Nuclear Event Rating Scale

Just as hurricanes are rated for severity, and earthquakes have their Richter scale, so the International Atomic Energy Agency (IAEA) communicates the safety significance of nuclear events with a consistent numerical protocol. Not widely known outside the nuclear community, the International Nuclear Event Scale (INES) is the mechanism used to classify and report events to the world at large.

Cynthia Jones, who is the US representative to the INES Advisory Committee and is also a senior technical advisor on nuclear security at the Nuclear Regulatory Commission (NRC), reported at this week’s annual meeting of the Health Physics Society (in Portland, Oregon) on the use of the scale, and how it is used in reporting nuclear events relating to things like radioactive-material transportation and radiation exposure.

(To see the chart go to the ; INES website: http://www-news.iaea.org/news/inesmanual/default.asp) More than 60 countries have agreed to report nuclear events to the IAEA, most within 48 hours. Here is what the designations mean: A scale 1 event is referred to as an anomaly; a rating of 2 is an incident (where, for example, the regulatory limit for a radiation worker has been exceeded); 3 is a serious incident; 4 corresponds to an accident with mainly local consequences; 5 an accident with wider consequences; 6 a serious accident; and 7, the highest rating, is for major accidents.

On this scale, the Chernobyl accident (1986) is a 7, while the Three Mile Island accident (1979) receives a 5 rating. Jones (cgj@nrc.gov) says that US is a frontrunner in rapid reporting of events. (For additional information, see IAEA website: http://www-news.iaea.org/news/; Paper MPM-C.3, http://hps.org/documents/52_final_program.pdf)