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Thursday, March 15, 2012
Fukushima soil fallout far short of Chernobyl
Comparison of atmospheric conditions left out of report
By JUN HONGO
In terms of soil contamination, the nuclear crisis at the Fukushima No. 1 power plant is only about an eighth as severe as the meltdown at the Chernobyl plant, in what is now Ukraine, in 1986, according to a report by the science ministry released Tuesday.
The study, which began in June and was conducted by the ministry in cooperation with universities and semigovernmental bodies including the Japan Atomic Energy Agency, looked at 2,200 sites within a 100-km radius of the Fukushima plant, which had three reactor meltdowns.
The group studied the radioactive isotopes in samples of the top 5 cm of soil at each site.
The site farthest from the plant to have high levels of contamination, at 1.48 million becquerels of cesium per square meter, was the town of Namie, in Fukushima, located 32.5 km from the power plant, the research revealed.
The 1.48 million becquerel benchmark was used to define the exclusion zone after the Chernobyl meltdown. Such levels of contamination were found 250 km from the Chernobyl plant, or eight times farther than from the Fukushima plant, the report said.
In 1986, some parts of Norway as far as 1,700 km from Chernobyl saw radiation spike to 40,000 becquerels of cesium per square meter, a condition seen only within 250 km of the Fukushima No. 1 plant, the report added.
The report, however, did not give comparative analyses of atmospheric and prevailing wind conditions between the landlocked Chernobyl facility and the seaside Fukushima plant, or of the differing reactor types that suffered meltdowns and how their makeup would effect fallout levels.
The research "confirms that areas affected by the Chernobyl accident are substantially wider" than that of the Fukushima plant, the ministry said in the report.
According to estimates by the Nuclear and Industrial Safety Agency and the Nuclear Safety Commission, the cesium released from Fukushima is one-sixth to one-eighth the level of Chernobyl's fallout.
The strongest concentration of strontium-90, at 5,700 becquerels per square meter, was found slightly under 5 km from the Fukushima plant, according to the science ministry report. The same level of strontium contamination was detected more than 30 km from the Chernobyl plant.
Maps of contamination levels created by the study "should be utilized in the decontamination process as well as for research on how the level of radiation contamination changes over time," the report said. In April, NISA and the Nuclear Safety Commission raised the severity level of the Fukushima crisis from level 5 to the maximum 7 on the International Nuclear Event Scale, putting it on a par with Chernobyl.
The International Atomic Energy Agency's International Nuclear Event Scale describes a level 7 event as a "major accident," which requires planned and extended countermeasures to avoid health and environmental effects due to a massive release of radioactive material.
Isotopes 30 cm deep?
Radioactive materials from the Fukushima No. 1 power plant were found 5 cm beneath the ground three months after the crisis started and now are believed to have penetrated between 5 and 25 cm deeper, according to a research institution.
The hazardous materials likely seeped into the soil with rainwater, researchers with the Japan Atomic Energy Agency said Wednesday. "Further delay in decontamination work will allow the radioactive materials to sink into the ground deeper, and it will impose more burdens on those involved in the decontamination," said Haruo Sato of the agency's Horonobe Underground Research Center in Hokkaido.