Because coal desposits in the ground have bits of Uranium and Thorium which are radioactive, they get concentrated in coal fly ash, and blow out the chimney in the smoke from a coal power plant, and kill people, they leach into the soil and waterways, and kill people.
That is, nuclear power plants only kill people by radioactivity in the case of an accident. Coal power plants do it in normal operation. As well as coal dust having a PM2.5 dust problem which kills people.
Make it about nuclear vs coal because people say coal is better than nuclear because it's not scary radiation, and it actually is.
> "Both are bad"
Nuclear generates more power from a Kg of fuel, with less CO2 pollution and fewer deaths. It's not bad, but even if it was bad it's not "both sides", it's much less bad.
[yes coal disasters also kill hundreds of people: https://en.wikipedia.org/wiki/Aberfan_disaster ]