Three Mile Island Nuclear Accident: Facts, Impact, Today

What Killed Nuclear Power in America?

3 mile island nuclear power plant
The view looking towards Middletown Pennsylvania reveals Three Mile Island and the damaged reactor number two in the foreground, March 15, 1999 in Middletown, PA. Photo by John S. Zeedick/Getty Images

The Three Mile Island accident halted the development of the U.S. nuclear power industry for 30 years. During that time, no new nuclear power plants were approved. Several that were under construction at the time of the accident were completed. As a result, the United States lost its competitive edge in nuclear engineering ability. 

What Happened?

The Three Mile Island plant was located near Harrisburg, Pa.

It had two pressurized water reactors. TMI-1 entered service in 1974 and still operates safely. TMI-2 was brand new when the accident occurred.

On March 28, 1979, a cooling circuit malfunctioned, allowing the primary coolant to overheat. The reactor shut down immediately. The release valve opened for ten seconds. That allowed enough coolant to escape to reduce pressure and heat. But it got stuck in the open position. As a result, all the coolant was released.  There wasn't an instrument that could have alerted engineers that this had happened.

New coolant rushed into the tank, but the engineers now thought that there was too much. They reduced the flow. The remaining coolant turned to steam. The fuel rods overheated, melting the protective coating. It released radioactive material into the coolant. When the steam was released, the radioactive contaminant was released into the surrounding area.

Fortunately, the amount released was not enough to harm local food supplies, animals, or people.

The TMI-2 reactor was shut down. It took 12 years and cost $973 million to decontaminate to low levels of radiation. There were 10.6 megalitres of radioactive coolant that were processed, stored, and safely evaporated.

About 100 tons of damaged radioactive fuel was put into 342 canisters. They were shipped to the Idaho National Laboratory and stored concrete containers. 

Three Mile Island Today

According to the World Nuclear Association, no verifiable health effects were found. Instead:

  • The Pennsylvania Department of Health followed the health of the 30,000 people who lived within five miles of Three Mile Island. It was discontinued after 18 years when no evidence of unusual health effects was shown.
  • The Harrisburg U.S. District Court dismissed a 17-year class action lawsuit in June 1996. Judge Sylvia Rambo said there was no proof to substantiate the plaintiffs' claims of health damages from the accident. The appeal is before the U.S. Third Circuit Court of Appeals.
  • At least a dozen studies assessed the release of radiation and possible effects. None found adverse health effects. 

On the other hand, several documents allege that there was damage. They claim that the government is not being completely honest. For example:

  • A local survey of 450 residents in the area found nine cancer deaths between 1980 and 1984. That's more than seven times above normal.
  • Hundreds of lawsuits were settled out-of-court. Millions of dollars compensated parents of children born with birth defects in the area. 

For more examples, see Startling Revelations About the Three Mile Island Nuclear Disaster.

Economic Impact 

Construction of new nuclear plants was halted for thirty years after the accident. Today, there are 99 reactors in use today, supplying 20 percent of the nation's electricity,  The Department of Energy supports more nuclear plants as a way to decrease U.S. reliance on foreign oil and to cut greenhouse gas emissions.

In 2007, companies once again started applying to the U.S. Nuclear Regulatory Commission to build new plants.

Since then, five have begun construction, and 12 more companies are looking into it. It takes about nine years for the whole process, including four years of construction. (Source: "Building New Nuclear Energy Facilities,"

The Department of Energy asked Japan to assist in developing new nuclear power plants. Japan has more expertise in advanced, fast reactors that produce less radioactive waste while producing more energy. Former U.S. Energy Secretary Samuel Bodman admitted that Japan has the best scientists and engineers for these new types of reactors.  (Source: U.S. Department of Energy, United States-Japan Cooperation on Energy Security," Environment News Service, U.S. and Japan Sign Nuclear Power Cooperation Plan, January 10, 2007)

Comparison to Other Disasters

The economic cost of the Three Mile Island disaster is nowhere near the expense of other nuclear power plant accidents. Japan's nuclear meltdown could cost $200 billion. The Chernobyl nuclear disaster cost several hundreds of billions of dollars.

In the United States, Hurricane Katrina was the most expensive U.S. disaster. It cost between $125 billion to $250 billion. It knocked GDP growth to 1.3 percent in the 4th quarter 2005. It affected 19 percent of U.S. oil production and briefly spiked gas prices to $5 a gallon.