INES (International Nuclear Event Scale) 1
INES (International Nuclear Event Scale) 1 : A simple scale, designed for promptly communicating to the public in consistent terms the safety significance of events at nuclear facilities. The Scale should not be confused with emergency classification systems, and should not be used as a basis for emergency response actions. The INES terminology - particularly the use of the terms incident and accident- is different from that used in safety standards, and great care should be taken to avoid confusion between the two. Unless otherwise indicated, the terms incident and accident are used in this Safety Glossary with their safety standards meaning (See: Accident (1) and Under Event) and the term event is used with its normal English meaning. Level 0 (deviation): An event with no safety significance. Level 1 (anomaly): An event beyond the authorized operating regime, but not involving significant failures in safety provisions, significant spread of contamination or overexposure of workers. Level 2 (incident): An event involving significant failure in safety provisions, but with sufficient defence in depth remaining to cope with additional failures, and/or resulting in a dose to a worker exceeding a statutory dose limit and/or leading to the presence of activity in on-site areas not expected by design and which require corrective action. Level 3 (serious incident): A minor accident, where only the last layer of defence in depth remained operational, and/or involving severe spread of contamination on-site or deterministic effects to a worker, and/or a very small release of radioactive material off-site (i.e. critical group dose of the order of tenths of a millisievert). Level 4 (accident without significant off-site risk): An accident involving significant damage to the installation (e.g. partial core melt), and/or overexposure of one or more workers resulting in a high probability of death, and/or an off-site release such that the critical group dose is of the order of a few millisieverts. Level 5 (accident with off-site risk): An accident resulting in severe damage to the installation and/or an off-site release of radioactive material radiologically equivalent to hundreds or thousands of TBq of 131I, likely to result in partial implementation of countermeasures covered by emergency plans. e.g. the 1979 accident at Three Mile Island, USA (severe damage to the installation), or the 1957 accident at Windscale, UK (severe damage to the installation and significant off-site release). Level 6 (serious accident): An accident involving a significant release of radioactive material and likely to require full implementation of planned countermeasures, but less severe than a major accident. e.g. the 1957 accident at Kyshtym, USSR (now in Russian Federation). Level 7 (major accident): An accident involving a major release of radioactive material with widespread health and environmental effects. e.g. the 1986 accident at Chernobyl, USSR (now in Ukraine)
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