So, instead of 4,700 terabecquerels of radioactive iodine and cesium as TEPCO announced back in May, JAEA says it was 15,000 terabecquerels that leaked into the Pacific Ocean, and that it could have been leaking since March 21, not from April 1.
From Yomiuri Shinbun (9/9/2011):
東京電力福島第一原子力発電所の事故で、汚染水や大気中からの降下分も含めて、海に流出した放射性物質の総量を１万５０００テラ・ベクレル（テラは１兆倍）とする試算を、日本原子力研究開発機構の小林卓也研究副主幹らがまとめた。
Researchers at Japan Atomic Energy Agency (JAEA) led by Takuya Kobayashi has come up with the estimate that puts the total amount of radioactive materials leaked into the ocean from Fukushima I Nuclear Power Plant at 15,000 terabecquerels. Their estimate includes the radioactive materials in the contaminated water and in the air that fell in the ocean.
東電が推定した値の３倍以上になっている。１９日から北九州市で始まる日本原子力学会で発表する。
The JAEA estimate is three times as much as the estimate by TEPCO. It will be announced during the Atomic Energy Society of Japan conference set to begin in Kitakyushu City from September 19.
東電は高濃度汚染水の流出を４月１～６日に限定しており、その間の放射性物質（ヨウ素１３１、セシウム１３４、１３７）の量を４７００テラ・ベクレルと推定していた。
TEPCO limited the time period of the contaminated water leak from April 1 to 6, and estimated the amount of iodine-131, cesium-134 and cesium-137 to be 4,700 terabequerels.
小林副主幹らは、原発の取水口付近での放射性物質の濃度をもとに、海で放射性物質が初めて検出された３月２１日から４月３０日までの流出量を逆算した。推計値をもとに海洋への拡散を模擬計算したところ、原発の周辺海域での観測値に合っていることも確かめた。試算ではセシウム１３４を含めていないため、総量はより多くなる。
Kobayashi et al calculated the amount of the leaked water from March 21 to April 30, based on the density of radioactive materials at the water intake of the plant. March 21 was when radioactive materials were detected in seawater for the first time. They also did the simulation of how the radioactive materials spread in the ocean based on their estimate, and confirmed that it matched the observed data in the ocean near the plant. The estimate does not include cesium-134, so the total amount of radioactive materials would be higher.
So the researchers concluded the leak may have been ongoing since March 21, based on the density of radioactive materials at the water intake that TEPCO was announcing. Duh. And TEPCO insisted that the leak started on April 1 or not so long before a worker noticed for the first time, and no one in the media questioned at that time. No one is saying anything now either about this extremely contaminated water that may have been leaking for 10 days before TEPCO even noticed.
(Note to self: Think.)
Asahi Shinbun has different details:
The main factor that pushed the number up was the radioactive materials in the air that fell into the ocean;
Iodine-131 alone accounts for 11,400 terabecquerels, and cesium-137 for 3,600 terabecquerels.
Well I sure hope this number for cesium-137 is "iodine-131 equivalent". Otherwise the total amount of radioactive materials leaked would be approaching INES Level 7 on its own.
These government researchers are announcing their precious studies left and right, now that their papers have been peer-reviewed and set to be published.