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Titel |
Xenon-133 and caesium-137 releases into the atmosphere from the Fukushima Dai-ichi nuclear power plant: determination of the source term, atmospheric dispersion, and deposition |
VerfasserIn |
A. Stohl, P. Seibert, G. Wotawa, D. Arnold, J. F. Burkhart, S. Eckhardt, C. Tapia, A. Vargas, T. J. Yasunari |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250059241
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Zusammenfassung |
This presentation will show the results of a paper currently under review in ACPD and some
additional new results, including more data and with an independent box modeling approach
to support some of the findings of the ACPD paper.
On 11 March 2011, an earthquake occurred about 130 km off the Pacific coast of Japan’s
main island Honshu, followed by a large tsunami. The resulting loss of electric power at the
Fukushima Dai-ichi nuclear power plant (FD-NPP) developed into a disaster causing massive
release of radioactivity into the atmosphere. In this study, we determine the emissions of two
isotopes, the noble gas xenon-133 (133Xe) and the aerosol-bound caesium-137 (137Cs), which
have very different release characteristics as well as behavior in the atmosphere. To determine
radionuclide emissions as a function of height and time until 20 April, we made a first guess
of release rates based on fuel inventories and documented accident events at the site.
This first guess was subsequently improved by inverse modeling, which combined
the first guess with the results of an atmospheric transport model, FLEXPART,
and measurement data from several dozen stations in Japan, North America and
other regions. We used both atmospheric activity concentration measurements as
well as, for 137Cs, measurements of bulk deposition. Regarding 133Xe, we find
a total release of 16.7Â (uncertainty range 13.4-20.0)Â EBq, which is the largest
radioactive noble gas release in history not associated with nuclear bomb testing. There
is strong evidence that the first strong 133Xe release started early, before active
venting was performed. The entire noble gas inventory of reactor units 1-3 was set
free into the atmosphere between 11 and 15 March 2011. For 137Cs, the inversion
results give a total emission of 35.8Â (23.3-50.1)Â PBq, or about 42% of the estimated
Chernobyl emission. Our results indicate that 137Cs emissions peaked on 14-15 March
but were generally high from 12 until 19 March, when they suddenly dropped by
orders of magnitude exactly when spraying of water on the spent-fuel pool of unit 4
started. This indicates that emissions were not only coming from the damaged reactor
cores, but also from the spent-fuel pool of unit 4 and confirms that the spraying was
an effective countermeasure. We also explore the main dispersion and deposition
patterns of the radioactive cloud, both regionally for Japan as well as for the entire
Northern Hemisphere. While at first sight it seemed fortunate that westerly winds
prevailed most of the time during the accident, a different picture emerges from our
detailed analysis. Exactly during and following the period of the strongest 137Cs
emissions on 14 and 15 March as well as after another period with strong emissions
on 19 March, the radioactive plume was advected over Eastern Honshu Island,
where precipitation deposited a large fraction of 137Cs on land surfaces. The plume
was also dispersed quickly over the entire Northern Hemisphere, first reaching
North America on 15 March and Europe on 22 March. In general, simulated and
observed concentrations of 133Xe and 137Cs both at Japanese as well as at remote sites
were in good quantitative agreement with each other. Altogether, we estimate that
6.4Â PBq of 137Cs, or 19% of the total fallout until 20 April, were deposited over
Japanese land areas, while most of the rest fell over the North Pacific Ocean. Only
0.7Â PBq, or 2% of the total fallout were deposited on land areas other than Japan. |
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