Overview of the Radiation Exposure Doses of the Workers at Fukushima Daiichi Nuclear Power Station

Transcription

1 Click here for the corrections made < Reference > December 3, 212 Tokyo Electric Power Company Overview of the Radiation Exposure Doses of the Workers at Fukushima Daiichi Nuclear Power Station * As of December 212, the radiation exposure doses of all workers who engaged in work at Fukushima Daiichi Nuclear Power Station after the accident are still being examined. Thus, the data presented in this document is subject to change. 1

2 (Reference) Radiation Exposure Dose Limit for the Workers FY 21 Mar. 11 FY 211 Dec. 16 Step II completed FY 212 FY 213 FY 214 FY 215 Exposure dose limit Exposure dose limit in emergency 25mSv Exposure dose limit at normal times 5mSv/year and 1mSv/5 years (until 215) Limit 1 Exposure dose limit in emergency Workers exposed to specially high radiation dose: 1mSv Limit 2 Examples Worker A: Exposure dose exceeded 1mSv after emergency work Dismissed Not allowed to work after Step II 12mSv (For example) Worker B: Exposure dose below 1mSv after emergency work Normal operation: Limit 1 is applied (5mSv/year and 6mSv left until 215) 4mSv (For example) Operation which involves specially high radiation dose: Worker C: Engage in work after step II Limit 2 is applied (6mSv left) Normal operation: Limit 1 is applied (5mSv/year and 1mSv left until 215) Operation which involves specially high radiation dose: Limit 2 is applied (Less than 1mSv) 2

3 1-1 Cumulative Radiation Exposure Doses of Radiation Workers from Cooperative Companies (Cumulative Amount since March 11, 211) Time period: March 11, 211 to August 31, Cooperative company workers Number of workers The majority of workers fall into low radiation exposure dose level Exposure msv dose limit: 1mSv/5years Cumulative radiation exposure dose (msv) * The number of workers was counted in a unit of 1mSv (For example, approx. 2,2 workers fall into the range of 1mSv to 2mSv. Those with msv are counted as 1mSv.) 3

4 1-1 Breakdown Time period: March 11, 211 to August 31, Classification (msv) 25 and up 1 and less Total (Number of workers) Max. (msv) Ave. (msv) Number of cooperative company workers Exposure dose limit until the start of Step II: 25mSv No worker falls into the range Exposure dose limit after Step II: 1mSv/5years 21 workers who engaged in work right after the accident Of Of the the 2,171 2,171 workers who who engaged in in work work during during the the period period from from March March 11, 11, to to August August 31, 31, 212, 212, 2,15 2,15workers (99.9%): 1mSv or or less less 19,725 19,725workers (97.8%): 5mSv 5mSv or or less less (Cumulative) (Cumulative) 4

5 1-2 Radiation Exposure Dose Distribution among Workers Dismissed from Radiation Work (Cumulative Dose since March 11, 211) The exposure dose distribution among the workers dismissed from Fukushima Daiichi Nuclear Power Station is provided below. Workers dismissed during the period from March 11, 211 to August 31, Cooperative company workers Similar tendency as the workers still in operation Number of workers Exposure dose limit: msv 5mSv/year Exposure msv dose limit: 1mSv/5years 21 workers who engaged in work 1mSv right after the accident exceeded 21 the limit of 1mSv Cumulative radiation exposure dose (msv) 5

6 1-2 Breakdown Workers dismissed during the period from March 11, 211 to August 31, and up Classification (msv) 1 and less Total (Number of workers) Max. (msv) Ave. (msv) Number of cooperative company workers Exposure dose limit until the start of Step II: 25mSv Exposure dose limit after Step II: 1mSv/5years Similarly to to the the overall overall results, results, the the majority of of the the dismissed workers fall fall into into low low exposure dose dose level. level. Of Of the the 14,158 14,158 workers who who engaged in in work work during during the the period period from from March March 11, 11, to to August August 31, 31, 212, 212, 14,137 14,137 (99.9%): 1mSv or or less less 13,877 13,877 (98.%): 5mSv 5mSvor or less less (Cumulative) (Cumulative) 6

