Search

Saharan dust outbreaks have profound effects on ecosystems, climate, human health, and the cryosphere in Europe. However, the spatial deposition pattern of Saharan dust is poorly known due to a sparse network of ground measurements. Following the extreme dust deposition event of February 2021 across Europe, a citizen science campaign was launched to sample dust on snow over the Pyrenees and the European Alps. This somewhat improvised campaign triggered wide interest since 152 samples were collected from the snow in the Pyrenees, the French Alps, and the Swiss Alps in less than 4 weeks. Among the 152 samples, 113 in total could be analysed, corresponding to 70 different locations. The analysis of the samples showed a large variability in the dust properties and amount. We found a decrease in the deposited mass and particle sizes with distance from the source along the transport path. This spatial trend was also evident in the elemental composition of the dust as the iron mass fraction decreased from 11 % in the Pyrenees to 2 % in the Swiss Alps. At the local scale, we found a higher dust mass on south-facing slopes, in agreement with estimates from high-resolution remote sensing data. This unique dataset, which resulted from the collaboration of several research laboratories and citizens, is provided as an open dataset to benefit a large community and to enable further scientific investigations. Data presented in this study are available at https://doi.org/10.5281/zenodo.7969515 (Dumont et al., 2022a).

International audience; 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 137Cs contents in sediment with time during the abandonment phase in the region, from 2013 (238.20 fg g−1) to 2020 (4.28 fg g−1). Furthermore, based on the analysis of the 240Pu/239Pu 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 137Cs 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.

International audience; Every accident affecting industrial or nuclear facilities emits micrometric fragments of material into the environment whose elemental and isotopic compositions are characteristic of the process or event. Particle analysis, mainly implemented in the framework of the Non Proliferation Treaty to detect clandestine nuclear activities, provides a powerful tool to identify the origin of the nuclear particulate matter and to assess the environmental impact of nuclear accidents. Initially, particle-scale isotopic analyses aimed at the determination of the U isotopic composition. Now, focus is increasingly given on Pu isotopic measurements to address its origin and potential use. Such measurements are more challenging because of isobaric interferences, including those induced by hydride ions, like $^{239}$PuH+ on $^{240}$Pu+ and $^{238}$UH+ on $^{239}$Pu+ in Mixed Oxide (MOX). Such ions are generated during ionization processes by Secondary Ion Mass Spectrometry. Based on a parametric study aiming at the measurement of uranium oxide, uranium carbide and uranium single and double hydride rates, we determined that Pu and U should be detected as elementary ions to limit the impact of such interferences, although mono-oxide ions are more abundant. Thus, we developed an analytical methodology to obtain accurate$^{240}$Pu/$^{239}$Pu atomic ratios both for weapon grade Pu and MOX materials. Hydride rate is first measured in U oxide particles and then applied to correct $^{240}$Pu+ and $^{239}$Pu+ signals. The relative difference of corrected $^{240}$Pu/$^{239}$Pu isotopic ratios with expected values is reduced by a factor of 4 when measuring weapon grade Pu particles and by a factor of 10-100 when measuring MOX particles containing 1 to 10 wt% of Pu. We also proposed a method to determine the Relative Sensitivity Factor (RSF) based on the decay of Pu in order to quantify the Pu content in MOX samples. The estimated lowest measurable $^{239}$Pu/$^{238}$U atomic ratio in MOX particles is ∼1.6 × 10$^{-3}$

The Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) accident that occurred in March 2011 released significant quantities of radionuclides into the environment. Ten years after the accident, questions still remain, particularly about the processes that led to the partial core meltdown of reactors 1 and 3. So far, some answers have been provided by the investigation of particles containing caesium (Martin et al., 2020) and sometimes uranium (Ochiai et al., 2018). Indeed, the composition of particles, which were produced and spread at the time of the reactor explosion, reflect the conditions that prevailed in the reactor. Accordingly, the objective of the current research is to develop a method for specifically locating actinide-bearing particles in sediment samples collected in the vicinity of FDNPP. To identify and locate such particles, three already existing methods have been upgraded, including 1) the method of fission tracks already used in the field of non-proliferation studies, 2) the autoradiography through the use of imaging plates that are currently employed in the context of the localization of particles containing radio-caesium and the dismantling of nuclear facilities (Haudebourg and Fichet, 2016), and 3) a real time autoradiography method through the use of the BeaQuant® instrument which has been developed for detecting radioactive particles in biology and geosciences.In this study, a sediment sample collected nearby FDNPP, which may contain particles containing both radio-caesium and actinides, was selected. This sample was dried and sieved to 63 µm before being processed according to the different analysis protocols. A quality control sample containing only uranium oxide particles was also analysed, as these particles are devoid of gamma-emitters.The first results of this comparison of autoradiography methods for the detection of actinide-bearing particles in Fukushima samples will be presented. The method of fission tracks was particularly efficient for detecting both natural and anthropogenic uranium.The next steps of this study will be to implement this method identified as optimal to isolate and characterise a larger number of particles released by FDNPP. The full characterization of these particles (size, morphology, elemental and isotopic compositions) will provide novel insights to determine their origin and to improve our understanding of their formation processes within the reactors and anticipate their fate in the environment.References:Haudebourg, R., Fichet, P., 2016. A non-destructive and on-site digital autoradiography-based tool to identify contaminating radionuclide in nuclear wastes and facilities to be dismantled. J. Radioanal. Nucl. Chem. 309, 551–561. https://doi.org/10.1007/s10967-015-4610-7Martin, P.G., Jones, C.P., Cipiccia, S., Batey, D.J., Hallam, K.R., Satou, Y., Griffiths, I., Rau, C., Richards, D.A., Sueki, K., Ishii, T., Scott, T.B., 2020. Compositional and structural analysis of Fukushima-derived particulates using high-resolution x-ray imaging and synchrotron characterisation techniques. Sci. Rep. 10, 1636. https://doi.org/10.1038/s41598-020-58545-yOchiai, A., Imoto, J., Suetake, M., Komiya, T., Furuki, G., Ikehara, R., Yamasaki, S., Law, G.T.W., Ohnuki, T., Grambow, B., Ewing, R.C., Utsunomiya, S., 2018. Uranium Dioxides and Debris Fragments Released to the Environment with Cesium-Rich Microparticles from the Fukushima Daiichi Nuclear Power Plant. Environ. Sci. Technol. 52, 2586–2594. https://doi.org/10.1021/acs.est.7b06309

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident that occurred in March 2011 released significant quantities of radionuclides in the environment. So far, most of the research focused on radio-cesium and rarely on actinides. Until now, most of the studies on uranium and plutonium released by FDNPP were conducted on bulk environmental samples (soil, sediment, biota, etc.) and rarely on individual particles The investigation of individual particles allows working on the FDNPP signature alone compared to studies of bulk material which may also incorporate the signature of global fallout. Accordingly, the objective of the current research is to identify and characterize actinide-bearing particles in soil samples collected in the vicinity of FDNPP to get a better understanding of their formation mechanisms and of their fate in the environment. In order to identify and locate actinide-bearing particles in soil samples, we developed and implemented a method based on alpha-autoradiography (Jaegler et al., 2019), which allows identifying and locating specifically alpha-emitters, including plutonium isotopes 239Pu, 240Pu and 241Pu using a CR39 SSNTD device (Solid State Nuclear Tracks Detector).Before alpha-autoradiography samples were dried, grinded with an agate mortar and sieved to several cutoffs: 1mm, 700µm, 400µm, 200µm, 100µm and 63µm. Cutoffs were chosen according to the sizes of actinide-bearing particles detected by Satou et al (2018). The absence of significant loss of uranium particles by the sieving process was demonstrated by the analysis of a test soil sample with a 137Cs activity below 650 Bq/kg spiked with depleted uranium reference particles. After sieving, the test sample was deposited onto a carbon planchet for secondary ion mass spectrometry analysis in order to determine the particle recovery yield.Then, the detection of actinide-bearing particles by means of alpha autoradiography was performed on various soil samples collected in the vicinity of FDNPP. Longer exposure times logically improve the detection efficiency of alpha-emitters-bearing particles. However, the exposure time should not exceed two months to limit the impact of emissions from naturally-occurring alpha-emitters.We will present here the first results of detection of alpha-emitting particles in the analyzed soil samples. Relative impacts of naturally-occurring alpha-emitters (234U/238U, 235U, 232Th and daughter nuclides) and of plutonium isotopes on alpha-radiography trace observation will be discussed.The next steps of this study will be to develop and implement methods to sample and isolate alpha-emitting particles from the soil matrix and to characterize them in size, morphology, elemental and isotopic compositions. Full characterization of individual particles will be very helpful to determine their origin and to provide an understanding of their formation process and to determine their mobility and life-duration in the environment.References:H. Jaegler, F. Pointurier, et al., 2019. Method for detecting and characterising actinide-bearing micro-particles in soils and sediment of the Fukushima Prefecture, Japan. Journal of Radioanalytical and Nuclear Chemistry, 321 (2019), 57–69. doi:10.1007/s10967-019-06575-w Y. Satou, K. Sueki,et al., 2018. Analysis of two forms of radioactive particles emitted during the early stages of the Fukushima Dai-ichi Nuclear Power Station accident. Geochemical Journal, 52 (2018), 1-7. doi:10.2343/geochemj.2.0514.