There have been two major accidents in nuclear power plants. One was the failure of water cooling at the Three-Mile Island plant in Pennsylvania in 1979 that resulted in a partial melt-down of the reactor core. While there was a significant release of radioactive gases, studies have shown that there has been no increase in cancer that can be traced to the accident. Nevertheless, this accident has been cited as the major reason the growth in the use of nuclear power has essentially stopped in the United States.

The accident that caused the greatest loss of life and contamination was the explosion at Chernobyl—then in the Soviet Union, now in Ukraine—in 1986. The graphite-moderated reactor had a power spike during a test of the cooling system that led to explosions and fire. Radioactive material, four-hundred times the amount released by the Hiroshima bomb, was spread over a huge area of the Soviet Union and Western Europe. The estimates of the number of deaths range from 50 direct deaths to thousands due to cancers caused by the radiation.

Concerns over the build up of greenhouse gases and the environmental problems caused by coal mining has led to renewed interest in building new nuclear power plants. Advocates of construction point out that if a standardized plant could be designed, then licensing delays could be reduced and design costs minimized. In addition, several new types of plants have been suggested and undergone small-scale testing. These promise to be simpler and safer than traditional designs. While recycling nuclear fuel is an attractive option, the plutonium in used fuel rods raises issues of nuclear weapon proliferation. The problem of long-term storage of nuclear wastes still needs to be solved.