INES scale

The INES (International Nuclear Event Scale) has been developed by the United Nations International Atomic Energy Agency (IAEA), where incidents at nuclear power plants can be classified according to severity. In this way, the public and the media can get a quick and understandable explanation of how serious an event is.

Classification of events

The safety significance is classified on a scale from 1-7. The INES scale is used internationally and is a complement to the reporting system used between the nuclear facilities and the authorities.

INES 7

Chernobyl 1986. The accident at reactor 4 at the Chernobyl nuclear power plant in present-day Ukraine had far-reaching effects on the environment and human health.

Fukushima 2011. A strong earthquake with subsequent tsunami caused reactor failures in Japan, with radioactive discharges as a consequence.

INES 5

Windscale 1957. The accident at an air-cooled graphite reactor in what is now Sellafield in England caused radioactive discharges into the atmosphere.

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

INES 4

Saint Laurent 1980. The accident at the nuclear power plant in France caused part of the reactor core to be damaged, no external radioactive release occurred.

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

INES 3

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

INES 2

Forsmark 2006. A short circuit in a switchgear at Forsmark 1 caused a disturbance in the electricity supply. Only two of four reserve power units started. No emissions occurred.