information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise
10 Mai 2013
May 10, 2013
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May 10, 2013
Chaos reigned during the early phase of the Fukushima nuclear disaster, and people who fled the area have no idea how much radiation they were exposed to before the evacuation. But a scientist has come up with a novel approach to better evaluate their radiation doses by utilizing the logs of GPS-equipped cellphones.
Ryugo Hayano, a physics professor at the University of Tokyo, said he got the idea when he learned that Zenrin DataCom Co., a geographical information service firm, had acquired anonymous-format location logs of Global Positioning System-enabled cellphones with the consent of their users.
He and a co-worker estimated the flow of evacuees on an hour-by-hour basis by using logs of users who were in Fukushima Prefecture when the nuclear crisis began to unfurl. Those users account for roughly 0.7 percent of the entire population of Fukushima Prefecture.
The data shows how people ebbed away from the areas surrounding the stricken Fukushima No. 1 nuclear power plant after the crisis was triggered by the Great East Japan Earthquake and tsunami on March 11, 2011. The number of people continued to decrease as the central government expanded the target area of its evacuation orders from the initial 3-kilometer radius to 10 km and, finally, to 20 km.
While an estimated 76,000 people stayed within a 20-km radius of the nuclear plant before the disaster, that number plummeted to about 2,000 on the fifth day of the crisis. These observations are largely consistent with findings of a study by the National Diet's Fukushima Nuclear Accident Independent Investigation Commission.
The reconstructed flow of people shows that, as of March 15, 2011, only a limited number of people stayed in areas where the central government's simulator, the System for Prediction of Environmental Emergency Dose Information (SPEEDI), gave thyroid gland dose estimates of 100 millisieverts or more for a 12-day period from 6 a.m., March 12, through midnight, March 23, 2011. The SPEEDI doses tend to be overestimates, as they hypothesize a 1-year-old infant who stayed outdoors around the clock.
The government of Fukushima Prefecture has asked its residents to submit records of their whereabouts during the early phase of the disaster to allow their doses of external radiation exposure to be evaluated. The poor response ratio of less than 30 percent has been attributed to fading memories and other factors.
The latest analysis could be used to evaluate their doses more accurately, the researchers said.
The research results were published online on May 10 in Proceedings of the Japan Academy, an English-language journal.
http://mainichi.jp/english/english/newsselect/news/20130510p2a00m0na007000c.html
A University of Tokyo professor has learned the movements of evacuees after the Fukushima No. 1 Nuclear Power Plant disaster using cell phone GPS data, he announced on May 9.
GPS data provides objective information on people's movements, unlike testimony from evacuees, which he had relied on until now, said professor Ryugo Hayano.
Zenrin DataCom Co. Ltd., which provides GPS-related services, cooperated in the project. Hayano put together data for around 14,000 people, equivalent to about 0.7 percent of Fukushima Prefecture's population, for the period from March 10 to March 17, 2011.
From the data, he estimated the population in the 20-kilometer zone around the plant before the disaster began at around 76,000. From hourly GPS data, he was able to see how whenever an evacuation order was released from the government, people would move out from the zone.
He put the number of people in the zone from late March 14 to 15, when aerial radiation values from radioactive iodine are thought to have been at their highest, at 2,000 people at the most. However, as the data had been set up so that individuals' identities were hidden, he does not know if the people include young children, who are most susceptible to the effects of radioactive iodine.
Radioactive iodine has a short half-life, making estimates of people's exposure to it early in the disaster difficult. Hayano said, "By combining the data with predictions of the spread of radioactive iodine, I hope to understand people's radioactive exposure early on in the disaster."
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