[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.


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

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.



  1. FUKUSHIMA DIARY FR – [Réacteur 4] L’explosion a été causée par l’hydrogène de la SFP4 et du réacteur 3, tout deux en surchauffe.
    Par Mochizuki, le 7 juillet 2012.

    Dans son rapport final [http://naiic.go.jp/blog/reports/main-report/], la commission d’enquête affirme que l’explosion d’hydrogène du réacteur 4 a été provoquée par l’hydrogène gazeux de sa piscine en surchauffe (SFP4) et par le réacteur 3 en surchauffe aussi. Tepco persiste à dire que l’explosion n’était due qu’à l’hydrogène du réacteur 3, la SFP4 restant sans risque.


    (copie d’écran, texte japonais)
    L’explosion d’hydrogène du réacteur 4.

    ① Point inexpliqué
    Le réacteur 4 a explosé à 6:?? le 15 mars 2011. (c’est écrit comme ça dans la version originale) [cf. [Reactor4] Explosive shock was detected before the explosion : http://fukushima-diary.com/2012/06/reactor4-explosive-shock-was-detected-before-the-explosion/%5D Tepco explique que c’était parce que de l’hydrogène gazeux est arrivé du réacteur 3 jusqu’au 4e étage du réacteur 4 par un tuyau du SGTS (=Standby Gas Treatment System = système de traitement des gaz en attente) et qu’au 4e étage quelque chose s’est mis en marche, provoquant l’explosion. La quantité totale d’hydrogène issue du réacteur 3 est inconnue.
    A ce moment-là, il y avait assez de lumière à l’extérieur pour prendre une vidéo mais il n’en reste aucune, ni de photo. Il n’existe non plus aucune source objective pour établir l’heure exacte de l’explosion. La raison n’en est pas donnée.

    ② L’hydrogène produit par radiolyse de l’eau de la SFP4 (piscine à combustibles usagés du réacteur 4)
    Le 11 mars, le réacteur 4 était en inspection périodique, le blindage du RPV (=enceinte du cœur du réacteur) était en cours de remplacement. la SFP4 était pleine d’assemblages de combustible à chaleur résiduelle.
    Quand l’eau est à température ambiante l’hydrogène produit par radiolyse est négligeable. Toutefois, selon les études de la JAEA ou de l’université de Tokyo, lorsque l’eau devient si chaude qu’elle commence à bouillir la quantité d’hydrogène augmente fortement.
    En considérant le volume du bâtiment du réacteur 4, 13,7 m3 d’hydrogène sont suffisants pour constituer un mélange détonnant.
    18,1 m3 d’hydrogène ont sans doute été produits en une journée à partir de l’eau de la SFP4, ce qui est suffisant pour fabriquer le mélange détonnant.
    (gras) Il est donc logique de penser que l’hydrogène du réacteur 3 et de la SFP4 ont provoqué l’explosion (fin gras) mais tout évaluation quantitative demeure impossible.

  2. Hydrogen does not explode, it implodes so any “hydrogen explosion” is not an explosion. Every so called explosion is nothing but a lie. The reactors exploded not imploded, mini nukes or such but is is all a lie when they continue to say hydrogen explosions.

  3. It is amazing how they were able to keep this under the lid. When i heard about the problems with the reactors I knew that they were in big trouble even though they kept saying everything is fine.

  4. “Hydrogen does not explode, it implodes”
    Where the hell did you get that retarded idea? It’s an incredibly ignorant thing to say. So very incredible, that I have to wonder if you are some kind of disinformation shill. But anyway, for your education:

    What’s being discussed is a mix of hydrogen and air. Normally there’s zero H in air. When adding H from some source, as the proportion of H increases it approaches what’s called the LEL, or Lower Explosive Limit. In STP air the hydrogen LEL is 15.9% (and the UEL is 59%.)

    Google ‘hydrogen air LEL’

    The report quoted in the article is very interesting. I’d previously thought that TEPCO was probably right (for once) in their view that the H source in Unit 4 was leakage via piping from Unit 3. It’s clear that the Unit 4 SFP water never boiled down to a low enough level to expose any part of the fuel rods, and so burning of the Zirconium rod cladding in steam wasn’t a feasible source of H for the unit 4 explosion.

    But in the article they point out that H production via radiolysis is significant, if the water is boiling. Which it may well have been at that time. So maybe that *was* another source of H for the explosion – or even possibly the only source. Also, if there was significant radiolysis, it was also adding Oxygen as well as Hydrogen to the air in Unit 4. Which would result in a lowering of the LEL limit, ie making an explosive mix sooner. ‘Brown’s Gas’, aka Boom Gas.
    (Radiolysis, means ionizing radiation breaking water down into Hydrogen and Oxygen.)

    All of which just underlines the obvious – nuclear fission reactors are such complex systems that once something goes wrong, there are numerous unexpected ways they can really bite. Producing a radioactive wound that festers effectively forever, and can poison the entire planet.

    No more fission power. These insane things should never have been built. It’s time to shut them all down.

  5. Correction. On further reading, the LEL for H in air is 4%, not 15.9%. I thought that 15% seemed too high, and it was.
    eg Ref http://www.talkinggas.co.uk/pages/flammable-risk/combustion-of-gases-amp-vapours.php

    I wonder if ‘James’ ridiculous misconception came from reading about the H cores of nuclear H-bombs being ‘imploded’, and totally failing to understand what he was reading?
    But no. No one could be that stoopid. More likely he’s one of the government’s legion of paid disinformationists, who spend their days sowing confusion and lies; attempting to stifle effective public debate by raising the random noise level.

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About this site

This website updates the latest news about the Fukushima nuclear plant and also archives the past news from 2011. Because it's always updated and added live, articles, categories and the tags are not necessarily fitted in the latest format.
I am the writer of this website. About page remains in 2014. This is because my memory about 311 was clearer than now, 2023, and I think it can have a historical value. Now I'm living in Romania with 3 cats as an independent data scientist.
Actually, nothing has progressed in the plant since 2011. We still don't even know what is going on inside. They must keep cooling the crippled reactors by water, but additionally groundwater keeps flowing into the reactor buildings from the broken parts. This is why highly contaminated water is always produced more than it can circulate. Tepco is planning to officially discharge this water to the Pacific but Tritium is still remaining in it. They dilute this with seawater so that it is legally safe, but scientifically the same amount of radioactive tritium is contained. They say it is safe to discharge, but none of them have drunk it.


July 2012