> What's the absolute worst that could happen when a water mains breaks?

People drink contaminated, unpotable water and die.

> What's the absolute worst that could happen when a train derails?

People die.

> What's the absolute worst that could happen when a backhoe snacks on a fiber trunk?

Life-critical infrastructure that depends on the communication fails in a bad way and people die.

> Now, what's the absolute worst that could happen when a nuclear reactor spirals out of control?

People die.

Nothing in life is without risk.

Nuclear reactors spiraling out of control have killed fewer people per KWH generated than any other source of energy that human beings have come up with.