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14.3  THE INTERNATIONAL NUCLEAR EVENT SCALE - INES
 



ACCIDENTS  

LEVEL 7 - MAJOR ACCIDENT

  • External release of a large fraction of the radioactive material in a large facility (e.g. the core of a power reactor). This would typically involve a mixture of short and long-lived radioactive fission product (in quantities radiologically equivalent to more than tens of thousands of terabecquerels of iodine-131). Such a release would result in the possibility of acute health effects; delayed health effects over a wide area, possibly involving more than one country; long term environmental consequences.

Example: Chernobyl NPP USSR (now in Ukraine), 1986

 

LEVEL 6 - SERIOUS ACCIDENT

  • External release of radioactive material (in quantities radiologically equivalent to the orders of thousands to tens thousands of terabecquerels of iodine-131). Such a release would be likely to result in a full implementation of a countermeasures covered by local emergency plans to limit serious health effects.

Example: Kysthym Reprocessing Plant USSR (now in Russia), 1957

 

LEVEL 5 - ACCIDENTS WITH OFF-SITE RISK

  • External release of radioactive material (in quantities radiologically equivalent to the order of hundreds to thousands of terabecquerels of iodine-131).

  • Such a release would be likely to partial implementation of countermeasures covered emergency plans to lessen the likelihood of health effects. Such a release would be likely to result in partial implementation of countermeasures covered by emergency plans to lessen the likelihood of health effects.

  • Severe damage to the installation. This may involve severe damage to a large fraction of the core of a power reactor, a major criticality accident or a major fire or explosion releasing large quantities of radioactivity within the installation.

Example: Windscale Pile U , 1957; Three Mile Island, NPP, USA, 1979

 

LEVEL 4 - ACCIDENTS WITHOUT SIGNIFICANT OFF-SITE RISK

  • External release of radioactivity resulting in a dose to the critical group of the order of a few millisieverts *) . With such a release the need for off-site protective actions would be generally unlikely except possibly for local food control.

  • Significant damage to the installation. Such an accident might include damage leading to major on-site recovery problems such as partial core melt in a power reactor and comparable events at non-reactor installations.

  • Irradiation of one or more workers which resulting in an overexposure where a high probability of a early death occurs.

Example: Windscale Reprocesing Plant, U , 1973 Saint-Laurent NPP, France, 1980; Jaslovské Bohunice NPP A-1, 1977 I



INCIDENTS

LEVEL 3 - SERIOUS INCIDENT

  • External release of radioactivity resulting in a dose to the critical group of the order of tens millisievert.

  • With such a release, off-site protective measures may not be needed.

  • On-site events resulting in doses to workers sufficient to cause acute health effects and/or an event resulting in a severe spread of contamination for example a few thousand terabecquerels of activity released in a secondary contaiment where the material can be returned to a satisfactory storage area.

  • Incidents in which a further failure of safety systems could lead to accident conditions, or a situation in which safety systems would be unable to prevent an accident if certain initiators were to occur.

Example: Vandellos NPP, Spain, 1989

 

LEVEL 2 - INCIDENT

  • Incident with significant failure in safety provisions but with sufficient defense in depth remaining to cope with additional failures. These include events where the actual failures would be rated at level 1 but which reveal significant additional organizational inadequacies or safety culture deficiencies.

  • An event resulting in a dose to worker exceeding a statutory annual dose limit and/or an event which leads to the presence of significant quantities of radioactivity in the installation in areas not expected by design and which require corrective action.


LEVEL 1 - ANOMALY

  • Anomaly beyond the authorized regime, but with significant defense in depth remaining. This may be due to equipment failure, human error, or procedural inadequacies and may occur in any area covered by the scale, e.g. plant operation, transport of radioactive material, fuel handling, waste storage. Examples include: breaches of technical specifications or transport regulations, incidents without direct safety consequences that reveal inadequacies in the organizational system or safety culture, minor defects in paperwork beyond the expectations of the surveillance programme.


LEVEL 0 - DEVIATIONS

  • Deviations where operational limits and conditions are not exceeded and which are properly managed in accordance with adequate procedures. Examples include: a single random failure in a redundant system discovered during periodic inspections or tests, a planned reactor trip proceeding normally, spurious initiation of protection systems without significant consequences, leakages within the operational limits, minor spreads of contamination within controlled areas without wider implications for safety culture.

  • NO SAFETY SIGNIFICANCE

Note:    
*)   The doses are expressed in terms of effective dose equivalent (whole body dose). Those criteria where appropriate can also be expressed in terms of corresponding annual effluent discharge limits authorized by National authorities.


 
 
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