7 p g from Radiation Work (Cumulative Dose since March 11, 211) Exposure dose distribution (cumulative dose since March 11, 211) among the dismissed workers Ratio of each classification Cumulative ratio Exposure dose limit: 1mSv/5years 7 * Ratio Substantial margin to the exposure dose limit mSv or less 5mSv-1mSv mSv-15mSv mSv-2mSv mSv-25mSv mSv-3mSv mSv-35mSv mSv-4mSv mSv-45mSv.92 45mSv-5mSv.77 5mSv-55mSv *Ratio (%) = [Number of dismissed workers in each classification] / [Number of all dismissed workers] x 1 As for the 21 workers who engaged in work right after the accident, the exposure dose exceeded 1mSv. The exposure doses of 99.9% of all workers are 1mSv or less and 98.% of all workers are 5mSv or less. Though there are some workers with high exposure dose due to the emergency work they engaged in right after the accident, the doses of most workers have a substantial margin to the dose limit mSv-6mSv.47 6mSv-65mSv.22 65mSv-7mSv.15 7mSv-75mSv.12 75mSv-8mSv.16 8mSv-85mSv.5 85mSv-9mSv.6 9mSv-95mSv.5 95mSv-1mSv mSv or more 7

8 1-4 Cumulative Exposure Dose after the Accident --The majority of of the workers were dismissed with exposure dose substantially lower than the dose limit stipulated by by law, and therefore are still capable of of engaging in in radiation work. --Of Of the dismissed workers with exposure dose exceeding 1mSv or or close to to the dose limit stipulated by by law (exceeding 75mSv), 1 1 workers are still employed in in locations other than Fukushima Daiichi Nuclear Power Station. (Source: (Source: Interview Interview with with the the main main contractor contractor regarding regarding the the workers workers dismissed dismissed by by July July 31, 31, As As of of November November 212) 212) 8

9 2-1 Reduction in Radiation Exposure Dose per Month since the Accident (Monthly Average Dose) Monthly average exposure dose (msv)* mSv Exposure dose limit: 25mSv Monthly average exposure dose Equivalent to 2mSv/year Completion of Step II Exposure dose limit: 5mSv/year Monthly maximum exposure dose Monthly maximum exposure dose (msv) Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Jul Aug. Sep. *Average exposure dose = Total exposure dose in a given month / Number of workers who engaged in work in the month After Step II, the monthly average exposure dose and the monthly maximum exposure dose have been significantly reduced compared to right after the accident. 9

10 2-2 Change in the Monthly Average Exposure Dose (Close-up on lower dose level) Monthly average exposure dose (msv)* 1.6mSv Monthly average exposure dose Equivalent to 2mSv/year Completion of Step II Monthly maximum exposure dose Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep *Average exposure dose = Total exposure dose in a given month / Number of workers who engaged in work in the month After Step II, the monthly average exposure dose has been kept under 2mSv/year (1.6mSv/month). In FY 212 second quarter, the monthly average exposure dose was approx. 1mSv. In order to evaluate the current condition, the exposure dose distribution among workers who engaged in work in FY 212 is summarized. Monthly maximum exposure dose (msv) 1

11 3-1 Current Condition (Cumulative Radiation Exposure Doses of the Radiation Workers from Cooperative Companies, FY 212) Time period: From April 1 to August 31, 212 (5 months) 3 25 Cooperative company Number of workers Exposure dose limit: 5mSv/year Cumulative exposure dose (msv) 11

12 3-1 Breakdown Time period: From April 1 to August 31, 212 (5 months) Classification (msv) 5 and up or less Total (Number of workers) Max. (msv) Ave. (msv) Number of cooperative company workers Exposure dose limit per year: 5mSv No worker falls into the range. Exposure dose equivalent to 5 months of the dose limit per year (5mSv): 5mSv x 5/12 months 2mSv 167 workers Of Of the the 7,175 7,175 workers who who engaged in in work work in in FY FY (April (April to to August), 7,548 7,548 (97.8%): 2mSv 2mSvor or less less Given Given that that the the exposure dose dose equivalent to to 5 months months of of 2mSv/year is is 8.4mSv, 5,581 5,581 (72.3%): 5mSv 5mSvor or less less (Cumulative) (Cumulative) 12

13 3-2 Radiation Exposure Dose Distribution Among the Dismissed Workers (Cumulative Exposure Dose in FY 212) Target: Workers dismissed during the period from April 1 to August 31, 212 (5 months) 3 Cooperative company Number of workers Exposure dose limit: 5mSv/year Cumulative exposure dose (msv) 13

