How is nuclear power dangerous?

Nuclear energy as it is used to generate power can be dangerous. The nuclear reactors used to heat water to generate steam to spin turbines to generate electricity must be operated by individuals who know what they are doing. If something goes wrong, the duty crew must make all the right decisions and make them first time, every time. Failure to do so can cause structural elements of the core to fail and release both nuclear fuel and waste into the coolant passages in the core. (The fuel rods are designed to hold everything inside throughout the life of the fuel bundle.) This is what happened at Three Mile Island. Both mechanical failure and the failure of the duty crew to react correctly caused a meltdown. Spent fuel presents its own special problems. Fuel bundles must be recovered from the reactor and taken away and stored for an extremely long period of time before radiation levels are low enough to try to do anything with them. Fission byproducts are highly radioactive, and remain so for tens of thousands of years. Links are provided for further reading.