The BBC is reporting that the attention at Fukushima has indeed switched to reactor #4. Reactor #4 was shut down for maintenance before the earthquake struck. Now the problem is that spent fuel stored near reactor #4 is heating up, and they are unable to keep it under water. The pool, in fact, is entirely dry — which is not good news.
At a nuclear reactor, spent fuel rods are stored in a “spent fuel pool,” which is basically a reinforced pool with structures to hold the fuel rods in place and make sure they don’t get too close to each other. They are stored on site because of the complicated nature of disposing of spent nuclear fuel.
The fuel rods, which are highly radioactive, also stay thermally hot. They can potentially get hot enough to melt, in which case the structures keeping them together are compromised. That results in a release of radiation.
Bad news? Yes. Worse news? Tepco, the company that operates the plant, has told the BBC that the spent fuel rods may be about to go critical again.
What does that mean? It means that an active nuclear reaction could potentially start up again, which would heat the rods further, and create a much greater release of radiation. I am unclear on whether that means the entire spent fuel pool could potentially reach the melting point of zirconium alloy cladding and the other containment structures that hold them in place to make sure they don’t get too close together and go critical. What that would mean is that the fuel and the rest of stuff that goes into fuel rods, and the stuff around the pool — would get so hot it would all melt together.
The thing is, all the commentators I’ve read are sort of scratching their heads. Nobody seems to be sure what Tepco is talking about, because the “re-criticality” (the nuclear chain reaction starting again) of the fuel rods in a spent fuel pool is just plain not supposed to happen. It’s not so much that it’s a worst case scenario — it’s worse than anyone seems to have thought was even vaguely possible.
In a CORE meltdown — not a spent fuel pool — once the core melts, it becomes difficult if not impossible to stop the reaction. It just keeps melting. It probably congeals eventually — at Chernobyl a giant “elephant’s foot” of corium was found in the basement, having oozed there. I have no idea if that is physically possible in the case of a spent fuel pool, but it sort of seems like all the people who seem to know specifics like that are busy deriding me for asking. To hear many pro-nuke bloggers say it, instead of asking questions like that I should be educating my friends on how safe nuclear energy is.
There’s about 142 tons of fuel, according to a Bloomberg story, in which Cambridge physicist Geoff Parks says that the above scenario, in which the fuel rods go critical again, is remote. The temperature required would be 2,200 Celsius — almost 4,000 degrees Fahrenheit. That’s roughly the heat of a meltdown.
How did the overheating happen? The lack of water. Pro-nuke blogger Rod Adams said in an earlier post that we should all calm the hell down about the spent fuel, because the amount required to keep the spent fuel pool cool was about equivalent to a garden hose run for a couple of hours each day.
But how did it happen that the hot material can conceivably go critical again, pretty much the worst-case scenario for a spent fuel pool and one of those things we’ve been reassured over and over again by pro-nuke speakers, writers and bloggers is absolutely impossible? The spent fuel pools essentially consist of fuel rods stacked with material between them to ensure they don’t get too close together, with very strict limits on how many spent rods can be placed in a pool. Sometimes the pools get full, and they are then stacked closer together than is usually mandated, in that case, boron sheets are stacked between them.
OK…so…I have one last piece of very bad news: In the spent fuel pool at Fukushima I’s reactor #4, there is no containment structure. (The NRC chair told ABC News that “secondary containment has been destroyed,” but I believe this refers not to a full containment structure, since from what I can see there isn’t one.
There’s no containment structure for the spent fuel pool because the spent fuel rods properly stored put out only a fragment of the heat that active fuel rods do — something like 1% or less, maybe far less. So no problem, right?
Incidentally, the lack of a containment structure is one of the several chief matters that we’ve been told by the Pro-Nuke, Calm-the-Fuck-Down-Dipshit Commandos, was a problem at Chernobyl. The fact that all of Fukushima I’s six reactors (and the four at Fukushima II) have containment structures were trumpeted as proof that this would never become another Chernobyl.
It still won’t become another Chernobyl. Chernobyl was a graphite-moderated plant, very different than a water-cooled reactor like Fukushima. Chernobyl suffered a huge explosion while the reactor was fully active. The Chernobyl fire burned out of control for days. At Chernobyl the “corium” — nuclear material mixed with melted containment structure, machinery and reactor building — was visible from the air above Chernobyl, glowing red-orange. Notice how I’ve said Chernobyl over and over again? The reason is that I don’t want some sketchy content farm site-scrubber or, say, a dicey search engine like, oh, Google, or a scumbag panic-blogger to grab a teaser from this column and get the impression that any of these things are happening at Fukushima — they are not.
But you know what I would really like? I would like, when this is all said and done, representatives from General Electric, which built the plant, to sit down in front of the Japanese people and answer why it seemed like an awesome idea to build a storage pool for fuel rods without a containment structure.
Would it have driven their bid up $100,000 or something?
Or was it just, you know, not deemed necessary, because, as pro-nuclear bloggers love to remind us, this was a really big earthquake and who could have ever expected it, at the edge of a tectonic plate in one of the most active earthquake zones on Earth?
See, the nuclear industry planned ahead, all right. It planned for an earthquake to hit Japan.
It just didn’t plan for a big earthquake to hit Japan.
For that, it wants a pat on the back.
How about a swift kick in the nuts, instead?