Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646, Abiko, 270-1194, Japan.
Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646, Abiko, 270-1194, Japan.
J Environ Radioact. 2020 Apr;214-215:106173. doi: 10.1016/j.jenvrad.2020.106173. Epub 2020 Jan 27.
A series of accidents at the Fukushima Dai-ichi Nuclear Power Plant (1F NPP) following the Great East Japan Earthquake and tsunami of 11 March 2011 resulted in the release of radioactive materials to the ocean. We used the Regional Ocean Model System (ROMS) to simulate the Cs activity in the oceanic area off Fukushima, with the sources of radioactivity being direct release, atmospheric deposition, river discharge, and inflow across the domain boundary. The direct release rate of Cs after the accident until the end of 2016 was estimated by comparing simulated results with measured Cs activities adjacent to the 1F NPP. River discharge rates of Cs were estimated by multiplying simulated river flow rates by the dissolved Cs activities, which were estimated by an empirical function. Inflow of Cs across the domain boundary was set according to the results of a North Pacific Ocean model. Because the spatiotemporal variability of Cs activity was large, the simulated results were compared with the annual averaged observed Cs activity distribution. Normalized annual averaged Cs activity distributions in the regional ocean were similar for each year from 2013 to 2016. This result suggests that the annual averaged distribution is predictable. Simulated Cs activity attributable to direct release was in good agreement with measurement data from the coastal zone adjacent to the 1F NPP. Comparison of the simulated results with measured activity in the offshore area indicated that the simulation slightly underestimated the activity attributable to inflow across the domain boundary. This result suggests that recirculation of subducted Cs to the surface layer was underestimated by the North Pacific model. During the study period, the effect of river discharge on oceanic Cs activity was small compared to the effect of directly released Cs.
2011 年 3 月 11 日日本东海岸地震和海啸后，福岛第一核电站（1F NPP）发生了一系列事故，导致放射性物质释放到海洋中。我们使用区域海洋模式系统（ROMS）模拟了福岛附近海域的 Cs 活性，放射性物质的来源有直接释放、大气沉积、河流排放和域边界流入。通过将模拟结果与紧邻 1F NPP 的 Cs 活性测量值进行比较，估算了事故发生后直至 2016 年底的 Cs 直接释放率。通过将模拟的河流流量乘以通过经验函数估算的溶解 Cs 活性来估算 Cs 的河流排放量。根据北太平洋模型的结果设置了 Cs 穿过域边界的流入量。由于 Cs 活性的时空变异性很大，因此将模拟结果与每年平均观测到的 Cs 活性分布进行了比较。2013 年至 2016 年，区域海洋中归一化的年平均 Cs 活性分布在每年都相似。这一结果表明，年平均分布是可预测的。直接释放引起的 Cs 模拟活性与紧邻 1F NPP 的沿海地区的测量数据吻合良好。将模拟结果与近海地区的实测活性进行比较表明，模拟结果略低估了归因于域边界流入的活性。这一结果表明，北太平洋模型低估了俯冲 Cs 再循环到表层的作用。在研究期间，与直接释放的 Cs 相比，河流排放对海洋 Cs 活性的影响较小。
