福岛第一核电站(F1NPS)发生了一系列事故,在2011年3月11日地震和海啸之后,导致放射性物质释放到海洋中。特别是,大量放射性铯的释放损害了渔业,导致对捕鱼和运输的自愿限制。根据对放射性物质的路径和通量的估计进行的海洋扩散模拟为评估环境影响和制定减轻事故影响的措施提供了有用的信息。对于F1NPS站点的直接释放速率,利用附近监测的结果开发了一种估计方法,并使用数值模拟以目标体积估算海水交换率。然而,没有考虑体积对海水交换率的影响。在估计未来事故的影响时,必须考虑适当的数量。此外,由于分辨率低,在F1NPS事故的模拟中低估了定向沿海运输。为了估计放射性物质进入海洋的路径和通量,并根据海洋扩散模拟了解放射性物质浓度的分布,使用较高分辨率模型进行了一项研究.常规海洋弥散模型区域海洋模拟系统(ROMS)的水平分辨率,从1km增加到200m。研究了海水交换速率的最佳设置,更准确地反映了沿海方向的放射性铯输送过程。我们发现确定海水交换率的常规体积,包括释放源和观察点的位置,是最优的。使用先前海洋示踪剂释放实验的实验方程证实了这一发现的有效性。为了估计未来的释放率,它必须定义一个适当的体积,例如,取决于释放源的位置和观测点之间的距离。此外,由于更高的分辨率,观察到沿海运输过程模拟精度的提高,这增加了可重复性。然而,水平分辨率为200米,港口附近出现了可重复性的问题。更高的分辨率,使用嵌套或其他方法实现,处理比F1NPS事故中更小的释放是可取的。
A series of accidents at the Fukushima Daiichi Nuclear Power Station (F1NPS), following the 11 March 2011 earthquake and tsunami, resulted in the release of radioactive substances into the ocean. In particular, the release of large amounts of radioactive caesium has damaged the fishing industry, leading to voluntary restrictions on fishing and shipping. Oceanic dispersion simulations based on estimates of the pathways and fluxes of radioactive materials provide useful information for assessing the environmental impacts and formulating measures to mitigate the effects of the accident. For the direct release rate from the F1NPS site, an estimation method was developed using the results from nearby monitoring, and the seawater exchange rate was estimated in target volume using a numerical simulation. However, the influence of volume on the seawater exchange rate was not considered. Appropriate volumes must be considered when estimating the effects of future accidents. In addition, the directional coastal transport was underestimated in the simulations of the F1NPS accident because of the low resolution. To estimate the pathways and fluxes of radioactive material to the ocean and understand the distribution of the concentration of radioactive material based on ocean dispersion simulations, a study was conducted using a higher-resolution model. The horizontal resolution of the conventional ocean dispersion model Regional Ocean Modelling System (ROMS), was increased from 1 km to 200 m. The optimal settings of the seawater exchange rate were investigated, and the radioactive caesium transport process in the coastal direction was more accurately reflected. We found that the conventional volume for determining the seawater exchange rate, including the locations of release sources and observation points, is optimal. The validity of this finding was confirmed using experimental equations from previous oceanic tracer release experiments. To estimate future release rates, it an appropriate volume must be defined, for example, depending on the distance between the locations of the release sources and the observation point. In addition, improvements in the accuracy of the simulation of the coastal transport process were observed owing to the higher resolution, which increased reproducibility. However, with a horizontal resolution of 200 m, problems with repeatability near the harbours arose. A higher resolution, achieved using nesting or other methods, would be desirable to deal with releases smaller than those in the F1NPS accident.