The reason I've been silent on the subject since the tsunami hit has nothing to do with embarrassment.
A lot of people have been coming up to me saying, "So, nuclear power is safe, huh?" I've been getting messages like that from the more granola coders. And my stance at the time was simple --
I don't know enough to form an opinion.
If it turns out this is some fatal flaw in nuclear power, I will gladly eat crow. However, all I knew was that the plant blew up. There is a lot of sensationalism and misinformation flying around. Before I either renounced my beliefs or continued to espouse them, I wanted to know what happened so I could make a fully educated decision. Not to convert people, but just to explain my position.
Well, I think I finally found out what exactly went wrong. I mean, I figured there was some sort of safety failure, but what was it, and could it have been avoided? Now, I might have some details wrong, and some people could be misleading me to make themselves look better. Then again, they might do that if I was legitimate press, too.The answer takes a little bit, so I suggest you grab yourself a sandwich.
Got your food? Good. Let's begin.
First, some background. This nuke plant in Japan was a boiler. Such nuclear plants have the fissionable fuel inside the chamber along with the control rods. In the event of a reaction getting out of control, the rods enter to slow things down. The Japanese reactor had the rods at the bottom and they enter against gravity. It's an old design that works well. Or at least, it should work well. It clearly didn't this time. What went wrong?
When the rods drop (total shutdown), you still have a lot of heat in there that needs to radiate away. In fact, dropping the rods can produce a heat increase of about 2.8%. As long as the chamber remains sealed, this isn't a problem. Circulation of the cooling water continues, and the temperature can become managable within a day or two.
The tsunami hit the plant and breached the chamber. This is where things started going wrong. With the opening in the chamber, the heat started evaporating the cooling water inside. Normally, this starts emergency pumps to circulate more water and cool off the core quickly. There is no time to lose in these situations -- if the water level drops low enough to expose the nuclear fuel to air, the fission reaction releases hydrogen gas. If it hits the right air/fuel mixture and the core is hot enough to ignite it, KA-BOOM!
The emergency pumps for the plant were electrical powered.
I do not know if this is just general equipment failure or a design flaw. Bottom line: there was no power to run the emergency cooling pumps (they are currently using diesel pumps to circulate sea water into the chamber to cool off the core). The water evaporated, the fuel was exposed, hydrogen was generated, boom! And, since we are talking a rapid expansion of air in a contained area, part of the energy opened the chamber wider, and part of it (fluid dynamics, hydraulics) forced out more water, exposing more of the nuclear fuel. This is the part that has everyone worried.
So, whatever happened cuts back to the main emergency cooling system. I'm reasonably confident such a thing wouldn't happen in the US. The Nuclear Regulatory Commission has the authority to completely shut down nuke plants they feel are unsafe (and have done so several times, in fact). They like redundancies to make sure disasters don't happen. So I don't think this says anything bad about nuclear power in general. But I do wonder about the cooling failure. Could it have been avoided? Because if whoever designed that thing, whoever signed off on it, whoever implemented it, if they just didn't bother to check because they thought things would be fine?
I'm not that could ever be atoned for.