There were Multiple Proposals for trains that were Nuclear Powered.
Earliest Proposal[]
The Earliest Proposal was made by Dr Lyle Borst at the University of Utah, He suggested a 360 ton x-12 locomotive that carried a nuclear reactor fueled by Uranium-235. He went as far to contact the association of American Railroads as well as numerous railroad companies; as much as like nuclear submarines and boats that have nuclear reactors on board, a train operating with such a setup would technically be able to operate for months without refueling this particular design was intended to use urinal sulfate in a water solution instead of solid fuel elements, but this atomic train was never built due to the problems with nuclear reactors and the public.
British Rail's Proposal[]
On August 1, 1952, The Eagle Comic had featured an artist impression design of what a nuclear powered train would look like on British Railways'/British Rail's behalf on the Atomic Train Project. But that atomic train was never built either due to the problems with nuclear reactors and the public and also because they had already crashed a locomotive into a nuclear flask due to the public being scared of nuclear things.
Germany's Proposal[]
West Germany in the Mid 1950s also had an Atomic Train Design proposed by Krauss-Maffei that would look like on the Deutsche Reichsbahn's behalf on the Atomic Train Project. But that atomic train was never built either due to the problems with nuclear reactors and the public.
Soviet Union's Proposal[]
The Soviet Union proposed a massive cotton trekking train-setup driven by a nuclear reactor; the artists of that drawing had also drew a Deltic diesel Locomotive from English Electric mainly for a size comparison on the proposal, It was basically the Soviet Union's behalf on the Atomic Train Project. But that atomic train was never built either due to the problems with nuclear reactors and the public.
William Gregory Taylor's Proposal[]
There was another proposal by William Gregory Taylor in 2008 where he proposed a Maglev Train driven by a Nuclear Reactor, And that atomic train was never built at all either due to the same problems with nuclear reactors and the public.