From: Joseph McAllister
On Mar 16, 2011, at 17:00 , eckinator wrote:
I would kind of think that all this pumping of water onto fuel
rods glowing at somewhere between 800 and 2500 ?C would cause
instant evaporation and the corresponding shock waves of pressure
rises; AFAIK water expands 1700fold from liquid to vapor/gaseous
after all. wouldn't that cause enormous stress and ultimately
fatigue of the containment vessel? and are the pressure relief
valves designed to withstand this abuse for an extended period?
That is the challenge, once the fuel rods are uncovered. They get so
hot that trying to cover them again with anything that could help
reduce or stop the loss of coolant creates more steam which becomes
volatile in contact with the hydrogen being released by the degrading
fuel rods because it presents free oxygen to an increased amount of
hydrogen. Like H3 0.
So the helicopters that are currently (as I write this on Thursday
morning Japan time) dumping water on the hot (burning at times) spent
fuel rods would have to dump a lot in a short period of time to
prevent it being boiled off instantly. They should be, and may be,
dropping a slurry of water and sodium hydroxide (I think hydroxide,
maybe not).
The containments are already breached.
But the place where the helicopters are dumping water is a storage pool
for spent fuel rods, not inside the reactor. I think they've managed to
get some cooling water into the reactors.
I'm wondering how the water got out of the storage pool. The ones I'm
familiar with are massive reinforced concrete structures with walls many
feet thick set below ground level.
The ones I worked on back in the late 70s had walls & floors 10 feet
thick, all poured in one continuous pour. They had multiple layers of
#18 rebar on both the inside and outside faces with thousands of tie
rods linking the two faces. The earthquake might bounce it around a lot
and it should stay intact.
An earthquake strong enough to breach structure like that wouldn't leave
anything else standing, and I can see that there are towers and
buildings still standing at the site.
To get water out of the storage pool you had to suck it out uphill.
There's supposed to be enough water in the pool to cover the spent fuel
rod bundles and keep them cool even if they temporarily lose the ability
to add water to the pool.
If the pool is breached in some way that it has drained, they can't dump
enough water from helicopters to bring the reactions under control.
They're going to have to get multiple water pipe into that building to
get control of the situation.
Chernobyl was a dry pile design and the helicopters there were dumping
sand and cement on to the exposed core. The sand and cement didn't flow
away like water will. Over time it built up in layers to contain the
reaction so that they could get a more permanent cap in place.
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