The health effects from the Fukushima nuclear accident are substantially smaller than those from the Chernobyl disaster, and the increase in cancer incidence in Japan will be negligible, according to a U.N. panel’s estimates.
The health effects from the Fukushima nuclear accident are substantially smaller than those from the Chernobyl disaster, and the increase in cancer incidence in Japan will be negligible, according to a U.N. panel’s estimates.
The collective thyroid dose of Japanese people from radioactive materials released from the Fukushima No. 1 nuclear plant will be about one-30th of that of the exposed populations from the 1986 Chernobyl accident, according to a draft report by the U.N. Scientific Committee on the Effects of Atomic Radiation obtained by The Asahi Shimbun.
The draft also said the cancer incidence in Japan will rise only marginally and will be difficult to detect.
However, the report cautioned that data on released radioactive materials or actual measurements of radioactive iodine are insufficient, and that many uncertain factors remain about dose statistics.
It also pointed out that health effects of low-dose exposures have not been fully learned.
The draft report was compiled by 85 experts in and outside the U.N. panel over the past two years. Its contents will be discussed at a committee session that opens in Vienna on May 27 and submitted to a U.N. General Assembly session in September.
The report is expected to be reviewed several years later based on the latest data.
The draft report said the accident at the Fukushima No. 1 nuclear plant on March 11, 2011, was much more serious than the Three Mile Island accident in 1979, but the volume of radioactive materials released into the air was far less than in the Chernobyl accident.
The amounts of radioactive iodine-131 and cesium-137 from the Fukushima plant were less than one-third and one-fourth, respectively, of those from Chernobyl, while those of strontium and plutonium were extremely small.
The experts calculated the collective dose of the Japanese population of 130 million, multiplying the estimated dose in each region by the number of people affected.
The total thyroid dose over 10 years from the Fukushima accident is estimated at 99,000 person-sieverts, about one-30th of that of the 600 million people in the former Soviet Union and surrounding countries affected by Chernobyl.
The total whole-body dose is estimated at 32,000 person-sieverts in Japan, about one-10th of that from Chernobyl.
In addition to the limited volume of radioactive materials, the draft report said Japanese authorities evacuated residents and regulated food consumption relatively swiftly.
The experts also said the thyroid dose among Fukushima Prefecture residents outside a 30-kilometer radius of the nuclear plant was below 100 millisieverts over one year from the accident, a figure considered the threshold for increased cancer risk.
According to the estimates, the thyroid dose was 33-66 millisieverts for 1-year-olds and 8-24 millisieverts for adults. For 1-year-olds inside the zone, the thyroid dose was 20-82 millisieverts.
In the Chernobyl accident, about 6,000 people developed thyroid cancer, the only cancer whose link to a nuclear accident has been scientifically established, and more than 10 of them died.
Average thyroid dose after the Chernobyl disaster was 500 millisieverts for evacuees and 100 millisieverts for residents in the contaminated area. Figures for young children are estimated to be two to four times higher.
The experts working for the U.N. panel estimated the increase in thyroid cancer incidence over a lifetime if children in Fukushima Prefecture are exposed to 50 millisieverts, which is considered the average for 1-year-olds outside the 30-km radius.
According to the estimates, 0.8 in 100 girls and 0.2 in 100 boys naturally develop thyroid cancer. That rate will increase by 0.2 person for girls and by 0.05 person for boys due to the Fukushima accident.
The experts also estimated the whole-body dose of Fukushima Prefecture residents over one year.
The figures for adults and 1-year-olds outside the 30-km radius were less than 4 millisieverts and less than 7.5 millisieverts, respectively. Those for adults and 1-year-olds inside the zone were less than 10 millisieverts and less than 20 millisieverts.