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

Posted in Nuke geekery, The Freak's Shame | 12 Comments