How is nuclear power dangerous?
Fuel used in nuclear power plants are radio active substance like U 235 or P 239.
They emit radiation at high levels which is harmful for life forms of all kind.
If any accident or leak happens in the system huge amount of highly toxic materials escapee to atmosphere or water.
If some problem happens in control system it will lead to explosion or melt down
The waste products are difficult to dispose..
These radio active substances remains toxic for millions of years.