The Dark Knight Rises—nuclear effects

Disclaimer: this contains spoilers, albeit predictable ones. It’s also one of those whiny, “why isn’t the movie more realistic?” geek things. If that’s going to annoy you, stop reading now.

We’ve all got our todestrieb to deal with. The guy behind the Dark Knight Rises (Christopher Nolan) manages his by writing turgid dialogue and ridiculous action sequences; I deal with mine by thinking about nuclear weapons effects. And his script annoyed me.

Here’s the nuclear synopsis (stop now if you don’t want the “surprise” ruined): Gotham (a.k.a. NYC) is being held hostage by a madman who’s stolen Bruce Wayne’s cold fusion reactor. With the help of an errant Russian physicist, he’s turned the reactor’s core into a four megaton nuclear bomb that could go at any time. Somebody’s got their finger on the button, in case people try to flee the island (a.k.a. Manhattan). But we’re also told that the bomb is “unstable” and will explode in five months time. Just 90 seconds or so before the five months is up, Batman tows the bomb out to sea with his stealth helicopter and it detonates over the bay. A bunch of orphan kids look on from a bus as the mushroom cloud rises.

There was plenty of stupidity in the dialogue surrounding the device, but I appreciated the overall effort. The bomb was a fusion weapon, meaning it released energy through the fusion of atoms rather than fission splitting. That mechanism is consistent with the 4 MT yield. The idea that you could turn a reactor into a weapon is a big stretch, but it’s a movie; I’ll live with it. And if anyone could do it, it would be some batshit Russian weaponeer who’d been scratching out calculations in Sarov for the past ten years. He’d probably surround it with explosives instead of reprogramming it, but it’s the Internet age, and the kids would never relate.

Leaving the other problems in the movie aside, the actual moment of detonation was the real issue for me. Batman flies this thing out to sea in his stealth helicopter with around 1:30 seconds to go (why does something “unstable” have a countdown timer? I dunno, why does Batman’s knee heal halfway through the movie?). I’ll give him the benefit of the doubt—let’s say this helo is as fast as the fastest helicopter ever. According to Wikipedia the Sikorsky X-2 can move at 290 mph. That means it can fly about 7.25 miles in 1:30. Assume Gotham is equivalent to NYC, then the Batman’s got two choices: Flushing Bay or Sandy Hook Bay. I’m going with Sandy Hook—it’s (slightly) less populated.

If only there was some sort of online nuclear effects calculator that can estimate a ground burst. BAM!

Dumbo is shattered and Staten Island is on fire. Windows are busted all the way out to Queens. These orphans would have glass in their little orphan eyes if they’d actually looked. Of course, their poor little orphan retinas would already be scorched from the flash. Don’t believe the cynics: it pays to duck and cover.

And that’s another thing. In real nuclear blasts, the flash always precedes the shock wave. The flash wasn’t very bright in the movie and it arrived at exactly the same time as a low rumble (which is not what a nuke sounds like). Here’s the real deal with a 21 KT weapon at 7 miles (that’s around 200 times less powerful than the one in the movie):

Even I wouldn’t attempt to predict what happens with the fallout (maybe someone else would like to take a stab).  Needless to say, there’s a lot of radioactive water that needs to come down somewhere…

If you’re wondering who to blame for this pointless screed, blame my wife for not allowing me to explain all this to her as soon as I got home. And @eaterofsun for encouraging me.
Photo: Nuclear weapons archive

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12 Responses to The Dark Knight Rises—nuclear effects

  1. What an auspicious start to a fine new blog – I look forward to following its progress with rapt anticipation

  2. Adam Rutherford says:

    Some days you just can’t get rid of a bomb

  3. Alex W. says:

    I thought the nuclear explosion was poorly handled, too, but for different reasons — mostly aesthetic. It didn’t look anything like a real nuclear explosion — you didn’t go from flash to fireball to rising cloud. It went flash-to-cloud, instantly. As if the cloud just appears, and is not the result of the rising fireball.

    It’s really inexcusable in this day and age. There is lots of great precedent for realistic-looking nuclear explosions (Sum of All Fears is the most accurate one I’ve seen so far in a major Hollywood film). Even the blobby clouds from The Day After looked better. Heck, you can find better renderings by total amateurs on YouTube.

