So that's the beauty of it being a nuclear reactor as opposed to an radioisotopic thermoelectric generator. An RTG will be very radioactive at the time of launc

So that's the beauty of it being a nuclear reactor as opposed to an radioisotopic thermoelectric generator. An RTG will be very radioactive at the time of launch, a nuclear reactor need not be. As long as one doesn't start the reactor before launch by removing the fuel rods, it's practically inert. One might even start the reactor only when the probe is confirmed to be on an escape trajectory from Earth to avoid the possibility of contamination.