著者

津旨 大輔 坪野 考樹 三角 和弘 立田 穣 三浦 輝 青山 道夫

出版者

公益社団法人 日本アイソトープ協会

雑誌

アイソトープ・放射線研究発表会 第58回アイソトープ・放射線研究発表会 (ISSN:24364487)

巻号頁・発行日

pp.45, 2021 (Released:2021-09-06)

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福島第一原発敷地からの直接漏洩は大幅に減少したものの、引き続き継続している。海洋分散シミュレーションを2020年9月まで延長した。年平均表層放射性セシウム濃度分布の観測結果とシミュレーション結果は、よく一致した。敷地からの直接漏洩の影響が大きいが、特に2019年10月の豪雨時には、河川からの粒子態による放射性セシウムの供給の影響が大きいことが示唆された。

著者

津旨 大輔 坪野 考樹 三角 和弘 立田 穣 豊田 康嗣 恩田 裕一 青山 道夫

出版者

日本地球惑星科学連合

雑誌

日本地球惑星科学連合2018年大会

巻号頁・発行日

2018-03-14

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A series of accidents at the Fukushima Dai-ichi Nuclear Power Plant following the Great East Japan 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. A 6 years, regional-scale simulation of 137Cs activity in the ocean offshore of Fukushima was carried out by the Regional Ocean Model System (ROMS), the sources of radioactivity being direct release, atmospheric deposition, the inflow of 137Cs deposited into the ocean by atmospheric deposition outside the domain of the model, and river discharges.Direct releases of 137Cs were estimated for 6 years after the accident by comparing simulated results and measured activities adjacent to the accident site. In addition, river discharge rates 137Cs were calculated by multiplication between river flow rate and 137Cs activity. River flow rates were simulated by a water circulation analysis model for each catchment. Temporal change of 137Cs activity both of particle and dissolved forms were measured at 8 rivers and normalized by the inventory of 137Cs in each catchment. 137Cs activity in other 4 rivers were estimated by the normalized 137Cs activity and inventories of catchments. After 2013, direct release and river discharge were dominant for input of 137Cs to the ocean. Apparent half-life of direct release and river discharge of were estimated to be about 1 year and 2 years, respectively.Apparent half-life of measured 137Cs activity adjacent to 1F NPP was about 1 year, on the other hand, the ones in the coastal zone away from 1F NPP were about 2 years after 2013. Apparent half-life of simulated results with river discharge was in good agreement with the one in the coastal zone away from 1F NPP. River discharge affected on temporal change of 137Cs activity there. On the other hands, simulated 137Cs activities with river input were one order of magnitudes smaller than observations. This underestimation suggests modifications of river input process, such as estuary mixing process, removal from particle form 137Cs and inputs from small rivers around the 1F NPP.

著者

津旨 大輔 坪野 考樹 三角 和弘 立田 穣 青山 道夫 広瀬 勝巳

出版者

日本地球惑星科学連合

雑誌

JpGU-AGU Joint Meeting 2017

巻号頁・発行日

2017-03-10

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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. The activities attributable to the direct release were observed adjacent to the 1F NPP site. The sea side impermeable wall was closed at 26 October 2015. We estimated the direct release rate of 137Cs, 90Sr and 3H for more than four-and-a-half years after the accident by the Regional Ocean Model System (ROMS).Direct release rate of 137Cs were estimated by comparing simulated results and measured activities adjacent to the 1F NPP site (adjacent to 5,6 discharge and south discharge). Direct release rate of 137Cs was estimated to be 2.2 x 1014 Bq/day and decreased exponentially with time to be 3.9 x109 Bq/day by 26 October 2015. Estimated direct release rate have exponentially decreased with constant rate since 4 November 2011. Apparent half-life of direct release rate was estimated to be 346 days. The estimated total amounts of directly released 137Cs was 3.6±0.7 PBq from 26 March 2011 to 26 October 2015. 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.90Sr/137Cs activity ratio of stagnant water was 0.05 in the basement of the 1F NPP reactor 2 turbine building on 27 March 2011. Direct release rate of 90Sr was estimated to be 1.1 x 1013 Bq/day from 26 March to 6 April 2011 using the activity ratio in stagnant water because the stagnant water released to the ocean in this period (Tsumune et al., 2012). And the temporal change of direct release rate was estimated by the measured 90Sr activity adjacent to 1F NPP. Directly release rate decreased exponentially to 3.9 x 1010 Bq/day by 30 April 2011. The direct release rate was constant and decreased exponentially from 27 June to 16 December 2013. And the direct release rate was 2.9 x 109 Bq/day by 26 October 2015. The estimated total amounts of directly released 90Sr was 208 ± 42 TBq.3H/137Cs activity ratio of stagnant water was 8.7 x 10-3 in the basement of the 1F NPP reactor 2 turbine building on 27 March 2011. Directly release rate of 3H was estimated to be 1.9 x 1012 Bq/day from 26 March to 6 April 2011 and decreased exponentially by 16 April 2011. The rate was decreased exponentially with constant rate by 26 October 2015. The direct release rate was estimated to be 7.7 x 109 Bq/day at 26 October 2015. The estimated total amounts of directly released 3H was 131 ± 26 TBq.