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Nuclear
accidents/incidents
To
aid public understanding of the safety significance of events at nuclear
installations and their consequences, the IAEA and the Nuclear Energy
Agency of the OECD have developed the International Nuclear Event Scale
("INES").
The
levels and criteria are summarised below:
| level 0 |
Below scale. No safety significance |
| level 1 |
Anomaly. Variation from permitted procedures |
| level 2 |
Incident with potential safety consequences on site but with sufficient
safety defences remaining. Insignificant release of radioactivity
off site. |
| level 3 |
Serious Incident. Very small release of radioactivity. Radiation exposure
off site a fraction of the prescribed limits. Local protective measures
unlikely except for some food monitoring and control. Possible acute
health effects to a worker. |
| level 4 |
Accident without minor release of radioactivity. Radiation exposure off
site of the order of prescribed limits. Local protective measures
unlikely except for some food monitoring and control. Significant
plant damage. Fatal exposure of a worker. |
| level 5 |
Accident with off site risks. Release of radioactivity. Severe plant damage.
Partial implementation of local counter measures |
| level 6 |
Serious accident. Significant release of radioactivity. Full implementation
of local counter measures |
| level 7 |
Major accident. Major release of radioactivity. Acute health and long term
environment effects |
As
shown in the table, only events at level 4 and above are accidents with
a significant release of radioactivity off-site. The accident at an RBMK
reactor at Chernobyl, in the former Soviet Union in 1986, was retrospectively
classified as level 7. The accident at Three Mile Island in the United
States in 1979 was retrospectively classified as level 5. In 1957, in
the early stages of development of the UK nuclear programme, an accident
occurred at the UKAEA's site at Windscale in Cumbria involving a prototype
reactor. This has been retrospectively classified as a level 5 accident
and is the highest rated accident which has occurred in the UK.
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