Cashing in on the 1950s fascination with atomic energy Louis Marx and Company released the Linemar Atomic Reactor. It was actually a steam engine, with its boiler disguised as the reactor dome and a battery powered cooling tower that had moving lights in it. I guess the moving lights simulated the atomic power surging within the plant.
The German company Wilesco with their R200 Nuclear Reactor steam engine (in the above video) was another steam powered nuclear power plant facsimile. It was released in the 1960s and its high price, coupled with a growing stigma attached to nuclear power, led it not being successful in the toy steam engine market.
Finally, above is an actual radioactive toy from the 1950s. It is the Gilbert Radioactive Atomic Energy Lab Kit with Uranium. I'm sure I would have lusted after it in my boyhood and happily irradiated myself conducting experiments and what-not.