Misumi Kazuhiro, Tsumune Daisuke, Tsubono Takaki, Tateda Yutaka, Aoyama Michio, Kobayashi Takuya, Hirose Katsumi
Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko, Chiba 270-1194, Japan.
Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko, Chiba 270-1194, Japan.
J Environ Radioact. 2014 Oct;136:218-28. doi: 10.1016/j.jenvrad.2014.06.004. Epub 2014 Jun 27.
We used numerical simulations to investigate major controls on spatiotemporal variations of (137)Cs activities in seabed sediments off the Fukushima coast during the first year after the Fukushima Daiichi Nuclear Power Plant accident. The numerical model we used includes (137)Cs transfer between bottom water and sediment by adsorption and desorption, and radioactive decay. The model successfully reproduced major features of the observed spatiotemporal variations of (137)Cs activities in sediments. The spatial pattern of (137)Cs in sediments, which mainly reflected the history of (137)Cs activities in bottom water overlying the sediments and the sediment particle size distribution, became established during the first several months after the accident. The simulated temporal persistence of the (137)Cs activity in the sediments was due to adsorption of (137)Cs onto the sediment mineral fraction having a long desorption timescale of (137)Cs. The simulated total (137)Cs inventory in sediments integrated over the offshore area, where most of the monitoring stations were located, was on the order of 10(13) Bq; this value is consistent with a previous estimate based on observed data. Taking into account (137)Cs activities in sediments in both the coastal area and in the vicinity of the power plant, the simulated total inventory of (137)Cs in sediments off the Fukushima coast increased to a value on the order of 10(14) Bq.
我们利用数值模拟研究了福岛第一核电站事故发生后第一年福岛海岸附近海床沉积物中¹³⁷Cs活度的时空变化的主要控制因素。我们使用的数值模型包括¹³⁷Cs通过吸附和解吸在底层水和沉积物之间的转移以及放射性衰变。该模型成功再现了沉积物中¹³⁷Cs活度观测到的时空变化的主要特征。沉积物中¹³⁷Cs的空间分布模式主要反映了覆盖沉积物的底层水中¹³⁷Cs活度的历史以及沉积物颗粒大小分布，在事故发生后的最初几个月内就已形成。沉积物中¹³⁷Cs活度的模拟时间持续性是由于¹³⁷Cs吸附到沉积物矿物组分上，而¹³⁷Cs的解吸时间尺度很长。在大多数监测站所在的近海区域，沉积物中¹³⁷Cs的模拟总存量约为10¹³Bq；该值与基于观测数据的先前估计一致。考虑到沿海地区和核电站附近沉积物中的¹³⁷Cs活度，福岛海岸附近沉积物中¹³⁷Cs的模拟总存量增加到约10¹⁴Bq。
