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Faye-M
11-05-2014, 06:42 AM
This Wiki article (http://en.wikipedia.org/wiki/Underground_nuclear_testing) has answered a few of my questions but, as I'm sure all writers know, your average research source tends to tell you what has already happened or how things that haven't happened have been avoided, not what would happen in X scenario in a totally fictional world. Which is inconvenient.

What I need to figure out is how close someone would have to be to an underground nuclear explosion in order to get some amount of radiation poisoning, and how deep/not-deep this explosion would have to be in order to not cause a whole heck of a lot of damage on the surface. These are questions that probably no one can answer with any certainty, but speculation is more than welcome!

Basically, I need to have a nuke go off in an underground facility that's meant to protect people from nuclear explosions. Think Cheyenne Mountain (I'm toying with using it rather than creating a fictional facility that's basically the same thing), which is apparently "2,000 feet deep in granite" and "originally designed to withstand a 5 megaton nuclear explosion at a distance of 1.7 miles." Anybody know how I'd blow that sucker up without destroying the entire mountain? And, like I said, have people close enough to it that they'd experience a slow death by radiation poisoning?

Drachen Jager
11-05-2014, 10:14 AM
There is no distance from a nuclear explosion underground that would give someone radiation poisoning without killing them.

That entire thought is flawed.

The burst of radiation in the initial blast is like lying in the sun in terms of damage, you may get 1 week's worth of baking in the sun in a few seconds, but it's not radiation poisoning per se. This burst radiation would be entirely absorbed by the rock in your scenario anyhow. Even Gamma radiation cannot penetrate anywhere near that far.

Radiation poisoning comes from the fallout. So it's not the proximity to the blast but how long they stay in the area, their protection and activity, prevailing wind currents etc. etc. that will determine the level of radiation poisoning.

There has been extensive underground testing, and at a depth of 2,000 feet there's very little damage on the surface and essentially no fallout, but the good news is the mountain would be intact.

I think you're trying to build an impossible scenario.

http://en.wikipedia.org/wiki/Underground_nuclear_testing

King Neptune
11-05-2014, 04:50 PM
I think that a 5 megaton bomb going off in an enclosed space would blast the sides of that space right nicely. If the space is large enough, then the air might be able to distribute the pressure enough, but the pressure would have to get out. I think that there would be a section of mountainside that would pop out or crumble to dust and be blown away. If there are doors as in Cheyenne Mountain, then they might be expelled rapidly followed by jets of superheared gas.
You've probably seen video of the surface effects of an underground explosion, and most of those were less than a megaton and a couple thousand feet deep.

robjvargas
11-05-2014, 05:18 PM
Did you ever see the movie Armageddon? In it, there's an explanation of why a nuclear weapon on the surface of the impending asteroid would be useless.

Paraphrased, "If you light a firecracker, what happens? Firecracker goes off, you burn your hand. Done. If you close your fist around the firecracker, it can blow your hand clean off."

It doesn't take as large of a blast to destroy a facility from the inside as from outside. It's entirely possible that a facility like Cheyenne Mountain, that can take a 5 megaton blast from the outside, would collapse from a "tiny" nuke of a few hundred kilotons inside.

Someone outside the facility isn't likely to get enough radiation to get sick (much less die), unless the blast manages to exhaust in some explosive fashion. As Drachen Jager mentioned, the metalwork and intervening ground will just about absorb the initial burst of radiation. So the only real chance of radiation-induced sickness is from some kind of fallout scenario

Faye-M
11-05-2014, 06:37 PM
That's cool, I'm not married to the radiation poisoning idea. The place needs to be evacuating when the bomb goes off, is all, and some of the characters are going to die somehow or other. But if I'm understanding you right, Drachen Jager, anyone nearby would be severely burned? I could work with that.

If people stay in the area to rescue survivors, would they be exposed to the fallout then? How soon would that happen?


If there are doors as in Cheyenne Mountain, then they might be expelled rapidly followed by jets of superheared gas.

Ohh, I like that idea...


It's entirely possible that a facility like Cheyenne Mountain, that can take a 5 megaton blast from the outside, would collapse from a "tiny" nuke of a few hundred kilotons inside.

Yes, I'm definitely planning to make it a smaller one.

King Neptune
11-05-2014, 07:30 PM
Fallout is particulate matter that has become radioactive from the bomb and thaqt rises into the atmosphere to later fall. Whether there would be fallout would depend on how much particulate material was blasted into the atmosphere. If you have seen videos of underground tests, then you probably saw a small plume of dust shoot up, and then fall back down or disperse.

I was imagining Cheyenne Mountain, and if that got the blast there might be some holes that would blast through, but the main power of the blast might be spent lifting most of the mountain a hundred feet up. Then the mountain would fall, and there would be rock dust, but there wouldn't be much material injected into the atmosphere, no mushroom cloud. But that idea could be completely wrong.

