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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 |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 5 ; Nr. 12, no. 5 (2012-03-01), S.2313-2343 |
| Datensatznummer |
250010847
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| Publikation (Nr.) |
 copernicus.org/acp-12-2313-2012.pdf |
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| Zusammenfassung |
| 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
developed into a disaster causing massive release of radioactivity into the
atmosphere. In this study, we determine the emissions into the atmosphere 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 it
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 15.3 (uncertainty range 12.2–18.3) EBq, which is more than
twice as high as the total release from Chernobyl and likely the largest
radioactive noble gas release in history. The entire noble gas inventory of
reactor units 1–3 was set free into the atmosphere between 11 and 15 March
2011. In fact, our release estimate is higher than the entire estimated
133Xe inventory of the Fukushima Dai-ichi nuclear power plant, which we
explain with the decay of iodine-133 (half-life of 20.8 h) into 133Xe.
There is strong evidence that the 133Xe release started before the first
active venting was made, possibly indicating structural damage to reactor
components and/or leaks due to overpressure which would have allowed early
release of noble gases. For 137Cs, the inversion results give a total
emission of 36.6 (20.1–53.1) PBq, or about 43% 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 at the time when spraying of water on
the spent-fuel pool of unit 4 started. This indicates that emissions may not
have originated only from the damaged reactor cores, but also from the
spent-fuel pool of unit 4. This would also confirm that the spraying was an
effective countermeasure. We 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. Radioactive clouds
reached North America on 15 March and Europe on 22 March. By middle of April,
133Xe was fairly uniformly distributed in the middle latitudes of the
entire Northern Hemisphere and was for the first time also measured in the
Southern Hemisphere (Darwin station, Australia). In general, simulated and
observed concentrations of 133Xe and 137Cs both at Japanese as well
as at remote sites were in good quantitative agreement. Altogether, we
estimate that 6.4 PBq of 137Cs, or 18% 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 0.7 PBq, or 1.9% of the total
fallout were deposited on land areas other than Japan. |
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