[ RadSafe ] FW: Fukushima ranked Level 8 on newly developed nuclear scale, above Chernobyl (CHART)
sperle at mirion.com
Tue Aug 14 16:17:33 CDT 2012
Please see the following information from Cyndi Jones, provided with her permission:
The INES rating for accidents rated at level 6 and 7 is exclusively based on the amount of radioactivity released to the environment. The threshold for Level 7 is at a value which is well below that of the two Level 7 accidents to date. The INES rating is an indication of the severity of what happened at the site and is deliberately not based on potential consequences. It is not dependent on the wind direction, the population density, or the success of countermeasures although these factors will clearly affect the consequences of the release to the public and the environment.
Level 7, being the highest level of the scale, covers a considerable range. The threshold for Level 7 was set well below the known magnitude of the release from Chernobyl, so it is quite possible to have accidents that would rate at Level 7 but with different amounts of activity released to the atmosphere.
A process for reviewing the INES rating criteria exists and involves the IAEA INES Advisory Committee and the INES National Officers. After the accident at Fukushima, this process , was specifically initiated and the conclusion was that the current criteria represent the best overall approach.
This issue was also debated at length when INES was developed. Some of the key factors in choosing 7 levels were:
. Having too many levels, would be seen by some stakeholders as a means of deliberately reducing the importance of incidents reported at Levels 1 or 2.
. The upper levels of the scale cover the different types of accidents that can occur and there is no need to have more than 7 levels. Events at:
o Level 5 would have limited public health consequences but might result in severe damages to the installations of the facility;
o Level 6 involves wider consequences with probably full implementation of protective actions for the public
o Level 7 has major consequences for people and/or the environment with possible transboundary / transnational consequences.
It was felt that a level going beyond ""major consequences for people and/or the environment with possible transboundary / transnational consequences" would make no sense. It was known that the threshold for Level 7 was set well below the level of activity released from the accident at Chernobyl NPP that occurred 4 years before the scale was developed. The review of this topic, which is part of the process mentioned above, concluded that there was no need or benefit in adding additional levels to the scale.
It was also noted that changing the number of levels now would lead to confusion. It would be necessary to explain whether the rating was based on the new scale or the old one. This would detract from the purpose of INES, which is to help the public understand the safety significance of events.
The IAEA working with the INES Advisory Committee and Public Communication Experts will be providing additional guidance to users on these and other Qs that were raised following the Fukushima event. For more info on the scale itself, please see http://www.nrc.gov/about-nrc/emerg-preparedness/emerg-classification/event-scale.html
Thanks for asking-
Cynthia G. Jones, Ph.D.,
INES National Officer and Advisory Committee Member ENAC National Contact Sr. Technical Advisor for Nuclear Security U.S. Nuclear Regulatory Commission Office of Nuclear Security & Incident Response Mail Stop T4-D22A, Washington, D.C. 20555
Sander C. Perle
Dosimetry Services Division
2652 McGaw Avenue
Irvine, CA 92614
+1 (949) 296-2306 (Office)
+1 (949) 296-1130 (Fax)
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