Dec 29

“Now They Tell Us” Series: NISA Says Reactors 1 and 3 Explosions May Have Been Caused by Vent (EX-SKF, Dec. 28, 2011):

(In case you haven’t read about it during my absence…)

Nikkei Shinbun reports that NISA admitted the hydrogen explosions that took place in Reactor 1 and Reactor 3 at Fukushima I Nuclear Power Plant in March may have been caused by hydrogen flowing back from the exhaust stack. In other words, vent may have caused the explosions.

From Nikkei Shinbun (12/27/2011):

経 済産業省原子力安全・保安院は27日開いた東京電力福島第1原子力発電所の事故原因に関する専門家の意見聴取会で、1、3号機の水素爆発の一因として、原 子炉格納容器からベント(排気)した水素が別の排気管を通って建屋内に逆流した可能性があると公表した。津波による電源喪失で排気管の弁が開き、水素の逆 流を防げなかったという。

The Nuclear and Industrial Safety Agency under the Ministry of Economy, Trade and Industry disclosed during the experts hearing on December 27 on the cause of the Fukushima I Nuclear Power Plant accident that a possible cause of the hydrogen explosions in Reactors 1 and 3 may have been that the hydrogen that was vented from the Containment Vessel [to the exhaust stack] flowed back into the reactor building through a different pipe. As the power was lost due to tsunami, the valve of this different pipe remained open, and unable to prevent the reverse flow of hydrogen, according to the NISA.


In Reactors 1 and 3, hydrogen accumulated in the Containment Vessels after the core meltdowns, and TEPCO carried out the vent in order to remove hydrogen. The exhaust pipe for the vent connects to the exhaust pipe for the “standby gas treatment system” for the air ventilation of the reactor building, and then to the exhaust stack.


The valve of the exhaust pipe for the standby gas treatment system opened when the power was lost, so that the air ventilation of the reactor building would continue. In fact, the investigation of Reactor 3 after the accident showed the valve was open. When TEPCO did the vent, hydrogen may have flowed back to the reactor building through the open valve, and with the hydrogen leaked from the top lid of the Containment Vessel caused the hydrogen explosion.


All the other nuclear reactors in Japan has the same system whereby the valve opens when the power is lost. As a countermeasure, the NISA suggests two separate exhaust pipes and installing a valve to prevent backflow. Professor Tadashi Narabayashi of Hokkaido University points out that the vent process needs to be improved fundamentally.

Narabayashi, one of the “Three Plutonium Brothers” who said the toxicity of plutonium was the same as salt, used to work for Toshiba.

So after more than 9 months since the accident NISA feels like telling the truth for some reason, now that the accident is officially “over”.

The very act of venting probably caused the explosions, says NISA. How about that, GE?

Product liability lawsuits anyone?

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