Nuclear Meltdown

Cyia said:

If a power plant completely melts down to the point of explosion, how far away would the tremors be felt? Would there be a mushroom cloud or flash?

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In the worst case scenario, the nuclear fuel melts and pools into one tight shape that reaches critical mass, causing a low-level atomic explosion. That would cause a boom, yes. Whether or not it causes a flash or a mushroom cloud depends on how far below ground the meltdown went critical.

But that's a very unlikely scenario. Nuclear cores are designed so that if the fuel melts it drains off into separate pieces and doesn't flow into a single whole. Containment vessels are designed tough enough to hold molten uranium so it doesn't burrow into the ground. (Those two safety measures kept Chernobyl from being even worse than it was.) It's almost impossible for a competently-designed nuclear plant to undergo an atomic explosion.

What it can have is a steam explosion, as Chernobyl did. Just before the fuel melts its temperature and radiation spikes drastically, and if there is insufficient coolant all of the water will turn into steam. This can explode out of the containment vessel, carrying dust (from broken concrete) and smoke (from burning fuel) into the air, all of it highly radioactive. This would not create a flash or mushroom cloud, just a big boom and a plume of debris.

It isn't the stacks, its the containment vessel. What you call the 'stacks' are the cooling towers. Nuclear power plants AND coal fired plants both have cooling towers. They are nothing but huge things that allow hot water to spread out and cascade down, shedding heat. The business end of the nuclear power is in the containment vessel, which is often underground, and always shielded by reinforced concrete, lead and steel.

Cyia said:

*sigh*

That's what I was afraid of. So much for my visual.

Thanks, Remus.

Would the effect be different perhaps if the plant wasn't exactly well maintained or had cracks in the stacks?

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The only way you'd get a nuclear explosion if it were a very old plant (1960s, preferably Russian, preferably a plutonium fast breeder reactor which is not a power plant design), or if someone intentionally tried to make it explode (and didn't care much about their own safety, as they'd have to pull the nuclear fuel and pile it in a corner somewhere). Even then it wouldn't be a large explosion, it would be very inefficient. You'd get some light and a small mushroom. (And if you saw either, you'd be standing close enough to be dead from radiation soon afterward.)

I doubt you can change the setting, but you're much more likely to get an atomic explosion at an atomic bomb manufacturing facility. Cross the wires wrong and the thing might go off.

You could always have someone build their nuclear plant's reactor on an active fault line. The actual physics probably don't agree with what intuition thinks might well happen.

While it is unlikely that a reactor would blow up, unexpected things happen. The Chernobyl reactor almost blew up, but too much matrial vaporized. If you are writing fiction, then unlikely things can happen. As mentioned, if the fuel pooled and reached critical mass, then there could be an explosion. You could have the fuel melt and form two pools that would then meet, and that would be more likely to make an explosion than one pool.

ClareGreen said:

You could always have someone build their nuclear plant's reactor on an active fault line. The actual physics probably don't agree with what intuition thinks might well happen.

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After the bad Haiti earthquake a few years ago, as I recall, some seismologists discovered that the Haiti quake occurred around a previously-unknown fault line. (There were other known fault lines around Haiti, but somehow they determined that THIS quake happened on an unknown fault.)

There are also many known-but-inactive fault lines. The New Madrid fault in Missouri was responsible for the worst earthquake ever known to have occurred in North America, but that was over 200 years ago and there hasn't been a really serious tremor since.

melindamusil said:

The New Madrid fault in Missouri was responsible for the worst earthquake ever known to have occurred in North America, but that was over 200 years ago and there hasn't been a really serious tremor since.

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Actually, there have been some pretty big ones in the New Madrid area, 6-7 Richter range, which have caused damage. But nothing to the scale of the three colossal tremors in 1811-1812. As for "worst earthquake" in North America, that's somewhat conjectural, as there were no seismic instruments in existence, and the immediate region was sparsely populated.

By standard means of assessment, for human casualties and property damage, the worst earthquake in North American history was the San Francisco quake of 1906. By sheer energy release, the worst was the Alaska quake of 1964, which remains the second most powerful quake anywhere on Earth ever measured by modern seismic instruments.

As for nuclear plant disasters, we most recently have the Fukushima incident in Japan in March 2011. Video exists of at least two of the big hydrogen gas explosions blowing the roofs off the containment vessels. Whether or not those showed up on seismic instruments nearby, I don't know.

caw

My knowledge of nuclear physics is pretty limited (college level physics and loads of documentaries) but a nuclear power plant will not ever explode like a nuclear bomb. They are radically different things.

We have had plenty of criticality events happen where you get a burst of heat and light (and radiation) but no mini mushroom clouds or any such thing. That's because people were working on building up enough fissile material to make a reactor. Making a bomb is an entirely different beast and you deal with hugely different purities of fissile materials. One source I read said you need about 4% pure U235 for your standard reactor. If things go haywire and the reactor melts down, you'll still have a nasty puddle of goopy, hot radioactive material. Bomb grade stuff has been purified into the 90% range and you need to smack it around a bit to really get it going. You just won't find those conditions in a power plant (hooray for small mercies).

Here is a chilling documentary about Chernobyl and its meltdown. It's still the current worst-case reactor failure that has ever occurred (though Fukishima is right up there) and you will hopefully get some good ideas out of there: http://www.youtube.com/watch?v=UQJO0VKxmuU


Some helpful things:
- Seismographs are *very* sensitive. The steam explosion that blew the top of the reactor vessel open and caved in the ceiling was registered as an earthquake with a 3.87 magnitude.
- An earthquake with that magnitude would definitely be felt for probably tens of miles away. The further you go from the center, the less and less it will be apparent. It'll be detected much much further away though.
- There was a nasty plume of steam rising up from the plant carrying radioactive particles. No mushroom cloud, just a steam plume that got picked up and carried away by the wind. You'd see it clearly from a few miles away but it would disperse pretty quickly.

