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| Titel |
Reconstruction of 137Cs activity in the ocean following the Fukushima Daiichi Nuclear Power Plant Accident |
| VerfasserIn |
Daisuke Tsumune, Michio Aoyama, Takaki Tsubono, Yutaka Tateda, Kazuhiro Misumi, Hiroshi Hayami, Yasuhiro Toyoda, Yoshiaki Maeda, Yoshikatsu Yoshida, Mitsuo Uematsu |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094170
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| Publikation (Nr.) |
 EGU/EGU2014-9566.pdf |
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| Zusammenfassung |
| A series of accidents at the Fukushima Dai-ichi Nuclear Power Plant following the
earthquake and tsunami of 11 March 2011 resulted in the release of radioactive materials to
the ocean by two major pathways, direct release from the accident site and atmospheric
deposition. We reconstructed spatiotemporal variability of 137Cs activity in the ocean by the
comparison model simulations and observed data. We employed a regional scale and the
North Pacific scale oceanic dispersion models, an atmospheric transport model, a
sediment transport model, a dynamic biological compartment model for marine biota
and river runoff model to investigate the oceanic contamination. Direct releases
of 137Cs were estimated for more than 2 years after the accident by comparing
simulated results and observed activities very close to the site. The estimated total
amounts of directly released 137Cs was 3.6±0.7 PBq. Directly release rate of 137Cs
decreased exponentially with time by the end of December 2012 and then, was
almost constant. The daily release rate of 137Cs was estimated to be 3.0 x 1010 Bq
day-1 by the end of September 2013. The activity of directly released 137Cs was
detectable only in the coastal zone after December 2012. Simulated 137Cs activities
attributable to direct release were in good agreement with observed activities, a result that
implies the estimated direct release rate was reasonable, while simulated 137Cs
activities attributable to atmospheric deposition were low compared to measured
activities. The rate of atmospheric deposition onto the ocean was underestimated
because of a lack of measurements of dose rate and air activity of 137Cs over the
ocean when atmospheric deposition rates were being estimated. Observed 137Cs
activities attributable to atmospheric deposition in the ocean helped to improve the
accuracy of simulated atmospheric deposition rates. Although there is no observed
data of 137Cs activity in the ocean from 11 to 21 March 2011, observed data of
marine biota should reflect the history of 137Cs activity in this early period. The
comparisons between simulated 137Cs activity of marine biota by a dynamic biological
compartment and observed data also suggest that simulated 137Cs activity attributable
to atmospheric deposition was underestimated in this early period. In addition,
river runoff model simulations suggest that the river flux of 137Cs to the ocean was
effective to the 137Cs activity in the ocean in this early period. The sediment transport
model simulations suggests that the inventory of 137Cs in sediment was less than
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