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I was reading in the physics forum and found an interesting theory about the explosion in 3

with one photo

How do we explain the upward explosion catapulting the FHM in the air?

Cheers

|Fred:

The short answer is that a hydrogen explosion on the top floor does not explain what we see and cannot launch the FHM upward. That is the key.

The only thing that launches the FHM upward is steam, because if all the water is gone, then the pool is just full of hydrogen like the rest of the upper floor and there is no differential pressure under the FHM when it blows.

How do we get steam under the FHM? Only way is superheated gas blasting out the transfer chute.

How does that happen? The containment is full of nitrogen and hydrogen venting occurs to the outside of the containment.

Remember the lateral acceleration forces from the 9.0 quake that exceeded the design parameters of Unit 3? I was wrong about the weak spot being the torus-to-primary containment link.

Here is a radiologist's interpretation of Fig. 3, which is the critical information needed here.

i306.photobucket.com

That big old steel reactor vessel sets on a pedestal like a long, skinny boiled egg. It is made of heavy steel, and it is full of water and one of the densest things I know of -- uranium.

The structures in red are pneumatic shock absorbers of some sort. They are intended to stabilize said "egg" in an earthquake if anything gets tippy.

The torus is in the ground and all that massive concrete structure, not to mention the steel liner inside the primary containment are MASSIVE and firmly anchored to the ground.

If the lateral acceleration forces exceed the design parameters, the pressure vessel risks becoming the upside down clanger in a giant bell shaking at about a 9 on the Richter scale.

The key vulnerable structure if that happens is the high pressure steam outlet pipe. If that cracks or leaks, then you have high pressure steam and shortly thereafter, hydrogen in the primary containment, but not in a huge blast, as the torus suppression pool is meant to (hopefully) handle. Apparently that didn't work out so well at Unit 2.

Now, I can put live steam and hydrogen gas in the primary containment displacing the nitrogen. I can't tell you the exact route to the lower building -- probably via the torus pool then lower floors and up through the lift shaft.

Anyway, pressure differential vs. atmospheric pressure in the vessel doesn't go to zero, but neither does the pressure build to the same level as an RPV without the damaged pipe and leak. Operators might interpret that as "hold off a short while and let's hope to God the generator gets hooked up and we can cool this off before the pressure goes too high, because Unit 1 exploded when we had to do that the last time!" *

Addendum:
*actually the operators had already manually vented the primary containment at 8:42 AM -- but perhaps this also let to more hydrogen in the upper containment, but it means the leak, if there was one either was not so large as to negate the need to vent the RPV, or, perhaps that the rising pressure in the RPV added to the severity of the leak before it was vented.

In the meantime, some hydrogen could have escaped the the drywell cap seal as well as the transfer gate seal, maybe even a pressurized stream venting to the upper building.

The reactor vessel is now mostly dry, really, really (red?) hot, and making hydrogen and oxygen. **

Addendum: ** the explosion(s) occur at 11:15 AM. Thanks for the timeline chart (below)

BOOM! Gas in the primary containment ignites, blows the drywell cap, and blows out of the transfer chute, and to a lesser extent, out of the gate to the equipment pool. This 1) causes a secondary explosion of the hydrogen above, but more importantly, 2) vaporizes the remaining water in SFP3, turning it into a steam cannon and the FHM goes ballistic. BOOM!!

The fire and explosion in the upper building propagates to the lower floors which have their own hydrogen, but the pressure from above means that the primary force of the tertiary explosion in the lower floors goes outwards through any path it can find. BOOM!!!

Now you have the mechanism for the initial fireball at the southeast corner, a ballistic FHM, damage to the equipment pool, blown out upper building, and blown out lower building including the access tunnel, all without a gross breech of the RPV (ie, melted fuel melting through the steel of the RPV).

there is also a FHD.. mentioned

it's on page 184

i cantseeiton my phone ch but i did watch ita whileback in daylight and it is the plant