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| Titel |
Spatial and temporal variations and budget of radiocesium in the ocean following the Fukushima Daiichi Nuclear Power Plant accident |
| VerfasserIn |
Daisuke Tsumune, Michio Aoyama, Mizuo Kajino, Taichu Tanaka, Tsuyoshi Sekiyama, Takaki Tsubono, Kazuhiro Misumi, Yoshiaki Maeda, Yoshikatsu Yoshida, Hiroshi Hayami, Yasunori Hamajima, Toshitaka Gamo, Mitsuo Uematsu, Takeshi Kawano, Akihiro Murata, Yuichiro Kumamoto, Masao Fukasawa, Masamichi Chino |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250075450
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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 determined the inventory of radiocesium released by the TEPCO Fukushima
Dai-ichi Nuclear Power Plant (FNPP1) accident to the North Pacific Ocean based on
measurements of seawater samples collected in the North Pacific Ocean after the
accident. Comparison of the observed inventory with the model-simulated results
allowed us to obtain realistic values of 10–13 PBq for the total atmospheric deposition
of 134Cs and 137Cs released by the FNPP1 accident in the North Pacific. Before
the Fukushima accident, 137Cs inventory in the North Pacific Ocean was about
69 PBq, the 12 - 15 PBq of 137Cs newly added by atmospheric deposition and
the 3.5 ± 0.7 PBq added by direct discharge, therefore increased the total 137Cs
inventory in the North Pacific Ocean by 22–27 %. We also determined that the total
atmospheric release of 134Cs and 137Cs by the FNPP1 accident was about 14–17 PBq,
respectively.
Using global simulated results as boundary conditions, a 1-year, regional-scale simulation
of 137Cs activity in the ocean offshore of Fukushima was also carried out, the sources of
radioactivity being direct release, atmospheric deposition, and the inflow of 137Cs deposited
on the ocean by atmospheric deposition outside the domain of the model. The contributions
of each source were estimated by analysis of 131I/137Cs and 134Cs/137Cs activity
ratios and comparisons between simulated results and measured activities of 137Cs.
Simulated 137Cs activities attributable to direct release were in good agreement with
measured activities close to the accident site, a result that implies that 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 deposition onto the ocean when atmospheric deposition rates were
being estimated. Measured 137Cs activities attributable to atmospheric deposition
helped to improve the accuracy of simulated atmospheric deposition rates. Simulated
137Cs activities attributable to the inflow of 137Cs deposited onto the ocean outside
the domain of the model were in good agreement with measured activities in the
open ocean within the model domain after June 2012. The contribution of inflow
increased with time and was dominant (more than 99 %) by the end of February
2012. The activity of directly released 137Cs, however, decreased exponentially
with time and was detectable only in the coastal zone by the end of February 2012. |
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