I'm not one to be all doom and gloom about ai, but giving one its own small nuclear reactor, presumably one that's in close proximity to it and separate from the local power grid... that's obviously going to have substantial security measures around it... and be that much more difficult to cut off if need be....
I mean, it's starting to sound a lot like an unbelievable plot hole in a bad sci fi movie isn't it?
That's a nice sci-fi thought, but also not really how it works irl.
Physical proximity is not really a factor here.
There's a lot more going on at all levels that makes this absurd at best. Movies are not a good representation of reality, they can't be if they are meant to be entertaining.
Why are you saying this as if the AI would have control over the reactor.
It's unlikely they'd even be in the same building, or even the same campus. We have these crazy things called "wires" that let us transmit a lot of power over distances, so your small nuclear reactor can be remote, safe and secure and your AI lab can just be on your main campus.
You do konw, that it is IMPOSSIBLE for a nuclear reactor to explode in a nuclear fission explosion, aka become a nuclear bomb. Reaching critical mass isn't possible. Nuclear reactors can catch on fire, if built using graphite, that isn't done anymore, or have a steam explosion. but that's it.
They can also get hot enough to melt the metallic components (including the fuel itself) if the reaction isn't properly regulated (hence, "meltdown"), but you're correct that that's still not a fission explosion.