Someone called AVHistoryBuff posted a very interesting video on YouTube recently: Hot Flight: The Quest for Nuclear-Powered Flight. I highly recommend it; it's an old Air Force propaganda film from the '50s discussing the Convair NB-36H flights. For those not familiar with this, they installed a 1 MWth research reactor in the bomb bay of a B-36 and flew it around - it didn't propel the airplane, it was only used to gather data on radiation shielding.
Incidentally, there's no mention in the film of the cargo plane full of paratroopers that supposedly trailed the NB-36H in case it crashed. I've been wondering for a while now if that may be just an urban legend.
(Hat tip sferrin of the Secret Projects forum.)