    I’m not sure it was supposed to be cold fusion; it looked like it was a riff on inertial confinement fusion to me. But in any case, fallout wouldn’t be much of an issue — it was a pure fusion device, which would not generate much fallout. The megaton weapons that were detonated during the Cold War were fission-fusion-fission hybrids, which made them very “dirty.” But even a very large pure fusion weapon would not be very dirty; it would just have a big dose of prompt radiation, blast, and thermal effects. Bad, to be sure, but not fallout.

    But I agree that it didn’t look anything like a megaton-class nuclear explosion, even if it was “run down” or whatever had happened to it over time.

    All of this ignores the real criticism here. Flying the nuclear bomb away, just in the nick of time, in an almost self-sacrificing way… isn’t that Superman’s schtick?

    • You’re a man after my own heart Alex. Agreed on all points. The fallout question remains an open one for me. Depending on the fusion mechanism, the device could have produced a high neutron flux that would have irradiated the water (and impurities therein). No long-lived fallout, sure, but I still wouldn’t want to be anywhere near it for a few days or weeks.

  4. ellindsey says:

    Given actual physics, the entire scene should have been unnecessary. A fusion bomb is a delicate and complicated machine. Achieving fusion is *hard*, and achieving enough of it to make an explosion requires a large number of precisely timed events to take place inside the bomb exactly as designed. If you smash or otherwise destroy a nuclear bomb, you don’t get a nuclear explosion. You get a pile of mildly radioactive scrap metal. There shouldn’t have been any need to fly the bomb out to a safe distance, when merely shooting it with the guns on the bat-bike would have destroyed it safely.

  5. Rosa says:

    Can you comment on the crashing around in the van and against the ground that the bomb did in the last eleven minutes of its countdown? I thought it was ridiculous that didn’t set it off (the only ridiculous aspect of the movie, of course)

    • HI Rosa: see Ellindsey’s comment. It’s actually more likely that the bomb would have been damaged than accidentally detonated. But without knowing the exact fusion mechanism (which Nolan wisely left out), and the nature of the perfectly timed “instability” the device suffered from, it’s difficult to say for sure either way.

  6. Salvatore Bonfiglio says:

    Nice article, I was also disappointed about the removal of the nuclear weapon, I was sure nuclear fallout and the blast would destroy the city, I mean, Imagine the tidal wave that came after that bomb. It would have doused the city with irradiated water. Anyways, I just bit my tongue and said, “It’s a fictional movie.”

  7. Loren Pechtel says:

    Note that I have *NOT* seen the movie, I’m only going on what’s been said about this and I’m wondering if it’s really as bad as it’s being portrayed as.

    As Alex W says, this is a pure fusion device. There’s no fission component to create a bunch of fallout, the only lasting radioactivity will be from transmutation due to the neutron flux.

    As for your damage calculator–that’s assuming a surface burst. I see no reason to assume this–if you’re going to dispose of a nuke at sea would you not drop it a little bit early so it has time to sink? The water is going to absorb the energy of the blast. Of course that’s far too much energy, it’s going to promptly reappear. However the thermal pulse that would have set the city on fire is gone, the rest of the blast has been spread out which will rob it of a lot of it’s destructive power and the riverbed itself will deflect a lot of the energy up over the city instead of into it.

    Finally, going back to the neutron flux–lets say it detonates underwater but not on the bottom–other than the bomb itself basically everything around it is hydrogen or oxygen. What do they do under a neutron flux?

    H1 becomes deuterium, it’s stable.
    Deuterium becomes tritium, hot. However, only one part in 10,000 of the hydrogen is Deuterium.
    O16 becomes O17, it’s stable.
    O17 becomes O18, it’s stable.
    O18 becomes O19, *VERY HOT*. It’s half life is 26 seconds, it decays to F19 which is stable. We have a cloud that’s going to head very high in the atmosphere before it falls back, any O19 created in the blast should have decayed by the time it comes back down.

    Thus less than 1 in 10,000 neutrons will induce radioactivity.

  8. What I want to know is how is Bruce Wayne alive at that cafe in Paris, When his ass was practically sitting on the bomb…he is NOT SUPERMAN or the THE HULK…is a regaular old human like us who can have vertabraes jammed into our back without being paralyzed…

  9. Pingback: Science online, solve for x edition – denimandtweed

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