There are many possibilities, and most of them should have been tested in the underground tests. Another kind of test that was done a little were designed to see whether nuclear explosives could be used for huge earth-moving projects. One such thing was a potential new canal in Central America, Those explosions were designed to move rock out of the way without spreading fallout.

badwolf.usmc
11-05-2014, 07:50 PM
A place like Cheyenne Mountain is designed to keep stuff out, not keep stuff in, which a building like that has a completely different design philosophy. The explosive force is going to escape somehow, usually through the weakest point.

Now, I would imagine that there are "secret" escape tunnels, and those would be weaker than the main doors...

Fun fact: The M-1 tank's ammunition compartment is designed with explosions in mind, so if the ammunition explodes then the force blows the top off the tank, saving the rest of the tank and its crew.

Drachen Jager
11-05-2014, 10:29 PM
That's cool, I'm not married to the radiation poisoning idea. The place needs to be evacuating when the bomb goes off, is all, and some of the characters are going to die somehow or other. But if I'm understanding you right, Drachen Jager, anyone nearby would be severely burned? I could work with that.

No. The mountain would shield them. You only get burned if you have line of sight to the explosion. Any intervening obstruction heavier than a bit of fabric would protect you (see the 'shadows' cast on walls at Hiroshima and Nagasaki.

If people stay in the area to rescue survivors, would they be exposed to the fallout then? How soon would that happen?

Yes. Their exposure depends on the explosion, how much dust was sent into the air, how high, etc. From the Wiki article, the reason many nuclear tests were done at a depth of 2,000 feet or greater is because there was little or no fallout from such an explosion, so probably minimal radiation exposure in your scenario.

If you had your blast exit the tunnel mouth, it would expel significant amounts of radiation, but only in a fairly small area.

I don't know quite what you want from your radiation poisoning, but it's a pretty slow process. You can be exposed to a lethal dose and not really notice the side effects for days or even weeks.

If the characters have any clue, they should protect themselves from dust, preferably with gas masks, but even a bit of cloth over the face will help. Do you want the radiation poisoning to come from ingestion or direct exposure? It would probably take hours to days to get a severe dose from direct exposure, but you could ingest a lethal dose of dust in seconds.

Drachen Jager
11-05-2014, 10:32 PM
Here, watch this documentary. It should give you a better feel for the effects of a nuclear explosion.

https://www.youtube.com/watch?v=9GJttnC8PoA

Casey Karp
11-05-2014, 10:32 PM
My understanding is that facilities like Cheyenne Mountain use a series of doors. Nobody expects any one door to withstand a nearby blast, but each one that goes will absorb some of the force. Hopefully, by the time force of the explosion dissipates, there will still be at least one door left standing.

If I'm correct, I'd bet that any hidden tunnels or the like would be built the same way. Let's face it, nuclear bombs are (largely) not directional weapons. Any hidden exit will need the same amount of protection as the main doors.

badwolf.usmc
11-05-2014, 11:04 PM
My understanding is that facilities like Cheyenne Mountain use a series of doors. Nobody expects any one door to withstand a nearby blast, but each one that goes will absorb some of the force. Hopefully, by the time force of the explosion dissipates, there will still be at least one door left standing.

If I'm correct, I'd bet that any hidden tunnels or the like would be built the same way. Let's face it, nuclear bombs are (largely) not directional weapons. Any hidden exit will need the same amount of protection as the main doors.

The effects of an explosion in a confined area are much different from an open area. That blast overpressure has to go somewhere. A facility like Cheyenne Mountain is engineered to withstand an outside blast, which will have a manageable PSI level, but a blast inside will have a massive PSI level that will not be manageable.

Facilities that are designed to "contain" blasts in reality channel the energy in a controlled direction. The energy has to go somewhere.

King Neptune
11-05-2014, 11:20 PM
The video that Drachen posted a link to does show a lot that will be helpful, and that's for a one megaton bomb. You could cut the size of the bomb without losing any effectiveness inside something like Cheyenne Mountain.

There probably are other videos that the U.S. government made during tests in the 1950's. Some of those tests were above ground and had houses, cars, etc. nearby to find out what would happen.

Faye-M
11-05-2014, 11:48 PM
Here, watch this documentary. It should give you a better feel for the effects of a nuclear explosion.

https://www.youtube.com/watch?v=9GJttnC8PoA

Wow... that video is both frightening and enlightening. Thanks!

Faye-M
11-05-2014, 11:53 PM
No. The mountain would shield them. You only get burned if you have line of sight to the explosion. Any intervening obstruction heavier than a bit of fabric would protect you (see the 'shadows' cast on walls at Hiroshima and Nagasaki.

But what about the heat? Wouldn't that alone be enough to burn anyone close by?

