Fuku I Hydrogen Gas Update: It Was 63% Concentration

and no need to worry, TEPCO will take care of it.

TEPCO also says since there is no oxygen in the pipe that leads to the Reactor 1 Containment Vessel, there is NO DANGER of explosion.

(Uh huh. "There is no danger of explosion" was what they said to the fire department and the Self Defense Force right before Reactor 1 blew up, and then before Reactor 3 blew up.)

From Yomiuri Shinbun (9/28/2011):

　東京電力福島第一原子力発電所１号機の格納容器に通じる配管から高い濃度の水素が検出された問題で、東電は２８日、濃度は６３％に上ると発表した。

TEPCO announced on September 28 that the concentration of hydrogen gas in the pipe that leads to the Containment Vessel of Reactor 1 at Fukushima I Nuclear Power Plant was 63%.

　配管内で酸素が検出されなかったことから爆発の恐れはないとしているが、東電は２９日に配管内に窒素を注入し、水素を排出する。

TEPCO says there is no danger of explosion because no oxygen was detected in the pipe. The company will inject nitrogen in the pipe on September 29 to expel hydrogen.

　高濃度の水素は、格納容器から放射性物質の漏出を抑えるための排気装置で使用する配管から見つかった。２、３号機でも同様の配管の水素濃度を調べる。

The high concentration of hydrogen was found in the pipe that was to be used as part of the filtering system to suppress the leak of radioactive materials in the Containment Vessel. TEPCO will measure the levels of hydrogen gas in the similar pipes in Reactors 2 and 3.

　水素は、事故直後に核燃料が高温になり燃料を覆う金属と水が反応して発生したものとみられる。空気中に４％以上の水素と５％以上の酸素が同時にあると爆発の危険性が高まる。東電では、格納容器の上部やほかの配管にも水素がたまっている可能性があることから、今後の作業では水素がある可能性を前提にして安全対策を行うとしている。

It is considered that hydrogen gas was generated when the nuclear fuel was heated to high temperature right after the accident and the cladding and water reacted. If there are more than 4% hydrogen and more than 5% oxygen in the atmosphere, the chance of explosion increases. It is possible that there is hydrogen gas in the upper part of the Containment Vessel and in other pipes. The company says it will take measures to address hydrogen gas before proceeding on any work from now on.

Looking at TEPCO's handout for the press on September 28 (Japanese only for now), all they will do is to try to expel hydrogen in the pipe alone by injecting nitrogen from the far end of the pipe. They must be operating on the assumption that all the hydrogen in the pipe is from the initial zirconium cladding and water interaction, not the recent or on-going radiolysis, and once the hydrogen currently in the pipe is expelled, that will be the end of the story.

The idea seems to be that as long as the "MO11" valve is closed off, they can just purge hydrogen from the pipe and not worry about any "fresh supply" if any from the Containment Vessel, and they are free to cut the pipe for their gas management system.

There's a word for that in Japanese, "ba-atari-teki", and it can be translated as "ad hoc". The word seems to describe how TEPCO has been dealing with the crisis very well. (Remember the bath salt as tracer?)

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