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information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise

Radiation doses

Survey reveals radiation doses / 58% of Fukushima residents likely exposed to less than 1 millisievert

FUKUSHIMA--About 58 percent of Fukushima Prefecture residents were likely externally exposed to radiation measuring less than 1 millisievert during the first four months of the Fukushima nuclear crisis, according to a survey released Monday by the prefectural government.


The prefectural government released its estimate of the external radiation doses of 10,468 people. The prefecture has a population of about 2 million people.


Of 9,747 people, excluding workers at the crippled Fukushima No. 1 nuclear power plant, 57.8 percent were estimated to have been exposed to levels less than 1 millisievert--which is considered the annual limit of radiation exposure under normal circumstances--during the first four months, according to the survey.

The survey found 94.6 percent of residents were considered to have been exposed to less than 5 millisieverts of radiation.


Only two women were estimated to have been exposed to radiation levels exceeding 20 millisieverts.

The main reason behind the two women's high exposure level is that the two stayed in the expanded evacuation zone--the area spanning five municipalities beyond a 20-kilometer radius around the power plant--for more than three months.


One of the women is thought to have been exposed to 23 millisieverts of radiation, the highest among people who did not work at the nuclear plant.


Among 1,693 people under 20 years old who were surveyed, one male was estimated to have been exposed to 18.1 millisieverts, but all others were exposed to less than 10 millisieverts.


Among workers at the nuclear plant, the highest level was 47.2 millisieverts.


"In past epidemiological examinations, obvious health effects have not been observed with cumulative doses of 100 millisieverts or less. The results of the survey show the level of radiation exposure will not likely impact residents' health," an official of the prefecture said.


A total of 431,720 people, or 21 percent of Fukushima residents, responded to the questionnaire by the end of January.

The released results are from 10,468 out of 29,103 residents in Iitate, Namie and the Yamakiya district of Kawamata, which are designated as expanded evacuation zones, and the no-entry zone within 20 kilometers of the nuclear plant.

Residents in these areas were surveyed before residents in other areas.


Based on the survey results, the estimated external exposure levels were calculated according to time-series data on air radiation levels at various locations.


Residents were asked to recall where they stayed and what they did for the first four months of the nuclear crisis that began soon after the March 11 earthquake and tsunami.


The data was calculated using the Education, Culture, Sports, Science and Technology Ministry's monitoring survey results and the System for Prediction of Environmental Emergency Dose Information (SPEEDI), the government's computer system that simulates the dispersal of radioactive substances.

(Feb. 21, 2012)

40% of residents' exposure tops annual limit



More than 40 percent of the people surveyed in 3 municipalities near the Fukushima Daiichi nuclear plant were exposed to radioactivity levels above the annual safety limit in the 4 months after the disaster.

Fukushima Prefecture released on Monday the results of its survey of external radioactive exposure among some 9,750 residents of 2 towns and a village after the accident last March. This number excluded people working in places with high radioactivity, such as a nuclear plant.

Participants were asked about their behavior over a 4-month period immediately following the nuclear accident in order to estimate their external exposure.

Forty-two percent of the respondents are estimated to have received more than one millisievert --- the annual limit for the general public --- in the 4 months following the disaster.

Estimated exposure exceeded 10 millisieverts for 71 people. The highest dose was 23 millisieverts for an adult woman.

Among young people under the age of 20 at the time of the accident, the highest exposure was 18.1 millisieverts over 4 months.

The prefecture is conducting the survey on all its 2 million residents.

Fukushima residents exposed to up to 23 millisieverts of radiation


The government's new radiation contamination map site is seen in this screen capture taken on Oct. 18. (Mainichi)

The government's new radiation contamination map site is seen in this screen capture taken on Oct. 18. (Mainichi)

FUKUSHIMA (Kyodo) -- The Fukushima Prefecture government said Monday residents of three municipalities near the crippled Fukushima Daiichi nuclear power plant are estimated to have been exposed to up to 23 millisieverts of radiation in the four months after the accident caused by the March 11 earthquake and tsunami.

"As annual radiation exposure of up to 100 millisieverts poses no specific cancer risks, the estimated radiation is unlikely to cause any adverse health effect," Fukushima Medical University Vice President Shunichi Yamashita told a press conference. "It is important to reduce future radiation exposure as much as possible."

While the allowable radiation exposure limit is set ordinarily at 1 millisievert per year, the International Commission on Radiological Protection has recommended an emergency limit of 20 to 100 millisieverts.

Of 9,474 residents, excluding nuclear plant workers, in Namie, Kawamata and Iitate, 5,636 persons, or 57.8 percent, were exposed to radiation of less than 1 millisieverts during the four months, the local government said.

Those exposed to radiation of 1 to less than 10 millisieverts totaled 4,040 persons, or 41.4 percent.

Some 71 people were exposure to 10 millisieverts or more, including two people exposed to more than 20 millisieverts. The maximum exposure was 23 millisieverts.

Radiation of 20 millisieverts was adopted as the standard for designating the planned evacuation zone -- outside the 20-kilometer emergency evacuation zone around the Fukushima Daiichi plant.

Including nuclear plant workers, the number of residents of the three municipalities exposed to 10 millisieverts or more of radiation totaled 95 people. The maximum exposure among that larger group was estimated at 47.2 millisieverts.

The prefectural government is now conducting a health survey of all its approximately 2 million residents. They were sent questionnaires, asking where they were after the nuclear crisis began and how they acted since then.

However, only 52.1 percent of the questionnaires sent to the residents of the three municipalities, and 21 percent of all the questionnaires sent throughout the prefecture, had been collected as of the end of January, according to the local government.



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