TEPCO thinks graphite melts? It vaporizes. At what temperature? Over 7,0000F degrees. Unless they know something else was going on inside Unit 3's reactor vessel (higher pressures, etc) they are still guessing to what happened.
Mock setups for meltdowns show fuel melts and collects in a blob to heat up the bottom of the reactor vessel then blasts out the bottom all at once with the help of overpressure from off-gassing. The iron bottom of the reactor vessel is going to glow red and give way long before any graphite does.
Unit 2 shows a hole in the grating from a hot blob passing thru. I suppose outer fringes of the reactor bottom might survive with some control rods and drive equipment intact below.
Simplyinfo has a pic of Unit 5's pedestal area in pristine condition to compare against.
From what I read, after Unit 4 blew, then Unit 3 pressures dropped. Possibly showing they might have been linked via tunnels and piping.
Doubt Unit 4's pool was ever hot enough to meltdown so melted fuel fallout releases were less possible. Might have been a lot of off-gassing (rod tube pressure failure) and some zirconium reactions there but not a lot of irradiation like at Unit 3 (neutron bombardment).
Still would like to know where all the scattered fuel pellets came from.
Unit 3's spent fuel condition will be hidden with the new cover being put in place.
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razzz if you run past that info about U3 pressure reducing when U4 blew, make sure you post it. Ive never seen that, that I recall.
This is not to go against your info about vaporization of graphite but I have seen graphite melted somehow with my own eyes. It looked like a black moon surface. Related to a nuclear reaction…
How can we know what the conditions in U4 sfp were? If there was a freshly unloaded fuel load, then how different is it than fuel in a shutdown RPV? Except no RPV pressure. Recall that large releases have been reported in the literature from U4. Also high neutron flux was reported there also
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Methinks the scattered fuel pellets at R4 shown in the header of my website, were experimental MOX they were planning on tossing into R4, recently souped up with a new reactor shroud, sitting on top of the used fuel. Many looked barely damaged.
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razzz, I didnt verify for Fuku, but nuclear fuel is usually UO2, melts at 5189F. But in the presence of oxygen (air or water) it will turn back in U3O8 at around 1600F, which will then melt at 2100F,
which then boils to U02 (again) at 2370F.
With MOX they also have PuO2 which melts at 2744F, but just milliseconds later in a uncontrolled chain reaction, will turn to gas at 2800F
hmmmm, do ya thinks all that Pu may have been gifted to the atmosphere via stretched reactor bolts and the most of it that melted through the reactor vessel and then "flashed off" to a gas just 56F after turning to a melt?
Did that massive pressure increase when turning into a gas, compress all the water vapor, thus changing the "reactivity" and thus creating a Moderated Prompt Criticality.
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Also quite curious, in September of 2011, the Journal of Nuclear materials published a big change in the melting point of PuO2, from 2450F up to 2744F. They discovered that using lasers.
Hmmm….so they figured out there is just a razors edge between between solid to liquid to flashing to gas at 2800F.
What else happened in 2011? Methinks they were investigating something of great interest to me.
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