Nuclear power is any method of doing work that makes use of nuclear fission or fusion reactions. In its broadest sense, the term refers to both the uncontrolled release of energy, as in fission or fusion weapons, and to the controlled release of energy, as in a nuclear power plant. Most commonly, however, the expression nuclear power is reserved for the latter of these two instances.

The world's first exposure to nuclear power came with the detonation of two fission ("atomic") bombs over Hiroshima and Nagasaki, Japan, events that help bring World War II to a conclusion. A number of scientists and laypersons perceived an optimistic aspect of these terrible events. They hoped that the power of nuclear energy could be harnessed to do much of the work that all human societies face. Those hopes have been realized to only a modest degree, however. Some serious...