I'm pretty sure any sort of practical space based radiator system would not use circulating coolant but would probably use heat pipes. No moving parts and for large systems you generally use many small pipes in parallel. Combine these and you get an extremely reliable system that fails gracefully. Which sounds like a good idea for any sort of nuclear reactor safety system.

The Shuttle used a combination of heat pipes and circulating freon (and dumped the waste heat during ascent into the cargo bay, poor cargo!), but also did not have a nuclear reactor on board.