Accordind to an article in "Luftfahrttechnik 7 (1961) Nr.2" from February 10th 1961, page 44, General Elecrtic did test a modified J-47 with an externally installed nuclear powered heat exchanger.
The 60´s have been an interesting time for engineers, when everything seems possible and problems were there to be solved.
Some of the (today silly looking) statements from the article. (translated from german) :
The danger of a crash are neglectable, it does make no difference whether a nuclear powered plane crashes, or a conventional powered (which meant piston engines these days
) crashes onto a nuclear power plant.
The danger of radiation is also neglectible, air shields gamma radiation very well, so the exposure to passengers is comparable to exposure during medical x-ray (which was believed to be safe these days ...). Only problem might be the flight crew, which is exposed for a longer duration, but next generation aircraft will fly high altitude anyway, so cosmic radiation will be about the same danger...
Google revealed the following links :
Nuclear Airplanes
NASA
(scroll down to "Nuclear Research Reactor Facility (1956-1961)" )
Aircraft Nuclear Propulsion
Technology
Atomic powered Aircraft