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Basic structure of the International Nuclear Event Scale
LEVEL


CRITERIA OR SAFETY ATTRIBUTES


Off-site impact
On-site impact
Defence-in-depth degradation

7

Major Accident


Major release : Widespread health and environmental effects

 
 

6

Serious Accident


Significant release: likely to require full implementation of planned countermeasures

 
 

5

Accident with off-site-risk


Limited release: likely to require partial implementation of planned countermeasures


Severe damage to reactor core/radiological barriers

 

4

Accident without significant off-site-risk


Minor release: public exposure of the order of prescribed limits
 

Significant damage to reactor core/radiological barriers/fatal exposure of a worker

 

3

Serious Incident


Very small release: Public exposure at a fraction of prescribed limits 


Severe spread of contamination/acute health effects to a worker
 

Near accident - no safety layers remaining

2

Incident

 

Significant spread of contamination/over exposure of a worker


Incidents with significant failures in safety provisions

1

Anomaly

 
 

Anomaly beyond the authorized operating regime

0

Below scale event deviation

 

No safety significance

 
Out of scale event
 

No safety relevance

 

The above information is provided by EMSD
EMSD

 

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