Uranium dioxides and debris fragments released to the environment with cesium-rich microparticles from the Fukushima Daiichi Nuclear Power Plant

International audienc

Novel Method of Quantifying Radioactive Cesium-Rich Microparticles (CsMPs) in the Environment from the Fukushima Daiichi Nuclear Power Plant

Highly radioactive cesium-rich microparticles (CsMPs) were released from the Fukushima Daiichi nuclear power plant (FDNPP) to the surrounding environment at an early stage of the nuclear disaster in March of 2011; however, the quantity of released CsMPs remains undetermined. Here, we report a novel method to quantify the number of CsMPs in surface soils at or around Fukushima and the fraction of radioactivity they contribute, which we call “quantification of CsMPs” (QCP) and is based on autoradiography. Here, photostimulated luminescence (PSL) is linearly correlated to the radioactivity of various microparticles, with a regression coefficient of 0.0523 becquerel/PSL/h (Bq/PSL/h). In soil collected from Nagadoro, Fukushima, Japan, CsMPs were detected in soil sieved with a 114 μm mesh. There was no overlap between the radioactivities of CsMPs and clay particles adsorbing Cs. Based on the distribution of radioactivity of CsMPs, the threshold radioactivity of CsMPs in the size fraction of <114 μm was determined to be 0.06 Bq. Based on this method, the number and radioactivity fraction of CsMPs in four surface soils collected from the vicinity of the FDNPP were determined to be 48–318 particles per gram and 8.53–31.8%, respectively. The QCP method is applicable to soils with a total radioactivity as high as ∼106 Bq/kg. This novel method is critically important and can be used to quantitatively understand the distribution and migration of the highly radioactive CsMPs in near-surface environments surrounding Fukushima

Isotopic signature and nano-texture of cesium-rich micro-particles: Release of uranium and fission products from the Fukushima Daiichi Nuclear Power Plant

Highly radioactive cesium-rich microparticles (CsMPs) released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) provide nano-scale chemical fingerprints of the 2011 tragedy. U, Cs, Ba, Rb, K, and Ca isotopic ratios were determined on three CsMPs (3.79–780 Bq) collected within ~10 km from the FDNPP to determine the CsMPs’ origin and mechanism of formation. Apart from crystalline Fe-pollucite, CsFeSi2O6 · nH2O, CsMPs are comprised mainly of Zn–Fe-oxide nanoparticles in a SiO2 glass matrix (up to ~30 wt% of Cs and ~1 wt% of U mainly associated with Zn–Fe-oxide). The 235U/238U values in two CsMPs: 0.030 (±0.005) and 0.029 (±0.003), are consistent with that of enriched nuclear fuel. The values are higher than the average burnup estimated by the ORIGEN code and lower than non-irradiated fuel, suggesting non-uniform volatilization of U from melted fuels with different levels of burnup, followed by sorption onto Zn–Fe-oxides. The nano-scale texture and isotopic analyses provide a partial record of the chemical reactions that occurred in the fuel during meltdown. Also, the CsMPs were an important medium of transport for the released radionuclides in a respirable form

Caesium fallout in Tokyo on 15th^{th} March, 2011 is dominated by highly radioactive, caesium-rich microparticles

In order to understand the chemical properties and environmental impacts oflow-solubility Cs-rich microparticles (CsMPs) derived from the FDNPP, the CsMPscollected from Tokyo were investigated at the atomic scale usinghigh-resolution transmission electron microscopy (HRTEM) and dissolutionexperiments were performed on the air filters. Remarkably, CsMPs 0.58-2.0micrometer in size constituted 80%-89% of the total Cs radioactivity during theinitial fallout events on 15th March, 2011. The CsMPs from Tokyo and Fukushimaexhibit the same texture at the nanoscale: aggregates of Zn-Fe-oxidenanoparticles embedded in amorphous SiO2 glass. The Cs is associated withZn-Fe-oxide nanoparticles or in the form of nanoscale inclusions of intrinsicCs species,rather than dissolved in the SiO2 matrix. The Cs concentration inCsMPs from Tokyo (0.55-10.9 wt%) is generally less than that in particles fromFukushima (8.5-12.9 wt%).The radioactivity per unit mass of CsMPs from Tokyo isstill as high as 1E11 Bq/g, which is extremely high for particles originatingfrom nuclear accidents. Thus, inhalation of the low-solubility CsMPs wouldresult in a high localized energy deposition by beta (0.51-12)*1E-3 Gy/h withinthe 100-micrometer-thick water layer on the CsMP surface) and may havelonger-term effects compared with those predicted for soluble Cs-species

