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Supporting Information For
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Fukushima Reactor Source Term Attribution using Cs Isotope
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Ratios from Contaminated Environmental Samples
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Mathew S. Snow*, Darin C. Snyder, James E. Delmore
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Idaho National Laboratory, PO Box 1625, Idaho Falls, ID 83415-2805, USA
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*Corresponding Author: mathew.snow@inl.gov
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1. Method Validations using IAEA-375 (Table SI-1) ................................................................ 2
2. 135Cs/137Cs ratios as a function of fuel rod height (Figure SI-1) .......................................... 3
3. Effects of nuclear weapons testing corrections to 135Cs/137Cs ratio (Figure SI-2) .............. 4
4. 135Cs/137Cs to predict the total quantity of radioactivity emitted (Discussion SI-1) ........... 5
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Table SI-1. Method Validations using IAEA-375. 135Cs/137Cs ratios are decay corrected to
4/26/1986.
135
This Work (n=7)
Taylor et al.[17] (n=3)
Zheng et al.[8] (n=3)
Cs/137Cs*
0.30 ± 0.01
0.30 ± 0.03
0.31 ± 0.01
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Figure SI-1. Variation in the expected 135Cs/137Cs ratios as a function of rod height for 2 fuel rods
in a typical boiling water reactor. Red lines represent 137Cs activities, while black datapoints
represent 135Cs/137Cs ratio measurements. Data adapted from Guenther et al.[21]
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Figure SI-2. Effect of nuclear weapons testing fallout corrections to the 135Cs/137Cs isotope ratio.
Less than 1% change in the ratio is observed.
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Discussion SI-1. Predicting the total quantity of radioactivity emitted using 135Cs/137C.
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As a sidenote, while the use of 135Cs/137Cs ratios for predicting the total quantity of
radioactivity emitted from each FDNPP source term has been previously suggested[8], caution
must be taken when attempting to do this. For this approach to apply, the samples being
utilized must be representative of the total combined radiocesium released from FDNPP
(enabling inference of the degree of mixing between each source term and subsequently the
relative quantity that each source term emitted). However, as meteorological data emphasizes,
samples taken from the ground are not well suited for this, as they can be biased by deposition
processes and the directionality of the plume. A more reliable type of sample could include air
filter samples such as those collected by Tsuruta et al.[3], particularly if temporally and spatially
resolved samples are analyzed and compared with each other.
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