Ministry of Health, Labour and Welfare

Ministry of Health, Labour and Welfare

In Focus: Radiation Protection at Works Relating to TEPCO's Fukushima Daiichi Nuclear Power Plant Accident

Exposure Dose Distribution of the Workers at Fukushima Daiichi Nuclear Power Plant

Updated on 30 Oct 2024

1. Radiation Exposure Dose Distributions

(1)The distribution of external exposure dose of the workers during the last 3 months
(Numbers of workers who entered each area every month)
Effective dose (E) mSv July-2024 August-2024 September-2024
TEPCO Contractors Total TEPCO Contractors Total TEPCO Contractors Total
100<E 0 0 0 0 0 0 0 0 0
75<E≤100 0 0 0 0 0 0 0 0 0
50<E≤75 0 0 0 0 0 0 0 0 0
20<E≤50 0 0 0 0 0 0 0 0 0
10<E≤20 0 0 0 0 2 2 0 0 0
5<E≤10 0 42 42 0 25 25 0 10 10
1<E≤5 16 424 440 13 347 360 11 376 387
E≤1 923 6308 7231 965 6084 7049 981 6149 7130
Total 939 6774 7713 978 6458 7436 992 6535 7527
Maximum(mSv) 4.20 9.40 9.40 2.70 11.10 11.10 1.67 7.20 7.20
Average(mSv) 0.08 0.29 0.26 0.07 0.23 0.21 0.06 0.22 0.19

(*)Exposure doses and the number of workers are subject to change due to the replacement of accumulated doses measured using PAD with monthly doses measured using an integrating dosimeter and the reflection of values for workers wearing only an integrating dosimeter (e.g., workers working only within a seismically isolated building).

(2)Combined Cumulative Effective Dose from April 2021 (Internal and External)
Effective dose (E) mSv April 2021 - August 2024 April 2021 - September 2024 Difference
TEPCO Contractors Total TEPCO Contractors Total TEPCO Contractors Total
100<E 0 0 0 0 0 0 0 0 0
75<E≤100 0 0 0 0 0 0 0 0 0
50<E≤75 0 29 29 0 40 40 0 11 11
20<E≤50 27 1155 1182 27 1173 1200 0 18 18
10<E≤20 64 1786 1850 65 1799 1864 1 13 14
5<E≤10 120 1600 1720 124 1623 1747 4 23 27
1<E≤5 366 2744 3110 366 2773 3139 0 29 29
E≤1 1294 8417 9711 1302 8487 9789 8 70 78
Total 1871 15731 17602 1884 15895 17779 13 164 177
Maximum(mSv) 32.12 58.52 58.52 32.21 59.44 59.44 - - -
Average(mSv) 1.87 5.17 4.82 1.89 5.21 4.86 - - -

(*) Exposure doses and the number of workers are subject to change due to the replacement of accumulated doses measured using PAD with monthly doses measured using an integrating dosimeter and the reflection of values for workers wearing only an integrating dosimeter (e.g., workers working only within a seismically isolated building).

(3) Combined Cumulative Effective Dose from April 2024
Effective dose (E) mSv April 2024 - August 2024 April 2024 - September 2024 Difference
TEPCO Contractors Total TEPCO Contractors Total TEPCO Contractors Total
100<E 0 0 0 0 0 0 0 0 0
75<E≤100 0 0 0 0 0 0 0 0 0
50<E≤75 0 0 0 0 0 0 0 0 0
20<E≤50 0 0 0 0 0 0 0 0 0
10<E≤20 0 78 78 0 115 115 0 37 37
5<E≤10 7 446 453 9 564 573 2 118 120
1<E≤5 93 1334 1427 113 1499 1612 20 165 185
E≤1 1203 6521 7724 1204 6494 7698 1 -27 -26
Total 1303 8379 9682 1326 8672 9998 23 293 316
Maximum(mSv) 6.60 15.50 15.50 7.49 15.50 15.50 - - -
Average(mSv) 0.29 1.02 0.92 0.33 1.15 1.04 - - -
(*)
Exposure doses and the number of workers are subject to change due to the replacement of accumulated dosesmeasured using PAD with monthly doses measured using an integrating dosimeter and the reflection of values for workers wearing only an integrating dosimeter (e.g., workers working only within a seismically isolated building).
(4) Distribution of sum of external exposure dose and internal exposure dose of workers engaged in specified high-dose work*
(Specified high-dose work has not been performed since October 2015.)
Effective dose (E) mSv March 2011- September 2015
100<E 1
75<E≤100 191
50<E≤75 233
20<E≤50 267
10<E≤20 186
5<E≤10 129
1<E≤5 145
E≤1 51
Total 1203
Maximum(mSv) 102.69
Average(mSv) 36.49

(As specified high-dose work has not been performed since October 2015, the table shows the data up to September 2015.)

(*)
Workers engaged in work to which dose limit (100 mSv) during emergency work is applied in line with Article 7 of the Ordinance on Prevention of Ionizing Radiation Hazards.
Specifically, these workers are those who are engaged in work to maintain the functions of a nuclear reactor facility or spent fuel storage pool, or in work to maintain functions to suppress or prevent the possible release of a large amount of radioactive materials due to a failure of or damage to the nuclear reactor facility at a location around the nuclear reactor facility, steam turbine, or accessory facility where hourly dose may exceed 0.1 mSv.
It should be noted that only TEPCO employees have so far been engaged in specified high-dose work.
(*)
The number of workers engaged in specified high-dose work is that of workers who were registered as such at least once during the period between March 2011 and September 2015.
(*)
Exposure doses and the number of workers are subject to change due to the replacement of accumulated doses measured using PAD with monthly doses measured using an integrating dosimeter and the reflection of values for workers wearing only an integrating dosimeter (e.g., workers working only within a seismically isolated building).
(*)
The results of re-evaluating committed doses in March 2011 reveal that maximum cumulative effective doses for the period between March 2011 and September 2015 exceeded 100.
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