out in the real world...
Palo Verde has containment units that can take an airplane impact, and the facility has some of the tightest security in the country.
Palo Verde emergency plan
Incidentally, blowing a hole in the containment unit isn't enough. You have to wreck the core and several other critical containment systems, too. Frankly, a bomb big enough to blow open the reactor entirely would have to be trucked in, and it would probably do more damage to Phoenix if you set it off downtown instead.