Event scale revised for further clarity

06 October 2008

The International Nuclear Event Scale has been revised to improve the clarity of reporting when things go wrong at nuclear facilities, clarifying the safety significance of nuclear and radiological events.
The revised scale was welcomed at the International Atomic Energy Agency's (IAEA's) General Conference last week, after input from the 25 of the 63 member countries. Each country has an INES National Officer who liaises with an IAEA reporting centre to disseminate information in consistent language.
Since 1990 the scale has been used at nuclear power plants, and was enlarged in 2001 to cover radioactive materials transport. Additional guidance on its use was added in 2006, while the forthcoming user manual consolidates clarifications and recommendations from INES users worldwide. Since 2003, the World Nuclear Association has operated an expert working group on Event Communication to develop industry views on the INES scale and to work with the IAEA secretariat toward this latest revision.
The scale remains essentially as before although a revised user manual is anticipated to be published in early 2009 will include certain changes, following the adoption of the revised scale in July 2008. Areas that have been developed include details of doses to individuals, the transportation of fissile material, events involving damage to nuclear fuel as well as consistency of terminology. Examples of nuclear events graded on the INES scale can be found on WNN's Nuclear Event Reports section.

The scale
Like the scales that describe earthquakes or major storms, each of the INES scale's seven levels is designed to be ten times more severe that the one before. After below-scale 'deviations' with no safety significance, there are three levels of 'incident', then four levels of 'accident'.
The selection of a level for a given event is based on three parameters: whether people or the environment have been affected; whether any of the barriers to the release of radiation have been lost; and whether any of the layers of safety systems are lost.
Broadly speaking, events with consequences only within the affected facility itself are usually categorised as 'deviations' or 'incidents' and set below-scale or at levels 1, 2 or 3. Events with consequences outside the plant boundary are classified at levels 4, 5, 6 and 7 and are termed 'accidents'.