Cesium contamination estimates around Fukushima Daiichi from IRSN report

[mheslep]

The beaches of Brazil measure as high as 83,245 Bq/kg. Greenpeace findings have become little better, I think, than Helen Caldicott findings.

 

[Astronuc]

The beaches of Brazil measure as high as 83,245 Bq/kg.

True, but as the abstract indicates, such values are above the limit of 370 Bq kg⁻¹ recommended for the safe use of building materials for dwellings by OECD. One would not want to dwell on a beach 83,245 Bq/kg, or rather, I would not recommend children or pregnant women dwelling for prolonged periods on those beaches.

Since I'm in a confessional mood, I guess I should also admit I don't really understand how the various isotopes of cesium are produced: is it correct to say that Cesium 135 is the decay/daughter product of Xe135 (which itself is a fission product of U235), and that Cesium 137 and 134 are the direct fission products of U235?

Concerning Cs-134, -135, -137, refer to the attached images.

Note the darker squares in the first image, which provides the fission yields for each radionuclide. The yield for Cs-134 and Xe-134 is rather low. The main source of Cs-134 is the precursor Te-134 (fis yield ~ 0.0622) with a trace from I-134. The successive chain is Te > I > Xe > Cs. Similar Cs-135 comes from decay of Te-135 and I-135. On the other hand, Cs-137 comes primarily from the decay of Xe-137 and I-137 (with yields of 0.0319 and 0.0262, respectively). These isotopes can also be produced by n-capture of their A-1 neighbors.

The second image shows the n-capture cross-sections for (n,γ) reaction. The third image shows the half-lives of the radionuclides. The half-life of Cs-135 is approximately 2.3 E6 years, which means is has a very low activity. Also note that Xe-135 has a high n-capture cross-section, and much of that is transmuted to Xe-136.

 

[swl]

Hello all,

I have a new question related to Cesium in the waste stream of a refuse incinerator located in Machida, western Tokyo.
The site began sampling for Cesium 134 and Cesium 137, in the Incineration residue, after the accident in 2011.
From the time they initiated sampling, until June of 2016, the Cs-134 activity was always equal to, or less than the Cs-137 activity. Starting in June of 2016 and on multiple occasions since then, the Cs-134 activity has been higher than the Cs-137 activity. With consideration to the much shorter half life of Cs-134, I would have expected the Cs-134 activity to fall more quickly than the Cs-137 activity, but the reverse seems to be true here.

Can any of you please kindly help me to understand why the Cs-137 activity would be falling faster than that of the Cs-134?

Also, if this could be a case of confusion between Cs-134 and Bi-214 in the measurement process, how might we be getting Radium into the Incinerator?

https://www.city.machida.tokyo.jp/kurashi/kankyo/gomi/shiryo/keikakutou/shisetu.files/zansa_housyanou.pdf

If you would like an English translation, please PM me and I'll be happy to email the translation to you.

Thank you for reading and helping me understand.
Scott

 

[Gary7]

I'm interested in this too.
My guess is that the values being measured lately are so negligible, the minuscule variances will be the result of the uneven concentrations to begin with. The initial dispersal was uneven, and the environment where these measurements are now being taken (the incinerator) would not produce predictable results, and so expecting a textbook decay ratio is probably a mistake to begin with. The more important takeaway from the data is the long-term trend. Both are dropping, and C134, when it is detected at all, is, on average, lower than the C137.
That is my gut feeling, but hopefully someone who knows more than I do will be motivated to provide a more accurate response. It does seem that the CS137 is falling very rapidly. Maybe there is a biological component to this also... what kind of trash is going into that incinerator. Household trash, or industrial trash? Are they now (or were they ever) accepting loads of trash from Fukushima? Maybe too many variables to get an accurate picture.