Got this from my friend Mike Barrett, who proabably picked it up from another source, but I think it is worth sharing. Good url-link, although I am not vouching for that source either.
The frustrating part about writing on this stuff is that people don’t seem to have any middle setting between “everything is fine” and “run in circles scream and shout”. So saying “no, it’s not Chernobyl” is interpreted as “it’s nothing.”
So let’s go ahead and make this clear: no, it’s still not Chernobyl. But no, it’s not nothing.
No one can tell you that there will absolutely not be a catastrophic failure — really catastrophic, like Chernobyl or worse — at one or more of the Fukushima reactors. At the absolutely worst case, some combination of accidents and failures could break through all three major containments and release a large amount of radiation through the “China Syndrome” or something like it.
It’s very likely that there has been at least a partial meltdown in one or more of the reactors — but “meltdown” doesn’t mean “catastrophic release.” The reactor would not just have to melt down, but also penetrate both the still containment vessel and the concrete outer layer, and both were designed explicitly to keep that from happening.
What we can say is that it’s not very likely to be a catastrophic accident, and gets less likely with every minute. The Japanese are cooling the reactors down, and adding boron, which “poisons” the nuclear reaction by absorbing neutrons, the “sparks” that make the reaction go.
The amount of radiation that has been released is, so far, actually very minor. Instead of being “another Chernobyl,” which the IAEA put at INES level 7, this is INES level 4 — and Three Mile Island was level 5. So far, Fukushima is not just not another Chernobyl, it’s not even another Three Mile Island.
And finally, when you hear someone in the media giving one of these catastrophic predictions, check who it is. So far, the catastrophic predictions are consistently coming from people who have been professionally and personally committed to shutting down nuclear weapons and nuclear power for decades.