See image below for reference.
First a hydrogen atom is shot at a uranium ( or other sufficient energy source) rod which causes nuclear fission. This creates heat energy. As you can see inside the rod container there is water. The heat energy causes the water to heat making steam. The steam is then sent to a steam turbine which transfers the heat energy to electrical energy.
Finally the steam is cooled and returned to the rod container to be re-heated by the nuclear fission.
Nuclear melt downs occur when there is not enough water to use as a transfer of heat from the heated uranium to the water. This is what happened at Chernobyl.
Essential Nuclear Energy is really steam energy, coming from a heat source that takes a very long time to run out because of its chemical density.
