The International Nuclear and Radiological Event Scale

The International Nuclear and Radiological Event Scale is used to classify the severity of nuclear accidents. To date, only the Chernobyl accident in April, 1986, has been classified as a “major accident”. The guidelines (warning: PDF) for assigning the rating are described in a 207 page document published by the International Atomic Energy Agency.

Right now, Fukushima is formally classified as being comparable to Three Mile Island. This is ridiculous. It is now well past the time when the Fukushima accidents should be reclassified as level 7, “Major accidents.”

Never before have multiple reactors at one site suffered simultaneous meltdowns, and never before has a beyond-design event or events (earthquake + tsunami in this case) occurred when the entire core fuel assembly of a 784 MW-electric power plant was outside containment for any reason. The Unit 4 core was being held in the “spent fuel pond” during a period of routine maintenance at the time of the earthquake and tsunami. The IAEA manual does not clearly and specifically contemplate multiple simultaneous major accidents at one site, but the precedent and practice (and legalese, by my reading, but I’m no lawyer) clearly are such that each reactor should be considered independently. Certainly, before the accident, any single reactor unit at Fukushima easily met the criteria for a maximum possible accident of severity 7. (One of the first steps in the classification of a specific event is to determine the maximum possible accident that each facility could have in principle.) Currently, none of the several units involved been rated as more than INES-5. (PDF) The most egregious rating is of unit 4, which currently has an INES-3 rating. Absurd. This was a full reactor core outside containment that dried out, not spent fuel. The fact that it was in a spent fuel pond makes this accident worse.

Since March 25, Greenpeace has had an analysis posted of the Fukushima accidents, making a persuasive case that there have been at least three INES-7 events there since the March 11 earthquake. Other competent organizations concur that the level is clearly 6 or 7 for each unit. By the time the final ratings are assigned, I am confident that the official rating will be that there were at least four INES-7 events (at units 1-4).

Why is it important to make this distinction? First, the classification of the Fukushima accidents as three or four INES-7 “major accidents” will cut through the confusion in the media and the industry-sponsored static to make it clear to the public that where before there had only been one major nuclear accident (Chernobyl), there now have been four or five. Second, the releases of large amounts of radiation into the ocean (predicted here at FDL for some time) will continue and likely accelerate in the coming days, weeks and months. However, the IAEA guidelines for the INES rating do not include the case of releases of any amount of radiation into bodies of water. There will therefore likely now be a period of time over which we become acclimated to the idea that the Pacific Ocean should be the final resting place of very significant amounts of radioactive substances. As inevitable as the ocean dumping may be, we should not allow a slow denouement to change our opinion of the severity of what has happened.

There is a period of time during which the initial narrative of an historical event takes root in the public domain. That narrative survives for a long time, regardless of further disclosures and discoveries. The INES ratings of the Fukushima accidents should now be raised to INES-7 for all units which are already known to have met the criteria, before the conventional wisdom becomes the story that TEPCO wants to tell.