[nukeman]

Yes, you can have the reactor offline, with control rods inserted for launch. Then when you reach the requisite altitude, withdraw the control rods and start up the reactor. In the event of a launch accident and potential destruction of the reactor, the enriched uranium fuel would be a chemical hazard (uranium is a heavy metal like lead), but only a mild radiation hazard (since there are no high-gamma fission products, and the uranium has undergone heavy purification prior to fuel fabrication).

[m4rtink]

I think this is the default for any launch of reactors from Earth - launch inert, possibly in pieces and ideally in re-entry proof capsules so you prevent contamination and can re-launch after a failure.