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| Titel |
Estimations of direct release rate of 137Cs and 90Sr to the ocean from the Fukushima Dai-ichi Nuclear Power Plant for five-and-a-half years |
| VerfasserIn |
Daisuke Tsumune, Michio Aoyama, Takaki Tsubono, Kazuhiro Misumi, Yutaka Tateda |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250147978
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| Publikation (Nr.) |
 EGU/EGU2017-12202.pdf |
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| Zusammenfassung |
| A series of accidents at the Fukushima Dai-ichi Nuclear Power Plant (1F NPP) 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. Additional release pathways by river input and runoff from 1F NPP site with
precipitation and were also effective for coastal zone in the specific periods before starting
direct release on March 26 2011. Direct release from 1F NPP site is dominant one year
after the accident. We estimated the direct release rate of 137Cs and 90Sr for more
than five-and-a-half years after the accident by the Regional Ocean Model System
(ROMS).
Direct release rate of 137Cs were estimated for five-and-a-half years after the accident by
comparing simulated results and measured activities adjacent to the 1F NPP site(at
5,6 discharge and south discharge). Directly release rate of 137Cs was estimated
to be the order of magnitude of 1014 Bq/day and decreased exponentially with
time to be the order of magnitude of 109 Bq/day by the end of September 2016.
Estimated direct release rate have exponentially reduced with constant rate since
November 2011. Apparent half-life of direct release rate was estimated to be 346
days. The estimated total amounts of directly released 137Cs was 3.7±0.7 PBq
for five and a half years. 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. Simulated 137Cs activity affected off coast in
the Fukushima prefecture. We used the measured 137Cs activities by the Tokyo
Electric Power Company (TEPCO) for the estimation of direct release. The sea water
samples were corrected from the coast. The averaged 137Cs activities from November
2013 to June 2016 were 391 and 383 Bq/m3 at 5,6 discharge and south discharge,
respectively. The averaged 137Cs activities measured by the Nuclear Regulation
Agency (NRA) is about five times smaller than the one by the TEPCO because
the NRA corrected seawater samples at 300-500m offshore by ship. Horizontal
resolution of the model was 1km x 1km, therefore it is important to consider the
difference of activities in the sub-grid scale for the detailed estimations of direct
release.
90Sr/137Cs activity ratio measured adjacent to the 1F NPP is variable with time. The
90Sr/137Cs activity ratio was 0.62 due to the global fallout before the accident. The
90Sr/137Cs activity ratio decreased to 0.01 after the accident before April 2011. And the ratio
increased to 1 by September 2013. And then the ratio decreased to 0.1-1. After October 2015,
the ratio decreased to 0.1-0.2. Directly release rate of 90Sr was estimated to be the order of
magnitude of 1012 Bq/day and decreased to the order of magnitude of 108 Bq/day by the end
of September 2016. The estimated total amounts of directly released 90Sr was 35 ± 7 TBq. |
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