#Fukushima I Reactor 3: TEPCO Pouring Boric Acid to Prevent Recriticality

Yomiuri Shinbun (10:02PM JST 5/15/2011):

　東京電力は１５日、福島第一原子力発電所３号機の原子炉で再臨界が起きないよう、原子炉の冷却水に、中性子線を吸収するホウ酸を溶かした上で、同日から原子炉への注水を始めたと発表した。

TEPCO announced on May 15 that it started to use boric acid in the reactor cooling water for the Reactor 3 at Fukushima I Nuclear Power Plant to prevent recriticality from happening. Boric acid absorbs neutrons.

　１、２号機も今後、同じ措置を取る。

TEPCO plans to do the same for the Reactors 1 and 2.

　再臨界は連続的な核分裂が再び起こる現象。１～３号機の原子炉圧力容器には当初、冷却のために海水を注入した経緯があり、東電はその塩分が中性子 線を吸収すると見ていた。ホウ酸を冷却水に溶かすのは、冷却水を海水から淡水に替えて以降、塩分濃度が下がっていると見られるためだ。

Recriticality is when the nuclear chain reaction is restarted. There is salt in the Reactor Pressure Vessels of the Reactors 1, 2 and 3, as TEPCO initially poured seawater to cool the RPVs. TEPCO thought the salt would absorb neutrons. TEPCO has decided to use boric acid in the cooling water because the level of salt in the cooling water may have decreased since TEPCO switched the cooling water from seawater to regular water.

　一方、３号機の圧力容器は、上端部の温度が急上昇している。東電は「注水用配管から水が漏れている可能性がある」として、１２日からは別の配管を 追加し、二つの配管で毎時計１２トンを注水した。１４日からは注水量を毎時計１５トンに増やしたが、上端部の温度は１５日午前５時までの２４時間で４６・ ５度上昇し、２９７度になった。東電は、「注水がまだうまくいっていない」と見ている。

In the meantime, the temperature at the top of the Reactor 3 RPV has risen rapidly. TEPCO increased the amount of cooling water to 12 tons per hour on May 12 using two water feeding systems, then to 15 tons per hour on May 14. However, the temperature at the top of the RPV increased by 46.5 degrees Celsius in 24 hours to 297 degrees Celsius as of 5:00AM on May 15. TEPCO thinks there's a problem with the pipes that feed water into the RPV.

In the latest measurement data (11:00AM 5/15) released by the Ministry of Economy, Trade and Industry (METI) , that temperature (the 4th column) appears to have dropped slightly to 291.7 degrees Celsius, although the data table is put up sideways and it is a bad scan and hard to see. The second digit could be 9, 8, or 3. An age-old trick by bureaucrats to discourage people from seeing the data... (My neck is hurting from trying to read the number.)

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