We know it’s safe enough because France has had a majority nuclear grid since the 1980s, and they’re not dead. They have reactors built in the 1960s that are still running. To my knowledge, the US Navy has never had a major nuclear meltdown either.

Undoubtedly there would be deaths from accidents. But people die. Way more people were killed by the tsunami that caused the Fukushima meltdown than by the nuclear accident. Every few decades the US will see an influenza-type event that kills 100,000+ people. Nuclear wouldn’t come close to that.