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April 15, 2006

Why a nuclear bunker buster would be a bust

The Union of Concerned Scientists explains why a nuclear bunker-buster strike on Iran's underground bunkers would be ineffective and deadly.

Thanks to ecoterrestrial and the other readers who sent me this link.


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I'm very skeptical of the claim that the RNEP would penetrate only a modest distance into the ground or rock. Existing conventional bunker busters can penetrate many tens of meters, and deep penetration weapons can go much deeper, either by being lofted from high up, or by rocket assist. Penetration depths are almost certainly well into the hundreds of meters. Gun-type nuclear weapons are extraordinarily robust - there are designs from the 1950s of warheads capable of surviving the forces involved in penetrating a hundred meters of rock. I assume that today, with better simulation tools and a more sophisticated knowledge of fracture dynamics and shock wave propagation, it ought to be possible to do a lot better than a hundred meters.

The second point I take issue with is the assumption that the warhead just goes boom as opposed to using blast shaping to most effectively couple energy into the target. This also affects fallout, since energy that goes into throwing dirt into the air is energy not directed into the target. There's still plenty of fallout, all the more so if the facility is a chemical weapons dump.

Using an RNEP would be a bad idea for numerous reasons. It would almost certainly destroy the target, though.

I'm afraid I'll have to disagree with you on possible penetration depths. "Hundreds of meters" in rock or reinforced concrete is virtually impossible. The penetration depths given in the UCS article are roughly correct based on discussions I've had with the people who've done R&D work on the RNEP and related earth penetrating munitions.

Also, despite work going on since the 80s, shaped charge nuclear explosives aren't a reality yet and may never be.

I had to open it in Explorer to get that link to work.

I've been participating in a bit of a "discussion" on this topic here. Here's a hint, I'm the grumpy asshole, and feeling just fine about it thank you.

Some of the links I've used there:
-RNEP Wikipedia article is a good place to start.
-Another article from 2004.
-Info on a conventional penetrator. Note the penetration depths for a reference. The RNEP would certainly be based on similar penetration technology, probably with a big slug of depleted uranium in the nose I'd guess. Rocket assist is a possibility certainly. There've been quite a few exagerated claims by advocates as to what the capabilities of the RNEP would be, and downplaying of the negative effects to non-combatants.

I would've thought that the timescale of the nuclear reaction would be far too short to shape the shock of a nuke. I'd bet you could do something with a tungsten prism the size of a Giza pyramid... ;-)

JE - base my "hundreds of meters" on studies done of the THOR proposal during the 1980s. They were confident of a penetration depth of 500 meters with a terminal velocity of 11 km/s. I assume that a more reasonable number would be on the order of half that, using high drop altitude and an acceleration stage, which would have to be quite large, but within reason based on my best estimate of the weight of a RNEP warhead and the carrying capacity of a B2 (18 metric tons), which allows a 1 ton penetrator to attain 5+km/s with a 17 ton solid booster having a mass ratio of 8 or so (2 tons empty weight). I figure depth of penetration probably scales with energy, so 1/2 the energy should give ~125 meters without any other measures being taken. Factor in improved understanding of high pressure dynamics of solid materials since the THOR work was done, and I figure 200+ is reasonable for a serious and well run program to develop.

In addition, I assume that high quality codes similar to the one I use at work could take the shaped charge work done in the 1950s and 1960s and bring it to fruition. The underlying dynamics of blast shaping are not all that complicated if you have good simulations.

I should clarify my reasons for posting the comment above: I was hoping to avoid commentorrhea, but it's too late. Whether or not the existing RNEP program can produce a warhead capable of destroying deep bunkers, it seems likely that such a warhead can be produced. If the existing program doesn't make it work, that's much more likely due to some combination of political interference, empire building by administrators, and scientists too focused on one possible approach to the problem. That may sound a little harsh, but the fact is that large bureaucracies, as an emergent phenomenon, prioritize survival as an organization above optimizing their work-product to the demands of the executive branch.

The secondary point is that even if a 100% guaranteed kill RNEP existed, and the fallout could be minimized and contained to a limited area, it is absolutely batshit crazy to use one. Once the US starts nuking people the rest of the world is going to nuke up as fast as possible. Once that genie is out of the bottle it's only a matter of time before we get a dose of our own medicine.

Any argument against use in this conflict based on the impossibility of RNEP being successful at taking out deep bunkers risks being discredited by a successful test. It takes attention away from the important thing: US security - nuking Iran will make things worse.

