First post here - but what the heck... pls bear with my english. ;) I think there should be some explanations of INES first - while INES is generally taken as a single assessment, it is in fact three:
1) People and the Environment (Maximum level of 7)
2) Radiological barriers and controls at facilities (Maximum level of 5)
3) Defence in depth (Maximum level of 3)
Every accident is rated in these three assessments. And the highest number is the final INES rating.
INES-Manual:
http://www-pub.iaea.org/MTCD/publications/PDF/INES-2009_web.pdfAs for Fukushima Daichi, Blocks 1-3 have only been rated in category two and three - they got a 3 for Defence in Depth and a 5 for Radiological Barriers, so the temporary rating is a 5. And since category 1 hasn't been rated yet, it can't go up any further.
Temporary INES-Rating of Fukushima Accidents as published on March 18th: http://www.nisa.meti.go.jp/english/files/en20110319-6.pdf Let's concentrate on category 1, impact on the environment. For INES levels from 5-7, INES-Manual gives us criteria of radioactive pollution to be met. The whole radioactivity release is converted into an equivalent activity of Jod-131. Other isotopes, such as Cäsium-137 for example, are multiplied by a factor (40 for Cäsium) which can be found on page 16 and added to the total number. These criteria can be found on page 17 (INES-Manual), but I will summarise: INES 5:
“An event resulting in an environmental release corresponding to a quantity of radioactivity radiologically
equivalent to a release to the atmosphere of the order of hundreds to thousands of terabecquerels of 131I.”
“An event resulting in a dispersed release of activity from a radioactive source with an activity greater
than 2500 times the D2 value, for the isotopes released.”
Example (numbers given by the manual): Three Mile Island, 500-700 TBq Jod-131 equivalenceINES 6:
“An event resulting in an environmental release corresponding to a quantity of radioactivity radiologically
equivalent to a release to the atmosphere of the order of thousands to tens of thousands of terabecquerels of 131I.”
Example (numbers given by the manual): Kyschtym, 20.500 TBq Jod-131 equivalenceINES 7:
“An event resulting in an environmental release corresponding to a quantity of radioactivity radiologically
equivalent to a release to the atmosphere of more than several tens of thousands of terabecquerels of 131I.”
Example (numbers given by the manual): Tschernobyl, 5.400.000 TBq Jod-131 equivalence
Summary up to this point: Criteria 1 with a maximum level of 7 has not been rated yet for Fukushima, level 7 will be necessarily acquired after a release of 50.000-100.000 TBq Jod-131 equivalence. So, what has escaped Fukushima? There are several different calculations, but none seems good:
Japan's nuclear safety commission expects a release of 33.000-110.000 TBq Jod-131. But I'm not sure if they are only referring to Jod, or if this is the equivalence.
Source:
http://www.asahi.com/english/TKY201103250204.html
IRSN expects 90.000 TBq Jod-131 and 10.000 TBq Cäsium-137, converted into Jod-131 the number would be 490.000 TBq
Source:
http://www.irsn.fr/FR/Actualites_presse/Actualites/Documents/NI-terme-source-22032011-tableau.pdf
ZAMG expects between 10.000-700.000 TBq Jod-131 and 1000-70.000 TBq Cäsium during the first week. But all their plume simulations use a number of 100.000 TBq Jod-131 per day.
Converted into Jod-131 this would be between 50.000 and 3.500.000 TBq during the first week.
Source: http://www.zamg.ac.at/aktuell/index.php?seite=1&artikel=ZAMG_2011-04-02GMT09:28 Which brings me to the conclusion, that the Fukushima Accident inevitebly has to be rated with INES-7 - if they are going to stick to the manual.
That's probably the reason why they still don't have rated category 1. Technically, the event is not over yet, so the radioactive release is still going on and you can't figure the final numbers.
But the numbers won't go down - regardless of how much radioactivity will be released during the next month, this accident reached the INES 7 category during the first few days.Edit: Whoever corrected the chaos I created with my wild replies - thank you very much. :)
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