Nuclear Explosions

[spacebrick3]

So a friend and I were discussing the Orion drive, and we disagreed over what would happen if one of the nuclear bombs went off inside the "fuel tank". I though that that would start a chain reaction, and blow up the other nuclear bombs in the tank, since the explosion of the first would be enough to compress the material inside the other bombs, but my friend said that to blow up a nuclear bomb a very specific set of conditions had to be met, and a nuclear explosion, big as it might be, wouldn't set off the other bombs (Yes, people gave us strange looks as we discussed this).

Anyways, what do you think? Would the other nuclear bombs go off, or would they simply rupture?

[sevenperforce]

Your friend is correct. A nuke requires an instantaneous supercritical mass to form under specific conditions. 

[YNM]

It depends on the precise conditions I think ? If any of the bomb explodes it means they've become critical. I mean... some bombs that have stages do sometimes uses one criticality to produce another criticality.

[Shpaget]

https://en.m.wikipedia.org/wiki/Fizzle_(nuclear_test)

It's not easy to trigger a nuke.

[Brotoro]

Your friend is correct. Getting a symmetrical implosion that is necessary for nuclear yield is highly unlikely in any of the other bombs.

[Capt. Hunt]

yeah, it's likely that the other pellets would be vaporized before their cores could reach criticality.  You might see partial fission, but not full order detonations.

[Nuke]

if the conventional explosives that initiate the fission reaction were to go off in an uncontrolled fashion, its not a nuke, its a dirty bomb. the implosion type device requires precise timing on the explosive charges, otherwise the shockwaves wont converge on the fissile material and you dont get perfect compression.

Edited March 26, 2017 by Nuke

[RCgothic]

Yup, fizzle at best (worst?).

If a core is not detonated precisely right, the heat of assymmetric fission will scatter the core, leaving the vast majority unfissioned and all that potential energy unreleased. And that's if any fission at all is achieved. Maybe you get none at all and the implosion charges just scatter uranium all over the place.

The trick of keeping a mass sub-critical and then making it go prompt super-critical on demand is exceptionally difficult.

Edited March 26, 2017 by RCgothic

[sevenperforce]

Paradoxically, the best way to stop a nuke from going off might be to shoot it with a gun or hit it with a sledgehammer. Of course you're dead, either from the implosion charges going off or from radiation poisoning as the core ruptures, but prompt supercriticality will be stopped before it starts. 

Modern two-point implosion nukes are designed specifically so that if there is even a fraction of a second of difference in the timing of the implosion charges going off (e.g. due to an impact rather than an intentional trigger), the fissile core will be smushed into an irregular shape and scatter. It will probably kill everyone within a block or two, but at least it doesn't go all Trinity.

Thermonuclear weapons use an extraordinary specific design (the Teller-Ullam model) to use the x-ray flux of a fission nuke to trigger thermonuclear fusion. Some of these use a fissionable tamper to further increase the yield. If an Orion ship had a premature detonation in the "fuel bay", it's possible the neutron flux from the first nuke might trigger some additional fission in any fissionable tampers in surrounding bombs. But increased energy from this would probably be less than the energy released by the conventional implosion charges. 

[Bill Phil]

Chain reactions of nuclear weapons are essentially impossible. The cores aren't capable of exploding on their own. They're very near to a critical/supercritical reaction, but the one bomb going off isn't going to compress the cores, it'll vaporize them. Or scatter them. Either way the Orion is toast... but since these aren't conventional bombs you're talking about a sub-kiloton explosion where a large portion of the energy is in a plasma cone. I'd be more worried about where that's heading.

Edited March 26, 2017 by Bill Phil

[DerekL1963]

22 hours ago, spacebrick3 said:

Anyways, what do you think? Would the other nuclear bombs go off, or would they simply rupture?

The other bombs would very likely go off (though far, far below nominal yield - essentially a fizzle).  What everyone here is missing is the proximity of the other cores to the freakin' enormous neutron flux of the bomb that detonates.  It's not often discussed in the open literature, but the 'popcorn effect' is very real.

That's one of the reasons why nuclear tipped ABM's were a thing - the neutron flux from the defending warhead would kick off a chain reaction in the incoming warhead.  Even if the reaction was insufficient to actually 'detonate' the warhead, there was a good chance it would get it hot enough to deform or to damage the explosive charge.

[StrandedonEarth]

Yeah, kinda off-topic, but seems like a good place to put this...

