| International Nuclear Event Scale |
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Information AboutInternational Nuclear Event Scale |
| CATEGORIES ABOUT INTERNATIONAL NUCLEAR EVENT SCALE | |
| nuclear accidents | |
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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 DETAILS The level on the scale is determined by the highest of three scores: Off site effects, on site effects, and Defence In Depth degradation. Level 7 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. Level 6 Significant off-site release, likely to require full implementation of planned countermeasures. Example: Mayak Accident (former Soviet Union) - 1957 . Level 5 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 . Level 4 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:
Level 3 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. Level 2 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. Level 1 This is an anomaly beyond the authorized operating regime. Level 0 This is a "below-scale event" of no safety significance. There are also events of no safety relevance, characterized as "out of scale". SEE ALSO
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