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 31 May 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 February-2024 March-2024 April-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 4 4 0 0 0 0 0 0
5<E≤10 0 35 35 0 37 37 0 27 27
1<E≤5 3 468 471 12 440 452 12 367 379
E≤1 1041 6460 7501 1005 6422 7427 1003 6031 7034
Total 1044 6967 8011 1017 6899 7916 1015 6425 7440
Maximum(mSv) 1.90 10.80 10.80 3.90 8.60 8.60 3.22 8.90 8.90
Average(mSv) 0.06 0.30 0.26 0.08 0.28 0.26 0.07 0.24 0.22

(*)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 - March 2024 April 2021 - April 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 2 2 0 1 1
20<E≤50 22 993 1015 25 1028 1053 3 35 38
10<E≤20 55 1689 1744 54 1714 1768 -1 25 24
5<E≤10 106 1576 1682 110 1585 1695 4 9 13
1<E≤5 358 2647 3005 367 2657 3024 9 10 19
E≤1 1212 7840 9052 1201 7962 9163 -11 122 111
Total 1753 14746 16499 1757 14948 16705 4 202 206
Maximum(mSv) 31.12 50.82 50.82 31.36 51.88 51.88 - - -
Average(mSv) 1.79 4.94 4.60 1.83 4.97 4.64 - - -

(*) 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
TEPCO Contractors Total
100<E 0 0 0
75<E≤100 0 0 0
50<E≤75 0 0 0
20<E≤50 0 0 0
10<E≤20 0 0 0
5<E≤10 0 27 27
1<E≤5 12 367 379
E≤1 1003 6031 7034
Total 1015 6425 7440
Maximum(mSv) 3.22 8.90 8.90
Average(mSv) 0.07 0.24 0.22
(*)
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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