20111110 http://ex-skf.blogspot.com/2011/11/fukushima-i-nuke-plant-reactor-4-tepco.html http://www.tepco.co.jp/en/news/110311/index-e.html SKF: The problems I have are these: Why did the hydrogen gas from Reactor 3 go to Reactor 4 to begin with, instead of out to the stack and into the atmosphere? Why didn't Reactor 4 blow up when Reactor 3 did, if it was filled with hydrogen gas? Instead, it waited another day till it finally blew. It does look like a hydrogen explosion, as I don't see any evidence of high temperature. The Spent Fuel Pool of Reactor 4 looks pretty much intact. Any insight, readers? --------------------------------- "Why did the hydrogen gas from Reactor 3 go to Reactor 4 to begin with, instead of out to the stack and into the atmosphere?" Just because H is lighter than air, doesn't mean it will go up a stack and out. It would if there was free convective movement in the ducts and stack, but that's very unlikely to be the case. Gates would be closed, etc. H gas movement would be via small leaks in gates, from pressurised side to lower pressure. In this case the H will just displace air, but can't really convect. Likewise, there'd have been closed gates all through the system, so where the H went would be determined by leaky seals and gates, not the 'normal' route of gas being deliberately, fan-driven, vented up the stack. So it's quite conceivable that H gas could have worked its way from unit 3 to unit 4. (Please don't take this as implying I believe a word TEPCO says. Just that this particular story is feasible. For once.) "Why didn't Reactor 4 blow up when Reactor 3 did, if it was filled with hydrogen gas? Instead, it waited another day till it finally blew." This too is feasible. Hydrogen (like any explosive gas) is only explosive when mixed with air/oxygen within a certain ratio range. This range is bounded by the LEL (lower explosive limit) and UEL (upper explosive limit.) It's possible that the H leaking through ducts from #3 to #4 was concentrated enough to be non-explosive, ie not even flammable. Not enough oxygen for the H to burn. So, H gas being produced in #3 somewhere, getting into the ducts in concentrated (and possibly pressured) form, but also leaking into the interior of #3 in a concentration able to detonate. So unit #3 has a H-air explosion, which moves stuff around in the SFP enough to trigger (milliseconds later) a prompt criticality. Meanwhile, the explosion blows away the ducts leading from #3 to the stack via conducted shockwave, but the ducts going on to #4 contain such concentrated hydrogen that they don't explode. And the shockwave isn't enough to take them out either. Time passes. The concentrated hydrogen that got into the #4 ducts diffuses through leaks into the volume of the #4 building, while air also gets back into the ducts. Likely also the #4 SFP water level goes down, exposes rods, and more hydrogen is released here. Result is a building with a variety of different concentrations of hydrogen in different areas, including the ductwork. Then a spark somewhere (or the SFP burning rods) triggers the hydrogen explosion. The detonation wave travels via complex paths, through different floors and ductwork. The floors blown up and down, and the outer wall panels blown out, are clearly the result of distributed overpressure, and lots of it. As for the explosion being 'in the ducts' like TEPCO says... bullshit. SOME of the explosion was in SOME of the ducts. But take 111110_06.jpg - those duct remnants have been crushed INWARDS. And in photo #7, those are duct remnants fallen from directly above (photo#6) so there's no way they were ducts being blown to pieces by internal overpressure. They got crushed and mangled, then fell down. Also, the contained volume of the ductwork (if that's where all the hydrogen was) isn't enough to provide overpressure sufficient to blow the walls and floors to bits like that. Had to be the entire building air volume involved. Just more so on some floors than others, hence differential pushes up and down on floors. "It does look like a hydrogen explosion, as I don't see any evidence of high temperature. The Spent Fuel Pool of Reactor 4 looks pretty much intact." To be more precise, anything that involved THICK reinforced concrete beams and plates survived, while thinner planes (roof, wall panels, some floors) didn't. The SFP and reactor containment are thick. Note that people making comparisons to WWII concrete bunkers are wasting everyone's time. Those things are many feet thick. Fukushima reactor building walls and some floors are only few inches thick. Stupid design, but there you go. What a pity no one seems to have been videoing the building when it blew. I can't recall, was the #4 explosion at night? ------------------ Hey, I just noticed. In photo #7, foreground just to R of center, there's an overpressure-crushed five gallon oil drum. From the symmetry of the crush, it looks like it must have been empty, or nearly empty. Safe to assume it had the cap on. From the amount of crush, it shouldn't be hard to work out the approximate amount of overpressure. To me it looks like less than +1 atmosphere (from my experience playing with crushing metal cans by applying vacuum to them.) That some of the outer wall panels stayed on #4, had suggested to me it wasn't a very big explosion. What luck the #4 SFP didn't do the same prompt criticality trick as #3 SFP. (And I still say the #3 SFP was THREE prompt criticalities in quick succession. Not just one as A.G says.) TerraHertz