Nishikiori Tatsuhiro, Suzuki Satoshi
Fukushima Prefectural Centre for Environmental Creation, 10-2 Fukasaku, Miharu Town, Fukushima 963-7700, Japan.
Fukushima Prefectural Centre for Environmental Creation, 10-2 Fukasaku, Miharu Town, Fukushima 963-7700, Japan.
J Environ Radioact. 2017 Oct;177:58-64. doi: 10.1016/j.jenvrad.2017.06.005. Epub 2017 Jun 12.
Extensive decontamination measures have been implemented in the area affected by the Fukushima Dai-ichi nuclear disaster. Typical decontamination measures, such as removing topsoil of several centimeters in depth, are not suitable for rivers where contaminated sediments have been deposited. A decontamination measure was tested that considered the spatial distribution of radiocesium at the lower part of a tributary of the Abukuma River in Fukushima. The radiocesium distribution in the flood channel was vertically and horizontally highly heterogeneous. In some parts, the activity concentration was high (>10 kBq/kg for Cs) even at depths of 25 cm in the sediment. This may be due to plant growth in the flood channel favoring the deposition of sediment with high activity concentration. On the basis of the radiocesium distribution, the flood channel sediment was removed to a depth of 15-35 cm, which accumulated the most radiocesium (>3.0 kBq/kg for the sum of Cs and Cs). The upper 5 cm of soil was removed from the dike slopes. The river bed was not decontaminated because the activity concentration was low (<1 kBq/kg) in the river bed sediment and because the water shields gamma rays emitted from the sediment. The test decontamination measure reduced the air dose rate by a factor of approximately two, demonstrating the effectiveness of our measures. Annual external doses were calculated for when this part of the dike and the flood channel is used for commuting to school and outdoor education. The doses during the activities at the test site accounted for only 1-2% of the value during daily life in the surrounding area, indicating that radiation exposure during riverside activities is limited.
在福岛第一核电站核灾难影响地区已实施了广泛的去污措施。诸如去除几厘米深的表层土等典型去污措施，并不适用于已沉积受污染沉积物的河流。在福岛阿武隈川一条支流下游，对一种考虑了放射性铯空间分布的去污措施进行了测试。行洪河道中的放射性铯分布在垂直和水平方向上高度不均一。在某些部位，即使在沉积物25厘米深处，活度浓度也很高（铯的活度浓度>10 kBq/kg）。这可能是由于行洪河道中的植物生长有利于高活度浓度沉积物的沉积。根据放射性铯分布情况，清除了行洪河道沉积物15至35厘米深度的部分，该深度积累的放射性铯最多（铯和铯的总和>3.0 kBq/kg）。从堤坝坡面清除了上部5厘米厚的土壤。河床未进行去污，因为河床沉积物中的活度浓度较低（<1 kBq/kg），且水会屏蔽沉积物发出γ射线。测试去污措施使空气剂量率降低了约一半，证明了我们措施的有效性。计算了堤坝这部分和行洪河道用于上学通勤和户外教育时的年度外照射剂量。测试场地活动期间的剂量仅占周边地区日常生活剂量值的1 - 2%，这表明河边活动期间的辐射暴露是有限的。
