I was wondering as much because a local chemical plant had an incident recently and advised that the near by residents turn off the HVAC as in response to a nuclear event.

The only connections between the inside and outside units are electrical and pipes (1 about 2" dia. including insulation, one copper about 1/4" dia. and the condensate pump line).

Power would depend on who and how big the exchange was. Unless they are shooting at the nuclear fuel plant near us, the next closest would be Oak Ridge Labs.