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 Apr 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 January-2024 February-2024 March-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 4 4 0 0 0
5<E≤10 0 18 18 0 35 35 0 41 41
1<E≤5 9 380 389 3 468 471 11 463 474
E≤1 984 6457 7441 1041 6460 7501 1006 6395 7401
Total 993 6855 7848 1044 6967 8011 1017 6899 7916
Maximum(mSv) 1.90 8.00 8.00 1.90 10.80 10.80 4.02 7.84 7.84
Average(mSv) 0.06 0.24 0.22 0.06 0.30 0.26 0.08 0.28 0.25

(*)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 - February 2024 April 2021 - March 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 1 1 0 1 1 0 0 0
20<E≤50 21 956 977 22 994 1016 1 38 39
10<E≤20 54 1648 1702 55 1694 1749 1 46 47
5<E≤10 99 1570 1669 105 1574 1679 6 4 10
1<E≤5 351 2640 2991 360 2661 3021 9 21 30
E≤1 1224 7728 8952 1211 7822 9033 -13 94 81
Total 1749 14543 16292 1753 14746 16499 4 203 207
Maximum(mSv) 30.52 50.72 50.72 31.07 50.72 50.72 - - -
Average(mSv) 1.74 4.87 4.54 1.79 4.94 4.60 - - -

(*) 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 2023
Effective dose (E) mSv April 2023 - February 2024 April 2023 - March 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 3 705 708 5 810 815 2 105 107
5<E≤10 24 1101 1125 28 1145 1173 4 44 48
1<E≤5 161 2082 2243 184 2153 2337 23 71 94
E≤1 1214 6397 7611 1199 6421 7620 -15 24 9
Total 1402 10285 11687 1416 10529 11945 14 244 258
Maximum(mSv) 11.70 16.80 16.80 13.92 17.01 17.01 - - -
Average(mSv) 0.54 2.26 2.05 0.59 2.39 2.18 - - -
(*)
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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