA vs measurement by Imanaka et al

1.E+06

1.E+05
1.E+05

1.E+06

1.E+07NNSA interpolation、Bq/m2

Compared with soil measurements by MEXT (53 points), Cs-137
contamination from NNSA data gave larger values at certain points,
while it agreed with measurement by Imanaka et al (11 points). Blue24
dot lines indicate ratio=2 or ½.

Uncertain factor - 2
Dose rate distribution outside and inside a typicalJapanese one-story wooden house in Iitate village

Sv/hA transmission factor of 0.4 seems to be reasonable.

Uncertain factor - 3
Time fraction staying inside and outside houses
Example of three males in Komiya settlement＜average time spent per day outside houses＞
Mr. I

Mr. M

Mr. F

March 2011

6.6 hr8.7 hr

4.5 hrApril 2011

5.3 hr

8.0 hr

4.2 hrMay 2011

6.4 hr

5.0 hr

3.3 hr<Average>

6.1 hr

7.2 hr

4.0 hrOur assumption of 8 hr is likely to be overestimated.
26

Direct comparison of dose estimates: our results vs.
Fukushima Health Management Survey for 73 persons

FHMS's estimates, mSv

30

20

1000

1020
Our estimates, mSv

3027

Summary
So far, 498 interviews were taken from Iitate resident
about behaviors of their families until July 31, 2011. In
total behavior information on 1,812 persons (about 30 %of the whole residents) was obtained.


Average cumulative external dose of 7.0 mSv wasevaluated until July 31, 2011 in Iitate village.
Biases related with settlements and age groups were notrecognized.

Our average is are about two times larger than that of FHMS, thereason of which is investigated.

Collective external dose of 43 person-Sv was estimatedfor the total residents inIitate village.
Based on “LNT theory” 2 – 17 cases of cancer deaths areexpected among 6,132 residents in Iitate village.

(Internal dose is not evaluated and will be our future task.) 28