The chances of a successful test may be quite small, particularly given this administration's peculiar gift for screwing up everything it touches, but I think my point about the practicality of an effective RNEP stands.

Are those figures for loose soil, or for solid rock? I would believe hundreds of feet in loose soil, but not solid rock. My understanding, from speaking with geophysicist friends of mine who are currently working on the project, is that penetrating solid rock much deeper than ~10 meters is not simply a matter of scaling up the mass or the kinetic energy of the projectile since there's only so much force you can strike the rock with before any known material that you can make the penetrator out of fails, and we're already at that limit, and have been for some time. So, it's not just a matter of penetration scaling up with energy, it's a matter of having to build your penetrator out of "unobtainium" in order to get the benefit of the increased energy, and "unobtainium" is, of course, impossible to get. Too bad, as I understand it also makes excellent point masses and frictionless surfaces.

Right now the answer to deeper penetration with a nuclear device is just using a much bigger nuke. The RNEP is outfitted with a B61 mod 11 nuclear warhead. It's a DAY ("dial a yield") neutron mirror/fission/fission-fusion warhead. It can be field set to detonate at any one of several distinct yields from ~ .3 kiloton on up to around 350 kilotons of explosive yield.

Here's a good article from "Physics Today" that explains the limitations of ground penetration in dry rock and why it's not just a matter of kinetic energy, plus it has some details on the effects of an RNEP.

In any case, we're just bickering over the minutae anyway. I wholeheartedly agree with you that whether or not it could be developed to be a completely successful weapon, it simply shouldn't be used. Pointing out that it won't work is really something of a secondary argument, in my opinion, to the moral high ground position that nuking people is just not an acceptable thing to do.

Thanks for the pointer, JE. I'm optimistic for the possibility of sneaking around some of the constraints of geophysics, but absent a few million dollar research program I'll have to admit that state of the art is up against a wall as far as penetration depths.

Incidentally, the numbers I gave above were for compact earth and soft rock. I thought I could find figures for granite in my references, but no luck.

Sorry about the 'commentorrhea', but here goes.

In a prior post I proposed that the White House and the DOD wanted the nuclear bunker buster (NBB) come hell or high water. When I said DOD, I mean Donald Rumsfeld and the civilian executive appointees. If we accept much of the Sy Hersh article, then the actual uniform-wearing soldiers and generals at the DOD are opposed to developing and using NBBs and prefer conventional bunker busters (CBB). It appears that the generals understand, all to well, the NBB whirlwind that we will reap for ourselves and our children.

Now put this in the context of the criticism of the retired generals who call for the resignation of Rumsfeld. At first blush this sounds like a whisper of sanity and courage we thought was extinct at the DOD. In part it is, but not so fast. True, the generals have learned from history and have tried very, very hard to put these lessons on warfare to practice. For example, General Colin Powell was one of the more aggressive and articulate proponents of overwhelming force, clear objectives, domestic political support, international participation, and decisive outcomes. Hersh states several times in his article how the military has studied history and learned from it, but the present civilian administration still believes that Hitler can win WWII by bombing London and demoralizing the population and getting the politicians to cry uncle. Need I say the same thing about the Allied bombing of German cities?

So does this mean that the military have got it right, and we ought to encourage more of the generals to speak out? This obvious question is really a false choice for us. To the extent that the uniformed members of the DOD believe the use of NBBs, or any tactical nukes, is insanity, then I'm for the generals. But, no NBBs is only part of the story. The generals have signed up for the notion that a nuclear capable Iran, or even just the potential to complete a nuclear weapons program, is TOTALLY AND COMPLETELY UNACCECPTABLE. They have signed up to the inevitability of military action, unless there is a complete capitulation by Iran on their nukes. However, they do not want to use NBBs or any kind of nukes when the time comes. The time may be very soon.

Prior to 9/11, Noam Chomsky and others talked about a plan for a series of wars in the Middle East that was ready to unfold from our DOD. Iraq was conveniently lauched after 9/11 because the fortuitous timing was just to good to pass up. Remember, Colin Powell had already signed up for the invasion of Iraq before 9/11. He wanted Bush to wait one more year, as did the rest of the brass, until we were better prepared, staffed, and armed. Powell was never an opponent of the Iraq war, only an opponent of going as soon as we did.

