Nuclear accidents around the world

The history of civil nuclear power is littered with accidents. There have been dozens of them (nuclear accidents are defined as any event with a severity of 4 to 7 on the INES scale). Here, we present those that have had the greatest impact on the general public:

  • The Three Miles Island accident (1979), of low severity (5 on the INES scale), led to a revolution in safety approaches.
  • The Chernobyl accident (1986) was the most serious to date, with around 50 deaths and over 4,000 cancers caused by radiation
  • TheFukushima accident (2011), although it occurred at the same time as two extreme phenomena (Japan’s most powerful earthquake and tsunami), led to the latest innovations in safety. In particular, it called into question the extreme measures taken to protect populations, which proved to be particularly lethal.

Three Miles Island

The Three Mile Island accident occurred on March 28, 1979, at a nuclear power plant in Pennsylvania, USA. It was one of the most serious nuclear accidents in the United States. The main pumps failed, followed by a valve malfunction that allowed pressurized water to escape. A further malfunction prevented the operators from realizing this, ultimately leading to a partial meltdown of the reactor and the release of radioactive steam.

While the event may have frightened the authorities and the public, requiring the evacuation of schoolchildren and pregnant women within an 8km radius, there were no identified health consequences. The main repercussions of the event were in terms of nuclear safety: plant emergency protocols have been improved to ensure that this type of error never happens again.


The Chernobyl accident occurred on April 26, 1986, at a power plant in the north of what is now Ukraine, then part of the USSR. A supposedly “routine” test degenerated into the biggest nuclear accident in history. As a result of quasi-voluntary malfunctions and criminal negligence caused by toxic management, the reactor spun out of control and the graphite (supposed to be the moderator) caught fire. The fire produced a plume of radioactive smoke that affected the whole of Europe.

The releases caused several thousand cases of thyroid cancer in the surrounding region, killed many local people and sickened many others. The reactor had nothing to do with modern technology (graphite moderation, no enclosure…) and the managerial malfunctions seem surreal. I’m not sure what lessons can be learned from this event.


The Fukushima-Daiichi accident took place between March 11, 2011 and March 15 (when all reactors could be cooled down, and after the leak in the containment of reactor 2). It was caused by the combination of the most powerful earthquake in Japan’s history, followed by a terrifying tsunami, which knocked out electricity supplies and emergency generators, and left operators without information. Three reactors partially melted down.

Radioactive discharges were much lower than at Chernobyl, with no clear health consequences. Deaths were mainly caused by evacuation: initially around 50, then around 2,000 as a result of the socio-economic consequences. This calls into question the methods used to protect populations. Do they really serve the interests of the latter, or do they protect decision-makers from criticism?

Despite its unique conditions, this accident has also encouraged the development of more reliable safety systems, highlighting (to be confirmed) the importance of redundant emergency systems and contingency plans.

Further information

  • Thread on the first nuclear accident in history, in 1942:
  • The safety of our reactors is presented by Tristan Kamin, nuclear safety engineer, in an article entitled L’accident nucléaire majeur : un scénario.