"The Norwegian study says the Japanese government estimate came only from data in Japan, and that would have missed emissions blown out to sea. Its says that Fukushima Daiichi radioactive releases equal 40 percent of those from the Chernobyl disaster in 1986.
A study by the French Institute for Radiological Protection and Nuclear Safety also stated that the amount of caesium-137 that flowed into the Pacific from the coastal plant is some 30 times more than was estimated by the plant’s owner, Tokyo Electric Power Co (TEPCO)."
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"According to the French report, an estimated an estimated 27.1 quadrillion becquerels of caesium-137 spilled into the ocean between March 21 to mid-July, Kyodo news agency reported. A quadrillion is equivalent to 1,000 trillion.
Of the amount, 82 percent had flowed into the sea by April 8, according to the study, which noted that the amount released as a result of the disaster triggered by the March 11 earthquake and tsunami was unprecedented."
http://www.bellona.org/articles/articles_2011/norwegian_estimates