The International Nuclear Event Scale
Rating Condition Definition Example
The INES definitions were expanded and revised in 2008. Note that I have reworded the definitions, especially for INES 1, which seemed very circular in the original documents. My goal was brevity with accuracy. I also chose my own examples for #1 and #2, since those documents provided none.
REF: Revised Nuclear and Radiation Events Scale Endorsed IAEA, 1 Oct 2008
7 Major
External release of much of the radiation in a large plant Chernobyl
6 Serious
External release of massive amounts of radiation Kyshtym
5 Accident with
Off-site risk
External release of large amounts of radiation,
or severe damage and contamination inside plant
4 Accident without
Off-site risk
External radiation release with worst exposure ≤ 10 mSv,
major damage to facility, or extreme exposure of any worker.
3 Serious
External exposure above authorized limits but ≤ 0.1mSv,
extreme worker exposure, or a "1-system-from-doom" case
Vandellos NPP
2 Incident Significant failure of safety measures but no major release
Alternatively, plant worker exposure above annual limits
Indian Point
1 Anomaly Any operation or condition that falls outside specified limits,
but without causing equipment damage or radiation release
Onagawa NPS
Accidents involving Nuclear Energy
– Copyright © C. P. Winter 2005