The fuel doesn't become dangerously radioactive until after the reactor powers up for the first time. The uranium fuel is only about as toxic as something like

The fuel doesn't become dangerously radioactive until after the reactor powers up for the first time. The uranium fuel is only about as toxic as something like barium or lead until the chain reaction starts generating fission products. This is in fact safer to launch than past space missions such as Pioneer, Voyager, and Cassini. Those used radiothermal generators that were far more radioactive and hazardous than a fresh reactor core.