More than 15 quadrillion becquerels of radioactivity are estimated to have been released from the crippled Fukushima No. 1 nuclear power plant into the sea between March 21 and April 30, according to a preliminary analysis by the Japan Atomic Energy Agency (JAEA) and other institutions.
That is more than three times the initial estimate of marine contamination by the plant's operator, Tokyo Electric Power Co. (TEPCO), which said only 4.72 quadrillion becquerels had been leaked. A quadrillion is 1,000 trillion.
The new total is believed to have been inflated by the inclusion of fallout from the atmosphere in addition to the direct runoff from the plant that TEPCO looked at.
Takuya Kobayashi, assistant principal researcher of coastal engineering at the JAEA, said his team had used the actual measurements of seaborne radioactivity near the nuclear plant's water outlets to estimate the amount of direct discharge of radioactivity. They also conducted simulations to quantify the amount of radioactive fallout from the air and added the two results together.
They concluded that 11.4 quadrillion becquerels of iodine-131 and 3.6 quadrillion becquerels of cesium-137 had been leaked into the sea. The latter figure is about 40 times the total amount of cesium-137 released on land and sea by the Hiroshima atomic bomb. Cesium-137 has a half-life of about 30 years.
With the inclusion of cesium-134, which was not estimated, the researchers said the total amount of radioactivity was likely to exceed 15 quadrillion becquerels.
Kobayashi said his team's estimate of direct runoff from the plant may have been larger than TEPCO's figures because of the inclusion of leaks that TEPCO had failed to report. He also said it was possible that his team's preliminary calculations had overestimated the amount of radioactive materials released, within a margin of error.
Neighboring nations, including Russia and South Korea, are extremely concerned about the release of radioactivity from the Fukushima plant into the ocean. An intentional discharge of low-level radioactive water by TEPCO in April drew strong international criticism.
The preliminary analysis will be presented at a meeting of the Atomic Energy Society of Japan in Kita-Kyushu from Sept. 19.
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