Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan.
J Environ Radioact. 2012 Sep;111:2-12. doi: 10.1016/j.jenvrad.2011.09.011. Epub 2011 Oct 8.
To understand how the high dose rate zones were created during the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident on March 2011, the atmospheric dispersion of radionuclides during the period from 15 to 17 March was reproduced by using a computer-based nuclear emergency response system, WSPEEDI-II. With use of limited environmental monitoring data, prediction accuracy of meteorological and radiological fields by the system was improved to obtain best estimates of release rates, radiation dose maps, and plume movements. A large part of current high dose rate zones in Fukushima was explained by simulated surface deposition of radionuclides due to major releases of radionuclides on 15 March. In the simulation, the highest dose rate zones to the northwest of FNPP1 were created by a significant deposition of radionuclides discharged from FNPP1 during the afternoon. The results indicate that two environmental factors, i.e., rainfall and topography, strongly affected the spatial patterns of surface deposition of radionuclides. The wet deposition due to rainfall particularly played an important role in the formation of wide and heterogeneous distributions of high dose rate zones. The simulation also demonstrated that the radioactive plume flowed along the valleys to its leeward, which can expand the areas of a large amount of surface deposition in complex topography.
为了了解 2011 年 3 月福岛第一核电站（FNPP1）事故期间高剂量率区是如何形成的，利用基于计算机的核应急响应系统 WSPEEDI-II 再现了 3 月 15 日至 17 日期间放射性核素的大气扩散情况。利用有限的环境监测数据，该系统提高了气象和辐射场的预测精度，以获得最佳的释放速率、辐射剂量图和羽流运动估计值。由于 3 月 15 日发生了重大放射性核素释放，模拟结果解释了当前福岛大部分高剂量率区的形成原因。在模拟中，FNPP1 下午排放的放射性核素大量沉积，导致 FNPP1 西北方向出现了最高剂量率区。结果表明，两个环境因素，即降雨和地形，强烈影响了放射性核素表面沉积的空间分布模式。降雨引起的湿沉积对高剂量率区广泛且不均匀分布的形成尤其重要。模拟还表明，放射性羽流沿着山谷流向背风面，这会扩大复杂地形中大量表面沉积的区域。
