Many years ago I was driving through the middle of nowhere Idaho throught the Idaho National Engineering Lab (INEL). I folowed the signs and stopped at an early commercial design atomic reactor (the first?) that had long ago been decommisioned and was turned into a museum. Unforuantely they had just closed for the day, but I did get out and look at two interesting things displayed in the parking lot.
I recognised them as some kind of power plant, but they were slightly different from each other. What really caught my eye is that there were mounted on railroad wheels, but were so big that they spanned two standard gauge tracks built parallel to each other. The informational sign explained that they were rail mounted so that they could be moved between the shop areas and the test area (in another location on INEL, they were trucked to the museum for display). They were relics of the early part of the cold war, and were indeed power plants as I had guessed. But what I could not have imagined, is that they were the prototypes for a steam powered jet bomber that could stay aloft almost indefinately - they were atomic reactors! It claimed that they were only the testing models, were succesful, but the project was cancelled before a working model for flight testing was developed. As I recall, it did state that the development of these resulted in several new alloys and other construction techniques that were applied elsewhere.
Can you imagine a nuclear bomber flying overhead carrying nuclear bombs? If you look back far enough in old Mechanics Illustrated (?), you will find that it was intended that this technology would also be used for locomotives. The reactor would have been surrounded by a primary shield, only the cab would have the secondary shielding. That would have taken the discussions about boilers here to a whole new level!