[Reactor4] Explosion was caused by hydrogen gas from heated SFP4 and reactor3

Following up this article..Investigation committee “there is a possibility that the earthquake damaged equipment”

The investigation committee stated on their final report [Link] that the hydrogen explosion of reactor4 was caused by hydrogen gas from heated SFP4 and reactor3. Tepco is insisting the explosion was only caused by hydrogen from reactor3, SFP4 remained safe.

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[Reactor4] Explosion was caused by hydrogen gas from heated SFP4 and reactor3

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Hydrogen explosion at reactor4
① Unexplained Point
Reactor4 had an explosion at 6:?? (It’s written like this in the original version) [cf. [Reactor4] Explosive shock was detected before the explosion] of 3/15/2011. Tepco explains it was because hydrogen gas came from reactor3 to the 4th floor of reactor4 through SGTS pipe, and something became ignition source on the 4th floor to cause explosion. The amount of hydrogen gas from reactor3 is not known.
At that time, outside was already bright enough to take a video, but no video or picture remain. There is no objective source to record the exact time of the explosion either. The reason is not explained.

② Hydrogen produced by radiolysis of SFP4 water
When 311 happened, reactor4 was in periodic inspection, shroud of RPV was being replaced. SFP4 had numbers of fuel assemblies with decay heat.
When the water is at room temperature, hydrogen produced by radiolysis is ignorable. However, according to the study of JAEA or Tokyo university, when water is so hot that steam air bubble comes up, the amount of hydrogen significantly increased.
Considering the volume of reactor4 building, 13.7m3 of hydrogen gas is enough to make detonating gas.
18.1m3 of hydrogen gas was probably produced within a day from the amount of water in SFP4, which is enough to make detonating gas.
It is therefore rational to think the hydrogen gas from both of reactor3 and SFP4 caused explosion, but quantitative assessment is still impossible.
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