So where does this discussion take us on NBBs and CBBs, what works and what doesn't, who's insane and who has their heads screwed on correctly? The generals know we are going to war with Iran and they approve. They just want to make sure it's done the right way, with all the proper planning and resources, without nukes, and without the fantasies and delusions of Rumsfeld, the DOD civilians, and the White House. Now add one more ingredient to this ready-for-war stew. Today, Israel's Peres said, "Ahmadinejad represents Satan, not God." 'Satan' is an image that more blantantly provokes American conservative Christians, and not so much for Israelis. Israelis do not need the image of 'Satan' to formulate their response to Ahmadinejad. American conservative Christians do.

Our administration is not going to blink. For everyone's sake, I hope Iran does.

'”Commentorrhea”? I thought that was what this was for.
Anyhow, my two cents.
From the Physics Today article linked by JE: “At higher velocities’… ‘materials plastically deform and erode when the impact pressure from the target approaches the finite yield strength of the penetrator…” Exactly. The whole bomb assembly would have to be made of various kinds and compositions of “unobtanium”. To concentrate enough kinetic energy to shatter and tunnel through more than a few tens of meters of rock or concrete would necessarily fluidize the penetrating device. That’s the principle behind depleted uranium armor-piercing munitions which are basically just uranium slugs/rods with flight stabilizing fins. Uranium is heavier than lead and if you smack a few kilos of it at high velocity against a small diameter spot on the side of a tank it imparts enough energy at that spot to melt the uranium slug and steel hull to a depth sufficient to penetrate into the tank. The slug carries no explosive as there would be no way to move it intact along with its detonator and container through the hull.

It would require some very fancy engineering indeed to decelerate a plutonium pit, explosive, timing circuitry, etc., slow enough to ensure it works while slamming the surrounding bomb into the ground with sufficient velocity to pulverize rock and reinforced concrete far enough to set the explosion off at any great depth.

Anyone who has dug a trench with a pick through rocky soil or drilled rock or concrete with a hammer and star bit chisel has some idea of what bunker-busting bomb engineers are up against. As a kid my friends and I would shoot stuff: junked cars, engine blocks, brick, wood, carcasses, bowling balls, etc. with various guns and various loads. Solid rock and solid concrete even at close range with high velocity, jacketed loads gets you a few spalled flakes, a flattened or disintegrated bullet and no penetration to speak of. Years ago, I read about a guy that contracted to bore tunnels with an old tank using sabotted concrete slugs fired at point-blank range. He’d fire all day and only go a few yards. If there were a really effective method of drilling rock with some sort of penetrating bomb, wouldn’t it be used for mining? Bunker busting bombs that will actually dig up anything buried very deep is a neocon Buck Rodgers fantasy. Good luck Mr. Bush.

I love getting extensive comments and long debates in the threads. I'm lucky to have such well-informed and passionate commenters.

TOGOLOSH commented, a week or so ago, about the use of a non-nuclear device, a tungsten rod, lauched from space or on a ballistic missile, which would be a 'supersized' version of the armor piercing depleted uranium rod. My understanding is that the incredible speed of impact would produce kinetic energy and destruction of near-nuclear yield. I do not believe using ballistic delivery systems of such weapons is palatable to other nations who would be horrified at watching 75 missiles being launched and unable to determine whether the warheads are filled with nukes or heavy metal rods, or be sure as the the intended targets. Such a use of ballistic missiles is also insane.

The Hersh article suggests, very strongly, that the uniformed military has no illusions about the difficulty of using conventional means (not just CBBs) for an attack on Iran's nuclear capabilities. But, they seem to feel it is doable with a lot more in the way of tactics and boots-on-the-ground special operations. Also, the military believe that taking out every single nuke facility, known and unknown, is not a necessity. In fact, there would only be a few that would be neutralized, along with many more non-nuke targets like command and control, communicatins, and air attack and defense. Very deep bunkers would be disabled by sealing them.

The expectation by the military is that such a strike would produce a collapse of the present government and a power-vacuum-filling rise of Irani political forces that we are preparing and funding. Both the brass and the Rumsfeld civilians (including Bush) agree on this, but the soldiers don't want any nukes, and they don't want any overconfidence in technology at the expense of manpower and good tactics.

