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Fukushima nuclear disaster

The Fukushima nuclear disaster was a major nuclear accident that began on 11 March 2011 at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Japan, after a powerful earthquake and tsunami disabled cooling and power systems.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

The Fukushima nuclear disaster was a major nuclear accident that began on 11 March 2011 at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Japan, after a powerful earthquake and tsunami disabled cooling and power systems. The accident caused core damage in three reactors, hydrogen explosions, radioactive releases, and the evacuation of surrounding communities.

Background and cause

A magnitude 9.0 earthquake off Japan’s northeast coast triggered a tsunami that inundated the Fukushima Daiichi site and disabled key safety systems. The loss of power and cooling caused reactor overheating and set off the nuclear accident.

Reactor damage and releases

Three reactors experienced severe core damage, and hydrogen explosions damaged reactor buildings. Radioactive substances were released into the air and nearby ocean, leading to elevated contamination in the surrounding environment.

Evacuation and human impact

Authorities evacuated residents from areas around the plant, with estimates ranging from about 120,000 to 164,000 displaced people. The evacuation and fear of radiation had major social and health consequences.

International classification and significance

The accident was rated Level 7 on the INES scale, placing it among the most serious nuclear accidents ever recorded. It is commonly described as the worst nuclear power plant accident since Chernobyl.

Key facts

  • The disaster began when the earthquake and tsunami knocked out electrical power and cooling at the plant.
  • Three reactor cores largely melted in the first three days of the accident.
  • Hydrogen explosions damaged reactor buildings and complicated emergency response.
  • The accident was classified as a Level 7 event on the International Nuclear and Radiological Event Scale.
  • Large-scale evacuations were ordered, creating a major long-term displacement crisis.
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Canadian context

The Fukushima disaster affected Canadian readers through international nuclear safety policy, Pacific Ocean environmental monitoring, and Canadian public discussions about emergency preparedness, energy policy, and radiation risk.

Frequently asked questions

What caused the Fukushima nuclear disaster?
A major earthquake and the resulting tsunami flooded the Fukushima Daiichi plant, cutting power and disabling cooling systems needed to keep the reactors safe.
How many reactors were damaged?
Three reactors suffered severe core damage, while the site’s four operating reactors were effectively written off after the accident.
How severe was the accident?
It was rated Level 7 on the INES scale, the highest classification for a nuclear event.
Were people evacuated?
Yes. Roughly 120,000 to 164,000 people were evacuated or displaced from surrounding areas.
How does Fukushima compare with Chernobyl?
It is widely considered the most serious nuclear accident since Chernobyl and one of only two events rated Level 7 on INES.

References

  1. World Nuclear Associationhttps://world-nuclear.org/information-library/safety-and-security/safety-of-plants/fukushima-daiichi-accident
    Supports: Earthquake/tsunami cause, reactor core meltdowns, INES Level 7, estimated radioactive release, site status
  2. OECD Nuclear Energy Agencyhttps://www.oecd-nea.org/jcms/pl_27411/fukushima-daiichi-nuclear-accident
    Supports: Earthquake, tsunami, and severe nuclear power plant accident context
  3. UNSCEARhttps://www.unscear.org/unscear/en/fukushima.html
    Supports: Date, major damage, radioactive release, evacuations, significance since Chernobyl
  4. German Federal Office for Radiation Protectionhttps://www.bfs.de/EN/topics/ion/accident-management/emergency/fukushima/accident.html
    Supports: Earthquake and tsunami cause, INES Level 7, evacuation numbers
  5. NCBI Bookshelfhttps://www.nia.gov/books/NBK253923/
    Supports: Three reactors with severe core damage, hydrogen explosions, radioactive releases
  6. Encyclopaedia Britannicahttps://www.britannica.com/event/Fukushima-accident
    Supports: Core overheating, partial meltdown, hydrogen explosions, radiation release, evacuation
  7. BBC Newshttps://www.bbc.com/news/world-asia-56252695
    Supports: Date, tsunami, evacuation, INES Level 7, public impact
  8. International Atomic Energy Agencyhttps://www.iaea.org/topics/response/fukushima-daiichi-nuclear-accident
    Supports: Level 7 classification and accident context