Can you elaborate on how meltdowns are supposed to be able to kill millions of people? We've already experienced the worst-case scenario in a nuclear catastrophe: Chernobyl.
I'm not exaggerating when I say this was a worse-case scenario: A complete reactor containment failure with no secondary containment. Burning fuel rods were directly exposed to the atmosphere for days. In the end this directly killed 50 people. A few thousand were estimated to eventually die from cancer related to the incident. But to date only 60 people are known to have died due to radiation exposure from Chernobyl.
So yeah I think you're several orders of magnitude off in your risk assessment of nuclear power.