Faye-M
11-05-2014, 11:57 PM
The effects of an explosion in a confined area are much different from an open area. That blast overpressure has to go somewhere. A facility like Cheyenne Mountain is engineered to withstand an outside blast, which will have a manageable PSI level, but a blast inside will have a massive PSI level that will not be manageable.

Facilities that are designed to "contain" blasts in reality channel the energy in a controlled direction. The energy has to go somewhere.

That's what I've pictured in my mind - a facility structurally sound enough to withstand an outside blast would try to contain the pressure of an inside blast, and that wouldn't end well.

Drachen Jager
11-06-2014, 12:13 AM
But what about the heat? Wouldn't that alone be enough to burn anyone close by?

Only through air.

The mountain would shield everyone outside from the heat. That amount of rock is more than enough to shield people.

Do a google image search for Hiroshima Shadow, you'll see that even a bicycle is enough to mostly protect the paint on the wall behind from the radiant heat blast. Nothing like that would get through a mountain.

King Neptune
11-06-2014, 03:09 AM
This has a video about Project Plowshare, using nuclear explosives for peaceful purposes.
http://agreenroad.blogspot.com/2014/03/project-gnome-underground-nuclear-test.html

WeaselFire
11-06-2014, 04:28 AM
Keep in mind a nuclear reaction can be fission or fusion. The effects can make a difference for what you need. In the case of under ground, much of the damage is not from blast, but collapse. The reaction melts a significant sphere of material (how much depends on a lot of factors but no material is actually "safe") and then that open space collapses.

A few hundred feet of earth or rock (or water) can prevent almost all significant radiation from even large nuclear blasts. 50 feet can prevent enough radiation to protect people from any immediate effects and many long term effects.

The real key will be what you need for your story. And also keep in mind that Cheyenne Mountain's failure was that, while protected from radiation, the people could easily be permanently sealed in by even conventional weapons. Cheyenne Mountain was never designed to last for long, only long enough to provide for retaliation.

Jeff

Casey Karp
11-06-2014, 04:33 AM
Facilities that are designed to "contain" blasts in reality channel the energy in a controlled direction. The energy has to go somewhere.

Quite true, and I'm sure you're correct that a passage designed to protect against an outside blast would be far less resistant to one inside. (I have this mental image of a twisted mass of warped doors flying out of a tunnel followed by a plume of smoke and pulverized rock dust.)

I just wasn't comfortable with the notion of an escape tunnel having less protection because it's hidden. Unless it's a really, really long tunnel, it's going to be designed with the assumption that it will need to withstand the explosion of a missile that misses the known door it was targeted for.

King Neptune
11-06-2014, 05:47 AM
I don't know for sure, but I thought the escape tunnels would be long and have at least one right angle bend, but they wouldn't have doors big enough for a truck to go through and strong enough to survive a nearby nuclear blast.

Drachen Jager
11-06-2014, 08:09 AM
Cheyenne has huge tunnels you can drive a truck along.

Keep in mind, those tunnels are designed to keep the blast out. You're working with an entirely different set of forces, because the blast has plenty of other directions to go. From within, the only ways out are through solid rock, or out the tunnel.

badwolf.usmc
11-06-2014, 09:36 PM
I just wasn't comfortable with the notion of an escape tunnel having less protection because it's hidden. Unless it's a really, really long tunnel, it's going to be designed with the assumption that it will need to withstand the explosion of a missile that misses the known door it was targeted for.

It's not that they have any less protection, it is the kind of forces they are designed to defeat. Look at those big blast doors that are so iconic for Cheyenne Mountain. They are recessed into the mountain, so that is going to prevent a direct hit on the doors themselves. When that facility was built, ICMBs were not accurate enough to target a door like that, so all those door have to do is defeat a nuclear explosion that happens near the doors. While that may not seen that big of a deal, it is huge.

The same with escape tunnels. The best defense they would have is that they are hidden.

Casey Karp
11-06-2014, 09:56 PM
I'm not sure if we're saying the same thing in different ways or if we're just going to have to agree to disagree.


When that facility was built, ICMBs were not accurate enough to target a door like that, so all those door have to do is defeat a nuclear explosion that happens near the doors.

This is exactly my point.


The same with escape tunnels. The best defense they would have is that they are hidden.

But they still need to be designed to the same standard: a nuclear explosion that happens near the end of the tunnel. Not because they might be targeted, but because they may be near the explosion of one of those inaccurately targeted ICBMs that missed the main doors.

But I think we're wandering away from Faye's question. I'm going to shut up now and let her get on with the writing.

badwolf.usmc
11-07-2014, 01:28 AM
I'm not sure if we're saying the same thing in different ways or if we're just going to have to agree to disagree.


Perhaps the way I'm explaining the engineering behind the protection concepts is confusing, but I don't think we are disagreeing about anything important to Faye-M's question.