The German THTR-300 reactor operated with air cooling: https://en.wikipedia.org/wiki/THTR-300 https://en.wikipedia.org/wiki/THTR-300 But it was admittedly a h

The German THTR-300 reactor operated with air cooling: https://en.wikipedia.org/wiki/THTR-300 https://en.wikipedia.org/wiki/THTR-300 But it was admittedly a huge cooling system for a reactor that only produced 750 megawatts of thermal energy.