International Nuclear Event Scale; a scale with seven levels proposed by the IAEO to evaluate the events occurring in nuclear installations according to international uniform criteria, in particular with regard to the aspect of hazards to the population. The upper levels (4 to 7) include accidents, the lower levels (1 to 3) anomalies and incidents. Notifiable events of no safety-related or radiological significance according to the international scale are designated as „below the scale“ or “Level 0”. The events are evaluated according to three overriding aspects:

  • “Radiological effects outside the installation”,
  • “Radiological effects inside the installation”and
  • “Impairment of safeguards”.

The first aspect comprises events which lead to release of radioactive substances into the environment of the installation. The highest level corresponds to a catastrophic accident in which health and environmental consequences over a wide area are to be expected. The lowest level of this aspect – Level 3 – corresponds to a very low level of radioactivity release resulting in radiation exposure that amounts to about one tenth of natural radiation for the most severely affected persons outside the installation. The second aspect comprises Levels 2 to 5 and concerns the radiological effects inside the installation, i.e. ranging from serious damage at the reactor core to greater contaminations within the installation and impermissible high radiation exposure of the staff. The third aspect – assigned to Levels 0 to 3 – comprises events in which safeguards designed to prevent the release of radioactive substances have been impaired.

INES scale to classify events in nuclear installations