This was never an actual reactor design. Ford imagined a future where nuclear power could, maybe somehow, be miniaturized. It was a vision.

Even as early as 1956, textbooks said [1]: "The fantastic possibility has been envisaged of including in an automobile enough fissionable material, about the size of a pea, to last the life of the vehicle. In order to realize why this is not within the bounds of reality, it is necessary to understand something about the fission process."

[1] https://babel.hathitrust.org/cgi/pt?id=mdp.39015003994194&vi...