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 28 Jun 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 March-2024 April-2024 May-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 0 0 0 0 0
5<E≤10 0 37 37 0 24 24 0 22 22
1<E≤5 12 440 452 11 370 381 11 354 365
E≤1 1005 6422 7427 1003 6031 7034 949 6157 7106
Total 1017 6899 7916 1014 6425 7439 960 6533 7493
Maximum(mSv) 3.90 8.60 8.60 3.00 8.80 8.80 3.66 7.02 7.02
Average(mSv) 0.08 0.28 0.26 0.07 0.25 0.22 0.08 0.21 0.20

(*)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 - April 2024 April 2021 - May 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 2 2 0 4 4 0 2 2
20<E≤50 25 1028 1053 26 1060 1086 1 32 33
10<E≤20 53 1713 1766 56 1740 1796 3 27 30
5<E≤10 111 1580 1691 115 1566 1681 4 -14 -10
1<E≤5 364 2655 3019 365 2674 3039 1 19 20
E≤1 1204 7970 9174 1200 8119 9319 -4 149 145
Total 1757 14948 16705 1762 15163 16925 5 215 220
Maximum(mSv) 31.42 51.92 51.92 31.52 53.42 53.42 - - -
Average(mSv) 1.82 4.98 4.65 1.86 5.00 4.67 - - -

(*) 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 April 2024 - May 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 0 0 0 6 6 0 6 6
5<E≤10 0 24 24 0 92 92 0 68 68
1<E≤5 11 370 381 32 663 695 21 293 314
E≤1 1003 6031 7034 1070 6378 7448 67 347 414
Total 1014 6425 7439 1102 7139 8241 88 714 802
Maximum(mSv) 3.00 8.80 8.80 3.76 12.52 12.52 - - -
Average(mSv) 0.07 0.25 0.22 0.13 0.42 0.38 - - -
(*)
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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