The concern over the weird ratio of I131 & Cs137 at Fukushima

by nuclearhistory


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hey, here’s another favor you can do me
Friday, 22 April, 2011 1:45 AM
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“David Chanin”

“paul langley”


What’s amazing to me is that I seem to be the only one who thinks that I-131 levels should be decreasing with 8-day halflife because its only parents in the “standard NRC 60-nuclide list for reactors” are Te-131and Te-131m, both with shorter halflives, so they can’t be causing any I-131 buildup and certainly can’t cause the high levels of I-131 being reported in the flood of measurements that were published by TEPCO all on April 19, with measurements of seawater as far away as 15 km showing I:Cs rations of over 2:1 and as high as 3:1, but sometimes they’re equal, with few to none where I-131 is measured at levels less than Cs-134 and Cs-137 on a Bq/gram-water basis with 1000-second counting time of 1-liter sample, which matches up with usage of a gamma spectrometry machine like the GAM-AN1 by Canberra:

Can you do me a favor and ask one of your nuclear engineer contacts how and why I-131 can be over double the reported levels of Cs-134 and Cs-137, after five halflives of I-131?

I’m not a nuclear engineer who can try to run the Origen code for their reactors and the SNF pools to see what could be making the I-131. I’m the consequence analyst who developed the MACCS2 code and have used it and its predecessor MACCS since the 1980s for nuclear accident analysis.

All I know is that when people use the MACCS2 code, which is the NRC-approved code for reactor PRA consequence calculations, and is used worldwide for well over 500 nuclear facilities and operations since its release in 1997, the MACCS2 code shows ZERO consequences from I-131 from reactor accidents after 40 days of decay. It’s not just the direct exposure doses from groundshine and inhalation, it’s also the food doses calculated by the code with both of the “food models” that are available to the code user. Milk from cows grazing during a large release shows very low levels of I-131 after 40 days according to the MACCS2 calculations.

And it’s also my understanding that “normal levels” of I-131 in SNF pools should be practically zero, with the million-year, weak emitter, I-129 being the only iodine that should be detected to any significant degree in SNF water from an intact pool under normal operation. So, if my MACCS2 code is wrong about I-131, then all the safety analyses that use to MACCS2 to calculate nuclear accident impacts are also wrong. That’s why this is an important question.

Even if criticalities are ongoing, it’s impossible for me to imagine that they could be creating so much I-131. I’ve used “standard decay tables” that all derive from ICRP 38 and were calculated by Keith Eckerman, at ORNL, who calculates the internal and external DCFs for US and international agencies which all rely on the ICRP 38 decay chains, where decay-chain calcs are necessary because of the decay and buildup of progeny after an intake both on the ground for deposited material and in the human body from inhlaed or ingested material.

I have not tried to use this database from KfK to solve the puzzle.:

So my question, which you can forward around with all the above ane below is: Why are the I-131 levels of April 19 in “plant-water” and seawater from so high after 5 halflives? The NRC says that the MACCS2 code is essentially error-free. I’m curious if that’s true because I learned way back in school that there is no such thing a bug-free large-scale software such as MACCS2, which has received little-to-none verification and validation for complex scenarios.

I have no qualms whatsoever being known as the source of this request. I’ve never pretended to know everything.

David Chanin

Re NYT article of April 5, 2011, “U.S. Sees Array of New Threats at Japan’s Nuclear Plant”:

“Even so, the engineers who prepared the document do not believe that a resumption of criticality is an immediate likelihood, Neil Wilmshurst, vice president of the nuclear sector at the Electric Power Research Institute, said when contacted about the document. “I have seen no data to suggest that there is criticality ongoing,” said Mr. Wilmshurst, who was involved in the assessment.”

end quote.