I hope that helps.

Cyia said:

I don't even care if it's a nuclear explosion. I'm just trying for a scenario where the ground tremor or some other tell would be experienced / visible for several miles. (Basically, person standing at site A needs to see or hear something to indicate that site B has been demolished. There's no radio communication - even before you add in the radiation - and they're several miles apart.)

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Don't despair. Older nuclear reactors can undergo steam explosions (as happened in Chernobyl and almost happened in Fukushima) as well as hydrogen explosions (which happened in Fukushima). The Chernobyl explosion was plenty big and loud. Furthermore, mushroom clouds don't have anything to do with an explosion being nuclear per se. Nearly any moderately big explosion will make a mushroom cloud. This happens any time there is a hot column of air pushing upward into a big cloud of cooling smoke above. If you do a youtube search for footage of military bomb drops (say in Afghanistan), you'll see lots of mushroom clouds. Large industrial explosions regularly are heard from a mile or more away, and nearly any unusually large fire will create a noticeable smoke column.

The bad news is that every different nuclear reactor design has its own peculiar failure mode. Some are incapable of exploding. Some might explode, but are unable to break through their containment vessel. Chernobyl did explode and then spewed nuclear lava and burning graphite all over the place. Generally older, and more Soviet is more dangerous. Newer and more western is safer.

And don't forget that the explosion will never a nuclear explosion. Rather the nuclear fuel will make the steam hot, and the steam will cause the explosion. Thus no flash of light, and no multi kiloton yield.

I think Fukushima actually achieved, if that's the right word, meltdown, did it not?

As to the explosion/fault line thing, Indian Point, the nuclear power plant like 30 miles from NYC, is basically on a fault line. There's also a fault line running under upper Manhattan - I don't think they're the same fault but they may connect some way.

Everyone, believe me, knows it's there. Hence I think you don't have to necessarily have the giant boom/visible explosion come from the plant in order to cause the response you want. If it's a known danger/issue, a quake or some such there will make everyone basically turn to look that way.

Or, drop a small plane on it. I don't know about the construction of plants except for the very basic gleaned from news and X-Files episodes but a lot of things like that, that are built to withstand quakes, fires, etc., are surprisingly vulnerable to stuff falling from a great height, especially if that stuff has flammable contents. Maybe?

cornflake said:

Or, drop a small plane on it. I don't know about the construction of plants except for the very basic gleaned from news and X-Files episodes but a lot of things like that, that are built to withstand quakes, fires, etc., are surprisingly vulnerable to stuff falling from a great height, especially if that stuff has flammable contents. Maybe?

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No. Nuclear power plants are specifically designed to withstand the impact of a fully-loaded jet.

The news went on and on and on about this on 9/11. You can't melt down a nuclear reactor by flying planes into it.

Chasing the Horizon said:

No. Nuclear power plants are specifically designed to withstand the impact of a fully-loaded jet.

The news went on and on and on about this on 9/11. You can't melt down a nuclear reactor by flying planes into it.

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Ah. Just for the 'I'm not actually *that* dumb' record, I didn't have any belief it'd cause a meltdown to drop a plane onto a plant, just a giant explosion and resultant freakout. I presume the reactor/fissile material and whatever isn't in a place it'd be affected by that. The plant part, towers, whatever, I thought you could go boom maybe.

cornflake said:

Ah. Just for the 'I'm not actually *that* dumb' record, I didn't have any belief it'd cause a meltdown to drop a plane onto a plant, just a giant explosion and resultant freakout. I presume the reactor/fissile material and whatever isn't in a place it'd be affected by that. The plant part, towers, whatever, I thought you could go boom maybe.

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I wonder what shape the concrete would be in after 30 years. SUre the container could withstand a plane crash when it was new, but thirty years of weather and radiation and salt (if it were on the coast) together could weaken the concrete substantially.

Within the past year or two a cooling tower at one plant collapsed. Obviously that didn't cause a meltdown, but the plant had to be shutdown until adequate cooling could be restored. That was at the Vernon, Vermont plant. I find it strange that the tower was supported with wooden beams.
http://www.boston.com/news/local/articles/2007/09/14/vt_yankee_reports_on_collapse_in_tower/?camp=pm

The suggestion is that if a cooling tower could collapse after thirty years, then a container probably has weakened; although it probably does not have wooden beams ythat might rot..

If all you want is a big boom, even a flour mill will do.

Cyia said:

I think I could get the desired effect if I change the power plant to an armory. That should produce a big BOOM.

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I've visited a lot of forts (mostly 1700s-era, some 1600s or 1800s) that have an attached or interior armory, where they would store bullets, cannonballs, gunpowder, etc. Virtually all of them had a rule that no smoking and no fires were allowed within x feet of the armory because of the risk of explosions and fire, though even with the rule, there were a fair number of explosions due to the armory catching fire!

In fact, I think there may have even been one at the Tower of London...

Technically, the place where the gunpowder is kept is the magazine. The armory is where the weapons are kept.

set it on a faultline, like that one in Cali is located, that is moving in two different directions and then set off a 9.1 quake that rips the plant in two literally and exposes the cooling pools, ie they suddenly drain and the rods are now exposed to the air.