Japanese reactor crisis

[dreadgeek]

Originally Posted by Andrew, Jr.

I have been watching the news on Japan. I am not understanding what is going to happen to the outter core if it totally comes down or falls apart. It is already damaged.

I am thinking about the long term effects of radiation on people and animals. Harmful just isn't answering my question. The ripple effect of this crisis is going to last generations if you ask me.

Andrew:

I will do my best to explain to the limit of my own understanding.

IF the worst of all possible scenarios were to happen and one or more reactors experienced a catastrophic meltdown of the entire pile and IF it then melted through the primary containment vessel AND the outer containment vessel and IF it then melted into the earth and had enough energy to keep melting material until it reached the water table THEN there could be an explosive release of steam and what would then be highly radioactive dirt into the environment. But notice that there are a lot of conditionals before it gets there. A lot of things would have to go wrong for things to get that bad.

However, that is vanishingly unlikely while still having a probability that is larger than 0 (where 0 means that there's no chance of it happening and 1 means that it is certain to happen).

As I understand it, right now NONE of the reactors are undergoing active fission. This is good. That means that all they have to do is keep pumping water into the cores, keeping them submerged, until such time as the decay heat reaches a manageable level. Think about the inside of the core like you would either fireworks (the kind you buy from the Boy Scouts) or a hot pan. When I was a kid and we would do fireworks on the 4th of July, my job was to fill up a bucket or washtub with water. My dad would light the fireworks, they'd burn, we'd dunk them in water and the next day pour the water out and then dispose of the fireworks. So the reactor is the firework, the sea water represents the bucket of water. Even after the fuel rods are pulled from the core (meaning they are no longer undergoing fission) there is residual heat--this is called the decay heat. That's why the cores have to be covered by water until the rods and the core cool down.

The fires (and as I was writing this another fire broke out) are actually happening in a storage area for spent fuel rods. The problem is that the area around this pool is now too hot (radioactively, not thermally) for workers to approach to put water in to fill the pools to keep the spent fuel rods (which are in cases) from becoming uncovered. This is where I wish we had more sophisticated robotics.


Cheers
Aj