International Nuclear Event 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 things that must be there, for the accident to be of that level. 

There are 7 levels on the INES scale:

   7Major accident(maximum credible accident)
   6Serious accident
   5Accident with off-site risk
   4Accident without off-site risk
   3Serious incident
   2Incident
   1Anomaly
   0Deviation, no safety relevance

Details

Level 6 Accidents of this type have a large impact (pollution, radiation) outside the site where they occur. Several governments may need to do a lot to protect their population. Example: Mayak (former Soviet Union) 1957. Because of the levels of radioactive materials released, the Mayak accident would probably be rated at level 7 today.

Level 5 Accidents of this type 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 for 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 for 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".

 Other websites 
International Nuclear Event Scale , IAEA
International Nuclear Event Scale, User's Manual , IAEA, 2001

Category:Nuclear accidents