 

[Brotoro]

The nuclear propellant charges would almost certainly be boosted fission devices (to get much higher yield efficiency out of the amount of fissile material available)...and most of the charges in storage are not going to have their boost gas in their cores yet, since this gets injected shortly before detonation. So even if you did manage to set off a symmetrical implosion in one of the other charges (highly unlikely), you would still only get a very low yield with no boost gas.

[kerbiloid]

The charges close to the explosion would absorb the neutrons and melt/vapourize with a heat explosion.
They are too far away from the tiny zone where conditions are enough stressed to make the fission part critical or to ignite the fusion part.
They would just produce some secondary neutrons and spread their plutonium around to the great entertainment of young physicists, allowing them to build a reactor in the barn..

[sevenperforce]

Boosted fission devices are typically less susceptible to neutron radiation predetonation. But yeah, there will definitely be a lot of fissioning happening everywhere around the nuke; it's just that the whole "fuel bay" will blow itself apart faster than any individual nukes can go prompt-supercritical.

[p1t1o]

On 3/26/2017 at 3:15 PM, sevenperforce said:

Paradoxically, the best way to stop a nuke from going off might be to shoot it with a gun

I think I remember reading somewhere that this was actually procedure in some EOD manuals, under certain circumstances, like if a bomb fell off an aircraft and was damaged on impact.

With a quick google this was all I could find:

https://warisboring.com/when-to-shoot-a-nuclear-bomb-with-your-gun-f1f97093a64e#.ovpqdpho8

Quote

 

While at an air base almost certainly located in what was then West Germany, Agnew saw little evidence that nuclear weapons were under strict American control, as Congress expected.

At best there was what he later called a “token custodial arrangement” that he witnessed when he saw nuclear bombs hanging under West German aircraft with only the supervision of a young, lone American G.I. on the flight line.

“What are you going to do if these guys come running out and they’re going take off and no one has told you that it’s all right?” Agnew asked the soldier.

The soldier said he didn’t know what to do.

“What you ought to do is just shoot the bombs,” Agnew told him, counting on the high probability that bullets would disable the weapons. “Shoot those things and don’t worry about it.”

 

So less an "official" procedure then, but still...

[sevenperforce]

One of the safeties used for certain weapons systems was to have a coil of metal wire inside the hollow fissile core, with a tiny path leading to the outside. If the weapon was accidentally triggered, the wire in the center would throw off the precise implosion and render the bomb a dud at best and a fizzle at worst. To arm the bomb, the wire had to be pulled out.

Unfortunately, in some cases the wire became brittle and snapped off.

[Nuke]

even if the bombs dont go off the conventional explosives are probibly powerful enough to destroy the fuel bay and render the ship uninhabitable by spreading radiation everywhere.

[sevenperforce]

1 hour ago, Nuke said:

even if the bombs dont go off the conventional explosives are probibly powerful enough to destroy the fuel bay and render the ship uninhabitable by spreading radiation everywhere.

The first nuke would do that handedly.

Nuclear weapons are one of the few things that are actually entirely as terrible as the general population imagines them to be.

[Nothalogh]

The other thing to remember is that the energy release from the Propulsion Units is non spherical, unlike a conventional nuclear weapon.

These are nuclear shaped charges.

[YNM]

I guess I have to conclude here much like everyone else - it's probably unlike a nuclear bomb of nuclear bombs, more like just a reactor accident (of nuclear bombs).

[kerbiloid]

1 hour ago, Nothalogh said:

The other thing to remember is that the energy release from the Propulsion Units is non spherical, unlike a conventional nuclear weapon.

Until it hits a charge next to the exploded one and makes a spherical plasma cloud with spherical shockwave. I.e. it will get spherical in first 1 meter.

[Nothalogh]

Right, but you likely wouldn't even get a sympathetic detonation of the conventional explosives in adjacent devices, due to the low percentage of explosive per device

[p1t1o]

They are "shaped charges" but they are still nukes. You get a spherical explosion in terms of radiation, but it will send a pulse of denser debris in one direction, possibly two. Its not like being off the the side is "sorta ok", you still get vaporised.

Im not even sure what happens to high explosive when you vaporise it faster than a detonation wave can travel through it. I guess it still explodes.

Either way, it is certain the entire ship will be destroyed and only the first bomb will undergo a full yield detonation.

[kerbiloid]

56 minutes ago, p1t1o said:

but it will send a pulse of denser debris in one direction, possibly two.

Orion's - in one.