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Actually, it really can't happen to commercial-grade fuel. The classic movie scenario is three stages:
Stage 1
Fuel starts to get hot and melts the steel fuel holders (fuel bundle sheathing in Canada). This is probably what has happened here and everybody calls it a meltdown for dramatic effect.
Stage 2
Molten metal puddling in the bottom of the reactor vessel (very thick steel), and the ceramic fuel pellets (4% enriched uranium) also melt.
Stage 3
Melted fuel starts globbing together, and starts a sustained reaction, like a nuclear bomb, and burns all the way to China!
So, really, the whole thing only works if you have bomb-grade uranium, like the seismic death trap at Chalk River. For a commercial reactor, we just get slag at the bottom of the reactor. There is nothing to explode. Right now, it looks like the seawater is doing the trick even though they are just pouring it on the outside of the steel vessel. They probably can't get inside to the fuel because all the metal inside has melted. Now, the US made all its bomb plutonium from graphite reactors with bomb-grade uranium. Those things can have a meltdown!
4 comments:
There are some incredible images here. They didn't have a chance against the power of nature:
http://earthquakes.videohq.tv/2011/03/japan-aftermath-earthquake-89-mg.html
Very moving. :-(
The Fuel used in the Fukushima plant is MOX with plutonium mixed in. Very nasty if it goes to a full meltdown which most reports say won't happen.
Interesting coverage at Morgsatlarge – blogorific. and ANS Nuclear Cafe .
The mox is still manufactured at 4% equivalent with other ceramic junk (depleted uranium?). I think we've thrown it in Candus, but that would be mixed down to natural 1%.
I find the images quite disturbing. This whole scenario should have been practiced, but there probably no chance of evacuation, just like there is no chance of evacuation for Tokyo.
I was guessing that they were having steam leaks. According to the BBC, the zirconium in the fuel casings reacted with water to produce hydrogen gas, which exploded and blew the top off the reactor.
People have been saying that we shouldn't put reactors in a tsunami zone, but reactors are always near water for coolant, and any ocean coast can get a tsunami, even if there are no active faults, because of underwater landslides.
Hi, Harold!
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