[ RadSafe ] Re: Feds puzzled ....radionuclide speciation

[Peter Bossew]

Johansen, Kjell wrote:
> One aspect of this discussion about Cs-137 uptake as it relates to
> weapons testing fallout is that not all of the fallout Cs-137 was
> readily available for uptake in that it was bound to particles.  If I
> remember correctly, there was a paper in Science back in circa 1961
> which stated that about 40% of the deposited Cs-137 was tied up in
> particles/bomb debris from which it was not immediately available for
> biological uptake.  Does anyone know whether the similar fractionation
> occurred in the Chernobyl debris?
>
>  
>   

Yes there is a strong fractionation particle / condensed in Chernobyl 
releases. There is ample literature about the subject: e.g., a map of 
the percentage of particulate fallout out of total is given in 
Loshchilov et al. 1991, reproduced in Bar'yakhtar 1998. From the data, a 
weathering constant of highly oxidized particles (the ones released 
during the fire) of roughly 0.16 a^-1 can be estimated if an exp. 
weathering model is assumed. In a different physical model, for soil 
pH=5.5 (typical in the area) a loss of diameter of 0.237 um/a has been 
estimated (formulae given in Bar'akhtyar 1998).
At the site where I have mostly been working (Kopachi, ca. 6 km S of 
ChNPP; 1-3 MBq/m2 137Cs deposition) the initial particulate fraction was 
estimated >=75%. For that site I estimate (unpublished) 68% of the 
particles as of type 1 (highly oxidized; k-value<ca.25 ), the rest type 
2 (emitted during the initial explosion, more resistant against 
weathering, 25<k<250, k=ratio of 137Cs /154Eu, found to be a 
classification criterion, Zhdanova et al. 2000). Very few particles 
appear to be of condensed type (k>250) at that location. A small 
fraction of particles represents structural material (60Co, 94Nb). The 
condensed type particles, also called type A, became famous because some 
of them consisted almost only of Ru (volatile as oxide, RuO4 if I 
remember well), and could be found in air filters and environmental 
samples all over Europe, but this nuclide has decayed since. - Some of 
these HPs are also fine playgrounds for a-spectrometry, as they contain 
quite exotic (compared to what one usually finds in the environment) 
stuff like various Am and Cm isotopes.

One important radio-ecological effect of this fractionation is that 
soluble fractions of radionuclides, and therefore available for plant 
uptake, became available only gradually, which explains that TF and Tag 
values have found to be numerically time dependent, and increasing, 
simply because initially a large fraction was bound in particles.

pb


Bar’yakhtar V., V. Kukhar‘, I. Los‘, V. Poyarkov, V. Kolosha, V. 
Shestopalov (eds.)(1998): Comprehensive risk assessment of the 
consequences of the Chornobyl accident. Report, Science and Technology 
Center in Ukraine, Ukrainian Radiation Training Centre, Project No. 369

Loshchilov N. A., V. A. Kashparov, Ye. B. Yudin, V. P. Protsak, M. A. 
Zhurba, A. E. Parshakov (1991): Physical-chemical forms of the 
radioactive fallout from the Chernobyl reactor accident. In: 
Proceedings, Research coordination meeting on the rsdiobiological impact 
of hot beta particles from the Chrnobyl fallout: risk assessment. Eds. 
A. A. Moiseev, R. Mukherjee; Kiev 26-30 Aug 1991.

Zhdanova N., Redchitz T., Vasilevskaya A. I., Vember V., Fomina M., 
Zheltonozhsky V. A., Bondarkov M. D., Lashko T. N., Ukhin M. A., Olsson 
St., Mück K., Strebl F. & Gerzabek M. H. (2000): Interaction between 
biota micromycetes and hot particles after the Chernobyl NPP accident 
and atomic explosions and investigation of their influence on 
rehabilitating contaminated areas, Final Report INTAS Research Project 
No. INTAS-UKRAINE 95-0171, 20. Nov. 2000.

Also very interesting articles (among many others on the subject):

Salbu B. et al. (2001): High energy X-ray microscopy for 
characterization of fuel particles. Nuclear Instruments and Methods A 
467-468,1249-1252

Salbu B. et al. (2004): Radionuclide speciation and its relevance in 
environmental impact assessment. J. Env. Rad. 74, 233-242


-----------------------------------------------------
Peter Bossew 

European Commission (EC) 
Joint Research Centre (JRC) 
Institute for Environment and Sustainability (IES) 

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