Does anyone have any info on how in(?)vulnerable nuke stations are to terrorist attacks of various sorts? One could imagine planes being flied into them like 9-11, or Jihadists getting critical jobs (due to need to avoid discrimination against Muslims), and thereby getting to do just about anything from inside.

We've only had one Chernobyl so far, and that was disastrous enough for Ukraine which was fortunately a rather spacious country. How about if six Chernobyls were simultaneously unleashed by anti-Western suicide terrorists? At an already power-critical moment of course.

This issue has been extensively discussed in the comments to this article on a grand solar plan for the US.
http://www.sciam.com/article.cfm?id=a-solar-grand-plan&page=1

It boils down to nuclear reactors being quite tough targets, and heavily protected.
The containment vessel at Three Mile Island for instance, did its job and prevented major releases - even with terrorist control, which would not last long as members of the special forces would be told to take the kid gloves off, it would be fairly difficult to breach the vessel.

Bowing up a natural gas tanker or poisoning a water supply is by comparison trivially easy, as would pathogen release.