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On March 28, 1979, Three Mile Island experienced the most serious accident in U.S. commercial nuclear power plant operating history. However, this event led to no deaths or injuries to plant workers or members of the nearby community. It brought about sweeping changes regarding many areas of nuclear power plant operations – from emergency response planning to reactor operator training. It also caused the U.S. Nuclear Regulatory Commission to tighten and heighten its regulatory oversight.

Today, the Three Mile Island nuclear plant (TMI) generates enough electricity to power a city the size of Philadelphia. Its world class performance record demonstrates the exceptional focus and hard work of the people who safely and efficiently run the plant.

To learn more, click the links below:

The TMI-2 Accident – In Brief
What Happened and What Didn’t in the TMI-2 Accident
The TMI-2 Cleanup: Challenging and Successful
No Radiological Health Effects at TMI
Health Studies Find No Cancer Link to TMI
Frequently Asked Questions


On April 26, 1986, an accident destroyed the Chernobyl 4 reator at the Chernobyl Nuclear Power Plant near Kiev in the Ukrainian Republic of the former Soviet Union. With the release of radiation, human casualties, physical damage to the plant, and contamination of the surrounding environment, Chernobyl marked the worst accident in the history of nuclear power production. It also demonstrated the importance of strong safety culture, independent regulators, and well-designed plants, reinforcing nuclear safety efforts for the years to come.

According to the World Health Organization, the accident led to the fatalities of thirty-six workers. More than 200,000 people in the Ukraine and Belarus Republics were evacuated and resettled as a result of significant fallout from the Chernobyl accident. Land was contaminated in the Ukraine Republic, Belarus Republic, Russia, Europe, and Scandinavia. Recovery efforts continue to be managed by the international community.

The world nuclear community quickly determined that an accident similar to Chernobyl 4 could not happen in any other type of plant, due to higher design and operational standards outside the Soviet Union. The remaining Chernobyl-type reactors throughout the former Soviet bloc were modified for safe operation. Some were shut down; many are still in operation. Health and environmental studies are still going on, and will continue into the foreseeable future.

The World Association of Nuclear Operators (WANO), comprised of leaders from every commercial reactor in the world, was founded as a result of this tragedy.

To learn more, click the links below:

Chernobyl in Brief
What Happened – In Detail
Health Studies of Radiological Impact


On March 22, 2011 a major earthquake off the coast of Japan caused a 15-meter tsunami that resulted in the deaths of 15,800 people.  The earthquake caused automatic and safe shutdown of the Fukushima Daiichi nuclear power plants. The electric grid throughout the area was also affected, cutting the power supply to the plants, so cooling began with backup power from diesel generators at the site. Forty-five minutes later, a tsunami brought waves up to thirty feet high as much as six miles inland.  The tsunami flooded the Daiichi back up power generators. Without power, cooling stopped. Some 200,000 people were evacuated from the area. After the Fukushima Daiichi accident, nuclear power plants all over the world evaluated how they would respond to disasters that result in no electrical power being available.

The American Nuclear Society (ANS) commissioned the ANS Special Committee on Fukushima to provide a clear and concise explanation of what happened during the Fukushima Daiichi accident, and offer recommendations based on lessons learned from their study of the event.

To view the full report please visit


Scientific studies and measurements are clearly indicating that there is no public health hazard from radioactivity originating from the accident that occurred at the Fukushima Daiichi nuclear power plant in March 2011.

While nuclear professionals continue to monitor any potential dose consequences, any effect of radioactivity coming across the Pacific to the United States coast would be negligible,” noted Dr. Michaele Brady Raap, American Nuclear Society.

For more information, please review the article, Radiation dose rates now and in the future for residents neighboring restricted areas of the Fukushima Daiichi Nuclear Power Plant,  published by the Proceedings of the National Academy of Sciences of the United States of America.

‎What Happened at Fukushima?

What Type of reactor(s) are at Fukushima?

The reactors at Fukushima are typical BWR-3 (Unit 1) and BWR-4 (Units 2 – 5) designs. Prior to the accident Units 1, 2 and 3 were operating, Unit 4 was defueled, but not operating (planned maintenance), and Units 5 and 6 were fueled, but not operating (planned outage).

What lessons were learned from Fukushima?
  • Earthquake design basis adequate
  • Tsunami design basis and emergency planning insufficient for NPP and other key infrastructure
  • Must diversify, increase and secure onsite power supply to avoid core damage

The following report presents the reflections of members of the MIT Nuclear Science and Engineering faculty on the accident at Fukushima and is offered as a contribution to the debate on the implications of the accident for the nuclear industry. In it, they identify and discuss technical issues arising from the accident, and they begin a review of how the lessons learned can be used to improve the safety of current and future plants.

Buongiorno, J., Ballinger, R., Driscoll, M., Forget, B., Forsberg, C., Golay, M., Kazimi, M., Todreas, N., Yanch, J. (2011). Technical Lessons Learned from the Fukushima-Daichii Accident and Possible Corrective Actions for the Nuclear Industry: An Initial Evaluation, MIT-NSP-TR-025. Center for Advanced Nuclear Energy Systems. Retrieved from

What are U.S. plants doing to prevent such an event at home?
In the seven years since the event, the international nuclear community has rallied together to make sure that help and resources were made available to assist in evaluation, cleanup and radiation monitoring efforts. This effort has enabled the U.S. to enhance safety systems across the U.S. fleet. One of the primary enhancements is the planning for long-term loss of the diesel engines used at plants.

How many people died at Fukushima?
  • Number of residential buildings damaged or destroyed due to earthquake/tsunami: 475,000
  • Number of people dead due to the earthquake/tsunami:  > 20,000
  • Number of km2 inundated by tsunami: 560 km2 (215 mi2, about the size of Chicago)
  • Number of deaths due to tsunami at the nuclear power plant (NPP): 2
  • Number of deaths due to radiation exposure: 0
  • Number of cases of radiation sickness: 0

Sources: WNA Japanese Report to IAEA, June 2011

What has been done to prevent the spread of radioactive materials?
Sprayed dust inhibitor agents to mitigate spreading of powder dust containing radioactive materials.
Installed a reactor building cover on Unit 1.
Radiation dose at the site was held down due to rubble removal.

  • The removed rubble and waste resulting from restoration work, such as felled trees due to site cleaning, were transported after they were classified by type and radiation emitting amount at storage site.
  • The rubble was placed in containers and stored indoors in accordance with the radiation emitting amount.

PCV gas control systems were installed at Unit 1,2, and 3.

These strategies have ensured that radiation exposure from the event was minimized so that focus can continue to be on cleanup of the site.

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