Interesting that the concept is based on steam engine. Would there be a way to recondense the steam for reuse, or did they plan to just release all of them? Then they would need to run on water, much like the steam locomotives of the past.
given that the "fuel" was set to be replaced every 5,000 miles, i'm going to guess that it was going to be reused, but likely the need for weapons grade plutonium and the amount of shielding required made it not feasible to even think that far, so no idea what the end product would have entailed.
but there are a lot of reasons why it never made it into production.