No. Nuclear plants (at least in Belgium) open their LANs manually at random (by that I mean, when their network guy is ready, not that it's a random hour) only to download their software updates, get the SHAsum on another medium before verifying the downloads and then updating the software.

And this is recent. 5 years ago it was still a man in Lyon taking a locked briefcase with a usb stick inside driving from Alstom to the Belgian nuke plants. We can still go back to that if the WAN their LAN connect to seems to be compromised.

If LLMs were able to do anything about nuke plants, that would be the least of our worries. Also LLMs are shit at understanding networks. SD-WANs are their absolute limit atm.