Inner structure and inclusions in radiocesium-bearing microparticles emitted in the Fukushima Daiichi Nuclear Power Plant accident

Okumura, Taiga; Yamaguchi, Noriko; Dohi, Terumi; Iijima, Kazuki; Kogure, Toshihiro

doi:10.1093/jmicro/dfz004

Cited by 14 publications

(16 citation statements)

References 28 publications

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“…First is termed CsMP-Fc which is also described in the next section, second is CsMP-Sg which is a new specimen with homogeneous distribution of Cs (Fig. S5), and third is WHT-1 which were a previously reported CsMP with high concentration of Cs at the periphery 11 . Consequently, these CsMPs also contain more Na than other alkali elements although the Na/Si ratio in CsMP-Sg is relatively lower.…”

Section: Resultsmentioning

confidence: 99%

“…Another possible explanation is that the reactor atmosphere changed from reductive to oxidative during CsMP formation. We previously reported CsMPs with a higher concentration of Fe and Zn near the surface 11 and such an inhomogeneous distribution can also occur via atmospheric change because divalent cations in silicate glass tend to diffuse outward when the glass is exposed to an oxidative atmosphere after glass formation in a reductive atmosphere 26 . To explain the presence of trivalent iron at the rim regions, more CsMPs should be examined to confirm whether it is a general feature of CsMPs.…”

Section: Discussionmentioning

confidence: 99%

“…other alkali elements (K and Rb) are inclined to possess reversed distributions. Fe and Zn are also enriched near the surface in some CsMPs 11 . Results of quantitative analysis of the glass considering the radial distributions of the elements showed the SiO 2 component reaches 60-70 wt% 10 .…”

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confidence: 99%

“…Results of quantitative analysis of the glass considering the radial distributions of the elements showed the SiO 2 component reaches 60-70 wt% 10 . Further analysis using electron energy-loss spectroscopy (EELS) indicated that CsMPs do not contain boron 11 , which is easily incorporated into silicate glass if it exists in the surrounding atmosphere 12 . This infers that the B 4 C control rods created a eutectic alloy with stainless steel without vaporization during the accident.…”

mentioning

confidence: 99%

“…X-ray absorption near-edge structure (XANES) analysis using an SR X-ray microbeam indicated the high oxidation states of Fe, Zn, Mo, and Sn in the CsMPs, i.e., Fe 3+ , Zn 2+ , Mo 6+ , and Sn 4+ , suggesting that the CsMPs were formed in an oxidative atmosphere 8 . However, inclusions of chromian magnetite (Fe 2+ (Cr 3+ , Fe 3+ ) 2 O 4 ) were often found in the CsMPs, which conversely suggests that the atmosphere was rather reductive 11 . This discrepancy should be solved to determine the atmosphere inside the damaged reactor which might have filled with hydrogen and superheated steam during the accident 13 .…”

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Reactor environment during the Fukushima nuclear accident inferred from radiocaesium-bearing microparticles

