On April 26, 1986, reactor #4 at the Chernobyl Power Plant exploded, spreading radioactive contamination. There is much debate about the effects, the magnitude of the effects, and the causes, but we can put together a summary of the root cause analysis here.
It is estimated that thousands (perhaps tens of thousands) of people will die from the aftereffects of Chernobyl. More than 4,000 children have contracted thryoid cancer. Additionally, between 50 and 250 million Curies of radioactivity were released, more than 350,000 residents have been resettled, a large area remains contaminated, and over 20 countries received radioactive fallout.
The radioactivity, which had built up in the reactor, was released by an explosion and a fire that occurred due to an uncontrolled power surge. Inadequate containment resulted in the radioactivity spreading beyond the plant. The power surge resulted from several actions that increased power and disabled safety systems, and from an unsafe reactor design. (The reactor was designed so that increased steam production leads to an increase in power. US reactor designs are the opposite.)
The after-effects of Chernobyl continue. The applications of lessons learned from root cause analysis have been applied in many areas – nuclear power, evacuation planning, radiation health treatments, and food supply. The only remaining reactors of this type are being shut down. Hopefully this will not only ensure that another Chernobyl never occurs, but will also improve the safety of many other industries.