The government withheld findings on estimated radiation exposure for Fukushima returnees for six months, even though levels exceeded the long-term target of 1 millisievert a year at more than half of surveyed locations.
Individual radiation doses were estimated to be beyond 1 millisievert per year, or 0.23 microsievert an hour, at 24 of all the 43 surveyed sites, including ones in the Miyakoji district in Tamura, Fukushima Prefecture, The Asahi Shimbun learned April 15.
The revelation comes just two weeks after the central government lifted the evacuation order for the district on April 1.
Last July, the Cabinet Office’s working team in charge of assisting the lives of nuclear disaster victims asked the National Institute of Radiological Sciences and the Japan Atomic Energy Agency to measure air dose rates and estimate individual radiation doses at 43 locations.
The survey covered seven types of living spaces, including private residences, farmland and schools, in the prefecture’s three municipalities of Tamura, Kawauchi and Iitate.
The government’s decontamination work aims at bringing radiation levels in contaminated areas to within 20 millisieverts a year before it gives the go-ahead for residents to return.
It also intends to bring readings to 1 millisievert or less eventually. The International Commission on Radiological Protection says a reading of up to 20 millisieverts is acceptable in areas where cleanup is under way.
The central government has also proposed to distribute devices that measure individual radiation to returned evacuees, so residents can monitor their radiation doses on their own.
But some evacuees from areas affected by the Fukushima No. 1 plant nuclear accident, which was triggered by the 2011 earthquake and tsunami disaster, worry about the possibility they may be exposed to high radiation doses after returning to their homes.
For this reason, the government decided to study correlations between air dose rates and individual radiation doses around the crippled facility to prove that the amount of radiation to which residents will be exposed is sufficiently low, even when air dose rates are relatively high.
The National Institute of Radiological Sciences and the Japan Atomic Energy Agency last fall measured radiation levels at several dozens of spots at each of the 43 sites in the three municipalities. They found that individual radiation doses are typically 30 percent lower than air dose rates.
The government-affiliated bodies also discovered that average air dose rates exceeded 0.23 microsievert per hour at 27 of the 43 sites, while they estimated individual radiation doses at over 0.23 microsievert an hour at 24 locations.
In mid-October, the two agencies compiled a midterm report and submitted it to the government. But the Cabinet Office’s working team did not disclose the report until the evacuation order for the Miyakoji district was lifted. According to a member of the team, this was because the finding “has no direct relationship with lifting the evacuation orders.”
Although the government held numerous meetings with Miyakoji residents to discuss lifting the evacuation order, it never presented the survey results, nor did it even refer to the existence of the data.
The government only presented an outline of the results to the three municipalities earlier in April.
Asked to disclose the findings, the government released the survey results to The Asahi Shimbun and posted the midterm report on the website of the industry ministry.
The working team said it planned to reveal the survey’s findings and analysis of the data on April 18 after fine-tuning its final report. But the team changed its mind because The Asahi Shimbun’s request to disclose the findings made it realize that public interest in the survey was greater than expected.