Level Description People and environment Radiological barriers Defence-in-depth
7 Major accident Chernobyl, Ukraine, 1986 — Widespread health and environmental effects. External release of a significant fraction of reactor core inventory.
6 Serious accident Kyshtym, Russia, 1957 — Significant release of radioactive material to the environment from explosion of a high activity waste tank.
5 Accident with wider consequences Windscale Pile, UK, 1957 — Release of radioactive material to the environment following a fire in a reactor core. Three Mile island, USA, 1979 — Severe damage to the reactor core.
4 Accident with local consequences Tokaimura, Japan, 1999 — Fatal overexposures of workers following a criticality event at a nuclear facility. Saint Laurent des Eaux, France, 1980 — Melting of one channel of fuel in the reactor with no release outside the site.
3 Serious incident Sellafield, UK, 2005 — Release of large quantity of radioactive material, contained within the installation. Vandellos, Spain, 1989 — Near accident caused by fire resulting in loss of safety systems at the nuclear power station.
2 Incident Atucha, Argentina, 2005 — Overexposure of a worker at a power reactor exceeding the annual limit. Cadarache, France, 1993 — Spread of contamination to an area not expected by design. Forsmark, Sweden, 2006 — Degraded safety functions for common cause failure in the emergency power supply system at nuclear power plant.
1 Anomaly Breach of operating limits of a nuclear facility
0 No safety significance