Diacre Aurélie, Chalaux Clergue Thomas, Burban Soazig, Gauthier Caroline, Hubert Amélie, Humbert Anne-Claire, Lefevre Irène, Fauré Anne-Laure, Pointurier Fabien, Evrard Olivier
Commissariat à L'Energie Atomique et Aux énergies Alternatives (CEA, DAM, DIF), F-91297, Arpajon, France; Laboratoire des Sciences Du Climat et de L'Environnement (LSCE/IPSL), Unité Mixte de Recherche 8212 (CEA/CNRS/UVSQ), Université Paris-Saclay, Gif-sur-Yvette, France.
Laboratoire des Sciences Du Climat et de L'Environnement (LSCE/IPSL), Unité Mixte de Recherche 8212 (CEA/CNRS/UVSQ), Université Paris-Saclay, Gif-sur-Yvette, France.
Environ Pollut. 2023 Feb 15;319:120963. doi: 10.1016/j.envpol.2022.120963. Epub 2022 Dec 29.
In 2011, the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) accident released significant quantities of radionuclides into the environment. Japanese authorities decided to progressively reopen the Difficult-To-Return Zone after the decontamination of priority reconstruction zones. These areas include parts of the initially highly contaminated municipalities located to the north of the FDNPP, including Namie Town, an area drained by the Ukedo and Takase Rivers. Eleven years after the accident, research focused on the spatial distribution of plutonium (Pu) and radiocesium (Cs) isotopes at contrasted individual locations. To complement previous results, the current research was conducted on flood sediment deposits collected at the same locations after major flooding events during eleven fieldwork campaigns organised between 2013 and 2020 at the outlet of the Ukedo and Takase Rivers (n = 22). The results highlighted a global decrease of the Pu and Cs contents in sediment with time during the abandonment phase in the region, from 2013 (238.20 fg g) to 2020 (4.28 fg g). Furthermore, based on the analysis of the Pu/Pu isotopic ratios, the plutonium transiting these rivers (range: 0.166 - 0.220) essentially originated from the global fallout (0.180 ± 0.014 (Kelley et al., 1999)). Sediment showed contrasted properties in the two investigated rivers, which is likely mainly the result of the occurrence of Ogaki Dam on upper sections of the Ukedo River as it strongly impacts the material supply from this river to the Pacific Ocean. A statistical analysis highlighted the strong correlation between Pu activity concentrations and Cs activities in both rivers, confirming that both radionuclides are transported with a similar pathway. Despite it was detected early after the accident (2011-2013), the current research demonstrates that plutonium originating from FDNPP is no longer detected in these rivers draining the Difficult-To-Return Zone at the onset of the reopening of the area to its former inhabitants.
2011年，福岛第一核电站事故向环境中释放了大量放射性核素。日本当局决定在优先重建区域去污后逐步重新开放难以返回区域。这些区域包括福岛第一核电站以北最初高度污染的部分市镇，包括浪江町，该地区由宇久江和高濑川排水。事故发生11年后，研究集中在钚（Pu）和放射性铯（Cs）同位素在不同地点的空间分布上。为补充先前的研究结果，本次研究对2013年至2020年期间在宇久江和高濑川河口进行的11次野外考察中，主要洪水事件后在相同地点采集的洪水沉积物进行了研究（n = 22）。结果表明，在该地区的弃置阶段，沉积物中Pu和Cs含量随时间总体呈下降趋势，从2013年的238.20 fg/g降至2020年的4.28 fg/g。此外，基于对Pu/Pu同位素比值的分析，流经这些河流的钚（范围：0.166 - 0.220）主要源自全球沉降（0.180 ± 0.014（凯利等人，1999年））。沉积物在两条被调查河流中表现出不同的特性，这可能主要是由于宇久江上段的大垣大坝的存在，因为它强烈影响了该河向太平洋的物质供应。统计分析突出了两条河流中Pu活度浓度与Cs活度之间的强相关性，证实这两种放射性核素通过相似的途径传输。尽管在事故后早期（2011 - 2013年）就检测到了，但当前研究表明，在该地区重新向原居民开放之初，流经难以返回区域的这些河流中已不再检测到源自福岛第一核电站的钚。
