The generation of electricity through nuclear energy reduces the amount of energy generated from fossil fuels. Less use of fossil fuels means lowering greenhouse gas emissions.
Currently, fossil fuels are consumed faster than they are produced, so in the next future these resources may be reduced or the price may increase becoming inaccessible for most of the population.
The Chernobyl nuclear accident is, by far, the worst nuclear accident in the history. Different wrong decisions during the management of the nuclear plant caused a big nuclear explosion. There are still dangers but precautions have been taken to try and reduce the radiation.