The International Nuclear Event Scale (INES) was developed by the UN's International Atomic Energy Agency (IAEA), where incidents at nuclear power plants can be classified according to their severity. This allows the public and the media to get a quick and understandable explanation of the severity of an event.

Classification of events

Safety significance is classified on a scale from 1-7. The INES scale is used internationally and complements the reporting system used between nuclear installations and authorities.

INES 7Chernobyl 1986. The accident at reactor 4 of the Chernobyl nuclear power plant in present-day Ukraine caused widespread environmental and human health impacts.

Fukushima 2011: a powerful earthquake and subsequent tsunami caused reactor failures in Japan, resulting in radioactive releases.

INES 5Windscale 1957. The accident at an air-cooled graphite reactor at what is now Sellafield in England caused radioactive releases to the atmosphere.

Three Mile Island 1979. The accident at the nuclear power plant in the USA caused severe damage to the reactor core. The radioactive release outside the plant was very limited.

INES 4Saint Laurent 1980. The accident at the nuclear power plant in France resulted in damage to part of the reactor core, no external radioactive release occurred.

Tokaimura 1999. The accident at the Tokaimura combined reprocessing plant and fuel fabrication plant in Japan resulted in limited external radioactive releases.

INES 3Vandellos 1989. The incident at the Vandellos nuclear power plant in Spain did not result in an external release of radioactivity, nor did it cause any damage to the reactor core or contamination inside the plant.

INES 2Forsmark 2006: a short circuit in a switchgear at Forsmark 1 caused a disruption in the electricity supply. Only two of the four backup generators started. No releases occurred.

INES 1 Anomaly, for example minor problems with safety-related components.

INES 0 Anomaly with no impact on safety.