Michele Kearney's Nuclear Wire: BNC Fukushima rated at INES Level 7

Tuesday, April 12, 2011

BNC Fukushima rated at INES Level 7 - what dies this mean? by Barry Brook

Fukushima rated at INES Level 7 - what does this mean?

Barry Brook | 12 April 2011 at 4:49 PM | URL: http://wp.me/piCIJ-19h

Hot in the news is that the Fukushima Nuclear crisis has been upgraded from INES 5 to INES 7. Note that this is not due to some sudden escalation of events today (aftershocks etc.), but rather it is based on an assessment of the cumulative magnitude of the events that have occurred at the site over the past month (my most recent update on that is here).
Below I look briefly at what this INES 7 rating means, why it has happened, and to provide a new place to centralise comments on this noteworthy piece of news.

The International Nuclear and Radiological Event Scale (INES) was developed by the International Atomic Energy Agency (IAEA) to rate nuclear accidents. It was formalised in 1990 and then back-dated to events like Chernobyl, Three Mile Island, Windscale and so on. Prior to today, only Chernobyl had been rated at the maximum level of the scale 'serious accident'. A useful 5-page PDF summary description of the INES, by the IAEA, is available here.

A new assessment of Fukushima Daiichi has put this incident at INES 7, upgraded from earlier escalating ratings of 3, 4 and then 5. The original intention of the scale was historical/retrospective, and it was not really designed to track real-time events, so until the accident is fully resolved, any time-specific rating is naturally preliminary.

The criteria used to rate against the INES scale are (from the IAEA documentation):

(i) People and the Environment: considers the radiation doses to people close to the location of the event and the widespread, unplanned release of radioactive material from an installation.