A preliminary report says that the Fukushima nuclear accident may have discharged twice as much radioactive material as initially estimated by Japanese authorities.
A study posted Thursday on the website for the journal Atmospheric Chemistry and Physics made the conclusion, putting the Fukushima emissions at approximately 40% of the estimated release by the Chernobyl disaster of 1986 in the former Soviet Union.
The study’s estimation of the higher levels of radioactive caesium-137 comes from a global network of sensors. Study author Andreas Stohl of the Norwegian Institute for Air Research says the Japanese government’s estimate came only from data within Japan, which missed emissions that were blown out to sea and could not be measured by Japanese officials.
The Fukushima-Daiichi plant may have also started emitting radioactive substances before the tsunami arrived about 45 minutes after the magnitude-9 earthquake, contradicting government evaluations. The report says this indicates structural damage to the reactors during the earthquake, but Japan’s Nuclear and Industrial Safety Agency (NISA) remains convinced the quake did not cause significant damage to the plant, according NISA spokesman Tadashige Koitabashi.
The study did not look into health impacts of the radiation. According to the US Environmental Protection Agency, caesium-137 is dangerous because it can last for decades and exposure to it can increase the risk of cancer. The long-term effects of the Fukushima nuclear disaster are not clear due to the complexity of measuring radiation doses received by people. Stohl said in a telephone interview that emission estimates are so imprecise that finding twice the amount of caesium is not counted as a significant difference, and pointed out that some previous estimates had been higher than that of his study.
The report also says that about a fifth of the caesium fell on land in Japan, while most of the remainder landed in the Pacific Ocean.
Experts have no conclusive projections about how many cancers could result because they are still investigating how much radiation people received. While some radiation has been found in Tokyo and the US, experts say they believe these pose no significant health consequences in those places. No one has died from radiation exposure so far, but tens of thousands of people remain evacuated from areas in and around a 20-kilometre zone around the crippled Fukushima-Daiichi plant. Former prime minister Naoto Kan has also said the worst contaminated areas inside the evacuation zone could be uninhabitable for decades.
Concerns are still strong over radiation levels. Parents of small children in Tokyo worry about the discovery of radiation hotspots despite government reassurances that they do not pose a health risk.
Japanese authorities and the Tokyo Electric Power Company (TEPCO), which runs the Fukushima power plant, have not updated figures on radiation from the Daiichi station. TEPCO said last week that radiation leakage has fallen to about 8 million times less than at the height of the disaster.
Report: New report - Fukushima released twice as much radiation as government estimated (Washington Post, 28 Oct 2011)
Report: Study - Fukushima Fallout May be Much Higher Than Thought (VOA, 27 Oct 2011)
Report: Fukushima Station Discharged More Radiation Than Estimated (Bloomberg BusinessWeek, 27 Oct 2011)