Three Mile Island proved the dangers of nuclear energy. Three Mile Island actually proved the safety of nuclear energy. Radioactivity did escape from the reactor itself, but was held within the containment unit by a containment safety feature. All damage was restricted to the plant itself, and although the repairs were expensive, no living creature was harmed by the radioactivity and no environmental damage occurred.
Nuclear meltdowns are a serious and constant threat.
Furthermore, only one in 5,000 meltdowns would release dangerous amounts of radiation. Nuclear power plants release harmful amounts of radiation. Most nuclear power plants emit even less, emitting only one to three millirems of radiation per year. To put those numbers in perspective, the average American is exposed to roughly 350 millirems of radiation per year from sources all around them, most of which are natural. There are better ways to produce electricity than through nuclear power.