It would be so expensive as to be impossible to manufacture at a reasonable scale and drive like a literal lead brick. So maybe a PR stunt on the part of the nuclear industry to show how futuristic and safe their power source is that "soon" it will be powering your automobile. Get the government involved too as propaganda about the benefits of capitalism.
Man, I love retrofuturistic pulp like this, but no way is this plausible. Forget the economics, on a physical safety level the thought of having your average Joe driving around with a mini-nuclear reactor in his dash would be a nightmare for regulators, not to mention the possible leakage of radioactive mist if even the slightest crack were to emerge inside this nucleon engine.
Would have never worked. Way too complicated. Would have needed at least 3 pumps. Reactor cooling pumps, condensate and feed pumps. How would the reactor be controlled? Moving control rods? What about start up and shut down, transients? Then you would have to worry about primary and steam generator water chemistry. What about make up water for the primary and secondary? Just don’t see the outside air being an effective heat sink for the entire system.