Tokyo Electric Power Co.’s crippled Fukushima nuclear plant may have released twice as many radioactive particles than Japan’s government estimated, the utility said in a report today.
The Fukushima Dai-Ichi plant may have emitted about 900,000 terabecquerels of the iodine equivalent of radioactive iodine 131 and cesium 137 into the air at the height of the disaster, the utility known as Tepco said today in a statement. The amount is about 2 times more than the 480,000 terabecquerels estimated in February by the Nuclear and Industrial Safety Agency or NISA, the utility said.
The total radiation release at the Chernobyl accident was estimated to be about 5.2 million terabecquerels.
Several domestic and international studies have argued estimates by Japan’s nuclear regulator were too low on the radiation release from the Fukushima Dai-Ichi plant, which had three reactor core meltdowns after it was hit by an earthquake and tsunami on March 11 last year.
The operator of the plant provided its first estimate on the atmospheric radiation release more than 15 months after the disaster, which forced about 160,000 people to evacuate and left about 132 square kilometers as a no-go zone, some of it uninhabitable for decades.
Reports on how much radiation was emitted from the Dai-Ichi plant will continue to be published, with the United Nations Scientific Committee on the Effects of Atomic Radiation set to release a paper in May 2013. That report by the group known as UNSCEAR will be the the first global and independent assessment of the Fukushima nuclear accident.
The UNSCEAR report will be key as it will be arrived at by international consensus, not just Japanese authorities, said Hidenori Yonehara, director of the Regulatory Science Research Program at the National Institute of Radiation Sciences, in March this year. His research group is one of the Japanese agencies helping UNSCEAR.
UNSCEAR, which was the international body recognized as the authority on radiation fallout from the Chernobyl reactor explosion in 1986, 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 in March this year.
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.
About 60 industry officials and scientists from 18 countries, including those who investigated the 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 World Health Organization yesterday released a report estimating residents of Fukushima prefecture outside of the no- go zones were exposed to relatively low doses of radiation between 1 millisievert to 10 millisieverts. In prefectures neighboring Fukushima, the dose is estimated between 0.1 millisieverts to 10 millisieverts and the rest of Japan may have got as much as 1 millisieverts, it said.
Cumulative exposure to 100 millisieverts raises the risk of death from cancer by 0.5 percent, according to Japan’s National Institute of Radiological Sciences.
“I think it is very important that an international and neutral scientific body with the credibility of the WHO publish its first estimates of the potential doses received by those people living in the most-affected regions, as well as in Japan or the rest of the world,” said Evan Douple, Associate Chief of Research at the Hiroshima Radiation Effects Research Foundation.
“Although it relied heavily on information from the government of Japan, the body of experts incorporated some additional sources of information so as to confirm the early estimates and previously suggested appraisals that the levels of exposure doses were quite low to a large percentage of the exposed population,” said Douple.
The estimate released today by Tepco on the atmospheric release covers a period between March 12 and 31 as the emissions after April are estimated to be less than 1 percent of the amount leaked in March, the utility said.
Tepco said about 11,000 terabecquerels of iodine 131 and 3,600 terabecquerels of cesium 137 may have leaked into the sea from the plant between March 26 and Sept. 30.