The International Nuclear Event Scale (INES) was introduced in 1990[1] by the International Atomic Energy Agency (IAEA) in order to enable prompt communication of safety significance information in case of nuclear accidents.
The scale is inspired by the Richter scale that is used to describe the comparative magnitude of earthquakes. Each increasing level represents an accident ten times more severe than the previous level. However, compared to earthquakes, where the event intensity can be quantitatively evaluated, the level of severity of a man-made disaster, such as a nuclear accident, is more subject to interpretation. Because of the difficulty of interpreting these data, the INES level of an incident is frequently assigned well after the incident occurs. Therefore, the scale has a very limited ability to assist in disaster-aid deployment.
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; 3 incident-levels and 4 accident-levels
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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 with widespread health and environmental effects.
Only example: Chernobyl disaster, 26 April 1986. An uncontrolled power excursion in a reactor without a containment building caused a powerful steam explosion and fire that released a significant fraction of core material into the environment, resulting in a death toll of 57 as well as estimated 4,000 additional cancer fatalities among 600,000 people exposed to elevated doses of radiation.[2]
Significant off-site release, likely to require full implementation of planned countermeasures.
Only example: Kyshtym disaster at Mayak (former Soviet Union), 29 September 1957. A failed cooling system at a military nuclear waste reprocessing facility caused a steam explosion that released 70-80 tons of highly radioactive material into the environment. Impact on local population is not fully known.
Limited off-site release, likely to require partial implementation of planned countermeasures.
or
Severe damage to a reactor core/radiological barriers.
So far three events were classified as level 5:
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:
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 one or more workers.
or
It is a "near accident" event, when no safety layers are remaining.
Examples:
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:
This is an anomaly beyond the authorized operating regime.
Example:
This is a "below-scale event" of no safety significance.
There are also events of no safety relevance, characterized as "out of scale".
The International Nuclear Event Scale (INES) is a system introduced by the International Atomic Energy Agency (IAEA). It was introduced to allow people to communicate how serious a nuclear accident is. Other people are then able to react faster to take protection measures. For each level, there is a list of criteria (things) that must be there, for the accident to be of that level.
There are 7 levels on the INES scale:
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Level 7 is the highest level. Accidents of this type have a large impact (pollution, radiation) outside the site where they occur. The health of many people is put in danger. There are big effects on the environment. Example: Chernobyl accident (former Soviet Union) - 1986.
Level 6 : Accidents of this type have a large impact (pollution, radiation) outside the site where they occur. Several governments may need to take the full set of countermeasures to protect their population. Example: Mayak (former Soviet Union)- 1957.
Level 5 : Accidents of this type do release some radiation. Some groups of people which are at risk may need special countermeasures. Examples: Windscale fire (United Kingdom) - 1957, Three Mile Island accident (United States) - 1979.
The Levels 5-7 are related to severe damage of the reactor core and the radiological barriers.
Level 4 is related to significant damage of the reactor core / radiological barriers and/or a fatal exposure of a worker (or more), but the off-site impact is minor, resulting in public exposure of the order of the prescribed limits. Examples: Windscale (United Kingdom) - 1973, Saint-Laurent (France) - 1980, Buenos Aires (Argentina) - 1983.
Level 3 is characterized by very small off-site impact, although related to severe spread of contamination on-site / acute health effects to a worker (or more). It is a "near accident" event, when no safety layers are remaining. Example: Vandellos (Spain) - 1989, THORP plant Sellafield (United Kingdom) - 2005.
Level 2 is an incident with no off-site impact, related to significant spread of contamination on-site / overexposure of a worker.
Level 1 is an anomaly beyond the authorized operating regime.
Level 0 is a "below-scale event" of no safety significance.
There are also events of no safety relevance, characterized as "out of scale".
   | Classification of events with an off-site radiological impact at the Sellafield site between 1950 and 2000, using the International Nuclear Event Scale - Classification of events with an off-site radiological impact at the Sellafield site between 1950 and 2000, using the International Nuclear Event Scale |
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