Impact of changing the wet deposition schemes in ldx on 137-cs atmosperic deposits after the fukushima accident

Arnaud QuérelIRSN, IRSN/PSE-SANTE/SESUC/BMCA, Denis QuéloIRSN/PSE-SANTE/SESUC/BMCA, IRSN, Yelva RoustanCEREA, Anne MathieuIRSN, IRSN/PSE-SANTE/SESUC/BMCA, Mizuo KajinoMRI, Thomas SekiyamaMRI, Kouji AdachiMRI, Damien DidierIRSN, IRSN/PSE-SANTE/SESUC/BMCA, Yasuhito IgarashiMRI, Takashi MakiMRI
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Abstract

The Fukushima-Daiichi release of radioactivity is a relevant event to study the atmospheric dispersion modelling of radionuclides. Actually, the atmospheric deposition onto the ground may be studied through the map of measured Cs-137 established consecutively to the accident. The limits of detection were low enough to make the measurements possible as far as 250km from the nuclear power plant. This large scale deposition has been modelled with the Eulerian model ldX. However, several weeks of emissions in multiple weather conditions make it a real challenge. Besides, these measurements are accumulated deposition of Cs-137 over the whole period and do not inform of deposition mechanisms involved: in-cloud, below-cloud, dry deposition. In a previous study (Qu{\'e}rel et al., 2016), a comprehensive sensitivity analysis was performed in order to understand wet deposition mechanisms. It has been shown that the choice of the wet deposition scheme has a strong impact on assessment of deposition patterns. Nevertheless, a ``best'' scheme could not be highlighted as it depends on the selected criteria: the ranking differs according to the statistical indicators considered (correlation, figure of merit in space and factor 2). A possibility to explain the difficulty to discriminate between several schemes was the uncertainties in the modelling, resulting from the meteorological data for instance. Since the move of the plume is not properly modelled, the deposition processes are applied with an inaccurate activity concentration in the air. In the framework of the SAKURA project, an MRI-IRSN collaboration, new meteorological fields at higher resolution (Sekiyama et al., 2013) were provided and allow to reconsider the previous study. An update including these new meteorology data is presented. In addition, the focus is put on the deposition schemes commonly used in nuclear emergency context.
福岛核事故后改变ldx湿沉积方案对137-cs大气沉积物的影响
福岛第一核电站的放射性释放是研究放射性核素大气扩散模型的一个相关事件。实际上,可以通过事故发生后连续绘制的铯-137 测量图来研究地面的大气沉降。由于探测极限很低,因此可以在距离核电站 250 千米的地方进行测量。这种大规模沉积是用欧拉模型 ldX 模拟的。然而,在多种天气条件下进行数周的排放是一项真正的挑战。此外,这些测量结果是整个时期内 Cs-137 的累积沉积,并不能说明沉积机制:云中沉积、云下沉积、干沉积。在之前的研究(Qu{'e}rel 等人,2016 年)中,为了了解湿沉积机制,进行了全面的敏感性分析。研究表明,湿沉降方案的选择对沉降模式的评估有很大影响。然而,"最佳 "方案并不突出,因为它取决于所选的标准:根据所考虑的统计指标(相关性、空间中的概率和因子 2),排序是不同的。难以区分几种方案的一个可能原因是建模中的不确定性,例如气象数据造成的不确定性。由于没有正确模拟烟羽的移动,因此在应用沉积过程时,空气中的放射性浓度并不准确。在 MRI-IRSN 合作的 SAKURA 项目框架内,提供了更高分辨率的新气象场(Sekiyama 等人,2013 年),从而可以重新考虑之前的研究。本文介绍了包括这些新气象数据在内的最新情况。此外,还重点介绍了核紧急情况下常用的沉积方案。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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