The blinking red message at the core of Hersh's piece in the New Yorker is of course about the use of tactical nuclear weapons, specifically the ``B61-11'' bunker busters.
Hersh certainly gives no free pass to the danger of using such bombs, but suggests that the reason for going for them is this: conventional weapons won't do the trick.
As Robert W. Nelson, a PhD in theoretical physics who now works on arms control issues at the Union of Concerned Scientists, showed here
and in Physics Today, it just isn't that simple. It is hard to penetrate, make sure the nukes destroy the bunker, and impossible to limit massive fallout.
Nelson's arguments were sufficiently compelling that the led to the withdrawal of funding requests for ``robust nuclear earth penetrators'' by the Bush administration last year. My great concern: The Bushco decision makers simply don't care about this reality!
More below the fold.
The notion of bunker busters is relatiely simple. First, aim a missile right at the earth and bury the bomb. Second, detonate the bomb. The efficacy of buried nuclear weapons at generating blast shock and damage are sufficiently large that even a ``small'' one kiloton of TNT (1 KT) yield weapon, the nominal number for the B61-11 warhead, can do a lot of damage.
What are the problems with this?
1) Missiles cannot penetrate more than four times their length into the earth There are basic materials problems which inhibit earth penetration. Nelson provides this anecdote about early tests of unarmed B61-11s:
``In two drop tests from approximately 2.5 km (40,000 ft) near Fairbanks, Alaska an unarmed B61-11 penetrated into frozen tundra only 2-3 meters.''
Moreover, Nelson cites
``George Ullrich, the civilian deputy director of the Defense Special Weapons Agency:
`There is a limit to how deep you can get with a conventional unitary penetrator. Fundamentally, you're not going to come up with a magic solution to get 100 feet
or deeper in rock. If you go to higher velocities you reach a fundamental material limit where the penetrator will eat itself up in the process, and in fact that will achieve less penetration than at lower velocity. So you get into these different regimes where you are really just fundamentally limited, physically, in how deep you can get into rock'."
Nelson then goes onto argue in detail that you cannot penetrate to depths of greater than four times the missile length. For a 3m missile, that would be 12m, or about 40 ft. That is probably a reasonable ballpark number for the B61-11. Hersh states that the Iranian bunkers allegedly containing centrifuges for enriching uranium are at depths of greater than 75 feet.
2)The nuclear blast will not do enough damage if the bunkers have enough concrete reinforcement. Here I will just cite Nelson directly:
``A low-yield nuclear EPW would still only be able to destroy facilities relatively close to the surface. Despite the increased coupling of a buried explosion, even a 1-kiloton nuclear weapon cannot destroy a structure protected by more than about 30 m of concrete from the point of detonation.''
In the course of Nelson's article, you will find out that with the kind of penetration of the B61-11, direct blast will not likely reach the Iranian bunkers, but rather if they are destroyed it will be by seismic damage from the blast shock wave moving through the earth. Of course, we don't know the details of the Iranian centrifuge bunkers. In the absence of certainty there is this, a real concern for me since Cheney, Rumsfield, and Bush would be more likely to listen to the Curtis LeMay types than oh, say, JFK was:
``Very large yield ([much larger than]100 KT) weapons are still required to destroy facilities buried under the
equivalent of 100 m of concrete.''
That, you see, is large, in the range of strategic nuclear weapons. If Bush is determined to rout an Iranian threat, why would he hold back?
3) Even if only low yield weapons are used, fallout is large By burying the nukes, you guarantee that a large plasma (fully ionized gas) will blow from the earth and a big crater will be formed, even for a low yield explosion. The much larger than 1 KT blasts at Nagasaki and Hiroshima for example were in air and left no craters. This cratering by even small weapons, and the need to go very deep to contain blasts, were discoveries made in underground tests by the US. Nelson notes that even a 0.1 KT weapon has to be buried at depths of greater than 140 feet to avoid breaking the surface, and as we see above the nominal burial depth for the B61-11 is no better than 40 ft. Hence, there will be a lot of radioactive fallout generated from even rather small blasts. This is much worse than for surface or in air blasts. According to Table 2 of Nelson's paper, an 0.1 KT blast centered 30 m below the surface generated a 31 m radius crater, about 100 ft. A 1.2 KT blast at 5.2m below the surface made an 80 m (260 ft.) radius crater, and the same blast above ground made essentially no crater.
Nelson predicts tens of thousands of resulting deaths from the fallout under typical third world conditions. The Natanz enrichment facilities discussed in Hersh's article are close to Eshfahan, a city with a metropolitan area population of about 2.5 million. There could be a lot of damage.
So from my perspective, this are much worse possibilities than what Hersh points out. First, the Iranians are no dummies. They buried the facilities to make them impervious to straightforward attacks by the Israelis or us. Second, the nuke hungry crazies in the pentagon appear to have little or no restraint. Why would they stop with bunker busters?
As Hersh notes, these ``crazies'' include folks are not leading scientists, in contrast, to say The JASON Group. They are dominated by defense contractors and consultants and corporate types. Apart from one or two clear scientists/engineers, this does not look like the kind of group that would offer great technical advice or offer restraint. They are more prone, I would suspect, of not living in the reality based community.
Third, Bush has proven again and again that he has genuine contempt for the strictures of working within the constitutional framework of our government. Given his messianic self image, I see no reason for him to genuinely consult Congress on this, and of course he seems to be only talking to the congressional echo chamber according to Hersh.
Hersh has done the US and world a terrific service by putting this out there. With the window of time available, we should marshall all forces to get the word out that these ideas are simply crazy and in particular the nuke option must be put off the table, as the Joint Chiefs apparently want.
You can imagine if a city of 2.5M muslims is nuked, that the dogs of terrorist warfare will be unleashed--Hezbollah will be let off the leash, and we will be in a much less safe world. Let's go after the Iranian nuclear program in a different way, and urge Reid, Kerry, Boxer, Feingold, Pelosi, Durbin, et al to step up to the plate and constructively raise hell on this issue.