Safety concerns. In the United States, concerns about the safety of nuclear reactors increased after a serious accident in 1979 at the Three Mile Island nuclear power plant near Harrisburg, Pennsylvania. Mechanical and human failures resulted in a breakdown of the reactor's cooling system and the destruction of the reactor core. Scientists and technicians prevented a failure of the reactor vessel that might have released large amounts of radioactive isotopes into the reactor containment building. Cleanup of the plant was completed in the early 1990's.

Excerpt from the "Nuclear energy" article, The World Book Encyclopedia © 1999