14 3-2 Breakdown Classification (msv) 5 and up or less Total (Number of workers) Max. (msv) Ave. (msv) Number of cooperative company workers Exposure dose limit per year: 5mSv No worker falls into the range. Exposure dose equivalent to 5 months of the dose limit per year (5mSv): 5mSv x 5/12 months 2mSv 77 workers Similarly to to the the overall overall results, results, the the majority of of the the dismissed workers fall fall into into low low exposure dose dose level. level. Of Of the the 2,4 2,4 dismissed workers, 2,323 2,323 (96.8%): 2mSv 2mSvor or less less Given Given that that the the exposure dose dose equivalent to to 5 months months of of 2mSv/year is is 8.4mSv, 1,922 1,922 (8.1%): 5mSv 5mSvor or less less (Cumulative) (Cumulative) 14

15 3-3 Radiation Exposure Dose Distribution Among the Dismissed Workers (Cumulative Exposure Dose in FY 212) Cumulative exposure doses in FY 212 among the dismissed workers (5 months) Exposure dose limit: 5mSv/year Ratio of each classification Cumulative ratio 7 Ratio* mSv or less 5mSv-1mSv mSv-15mSv mSv-2mSv mSv-25mSv Substantial margin to the exposure dose limit 2mSv 5mSv 5/12 months 2mSv mSv-3mSv.92 3mSv-35mSv Max. 36mSv.83 35mSv-4mSv.21 4mSv-45mSv 45mSv-5mSv 5mSv-55mSv 55mSv-6mSv 6mSv-65mSv 65mSv-7mSv 7mSv-75mSv 75mSv-8mSv 8mSv-85mSv 85mSv-9mSv 9mSv-95mSv 95mSv-1mSv 1mSv or more *Ratio (%) = [Number = of dismissed workers in each classification] 1 / [Number of all dismissed workers] x The exposure dose was 2mSv or less for 97% of all the dismissed workers. 15

16 3-4 Comparison between FY 212 First and Second Quarters The table below shows the comparison between the first quarter (April to June) and the second quarter (July to September) of FY 212. Second quarter (Number of workers) Did not work 5mSv or less 5-1mSv 1-15mSv 15-2mSv 2-25mSv 25-3mSv Total First quarter (Number of workers) 35-4mSv 2 2 Range exceeding 3-35mSv 11 the exposure dose mSv limit mSv mSv mSv mSv mSv or less Did not work Total There is no worker with exposure dose close to the limit. - The workers with high exposure dose in the first quarter tend to have low exposure dose in the second quarter and vice versa. Workers are put on rotation between high and low exposure operations. 16

17 3-5 Current Condition --After Step Step II, II, the the monthly average exposure dose has has been kept kept under 2mSv/year (1.6mSv/month), and and was was approx. 1mSv in in FY FY second quarter. --The The majority of of the the workers were dismissed with with exposure dose substantially lower than than the the dose limit limit stipulated by by law, law, and and therefore are are still still capable of of engaging in in radiation work. --Based on on the the exposure doses in in the the first first and and the the second quarters, workers seem to to be be put put on on rotation between high high and and low low exposure operations. --Of Of the the 5 5 dismissed workers with with exposure dose exceeding 2mSv, workers are are still still employed in in locations other than than Fukushima Daiichi Nuclear Power Station. (Source: Interview with with the the main contractor regarding the the workers dismissed by by the the end end of of July. July. As As of of November 212) 17

18 4. Summary Overall, the radiation exposure condition in the power station has improved. - Looking at the exposure doses of workers who engaged in work after the accident, there is a substantial margin to the dose limit (1mSv) for most workers. - After Step II, there is also a large margin to the dose limit of 5mSv/year. - The monthly average exposure dose has been kept under 2mSv/year (1.6mSv/month) since the start of Step II. - Though it is still necessary to continue considering work allocation/rotation, the current condition allows for exposure dose reduction. The The majority of of the the workers were were dismissed with with exposure dose dose substantially lower lower than than the the dose dose limit limit stipulated by by law, law, and and therefore are are still still capable of of engaging in in radiation work. work. We will continue our efforts in reducing exposure dose in the work environment and monitor workers exposure doses. 18