Sure. A nuclear reactor can be sent up "cold". If it is not critical (i.e., no chain reactions) you could walk up and kiss it.
Once in space, you "turn it on" by positioning reflectors and/or moderators to make the reaction "critical".
The Russians orbited enormous reactors to power sea-scanning radars. One of them fell on Canada several years back.
The containment of a space reactor would be very robust. I've seen high-speed film of containment vessels for RTGs being tested for integrity. Basically they are launched into a reinforced-concrete wall by a cannon or rocket. The wall loses.
--Boris