Godzilla '14: Good, But Sadly Disappointing (Spoilers, Duh)

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JerCotter7 said:

They also don't care that a nuke doesn't give off radiation before it has detonated so they also stuffed that in the movie.

For all we know they have some other sense for locating nuclear material. It's a giant monster movie, virtually anything goes when it comes to the monster's capabilities, hence Godzilla's atomic heat ray, which isn't exactly biologically plausible, but is still awesome.