There were indeed real nuclear reactors with thermoelectrics being launched in the cold war.
However, thermoelectrics have an efficiency well below 10% (maybe a bit better with this improvement but not much). For that reason, future reactors in space will likely use Stirling engines instead.
However, thermoelectrics have an efficiency well below 10% (maybe a bit better with this improvement but not much). For that reason, future reactors in space will likely use Stirling engines instead.