Okumura

Yamaguchi

Suga

et al. 2020

Sci Rep

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Radiocaesium-bearing microparticles (csMps), which are substantially silicate glass, were formed inside the damaged reactor and released to the environment by the fukushima Dai-ichi nuclear power plant accident in March 2011. The present study reports several valuable findings regarding their composition and structure using advanced microanalytical techniques. X-ray absorption near-edge structure of Fe L 3 -absorption indicated that the oxidation state of the iron dissolved in the glass matrix of the csMps was originally nearly divalent, suggesting that the atmosphere in which the csMps were formed during the accident was considerably reductive. Another major finding is that sodium, which has not been recognised as a constituent element of CsMPs thus far, is among the major elements in the glass matrix. The atomic percent of Na is higher than that of other alkali elements such as K and Cs. Furthermore, halite (NaCl) was found as an inclusion inside a CsMP. The existence of Na in CsMPs infers that seawater injected for cooling might reach the inside of the reactor before or during the formation of the CsMPs. these results are valuable to infer the environment inside the reactor during the accident and the debris materials to be removed during the decommissioning processes.A significant amount of radionuclides, including radiocaesium ( 134 Cs and 137 Cs), were released into the environment by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011 1 . Radiation contamination around the nuclear plant is now mainly caused by 137 Cs because of its relatively high amount and long half-life (30.2 years). Most of the released radiocaesium was in a gaseous state at the time of the accident, fell onto the ground, and fixed to mineral grains, such as partially vermiculitised biotite, on the ground 2 . However, part of the radiocaesium was incorporated into micron-sized particles inside the reactor and these particles, termed radiocaesium-bearing microparticles (CsMPs), were emitted from the damaged reactor. In addition to the CsMPs which are also termed Type-A particles in some literature, Type-B particles larger than several dozen microns were found around the nuclear plant 3-5 . Although Type-B particles generally possess higher radioactivity than Type-A particles, specific radioactivity of Type-A is far higher than that of Type-B. Based on the activity ratios of the radiocaesium isotopes ( 134 Cs/ 137 Cs), Type-A and B particles are considered to have been formed in the Unit 2 or 3 and Unit 1 Reactors, respectively, because the activity ratios are varied by fuel burnup differences among the units 6 . All the CsMPs analysed in this study are classified to Type-A particles because they were spherules of a few microns and caesium could be detected using X-ray composition analysis owing to the high specific radioactivity 4 .CsMPs were first identified in aerosol filters collected in Tsukuba, Japan 7 . Microscopic analyses using synchrotron radiation (SR) X-ray and transmission electron microscopy (TEM) show...

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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Reactor environment during the Fukushima nuclear accident inferred from radiocaesium-bearing microparticles

Okumura

Yamaguchi

Suga

et al. 2020

Sci Rep

Self Cite

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Structure, Composition, and Physicochemical Properties of Radiocesium-Bearing Microparticles Emitted by the Fukushima Daiichi Nuclear Power Plant Accident

Okumura,

Yamaguchi,

Kogure

2023

Agricultural Implications of Fukushima Nuclear Accident (IV)

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During the accident at TEPCO’s Fukushima Daiichi Nuclear Power Plant, radiocesium-bearing microparticles (CsMPs) were released from damaged reactors into the environment. These micron-sized spherical particles with high specific radioactivity have not been reported in previous nuclear accidents. Herein, the current understanding of the structure, composition, and physicochemical properties of CsMPs is summarized. Electron microscopy revealed that the CsMP matrix is composed of silicate glass containing Na, Cl, K, Fe, Zn, Rb, Sn, and Cs as major constituents. These elements are often inhomogeneously distributed, depending on the particle radius, and Cs was concentrated around the outer side of the particles. In addition, nanocrystals including Cr-rich oxides and chalcogenides were frequently found inside CsMPs. The average valence state of Fe in the CsMP glass matrix was almost Fe2+, indicating formation under a reducing atmosphere through condensation from the gas phase. Radiocesium diffused away from the CsMPs when heated to >600 °C. Accordingly, CsMPs may lose their high specific radioactivity when related radiation-contaminated waste is incinerated at sufficiently high temperatures. Although CsMP solubility is low, they cannot be regarded as “insoluble” materials owing to their small size. CsMP dissolution rates depend on the pH and dissolved species in the solution, and their dissolution behavior is comparable to that of silica-rich glass. Based on these dissolution properties, a method for estimating CsMP abundance and spatial distribution in the environment was proposed. The findings detailed herein contribute to the comprehensive elucidation of CsMP environmental dynamics.

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Analysis of volatile nuclides’ behavior in the atmosphere released due to the FDNPP accident

Nishiyama

Kamida

Moriizumi

et al. 2022

Journal of Environmental Radioactivity

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Inner structure and inclusions in radiocesium-bearing microparticles emitted in the Fukushima Daiichi Nuclear Power Plant accident

Cited by 14 publications

References 28 publications

Reactor environment during the Fukushima nuclear accident inferred from radiocaesium-bearing microparticles

Reactor environment during the Fukushima nuclear accident inferred from radiocaesium-bearing microparticles

Structure, Composition, and Physicochemical Properties of Radiocesium-Bearing Microparticles Emitted by the Fukushima Daiichi Nuclear Power Plant Accident

Analysis of volatile nuclides’ behavior in the atmosphere released due to the FDNPP accident

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