Caesium fallout in Tokyo on 15th^{th} March, 2011 is dominated by highly radioactive, caesium-rich microparticles

In order to understand the chemical properties and environmental impacts oflow-solubility Cs-rich microparticles (CsMPs) derived from the FDNPP, the CsMPscollected from Tokyo were investigated at the atomic scale usinghigh-resolution transmission electron microscopy (HRTEM) and dissolutionexperiments were performed on the air filters. Remarkably, CsMPs 0.58-2.0micrometer in size constituted 80%-89% of the total Cs radioactivity during theinitial fallout events on 15th March, 2011. The CsMPs from Tokyo and Fukushimaexhibit the same texture at the nanoscale: aggregates of Zn-Fe-oxidenanoparticles embedded in amorphous SiO2 glass. The Cs is associated withZn-Fe-oxide nanoparticles or in the form of nanoscale inclusions of intrinsicCs species,rather than dissolved in the SiO2 matrix. The Cs concentration inCsMPs from Tokyo (0.55-10.9 wt%) is generally less than that in particles fromFukushima (8.5-12.9 wt%).The radioactivity per unit mass of CsMPs from Tokyo isstill as high as 1E11 Bq/g, which is extremely high for particles originatingfrom nuclear accidents. Thus, inhalation of the low-solubility CsMPs wouldresult in a high localized energy deposition by beta (0.51-12)*1E-3 Gy/h withinthe 100-micrometer-thick water layer on the CsMP surface) and may havelonger-term effects compared with those predicted for soluble Cs-species

Caesium-rich micro-particles: A window into the meltdown events at the Fukushima Daiichi Nuclear Power Plant

International audienc

Dissolution of radioactive, cesium-rich microparticles released from the Fukushima Daiichi Nuclear Power Plant in simulated lung fluid, pure-water, and seawater

To understand the chemical durability of highly radioactive cesium-rich microparticles (CsMPs) released from the Fukushima Daiichi Nuclear Power Plant in March 2011, we have, for the first time, performed systematic dissolution experiments with CsMPs isolated from Fukushima soils (one sample with 108 Bq and one sample with 57.8 Bq of Cs-137) using three types of solutions: simulated lung fluid, ultrapure water, and artificial sea water, at 25 and 37 degrees C for 1-63 days. The Cs-137 was released rapidly within three days and then steady-state dissolution was achieved for each solution type. The steady-state Cs-137 release rate at 25 degrees C was determined to be 4.7 x 10(3), 1.3 x 10(3), and 1.3 x 10(3) Bq . m(-2)s(-1) for simulated lung fluid, ultrapure water, and artificial sea water, respectively. This indicates that the simulated lung fluid promotes the dissolution of CsMPs. The dissolution of CsMPs is similar to that of Si-based glass and is affected by the surface moisture conditions. In addition, the Cs release from the CsMPs is constrained by the rate-limiting dissolution of silicate matrix. Based on our results, CsMPs with similar to 2 Bq, which can be potentially inhaled and deposited in the alveolar region, are completely dissolved after >35 years. Further, CsMPs could remain in the environment for several decades; as such, CsMPs are important factors contributing to the long-term impacts of radioactive Cs in the environment. (C) 2019 Elsevier Ltd. All rights reserved.Peer reviewe

Novel Method of Quantifying Radioactive Cesium-Rich Microparticles (CsMPs) in the Environment from the Fukushima Daiichi Nuclear Power Plant

International audienc

Radioactive Cs in the severely contaminated soils near the Fukushima Daiichi Nuclear Power Plant

Radioactive Cs isotopes (137Cs, t1/2 = 30.07 y and 134Cs, t1/2 = 2.062 y) occur in severely contaminated soils within a few km of the Fukushima Dai-ichi nuclear power plant at concentrations that range from 4×10^5 to 5×10^7 Bq/kg. In order to understand the mobility of Cs in these soils, both bulk and submicron-sized particles elutriated from four surface soils have been investigated using a variety of analytical techniques, including powder X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and analysis of the amount of radioactivity in sequential chemical extractions. Major minerals in bulk soil samples were quartz, feldspar, and minor clays. The submicron-sized particles elutriated from the same soil consist mainly of mica, vermiculite, and smectite and occassional gibbsite. Autoradiography in conjunction with SEM analysis confirmed the association of radioactive Cs mainly with the submicron-sized particles. Up to ~3 MBq/kg of 137Cs are associated with the colloidal size fraction (98% of Cs within top ~5 cm of the soil. These results suggest that the mobility of the aggregates of submicron-sized sheet aluminosilicate in the surface environment is a key factor controlling the current Cs migration in Fukushima