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 27 Sep 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 June-2024 July-2024 August-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 1 1
5<E≤10 0 28 28 0 42 42 0 24 24
1<E≤5 18 529 547 16 424 440 14 349 363
E≤1 1024 6201 7225 923 6308 7231 964 6084 7048
Total 1042 6758 7800 939 6774 7713 978 6458 7436
Maximum(mSv) 3.80 7.70 7.70 4.20 9.40 9.40 2.69 11.24 11.24
Average(mSv) 0.08 0.31 0.28 0.08 0.29 0.26 0.07 0.22 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 - July 2024 April 2021 - August 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 19 19 0 29 29 0 10 10
20<E≤50 27 1144 1171 27 1154 1181 0 10 10
10<E≤20 60 1770 1830 64 1788 1852 4 18 22
5<E≤10 121 1581 1702 121 1596 1717 0 15 15
1<E≤5 364 2727 3091 367 2760 3127 3 33 36
E≤1 1272 8351 9623 1292 8404 9696 20 53 73
Total 1844 15592 17436 1871 15731 17602 27 139 166
Maximum(mSv) 31.92 57.52 57.52 32.08 58.51 58.51 - - -
Average(mSv) 1.86 5.12 4.78 1.87 5.17 4.82 - - -

(*) 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 - July 2024 April 2024 - August 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 44 44 0 78 78 0 34 34
5<E≤10 4 349 353 7 441 448 3 92 95
1<E≤5 73 1244 1317 97 1383 1480 24 139 163
E≤1 1174 6487 7661 1199 6477 7676 25 -10 15
Total 1251 8124 9375 1303 8379 9682 52 255 307
Maximum(mSv) 6.30 14.80 14.80 6.60 15.72 15.72 - - -
Average(mSv) 0.24 0.87 0.78 0.28 1.01 0.91 - - -
(*)
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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