TEPCO to Recalculate the Amount of Radioactive Materials Leaked into the Ocean

Not only foreign researchers but also Japanese researchers have raised issues with TEPCO's estimate on the amount of radioactive materials that leaked (on its own, or intentionally) into the Pacific Ocean, TEPCO has said it will recalculate the number. The company hopes to announce the result of the recalculation by the end of this month.

So far, TEPCO's number is 4,700 terabequerels (iodine, cesium).

From Chunichi Shinbun (11/23/2011; don't expect the link to last long on this paper):

福島第１原発の事故で、４月に判明した高濃度汚染水の海洋流出をめぐり、東京電力が公表した放射性物質の流出量は少なすぎるとして、国内外の研究者から異論が続出している。東電の値には３月の流出分が含まれていないためだが、この値を加えると、過去最悪の海洋汚染になる可能性がある。突き上げを受けた形で、東電は月内の公表を目指し、再計算に乗り出した。

Researchers in Japan and abroad have been disputing the number that TEPCO had announced regarding the amount of radioactive materials in the highly contaminated water at Fukushima I Nuclear Power Plant that leaked into the ocean. The leak was discovered in April. TEPCO's number does not include the amount that leaked in March. If the March number were to be added, it could be the worst marine contamination ever. In response to the criticism, TEPCO has started the recalculation, and hopes to announce the result by the end of this month.

　東電は５月、２号機の取水口近くなどから流出した放射性物質の量は、ヨウ素やセシウムなど３種類で計４７００兆ベクレルだったと公表した。１９７５年に英国セラフィールド核燃料再処理施設から流出したセシウム１３７の総量５２００兆ベクレルより少ないとされた。

In May, TEPCO announced that the amount of radioactive materials that leaked from the water intake of Reactor 2 was 4,700 terabecquerels, total of 3 nuclides including iodine and cesium. It was claimed at that time that the amount was less than 5,200 terabequerels of cesium-137 that leaked from UK's Sellafield nuclear fuel reprocessing plant in 1975.

　だが、９月に日本原子力研究開発機構と、東電の“身内”でもある電力中央研究所の研究者が、実際の流出量は東電発表の約３倍だったとの試算値を相次いで学会発表し、波紋を広げた。

However, in September, researchers at the Japan Atomic Energy Agency and the Central Research Institute of Electric Power Industry (a TEPCO insider, in a way) published the results of their calculations in academic society meetings, showing the actual amount of the leak could be 3 times as much as what TEPCO had announced, creating a stir.

　さらに１０月、フランスの放射線防護原子力安全研究所（ＩＲＳＮ）が、セシウム１３７だけで２・７京ベクレル（京は兆の１万倍）と見込まれるとする試算値を発表。東電発表の実に２８倍に当たる。

Then in October, IRSN of France announced their result of calculation which was 27,000 terabecquerels for cesium-137 alone, 28 times as much as what TEPCO had announced.

　日本の研究者の間では、ＩＲＳＮの試算値は海中でセシウムなどが拡散する状況を適切に見ていない、といった疑問の声も多い。

There are researchers in Japan who cast doubt over the IRSN number as not taking into consideration the dispersion of radioactive cesium in the ocean water.

TEPCO's calculation only counts radioactive materials from April 1 to April 6. The French IRSN thinks the leak started around March 21, when an elevated level of radioactive materials was first observed near the water drain, and lasted till the end of July, though they say the bulk of the leak happened before April 8 (see my post on October 27, 2011).

From my post on April 21, 2011, here are TEPCO's numbers for 6 days of leak:

• Iodine-131: 2.8 x 10^15 becquerels (2,800 terabecquerels)

• Cesium-134: 9.4 x 10^14 becquerels (940 terabecquerels)

• Cesium-137: 9.4 x 10^14 becquerels (940 terabecquerels)

• Total: 4.7 x 10^15 becquerels (4,700 terabecquerels)

JAEA said the amount of cesium-137 was 4 times as much as what TEPCO had announced. (See JAEA's paper, here.)

Whatever criticism that the Japanese researchers may have, the IRSN was the first in the world (as far as I know) to quickly publish the marine contamination simulation. They published the paper that included this simulation in early April, even before the leak of highly contaminated water was taken into account:

I guess the French researchers weren't thinking much about peer-reviewed science magazines, unlike the Japanese counterparts.

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