As five-year-olds charge through the corridors of a kindergarten in northeast Japan at lunchtime, teacher Junko Kamada says she is still unsure if their food is safe a year after the Fukushima nuclear accident.
Since the March 11 earthquake and tsunami wrecked the Fukushima plant, about 100 kilometers (62 miles) south of the Sakuragi Hanazono kindergarten in Tagajo city, parents of the 198 children have been seeking assurances that the school lunches are free of radiation.
“There’s so much information out there on radiation and it’s difficult to know what we can believe,” Kamada said as she held up two reports on the Fukushima disaster, one from the government and one by independent researchers in Japan. “Which one do you trust? There are so many conflicting reports.”
Kamada will need to wait at least another 14 months for a unified view on food contamination when the United Nations Scientific Committee on the Effects of Atomic Radiation issues the first global and independent assessment of the Fukushima nuclear accident. About 160,000 people, or 8 percent of the Fukushima prefecture residents, were evacuated due to radiation risk that has left about 132 square kilometers as a no-go zone.
The committee, known as UNSCEAR, will publish a report in May 2013 that aims to give an analysis of radiation dosages among citizens and forecast health risks in the coming decades, Chairman Wolfgang Weiss said by telephone from Vienna. It will give an estimate of the total radiation release from the Fukushima Dai-Ichi nuclear station and publish a study showing how children’s health is affected by radiation, he said.
‘Suspicion and Mistrust’
“This is a major accident and we were aware that people would be anxious and there’d be suspicion and mistrust,” Weiss said. “The huge work is to read this data and interpret it.”
The study is crucial because radiation estimates from the Japanese government and plant operator Tokyo Electric Power Co. are as much as 77 percent less than some estimates from overseas organizations. The Japanese estimates have been revised twice as more information became available.
“The UNSCEAR report is important because information released is not only from the Japanese government but also other sources summarized with an international consensus,” said Hidenori Yonehara, director of the Regulatory Science Research Program at the National Institute of Radiation Sciences, one of the Japanese agencies helping UNSCEAR.
About 60 industry officials and scientists from 18 countries, including those who investigated the 1986 Chernobyl accident, met for the first time in October to start on the report, Weiss said. The committee is working with five other UN agencies, including the World Health Organization and the Food and Agriculture Organization, and Japanese counterparts.
The ability of UNSCEAR to draw upon all the available data globally will make the committee’s report “the most official one in the world,” said Toshimitsu Homma, head of safety research at the Japan Atomic Energy Agency, based in Ibaraki prefecture.
The final report will be available to the public in October 2013 after approval by the UN’s science committee, he said. UNSCEAR also published reports after the 1986 Chernobyl nuclear plant accident in the Soviet Union.
Japan in April raised its rating of the Fukushima accident from 5, the same as the 1979 partial meltdown at Three Mile Island in Pennsylvania, to the highest level of 7 on the international scale of nuclear emergencies, putting it on par with Chernobyl.
The move was actually “misleading,” Weiss said. Though ranked the same as Chernobyl, Fukushima affected a land area 10 times smaller and avoided significant fallout of high-risk uranium and strontium elements outside a no-go zone circling the reactor, he said.
Japan’s estimates of radiation release from Fukushima could be wrong and the actual amount could be half or double of what the government reported, said Jun Sugimoto, a nuclear engineering professor at Kyoto University working with UNSCEAR. The UN effort will not gather new data for the report, he said.
According to Japan’s Nuclear and Industrial Safety Agency, or NISA, the Fukushima plant has so far released 8,200 terabecquerels of cesium 137. That’s less than a quarter of the 35,800 terabecquerels estimated in a study led by Andreas Stohl of the Norwegian Institute for Air Research and published in the Atmospheric Chemistry and Physics journal Oct. 20.
The discrepancies occurred because of “huge uncertainties,” including missing data on fuel temperatures inside the reactors, said Japan Atomic Energy Agency’s Homma.
Still, even with the international resources the task of gathering all the data and making an accurate estimate of the total radiation release may end up being “almost impossible” as investigators have yet to check conditions inside Fukushima reactors, Homma said.
The hardest part may be calculating the radiation released into the Pacific Ocean, where Fukushima Dai-Ichi faces, he said.
France’s Institute for Radiological Protection and Nuclear Safety said in October that the accident led to the biggest discharge of radioactive material into the ocean in history. The institute estimates 27,000 terabecquerels of radioactive cesium 137 leaked into the sea from the Fukushima plant.
Tokyo Electric last April estimated 940 terabecquerels of cesium 137 had leaked from April 1 to April 6, it said. The utility assumed different durations of the water leak, which may be the reason for the discrepancies, Tokyo Electric spokesman Tsuyoshi Shiraishi said March 2.
The utility still hasn’t said when it will make public its estimate of the total radiation release from the Dai-Ichi plant. The task “needs careful analysis,” Shiraishi said.
So far, measurements of radiation exposure in Japan have been reassuring, Weiss said.
Among the local population, the doses are “well below 20 to 25 millisieverts and most of these doses were very low, below 5 millisieverts,” Weiss said. “If it turns out that this is correct then we would not expect to see any measurable increase of cancer risk in the population.”
The highest exposure for a Dai-Ichi worker was recorded at 680 millisieverts, almost seven times the level at which the risk of cancer starts to increase.
The UNSCEAR report isn’t directed at government policy although the information can be used for decisions on decontamination, relocation of people and other issues, Weiss said.
“We cannot answer all the questions,” Weiss said. “People will want to know if it’s not dangerous today, will it be in the next 10 years?”
Back at the Sakuragi Hanazono kindergarten, damage to classrooms from last year’s tsunami has been repaired.
“The school has been cleaned up and we were able to restart classes quite quickly, and in a lot of ways things are getting better,” said Kamada, the teacher. Still, “our number one worry is radiation and food.”