Once again this sounds so much like, "The repressed citizens will rise up against their oppressors, they will greet us with flowered wreaths, and welcome us as their liberators." Before we dismiss this as one more example of not learning from our own mistakes, consider this: Christopher Hitchens, and to a lesser extent Thomas Friedman, proffer the notion that Iranis would be so grateful if the U.S. came in, destroyed the nukes, got rid of the Mullahs, and then left right away. Whether this is true or not, or makes good policy or not, is beside the point. This is what 'Nuke-'em' Rumsfeld and the 'Near-Nuke-'em' military believe they can accomplish, regime change and all, It will begin with the Bush administration identifying several Irani nuke facilities, ordering the Iranis to shut them down and submit to inspections, declaring that all vehicles and personnel that approach entrances or depart from exits will be destroyed, and a time certain ultimatum delivered to Ahmadinejad.

As much as I hate to see a policy of quick-draw succeed and persist into the future, there is a very real possibility that our military could pull it off. If the Iranis capitulate on their nukes before a strike, the policies of this administration would be validated for some time to come.

The gauntlet has already been thrown down. I repeat the close of my last post, "Our administration is not going to blink. For everyone's sake, I hope Iran does."

Not to be nasty or anything, but why not just aim to kill all the skilled nuclear industry workers?

Wouldn't the americans just identify all the bunker entrances and any sleeping dorms nearby, hit them with big precision bombs, kill the off-shift skilled workers and seal in the rest? They're probably more valuable and hard to replace than the equipment itself.

When the rescue crews arrive, just hit the entrances a second time, to ensure the remainder of the trapped workers suffocate.

Evil Canuck - your idea beats the hell out of crossing the line with NBBs.

I'm generally a technological optimist (since I develop some slightly wacky technologies as part of my job), so I think there are almost certainly ways to achieve the objective of taking out Iran's nuclear infrestructure without some of the negatives associated with NBBs. The larger issues are not technological, so despite my differences of opinion with some of the (notably well informed) commenters here regarding technical possibilities, I think we all agree that "will technology X work" is not the issue - it's nuke use as a major bad precedent on the one hand, and the negatives associated with a war involving Iran, particularly with the Keystone Kommandos leading the charge from the rear.

togolosh, agreed, nuke use is a terrible precedent (that we've already set, but that's another story).

>the rest of the world is going to nuke up as fast as possible. Once that genie is out of the bottle

Aren't we there already? Pakistan (though at the moment they're friends with us, but we're also allying with India at the moment, so I hardly think it's a given that that's stable), and North Korea, with the most batshit-loonball dictator this side of Robert Mugabe, already have them. And the third and fourth-most-batshit-loonball dictators in the world being found in the former SSRs of the Central Asian -stans, does anyone know which of them have nukes? I know Kazakhstan ended up keeping some of the many nukes that were there, but I don't know about the rest of the newistans. Tajikistan's leader is far crazier than Iran's leaders.

It's no longer feasible to go to war with every emerging country, even every one that's our ideological enemy, when they start a nuke program.

1984 - I think that the genie can be significantly slowed in getting out of the bottle. For reference, I think that the point where counterproliferation can be counted a definitive bust is when nuclear weapons are as freely available on the international arms market, the way supersonic fighters or IRBMs are. At that point I think we can agree that the genie is firmly out of the bottle, and the only rational use of national resources is trying to evacuate from the planet completely.

We'll be evacuating all right (ok, sorry :))

Fair enough, togolosh, thanks. I may be projecting a decade or two into the future, when I say that we're already there, just as some in the administration react to the question as if it were still a few decades ago. Good that we're agreed on the most important question though.

I do think that Iran's friends in Russia and China are the ones who really have say-so in Iran, not us, unless we ruin Iran in order to save it. Also, it would be good if we readdressed the issue of guarding Russia's nuclear facilities, as a high priority global security issue. If we don't, then we'll hear the hissing of that genie tout de suite, and it won't look like Barbara Eden, either.

"Not to be nasty or anything, but why not just aim to kill all the skilled nuclear industry workers?"

While it seems old-fashioned to point this out, it would be a clear violation of the Geneva conventions. In fact, this is one of the most well spelled out scenarios. Civilian workers may not be targeted because of the skills they posess. You can bomb a factory and kill all of the workers. You can try and bomb a factory and kill the workers who live in nearby houses. You may not intentionally target the workers.

I do think that Iran's friends in Russia and China are the ones who really have say-so in Iran, not us, unless we ruin Iran in order to save it. Also, it would be good if we readdressed the issue of guarding Russia's nuclear facilities, as a high priority global security issue. If we don't, then we'll hear the hissing of that genie tout de suite, and it won't look like Barbara Eden, either.
YES, it needs to affreid of us,Russians!

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