If there was to be a chain reaction at Fukushima.

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I didn't realize that you were worried about a nuclear reaction causing the fuel rods to explode in a nuclear reaction after being removed.

Look at it this way: if it were able to reach critical mass by themselves after being removed, then they would have already been at critical mass and would have already exploded.

Would this be like the three mile island incident?

Conceivably they could get a mass that heats up to the point at which the fuel melts again, and the molten fuel could flow into a space that promoted a more vigorous reaction, but even then...

They don't exactly publicize the way nuclear weapons work, but most high school physics students know that just glomming a bunch of fuel together is not enough. Warheads use shaped charges in specially designed containers to force the fissionable material together in a very particular way--and it's hard to do that. Very, very precise tolerances are required, the odds of such a thing happening by an accident approach zero.

Consider that warheads--nuclear weapons designed to go off--have been involved in aviation accidents that resulted in the loss of aircraft and total destruction of the weapon and not detonated. There are all kinds of bad things going on at Fukushima and risks of worse to come--but mushroom clouds are not among those risks.

There could be additional explosions like the ones that spectacularly damaged the buildings at the height of the crisis--but those are exploding gas by-products not nuclear detonations.

Back in the 1978 to 1980 time period, the magazine called "The Progressive" ran an article on how nuclear weapons work. There was a huge furor about it that delayed the publication for a bit, if I remember correctly. Eventually it was published and I happened to see the article. I was rather disappointed -- the article that would supposedly tell terrorists just how to build a nuclear bomb had absolutely nothing in it that any reasonably bright and inquisitive undergraduate in physics or may other subjects shouldn't have already known.

Reactor fuel is not weapons grade.

If you tossed all those fuel rods in a pile with no cooling, they'd never explode. They would get hot enough to melt into slag that could cut through most anything and slowly burrow to the earth's core, but they wouldn't' go up in an atomic fireball.

Reactor "explosions" are not the result of an uncontrolled nuclear reaction, it's usually a catastrophic failure in one of the reactor's systems.

Not that a "China Syndrome" outcome wouldn't have it's down sides, but it'd not be a nuclear fireball.

Technically, there's always a chain reaction happening -- it's just a matter of how much. In industrial accidents there's the term "nuclear excursion" for when you get more of a reaction than you meant to. Often, that just means that extra (maybe a lot extra, though) radiation is produced. If it's worse, then heat might become an issue. Getting to a-bomb levels, I think, would be impossible since the fuel isn't refined enough for that.

The kind of accident that worries me is the tubes having holes or cracks or whatever and losing the water and the fuel burning (or just in a fire created by their heat) and putting radioactive smoke into the air.

Tepco has got to know that the eyes of the world are watching and hopefully that will motivate them to do a good job.

Probably. Like Three Mile Island, the chances are that absolutely nothing will come of it.

Even Chernobyl should only have killed people working in the plant. Further deaths only came about because the Soviets didn't hand out iodine supplements, and because "survivors" have been ostracised and committed suicide.

I imagine anyone fleeing Fukishima by flying to, say, Beijing, will be exposed to more radiation by the altitude than they would have remaining in the town when the rods are removed.

As a Health physicist who deals with this kind of thing an awful lot, this statement by Walrus pretty much sums everything I would have to say (other than that there is no way to get that mess to explode at this point without quite a few highly educated and technically skilled people trying to do it on purpose).

There can be NO chain reaction at ANY lightwater reactor. The kind of uranium fuel used in light water reactors cannot produce a chain reaction.

Why not learn how nuclear reactors work before spouting off.

ruveyn

The first chain reaction that was the result of human actions took place during World War II at a football field at the University of Chicago. It wasn't a light water reactor, though.

I'm curious, though. If light water reactors do not use chain reactions, then what is the source of their power? I thought that every fission nuclear reaction necessarily involved a controlled chain reaction.

It was a graphite reactor and the fuel was U-235 the kind they make bombs from. The fuel in commercial light water reactors have a much lower percent of U-235 and and much higher percent of U-238 than the Fermi reactor had. Fermi was in the business of designing a bomb, not a power generator.

ruveyn

The point that I was trying to make was that in any non-fusion nuclear reactor, the source of the power is a chain reaction. That includes light water reactors.

If it wasn't for the chain reaction, then the fission rate of the Uranium would be far too low to be of much use, at least for power generation.