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The International Nuclear Event Scale (INES) was introduced by the International Atomic Energy Agency (IAEA) in order to enable prompt communication of safety significance information in case of nuclear accidents. A number of criteria and indicators are defined to assure coherent reporting of nuclear events by different official authorities. There are 7 levels on the INES scale:

7
Major accident
(maximum credible accident)

6
Serious accident

5
Accident with off-site risk

4
Accident without off-site risk

3
Serious incident

2
Incident

1
Anomaly

0
Deviation, no safety relevance

Contents 1 Details 1.1 Level 7 1.2 Level 6 1.3 Level 5 1.4 Level 4 1.5 Level 3 1.6 Level 2 1.7 Level 1 1.8 Level 0 2 See also 3 References 4 External links

The level on the scale is determined by the highest of three scores: Off site effects, on site effects, and Defence in depth degradation.

A large off-site impact, widespread health and environmental effects. Example: Chernobyl disaster (former Soviet Union) in the Ukraine - 1986. An example of a non nuclear accident which is about the same in magnitude would be the Bhopal disaster where thousands of deaths occurred off site.

Significant off-site release, likely to require full implementation of planned countermeasures. Example: Mayak (former Soviet Union) - 1957.

Limited off-site release, likely to require partial implementation of planned countermeasures. Example: Windscale fire (United Kingdom)- 1957

or

Severe damage to a reactor core/radiological barriers. Example: Three Mile Island accident (United States) - 1979.

Minor off-site impact resulting in public exposure of the order of the prescribed limits.

or

Significant damage to a reactor core/radiological barriers or the fatal exposure of a worker.

Examples: Sellafield (United Kingdom) - 5 incidents 1955 to 1979^[1], Saint-Laurent (France) - 1980, Buenos Aires (Argentina) - 1983, Tokai (Japan) - 1999.

A very small off-site impact, public exposure at levels below the prescribed limits.

or

Severe spread of contamination on-site and/or acute health effects to a worker(s).

or

It is a "near accident" event, when no safety layers are remaining.

Examples: THORP plant Sellafield (United Kingdom) - 2005.

This is an incident with no off-site impact, a significant spread of contamination on-site may have occurred.

or

Overexposure of a worker.

or

Incidents with significant failures in safety provisions.

Examples: The Forsmark Nuclear Power Plant (Sweden) - July 2006 incident.

This is an anomaly beyond the authorized operating regime.

This is a "below-scale event" of no safety significance.

There are also events of no safety relevance, characterized as "out of scale".

• Chernobyl disaster
• Fuel element failure
• List of civilian nuclear accidents
• List of military nuclear accidents
• List of nuclear reactors
• Loss of coolant accident
• Nuclear and radiation accidents
• Nuclear contamination
• Nuclear meltdown
• Nuclear power
• Nuclear power controversy
• Nuclear safety
• Radioactive contamination
• Radioactive waste
• Three Mile Island accident
• United States military nuclear incident terminology
• Windscale fire

• International Nuclear Event Scale, IAEA
• International Nuclear Event Scale, User's Manual, IAEA, 2001