More than 15 quadrillion becquerels of radioactivity may have hit the ocean from the crippled Fukushima No. 1 nuclear power plant March 21 and April 30.
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 leaked. A quadrillion is 1,000 trillion.
The new total may suffer from inflation as it includes fallout from the atmosphere in addition to the direct runoff from the plant that TEPCO looked at. The Japan Atomic Energy Agency (JAEA) is also warning its models may be overestimating the total radioactivity released.
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 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 researchers did not estimate, they said 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. But he also said it was possible that his team’s preliminary calculations had overestimated the amount of radioactive materials released.
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.