28 March 1979

A coolant leak at the Three Mile Island’s Unit 2 nuclear reactor outside Harrisburg, Pennsylvania leads to the core overheating and a partial meltdown.

The Three Mile Island nuclear accident was a significant nuclear accident that occurred on March 28, 1979, at the Three Mile Island Nuclear Generating Station near Harrisburg, Pennsylvania, United States. It is considered one of the most serious nuclear accidents in U.S. history.

The accident began with a combination of mechanical malfunctions and human errors. A series of equipment failures, including a stuck open pilot-operated relief valve in the secondary system, caused a partial meltdown of the reactor core in Unit 2 of the power plant. This led to the release of radioactive gases and iodine into the atmosphere.

The accident sparked widespread fear and panic among the public, as there was uncertainty about the extent of the release and its potential health effects. Although the amount of radioactive material released was relatively small compared to other nuclear accidents like Chernobyl, the incident had a significant impact on public perception of nuclear power in the United States.

In the aftermath of the accident, a thorough investigation was conducted to understand its causes and consequences. It revealed flaws in the design of the reactor, as well as shortcomings in training and communication among plant operators. The incident prompted major improvements in nuclear safety regulations, emergency response protocols, and operator training standards in the U.S. nuclear industry.

Despite the accident’s significant impact on public perception and policy, there were no immediate fatalities or injuries directly attributed to radiation exposure from the Three Mile Island incident. However, it had long-lasting effects on the nuclear industry, leading to increased scrutiny of nuclear power plants and contributing to a slowdown in the construction of new nuclear facilities in the United States.