My first thought would be "NO." Unless it is kept in an area where there are certain radiological distractions or reasons for the presence of such material. Except that fissionable material has to be so much more potent and pure that I think it would still set off alarms which would then be completely checked. I still think this nuke stuff is disinformation tactics. Look for the chemical or bio-attack or heck even truck bombs. It may come from multiple directions.
Funny, I just started the first book of the "Left Behind" series on the post RAPTURE world. This is a little eerie. LOL
I enjoyed the Left Behind series and the books are a very quick read. I have not yet read the most recent volume though. I know you'll enjoy the series, too!
Now, as far as nukes... Could a winch be used -- in a practical sense, I mean -- to transport a sizable nuke? I.e., consider this scenario: A winch hooked up to a Hummer, e.g., brings the nuke in from a small-town waterway that has NO air sniffers...then the nuke is transferred to a lead-lined vehicle or other carrier and parked out of the way somewhere in a lazy town until it is time to head for a specific target area. Possible or unlikely?