Nuclear-sized conventional explosions

In The Sum of All Fears, Tom Clancy writes about an 11-kiloton nuclear weapon, and states that it is not possible to create a conventional explosion of that size. Is it because the explosion’s expanding blast wave reaches un-detonated explosives and destroys them before they have time to go off? (If we were to stack 11,000 tons of TNT in a pile and set it off - or, for that matter, 11,000,000,000 tons of it.)

Related question: Is there such a thing as a small nuclear weapon (in today’s technology) that emits so little radiation that its detonation could be convincingly disguised as being merely that of a giant MOAB-type conventional bomb?

Just for information, since I know somebody will ask, Wikipedia, of course, has a detailed page of largest non-nuclear explosions. The top seems to be about 4-5 kilotons equivalent. That 11 kiloton figure has to be theoretical.

I’m fairly sure that any nuclear device puts out detectable radiation. The amount and the dispersion of the radiation depends greatly on whether it is exploded in the atmosphere or on the ground. However, there ain’t no way you’re getting 11,000 tons of TNT into the air so that ensures a distinction among ground blasts.

Can’t think of a theoretical reason for an upper bound on the mass of explosive that can be detonated in a single event. It’s possible there might be a problem with pressure at the bottom of a very large pile causing premature detonation, but you could solve this with engineering, e.g. some sort of shelving that bears some of the load.

The shock wave traveling through the mass of explosive is the very thing that sets it off; a very large explosion’s expanding blast wave won’t destroy explosive matter near the edge of the pile, it will just detonate it.

4 kilotons is about as big as we’ve deliberately set off; the F-4 Phantom in the foreground of the picture at that link should give you a sense of scale.

I’m not sure it’s possible to “destroy” a conventional explosive without releasing its energy, short of a very complicated chemical separations process. Conventional explosives are explosive because they contain oxidizers and chemicals that have huge potential energy when combined with oxygen.

An explosive shock wave, on the other hand, would tend to break down whatever structures are keeping the oxidizers and the fuel separate, detonating it even if it would normally require some more sophisticated detonator. But that’s just a WAG.

And I suppose it would be possible to have a shock wave that’s just strong enough to destroy detonators, but would leave the explosive unharmed…

ETA: Ninja-d by a Machine Elf, of all things… :wink:

Don’t recall where I saw this but the idea was that the largest blast with conventional explosives wouldn’t have all the explosive material in one big pile but several large piles of the stuff spaced some ideal distance apart. I’m not clear if there was simultaneous detonatation of all the piles or just one that would set off the rest. Maybe that doesn’t qualify as a single large explosion though.

I think perhaps trying to get 10,000 tons of TNT to cohesively explode may present an issue.
You would have to detonate it in a lot of places i think, thats a big big ball of TNT.

Perhaps not impossible, but totally impractical?

Again, any piece of explosive near the edge of the heap doesn’t know how much explosive has already detonated; all any individual chunk knows is that it’s being hit with a shock wave, and it’s time to release its own energy in response.

The Minor Uncle test in 1993:

So one initiation site, right at the center.

I think this is a pic of ground zero for the Minor Scale test, with the hemispherical dome behind them containing almost 5 kilotons of ANFO (explosive yield equivalent to 4 kilotons TNT). You could scatter initiators throughout the pile to achieve a more rapid detonation event, but consider this:

-the dome appears to have a 15-meter radius.

-the detonation velocity of ANFO is about 4200 meters per second.

-If you use a single initiator at the center, the blast wave will reach the outer edge (thereby completing the whole detonation event) in 0.003 seconds.

You could speed up the detonation event with multiple initiators, but not by much.

A nuclear weapon creates an explosion by superheating the air with X-rays as they are absorbed (called the thermal pulse). As the initial air heated by the thermal pulse expands and rises up, it creates a shock wavefront when meeting the still cool, unmoving air, which is what creates the blast overpressure and suction effects (mushroom cloud) characteristic of a nuclear explosion.

Conventional explosives cannot produce either the detonation wavefront speed or the thermal effects of a nuclear device. Very large explosions can produce a mushroom cloud, and thermobaric bombs can produce high velocity wavefronts, but neither would be confused for a nuclear blast by someone knowledgeable about nuclear weapons, nor will they produce residual radiation. Even the cleanest nuclear devices detonated in airburst will still have radioactive pieces of case debris and some amount of irradiating neutrons, and of course the characteristic electromagnetic emissions which will interfere with radio transmissions.


What do you think of the other details, Stranger? In Sum of All Fears, the terrorists have a budget of a few million, a former soviet weapons designer, they recovered a live nuclear weapon that was lost in the field, so they have the plutonium core, and they have some stolen tritium. Could they really put together a boosted fusion device?

I think it’s safe to say that when one of your available assets is a live nuclear weapon, you can use your assets to come up with a live nuclear weapon.

One of the things they don’t talk about much is you need more than just the plutonium core, you need a strong neutron source initiator you need to install. This initiator is highly radioactive and has a short half life and is not something you can just go order.

Polonium-210. Half life of 138 days. Or you need an electronic neutron source, which is not something they carry at radio shack…

The “live” nuclear weapon was a 60s era device that had sat in the ground for 30 years. It needed reengineering, and was just a source of plutonium.

My main problem with the plot was that a single former Soviet nuclear weapons engineer was an expert on plutonium criticality and metallurgy, shaped charge explosives and detonation timing, and tritium boosting. And was able to reengineering the device without the benefit of a supercomputer and software.

To be totally fair, he could have perhaps pulled up a set of stolen (from his workplace) blueprints for a simple and efficient Soviet era device, which would have had all the exact dimensions as worked out by their teams of mathematicians + computers. I agree, though, especially in the Soviet system - no one person would be an expert over that broad a scope.


Which, okay, that’s funny, but they then link to Misty Picture at the bottom of the page:

Nuclear explosives create a much “sharper” shock wave than chemical explosives, the results of which can be detected. For example, shocked quartz is created by nuclear explosions and meteorite impacts, but not chemical explosives or exploding volcanoes.

From that article:

So the charge was only 4675 tons of ANFO. And on the ground. To simulate an 8kt airburst you’d have to put your sensors a lot closer to the charge.

To add - conventional explosives are a mix of oxidiser and fuel. ANFO and gunpowder perhaps the best known. But high explosives tend not to be. They explode for the opposite reason. They are already reacted compounds, but compounds that are really really unhappy about staying so, and wish very much to become simpler separate compounds. The usual situation being compounds that have rather more nitrogen atoms in them than you might normally expect, and which seek to become much simpler compounds and a lot of nitrogen gas. TNT - tri-nitro-tolurene. There is already a clue in the name. Or gun-cotton (Nitrocellulose), Nitroglycerin, Pentaerythritol tetranitrate (one half of Semtex), RDX (O[sub]2[/sub]NNCH[sub]2[/sub])[sub]3[/sub] (the other half). Getting an idea of the pattern?

The point of these is that they will begin to disassociate with only a little provocation, such as a shock wave passing through them. They don’t actually burn in any sense, and no ignition is needed. An explosive that actually burns in some sense needs the reaction front to reach the unreacting material, and that front travels sub-sonically. Which means they are not high explosives.

A discussion of such chemicals is clearly incomplete without the required reference to Things I won’t work with.

If you’re going to link that blog in connection with nitrogen compounds, then you might as well go all the way. It’s almost physically painful to look at the molecular diagram in that one.

:smiley: - that was actually the one I was looking for, but I settled on the first I found that fitted. Not wrong, that is a seriously evil compound.

Yes, but maybe a perpetrator nation or group wouldn’t want to betray their nuclear hand.