The answer will surprise many.
There is much debate - growing debate - about the viability of using the "standard" method - explosives - to shut down the Deep Horizon (BP) oil well runaway. I think that there are many of us scientists who think that between American ingenuity using conventional explosives, and the Russian success using subterranean nukes, there has to be a viable answer using explosives. Empirically, this has always worked for shutting down runaway wells, and I tend to advocate going with what has worked before. But the Russian data is rather old, flaky, and skewed from the exact situation at hand. Moreover, there are a lot of oil cognoscentes over at "The Oil Drum" who are very skeptical about a nuclear option, much less a hastily constructed one, and those folks seem content to opt for the slow process of drilling relief wells.
I'm not sure which way to go at this point. But one thing is very apparent. Except for the physical scientists and well-read-in-science lay people, almost everybody posting has a very screwy view of nukes. While some of the realistic suggestions involve using nukes up to the size of "Little Boy" (about 15 kilotons) - basically to melt rock and seal the entire region of the top of the well - most folks are suggesting the use of much smaller devices to shift rock and decapitate the oil well, exactly along the lines of standard practice with conventional explosives. However, all of the more sensible ideas are getting lost in a witches brew of misconceptions about nukes.
An uncomfortably large majority of people seem to think that nukes are all huge and produce prodigious amounts of radiation that will destroy the Gulf for generations. Were this the case, they would be entirely correct that all nuclear options are basically Strangelovian. However, reality differs. And that's what this post is all about. Putting it in perspective. I'm not going to deal with the more technical questions of whether the geology of the Gulf allows for particular types of bursts to produce particular types of effects without particular risks. There is a lot of opinion here, and it's easy to see why the extreme lack of concensus would scare Obama away from any kind of gutsy option.
But there are simple facts about the size of nukes that are making people dismiss nuclear options as totally unworkable, when it's likely that they not only ARE workable - they may very well be needed in the future for faster action on oil well runaways. What might be a hasty option now could be a much better option in the future. Spills like this will happen again, and we really can't afford to go through months of relief-well-drilling and mega-pollution every few years. A faster method of emergency shutdown is advisable - if only as a trusted last resort.
Anyway, let's look at nukes.
Time for science class. How big is a nuke? Hiroshima? Bikini Atoll? Well, not necessarily. Consider a backpack nuke. Or a suitcase nuke. Remember the old encyclopedia picture of the nuclear artillery shell? Well, that was actually about as big as the Little Boy device dropped on Hiroshima - roughly 15 kilotons of TNT. The energy released by one of these smaller guys can be much less - as little as 10 tons of TNT, or as high as 1000 tons, meaning one kiloton, for one particular model. You can actually dial it down even smaller with a custom device, but let's just work with 10 tons for now. These are small devices, designed to take out a cluster of buildings, a dam, a really big bridge, or something similar. At their lowest setting, they are only moderately bigger than really huge truck bombs. You could use one to, say, demolish Mount Rushmore or Bear Lodge (that's Devil's Tower to most folks), or obliterate all of Times Square, or some revered building or buildings in Mecca. Now you see why we should ALL be afraid of these things falling into the wrong hands. They're VERY usable, particularly against small, sacred landmarks. But in the right hands, you could do something useful. Like the Russians did when they stopped their wells. Or, say, move a bunch of rock 20 feet outward in a circle. You might even do that to, say, chop off the head of an oil well on the sea floor and bury the rest under a bunch of rock..
You still don't believe me? You're still seeing Bikini Atoll in your mind? Big fireball in the Pacific? Hiroshima being flattened? I understand. Would numbers make you feel better?
One ton of TNT is 4.184 × 10^9 Joules (meaning 4 billion Joules)
Ten tons of TNT is therefore 41.84 × 10^9 Joules (or 42 billion Joules)
One barrel of oil is 6.1 × 10^6 Joules (meaning 6 million Joules)
Now, you would have a valid argument that this is looking at the volume of apples and doughnuts compared by caloric content. Which is true. But I'm trying to show you the BIG PICTURE. I'm trying to show you BIG OIL SPILL versus SMALL NUKE.
The reliable mainstream media estimates coming out now about the rate of the Deepwater Horizon spill - BEFORE they cut the pipe - are on the order of 20,000 to 40,000 barrels PER DAY. Put another way, they think that - by June 3 - 1.76 million barrels escaped. We can do lots of fun math with this.
Spilled Oil Daily (20,000 bbl) is 1.22 × 10^11 Joules (or 122 billion Joules)
Spilled Oil Daily (30,000 bbl) is 1.83 × 10^11 Joules (or 183 billion Joules)
Spilled Oil Daily (40,000 bbl) is 2.44 × 10^11 Joules (or 244 billion Joules)
At the upper limit there - which is less than some estimates of 50,000 bbl/day - we are basically talking a QUARTER TRILLION JOULES PER DAY. But let's just take the middle value of 30,000 bbl/day. That means...
4.37 nukes per day on the lowest setting.
Or better still...
Total Spill by 6/3 (1.76 × 10^6 bbl) is 10.7 × 10^12 Joules (or 11 trillion Joules)
which would be...
256 nukes on the lowest setting
2.5 nukes on the highest setting (for that model of small nuke device)
Now that's just the energy equivalent of the oil coming out versus the energy which would be partially used to move some rock over, crush the well, and stop it. It isn't designed to truly provide some magical parameter for choosing options. It doesn't really look at the apples-versus-doughnuts environmental costs of oil versus radiation - both of which have prompt and long-term costs. It doesn't even let you know if using a small nuke would work. It very well might not - even if it was without risk to the geology or the environment. But I hope that I've educated you as to the MAGNITUDE of small nukes. As in SMALLER THAN OIL. That is something that you are most likely not familiar with, as opposed to oil spills, which you CAN get your mind around for historical reasons. And you can also see that, even if the environmental damages are comparable (which they're not, but you have to get into a lot of nuclear mumbo-jumbo to understand that), something that's about 4 thousandths of the other just ain't that big. In fact, I would say that something that's a QUARTER of the other on the first day isn't exactly scary.
What's the point? Perspective. The nukes we're talking about are not the Godzilla-creating behemoths that vaporized entire islands in the Pacific Ocean. We're basically talking about things which range between super-truck-bomb and multi-block-buster size - and which are more viable than conventional explosives, because instead of being a mountainous pile of dynamite in the middle of a football field, they fit into something the size of a briefcase or an artillery shell.
If anything, these devices are MORE scary than big nukes, simply because they are so small. So portable. So...... usable.
And THAT may be Obama's real reason for not even going there.
PS - Since we actually explored a more interesting variant of the title question, because I just boggle at the idea of using nukes as a unit of measurement, the reciprocal problem of determining barrels is left for the reader.