March 15th, 2011 – NRC debates INES levels 3 days prior to actual upgrade to Level 5

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From: Jones, Cynthia In
Sent: Tuesday, March 15, 2011 3:47 PM
To: Sigmon, Rebecca
Subject: RE: INES rating

Thanks Rebecca-

I agree with you that its probably a level 5 but told the ExecTeam that Japan had not changed their INES rating nor increased the level despite IRSN and Canadian press indicating that they had.

I am back at the Ops Center tomorrow as PMT director for the next 3 days. And yes, I agree with you – very glad that we’re not over there-


From: Sigmon, Rebecca.. ……
Sent: Tuesday, March 15, 2011 3:20 PM
To: Jones, Cynthia (j”LI iQ
Subject: INES rating


I’ve been in touch with Rich Conatser (he actually sits just behind me, so that was easy) and explained how we would approach the rating.

NISA didn’t give much (any) explanation of their rating that I saw, but my impression is that it was based on radiation levels measured at the site boundary and the potential for exposure to the general public.

And that was before things took a decided turn for the worse over the weekend.

At this point I think there’s so much that we don’t know about what’s going on, but I think a final rating of at least a 5 is likely.

There is one minister who was quoted saying that about 5% of the fuel has melted in Unit 2, which would probably be a 5 (depending on how you define “more than a few percent,”) but until we have a better idea of the state of the cores, the level of the release, the exposure levels of the workers who are still onsite, consequences to the spent fuel pools, etc.

Not to mention that INES I don’t think anticipated the common cause effects on multiple units – does the fact that they’re dealing with potential fuel damage at 3 or even 4 different units on the same site affect the rating? It certainly complicates the response.

This will be a fascinating event to review; I’m very glad I’m not in the middle of it over there.

Rebecca Sigmon
Reactor Systems Engineer
Operating Experience Branch
(301) 415-4018
Rebecca. SiqmonDnrc.pov


IAEA Upgraded to INES Level 5 – 3 days later – March 18th, 2011

“Japanese authorities have assessed that the core damage at the Fukushima Daiichi 1 reactor unit caused by the loss of all cooling function has been rated as 5 on the INES scale.

This is an upgrade from a previous rating of 12 March as 4 on the INES scale, which was based on an abnormal rise of radioactive dose rate at the site boundary.”

“As reported earlier, a 400 millisieverts (mSv) per hour radiation dose observed at Fukushima Daiichi occurred between Units 3 and 4. This is a high dose-level value, but it is a local value at a single location and at a certain point in time. The IAEA continues to confirm the evolution and value of this dose rate. It should be noted that because of this detected value, non-indispensible staff was evacuated from the plant, in line with the Emergency Response Plan, and that the population around the plant is already evacuated.”

Source: IAEA

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